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7rhe Rickettsiai Diseases of ManIJ. A-ur. Med. Tewhol. 40 (1M) 73-7

\' (CarIE Pedrs-en,JV

T1 .1 General Prope aies ity rates range from less than 1% to as high as 90% in someThe rickettsial diseases endemic to North America in- untreated cases. Important differences in clinical manifesta-( cude: tions and severity of disease are in part dependent upon the

(1) Rocky Mountain spotted fever (caused by Rickettsia distribution of organisms and the extent of vascular in-rickettsii), (2) 0 fever (caused by Coxiella burneil), (3) en- volvement. The majority of rickettsial diseases are zoonosesdemic typhus (caused by Rickettsia typhi), (4) Rick- with the primary cycle of infection in animal hosts. The out-ettsialpox (caused by Rickettsia akan), and (5) Brill-Zinsser standing exception is epidemic typhus, in which man is thedisease (caused by Rickettsia prowazekii). In addition there reservoir. In nature rickettsiae are generally transmitted toare several other rickettsial diseases which occur through- man by arthropod vectors including ticks, lice, mites, andout the world. The study of rickettsiae has been emphasized fleas. C. burnetii is the exception as it is disseminatedin only a few laboratories in recent years; however, their primarily by aerosol. After a variable incubation period rang-potential for explosive epidemic outbreaks, coupled with the ing from 1 to 4 weeks, the onset of rickettsial illness is

LIJ continually rising number of cases of Rocky Mountain spot- generally abrupt, with severe headache, chills and fever,==! ted fever in this country, has spurred renewed interest in followed by a hemorrhagic rash. Once within the skin rick-IL.., these agents. The clinical outcome of disease very often ettsiae multiply within cells (division time is about 8 hours),

depends on correct early diagnosis and appropriate, timely circulate within the circulatory system (rickettsemia), and4 therapy. This report is an attempt to familiarize the reader reach endothelial cells of small blood vessels. The infected9 with the rickettsial diseases of man and the salient features cells enlarge, degenerate and cause thrombi. The vascular

which might be used for practical identification of the causa- lumen becomes occluded, and with infiltration of leuko-tive microorganisms. cytes and plasma cells, focal necrosis ensues. This, in tum,

Morphologically, rickettsiae resemble small, non-motile leads to increased permeability, rupture, petechiae, hemor-- boccobacillary, bacillary or pleomorphic bacteria. The small- rhage, and shock. In the case of C. burnefi primary atypical

est (C. burneil) measures 0.25 by 1.0 lm, while the largest pneumonia is the predominant lesion.(members of the spotted fever group) average 0.6 by 1.2 All rickettsial infections respond dramatically to adequateM m. They may be found singly, in pairs or chains. Ric- treatment with the broad spectrum tetracyclines (especiallykettsiae stain poorly by Gram's method (C. burnetli appears doxycycline) or chloramphenicol, supplemented with inten-Gram-positive; others Gram-negative); therefore, the stain- sive supportive measures. These drugs are rickettsiostaticing technique developed by Gimenez (1964) is strongly rec- in action, not rickettsiocidal.ommended. Using this procedure rickettsiae appear redagainst a contrasting blue background. Bipolar staining can While rickettsiae contain the necessary metabolic equip-be observed. They share several characteristics with bac- ment for survival, their membranes are permeable to essen-teria including: (1) division by binary fission; (2) contain DNA tial components which may either "leak out" or be borrowedand RNA; (3) contain muramic and diaminopimeflic acids in from the host cell. This may explain why these organismsthe mucopeptides of their complex cell walls; (4) possess have lost the ability to be self sufficient outside of host cells.enzymes for the Krebs cycle, electron transport system and These intracellular parasites are, therefore, protected fromprotein synthesis; and (5) growth is inhibited by several an- extracellular exposure by direct transmission from (1) ar-tibacterial compounds. Rickettsiae are highly fastidious mi- thropod to arthropod via infected ova, (2) mammal to ar-crobes which are obligate intracellular parasites (except thropod via infected blood, and (3) arthropod to mammal viaRochallmaea qulntana). By appropriate staining all ric- direct inoculation (bite). While most rickettsiae are fragilekettsiae are observed 'intracytoplasmically and occasionally and readily Inactivated outside of the intracellular environ-In the nucleus of cells (spotted fever group). ment, C. burnel Is extremely stable, resists degradation,

Diseases caused by rickettsiae vary from benign, self- and can be transmitted by the aerosol route.limited illness, to some of the most fulminating known. Fatal- Most rickettsiae, except R. quintana, grow luxuriantly In

Caspondence and/or mrp rint requma: Mslor CaI Pedftwen, J., QODA-SGRD"PL, W*VM, D.C. 20314. (P4$I' Pedwan Is In ftOffice of the Depuf Chlef of Staff for Reoawh Plans at Mhe Medical Resirch and Dskph Cmmwed.)

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Pedersenthe yolk sac of the developing chick embryo 6 or 7 days of [2.1 The Spotted Fever Groupage. After a variable incubation period at 35 C, smears The eight species in this group pathogenic for man in-show intracellular organisms. Suspensions of rickettsiae clude the etiologic agent of Rocky Mountain spotted fevermay be prepared from these yolk sacs by the method of (RMSF), the tick-borne rickettsiae of the Eastem Hemis-Craigie, which involves formalin inactivation followed by phere and Rickettsialpox. All of these organisms are anti-ether extraction. Vaccines have traditionally been prepared genically related in that they possess a common, soluble,from rickettsiae propagated in the chick embryo (Cox, 1941) group specific antigen, multiply in both the cytoplasm andor the intestinal tract of lice (Weigl, 1919). More recently, nucleus of infected cells, and are transmitted to man bycell cultures have been used to propagate rickettsiae for use ticks and mites. The diseases caused by these rickettsiaein vaccines or the production of antigens. In addition, cell have a worldwide distribution.culture techniques have been used for the primary isolation IA.] R. ricketsii causes RMSF in man after transmissionof spotted fever rickettsiae from ticks and other infected via the bites of several species of infected Ixodid ticks; prin-specimens, and spotted fever group rickettsiae can be cipally Dermacentor variabilis in the eastern United Statesquantitated by plaque assay. and D. andersoni in the western United States. The disease

Many laboratory animals may be infected experimentally was originally seen in parts of Montana and was first de-with rickettsiae; however, the guinea pig and white mouse scribed in Idaho by Maxey at the turn of the century. Spot-are employed extensively for primary isolation and identifi- ted fever has now been recognized in almost every state,cation. When attempting to isolate rickettsiae from man, and in parts of Canada, Mexico, Central and South America.blood (obtained prior to initiation of antibiotic therapy) is al- Currently, RMSF is most prevalent in the South Atlanticlowed to clot; serum is removed (and retained for serologic states and it appears that in 1977 for the first time there willassay for antibodies), and the clot is ground as a 10% sus- be over 1,000 reported cases.* In the early 1900's Rickettspension in Brain Heart Infusion. This suspension is injected experimentally transmitted the disease from man to guineaintraperitoneally into test animals. Guinea pigs may demon- pigs and monkeys, and also transferred the disease fromstrate several types of response involving fever, peritoneal animal to animal by the wood tick. In 1919 Wolbach demon-exudate, inflammation of the tunica vaginalis with swelling strated the intranuclear multiplication of these rickettsiae. Inand necrosis of the scrotum (Neill-Mooser reaction) and 1941 Cox developed a vaccine prepared from rickettsiaedeath. Spleen, brain and tunica vaginalis are tissues of propagated in the yolk sacs of chicken embryos.choice for serial passage of rickettsiae. There is consider- Disease in man generally occurs 1 to 2 weeks after theable variation in the pathogenicity of rickettsial species and bite of an infected tick. The hallmark symptoms include ab-strains within species. rupt onset, severe frontal headache, fever, and rash which

Concentrated suspensions of typhus and spotted fever first appears on the extremities on about the 4th day ofgroup rickettsiae as well as the Gilliam strain of R. tsut- fever. This rash spreads centripetally toward the trunksugamushi kill mice within a few hours after intravenous whereas the reverse is characteristic of the typhus fevers.inoculation. This "toxic effect" cannot be prevented by an- Rickettsemia can be demonstrated during the febrile period.tirickettsial drugs, and ultraviolet irradiation diminishes infec- Organisms are found in the endothelial cells of the vasculartivity without reducing toxicity. Death is caused by gross system in great number. Thrombocytopenia may occur anddamage to endothelial cells with concomitant leakage of intravascular thrombosis may lead to necrosis of the skinplasma, decrease in blood volume and shock. It has not and soft tissues. Marked azotemia is an unfavorable signbeen possible to separate a toxic component from the infec- and frank renal failure or shock may occur in the severely illtious particle, but the "toxin" is specific for the species of patient. In mild or moderate cases, disease is usually termi-rickettsiae. The "toxic effect" is prevented by addition of nated within two weeks and convalescence is rapid withouthomologous antiserum. Suspensions of some rickettsiae sequelae; however, complications may be seen. In fatalalso contain hemolysins capable of lysing the red blood cases death usually occurs during the latter part of the sec-cells of chicks, rabbits, and man. The hemolysin is distinct ond week.from the toxin. If the disease does not become far advanced it usually

reponds dramatically to chloramphenicol or the tetracyclinesTable 1. Spotted Fever Group Rickettsiae Pathogenic for Man. and defervescence occurs in 3 to 4 days. Headache and

Etiologic Agent Disease Geographic Distribution toxic signs abate within 24 to 48 hours following drug admin-Subgroup A istration and rash fades in 2 to 3 days. Appropriate suppor-

R. ickettsi RMSF, Sao Paulo Westem Hemisphere tive therapy must be instituted for symptomatic relief and totyphus, Flebre correct fluid electrolyte imbalances. Mortality rates are lowmnanchada (ca. 5%) when the disease is recognized early and treated

R. s/birlca Siberian tick typhus Eastern Hemisphere promptly. Without appropriate antibiotic therapy the caseSubgroup B fatality rate approaches 20%.

R. conorll Fievere boutonneuse, Eastem Hemisphere Differential diagnosis is predicated primarily on clinicalSouth African tick bite observation and serologic tests. The rash of RMSF must befever, Kenya tick distinguished from meningococcemila, rubella, rubeola, var-typhus, Indian ticktyphu, n icella and typhoid fever. History of tick-bite is very helpful.

Subgroup C The Weil-Felix reaction is positive, but variable (Table 2).R. eustrai/s Qusenslamd tick Eater Hemisphere

R. ekari Riftett x Northeast, USA, USSR "In 1977, 1,115 cam were reported by the CDC.

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Rickettsial Diseases

Table 2. Wel-Felix Reactions East adjacent to the Mediterranean, and the Black andDisease OX-19 OX-2 OX-K Caspian Seas. Clinical observations include an initial lesion

(eschar), found at the site of tick attachment, headache,Spotted Fevers 4+ (to 1+) 1 + (to 4+) - fever for up to two weeks, and a generalized maculopapularRickettsialpox - - -

Epidemic Typhus 4+ 1+ - erythematous rash usually involving palms and soles.Brill-Zinsser Disease variable variable - Pathologic lesions generally consist of thrombosis of capil-Murine Typhus 4+ 1 + - laries, small arteries and veins with the earliest changes inScrub Typhus - - 4+ the vascular endothelium. Chloramphenicol and the tet-O Fever - -Trench Fever - racyclines are effective therapeutically.

CF antibodies appear during the 2nd week; however,Agglutinins against Proteus strains OX-19 and OX-2, and Weil-Felix agglutinins to Proteus OX-19 and OX-2 frequentlyrarely OXK, appear in the serum of patients with spotted are found only in low titers. The species may be differ-fever. Agglutinins appear between the 5th and 12th days entiated by cross immunity in guinea pigs, mouse toxinand single convalescent titers of --1:320 may be considered neutralization and cross CF tests. Following intraperitonealdiagnostically significant. inoculation with R. conori and R. sibirica, guinea pigs de-

Complement-fixation (CF) tests may be performed using velop fever, splenomegaly and testicular changes. Whileether soluble, group specific antigens to differentiate spotted mice and guinea pigs are susceptible to R. austrais, thisfever rickettsiae from typhus and 0 fevers. Washed, type organism does not produce a "toxic effect" in mice.specific corpuscular antigens are used to distinguish among The primary animal host of R. conoi is the dog, withthe various members of the spotted fever group. CF an- Rhipicephalus sanguineus, the brown dog tick, serving astibodies appear during the 2nd or 3rd week of illness. Other the principal vector. R. australis appears to have a reservoirserologic techniques including immunofluorescence, in marsupials and at least four species of ticks are capableagglutination, and mouse toxin neutralization may be used of infecting man. Animal hosts of R. sibirica have not beenfor serologic evidence of disease. elucidated. Control of these diseases involves avoidance of

The host range of R. rickettsii is broad and numerous ticks. Effective vaccines for prevention are not commerciallyspecies of ticks, small mammals, and man are infected in available.nature. The male guinea pig is the animal most frequently [C.] Rickettsialpox was first recognized in New York inused for laboratory studies. When inoculated intraperitone- 1946 and has subsequently been described in many loca-ally with infectious material, it develops fever >40 C and a tions including the Soviet Union. The disease is a self-marked scrotal reaction consisting of a hemorrhagic rash limited, febrile illness transmitted from mouse to man byfollowed by necrosis and ulceration of the skin. Necrosis blood sucking mites, Aliodermanyssus sanguineus. Likeand sloughing of ears and footpads may also occur. With spotted fever rickettsiae, R. akari multiplies in both nucleusvirulent strains death may ensue during the 6th to 8th day of and cytoplasm of host cells and the common soluble anti-fever. Rickettsiae may be readily demonstrated in the gen reacts in CF tests with antibodies to the spotted feverspleen and tunica vaginalis, which are the tissues of choice group. The type specific particulate antigen and cross-for passage material, immunity in guinea pigs serve to differentiate R. akari from

Spotted fever rickettsiae are parasites of ticks which are other members of the spotted fever group. This rickettsiadistributed in several organs including the ovaries and sail- does not elicit Well-Felix agglutinins and has no "toxic ef-vary glands. Infected ova give rise to infected progeny, and fect" in mice. R. akar grows well in the yolk sacs of em-rickettsiae in saliva are transmitted to man by tick bite. Man bryonated eggs, causes a fatal disease in laboratory mice,is only accidentally infected when he intrudes into the tick and guinea pigs develop fever and mild scrotal swelling.environment, and is in no way necessary for survival of The house mouse is the natural mammalian reservoir forthese rickettsiae. As rickettsiae are passed transovarially, R. akar, and disease is usually seen in urban centers. Theticks serve not only as vectors, but also as primary reser- mite bite develops into a papule which forms an escharvoirs of disease. There is substantial evidence for natural which resembles a vaccinia inoculation. The illness has aninfection of several wild vertebrates with R. rickettsii abrupt onset with fever, headache, and a characteistic yes-(meadow mice, cottontail rabbits, squirrels, and chipmunks). icular rash which resembles chickenpox. The course of dis-Antibodies have been detected in a myriad of animal ease lasts from 1 to 2 weeks and is not fatal. Chloram-species. phenicol and the tetracyclines are markedly effective in

Control of RMSF is primarily a function of avoidance of treatment of patients with Rickettslalpox. Control measurestick infested areas. In addition man has been infected by involve rodent control and insecticides for mite diinlteta-accidental exposure to aerosols generated within the labors- tion.tory. A vaccine of questionable efficacy is available for per- [3.1 Typhus Groupsonnel at great risk of contracting disease. This group includes two species pathogenic for man, Rick-

B.] Tick-borne spotted fever rickeftsiae of the Eastern etta prowazeld, the etiologic agent of epidemic typhusHemisphere include organisms which cause mild to moder- fever and Brill-Zlnsser disease, and R. typhi, which causesate, generally nonfatal illness. These agents are widely dis- murine (endemic) typhus.trtbuted geographically and share a group antigen with R. [A.] Epidemic Typhus Fever has been intimately as-rickettait but have distinct type-specific corpuscular anti- soclated with human misery, poverty, and overcrowdrig forgens. R. conoril Is the prototype and causes disease centuries and is especially prevalent during wrarre. It is re-throughout Africa, India and parts of Europe and the Middle ported to have helped destroy hall a million men of Napo-J. A~r. Mod. Teekne.Aerv,", ,9r

Pedersen

leon's Army of 1812; ravaged an estimated 30 million Rus- part, be accounted for on the basis of occlusion of smallsians during World War I; and during World War l1 it was capillaries by swollen endothelial cells, thrombi, perivascularheavily encountered in the European theater of operations hemorrhages, extravasation of plasma, hemoconcentrationas well as in Africa, the Far East, Japan, and Korea. Suffice and shock.it to say that typhus fever has been one of the ma- With tetracycline or chloramphenicol therapy patientsjor epidemic diseases in the history of man.* Epi- usually respond within 12 to 24 hours and marked im-demic typhus is characterized by high fever, severe provement occurs within 2 to 3 days. Recovery is accom-headache and rash. During epidemics the case fatality rate panied by the absence of serious sequelae in addition to anis approximately 10% in persons between 20 and 30, and enduring immunity to the disease.may rise to 60% in those over 50. The etiologic agent R. Clinically, the early stages of typhus fever might be con-prowazekii was named by da Rocha-Lima in 1916 in honor fused with smallpox, meningitis, measles, malaria, typhoidof Dr. Howard Ricketts (American) and Dr. Stanislaus von fever, and other infectious diseases. With the appearance ofProwazek (Austrian) both of whom died of the disease while rash a more accurate diagnosis can be made. Theinvestigating its etiology. erythematous rash of typhus spreads from trunk to ex-

In nature R. prowazekii infects only man and the human tremities while the rash of RMSF ordinarily spreads cen-body louse, Pediculus humanus var. corporis, or less fre- tripetally. Epidemic typhus must then be differentiated fromquently the head louse P. humanus var. capitis. Body lice endemic typhus by means of serologic tests.nest and lay eggs in clothing, and as the nymphs mature Laboratory diagnosis, routinely performed on the basis ofthey emerge 4 to 6 times per day to take blood meals from serologic tests, detects antibodies by the Weil-Felix,the human host. If the ingested blood contains rickettsiae complement-fixation, rickettsial agglutination, precipitin, op-the louse becomes infected and organisms multiply in en- sonization, neutralization, or protection tests. Weil-Felixdothelial cells of the intestinal tract. These cells ultimately agglutinins (Table 2) for Proteus strain OX-19 may appearrupture, discharging rickettsiae into the feces. While feeding in the serum as early as the 7th or 8th day of illness, peak 2on human skin, the louse defecates, and since its bite to 3 weeks into the disease, then decline over a period ofcauses itching, the host rubs the infected feces into broken several months. Reliable results demand a titer of 1:160 orskin. R. prowazekii are present only in the intestinal cells greater, on single serum specimens, or a fourfold rise inand feces of infected lice; they have not been demon- titer with paired sera. Agglutinins for OXK do not appear.strated in other tissues and are not passed transovari- From serologic studies it is evident that subclinical infectionally. Infected lice die within 1 to 3 weeks; therefore, the occurs, especially in children.cycle of louse infection is required to maintain the human Male guinea pigs respond to epidemic typhus rickettsiaereservoir. Lice prefer a temperature approaching that of with fevers >40 C; and rarely, scrotal swelling. Guinea pigshuman skin, and, therefore, leave patients who either have do not develop a skin reaction and animals that survive dohigh temperatures or who have died. Lice neither fly nor so without sequelae. Spleen or brain is the organ of choicejump, and only crawl short distances which explains why for high titer passage material. Cotton rats are susceptibleepidemic typhus flourishes under conditions of extreme to lethal infection (with large doses of rickettsiae), whereascrowding. While monkeys, guinea pigs, rats, chick embryos white rats are not; white mice undergo only an inapparentand certain arthropods are susceptible, in varying degrees, infection.to experimental infection with R. prowazeldi, no natural res- Control of epidemic typhus in man is predicated on vacci-ervoir other than man has been demonstrated. nation or delousing of humans. The vaccine currently in use

Typhus rickettsiae are highly pleomorphic microbes 0.3 contains yolk sac grown rickettsiae which have been forma-to 0.6 by 0.8 to 4.0 psm which occur singly, in pairs, or short lin killed and extracted with ether as described by Coxchains. Optimal growth occurs in the yolk sac membrane of (1941) and Craigie (1945). This vaccine is reported to es-chick embryos and in a number of cell cultures. These rick- sentially eliminate mortality, and the course of disease inettsiae replicate only in the cytoplasm of infected cells, vaccinated individuals is milder and shorter than in naive

In man after a 10 to 14-day incubation period, the man- populations. A second type of vaccine prepared from theifestations of epidemic typhus include abrupt onset with living, attenuated strain E variant of R. prowazeii produceschills, fever, generalized pain, exhaustion, and headache (a a long lasting immunity in man and is currently being testedhallmark of this disease). A generalized eruption usually ap- in field trials.pears on the trunk from the 4th to 7th day of disease, which Delousing of human populations has been used to controlspreads peripherally to the extremities (sparing face, palms, epidemics since the early 1900s. Once deloused with DDT, jand soles). The macular (mulberry) rash may ultimately be- typhus patients are incapable of transmitting infection to -come petechial or frankly hemorrhagic. In severe cases others by contact, as rickettsiae are not found in saliva,prostration, stupor, delerlum, renal insufficiency, and rarely sputum, urine or feces. Recent reports indicate, however,gangrene of the extremities may occur. Thiomboels results that human body lice are capable of developing resistancefrom injury caused by rickettsial growth and rickettsiae may to DDT.be demonstrated in endothelial cells. Necrotic areas of the IB.] Brll-Zinsser Disease is a recrudescent form ofskin appear to be associated with thrombosis of capillaries, typhus. It was first reported by Brill (1898) in New York as aIn recovery the fever subsides during the 3rd week by rapid sporadic form of typhus which occurred in immigrants fromlysis. Pathological manifestations of disease can, in large Eastem Europe. It differs from classic epidemic typhus in' For exce~s t background Intormaffon the reader is referred to that (1) the disease is much milder, (2) ice need not beZD w's cfsic work.. "Rat, LUce and Htlary." present, (3) rash Is usually absent, and (4) antibodies ap-

82 .led. r e L82eWp 9

Rickettsial Diseasespear very rapidly (3-4 days after onset). In 1934 Zinsser susceptible. The use of DDT combined with rat poisons ishypothesized that this disease was a recrudescence of effective in reducing the incidence of this disease.epidemic typhus in persons who had previously experienced 14.J Scrub Typhusthe disease, due to exacerbation of a latent infection with R. Scrub typhus, a disease caused by Rickettsia tsut-prowazekii. The rapid rise in antibody titer is associated with sugamushi, was originally described in Japan and is cur-7S globulin which is typical of an anamnestic response to an rently recognized in a large triangular area roughly borderedinfectious agent. The Weil-Felix reaction is often negative in by Japan, India and Australia. During World War II aboutthis disease; however agglutination and CF tests are nor- 18,000 cases were reported among allied military person-mally positive. nel. Case fatality rates range from 1 to 35%, probably re-

The factors which precipitate recrudescence are unclear. flecting differences in virulence among diverse strains of R.Rickettsia apparently remain viable in sequestered sites in tsutsugamushi. Scrub typhus is a zoonosis with rodentsthe body, even in the presence of circulating antibody. Dis- serving as vertebrate hosts and larval trombiculid mitesease is apparently precipitated when the delicate balance (chiggers) acting as vectors. Over 400 species of Lepto-between the immune system and the parasite is disturbed. trombidium mites have been described, but only 14 attack

The epidemiologic significance of Brill-Zinsser disease man. The species L. akamushi and L. deliensis are the mostlies in the fact that carriers with latent infection may consti- important vectors due to their widespread distribution. In atute a reservoir for disease. Given conditions of overcrowd- silent cycle the disease is one of rodents and is spreading and louse infestation, individuals with Brill-Zinsser dis- among them by mites; however, by intrusion man be-ease are rickettsemic, so that they can serve as sources of comes accidentally infected. R. tsutsugamushi is not lethalinfection for lice. Small outbreaks of louse-borne epidemic for mites and is passaged transovarially; therefore, the mitetyphus have been described in Yugoslavia (1958) which may well serve as host and vector. Scrub typhus is con-originated from cases of Brill-Zinsser disease. These out- tracted within "typhus islands" where rodents, mites andbreaks were small due to the absence of crowding and low man come together. Typically this terrain is a cleared part ofrates of louse infestation. There are no effective control a forest, with low-lying grassy vegetation situated close tomeasures for reducing the incidence of Brill-Zinsser dis- rice fields which attract rodents. The rodents becomeease. Chloramphenicol or tetracycline are used even though parasitized by mites, which then attack man. Alternatively,the disease is relatively mild and of short duration, infections may be contracted in tropical rain forests. High

[C.1 Murine (Endemic) Typhus is a relatively mild form of humidity is a prerequisite for the maintenance of the charac-typhus fever transmitted from rats to man by the rat flea teristic focal areas of mite infestation.Xenopsylla cheopis. Rickettsia typhi causes a latent infec- When man is infected, multiplication of rickettsiae takestion in the rat host and arthropod vector. The flea becomes place at the site of inoculation often with the formation of ainfected by feeding on rats in the acute stage of disease; cutaneous eschar. Rickettsiae are disseminated and rick-rickettsiae multiply in the epithelial cells of the intestinal ettsemia ensues. The characteristic pathologic lesions aretract; thereafter, rickettsiae are discharged in feces for the found in the small blood vessels of the skin, heart, lungsduration of the flea's life. Humans accidentally exposed to and brain. Interstitial pneumonitis occurs in practically allinfected fleas are infected in a manner analogous to that fatal cases. The onset of illness is sudden, characterized bydescribed for epidemic typhus. The resultant disease is less fever, chills, conjunctival injection, generalized lymph-severe than that caused by R. prowazeki, but the two are adenopathy, and severe headache. By the end of the firstclinically indistinguishable. Case fatality rate is ca. 5% with- week a maculopapular rash appears on the trunk andout antibiotic therapy and far less with chloramphenicol or spreads to the extremities; normally the hands and face aretetracyclines. not affected. Fever increases during the first week and may

No fundamental morphologic or biochemical differences reach 104°F; a cough may be present at this time. Towardexist between R. typhi and the rickettsiae of epidemic the end of the 2nd week the rash fades, fever falls by lysis,typhus. R. typhi and R. prowazekii are antigenically related, the eschar is virtually healed and patients generally recover,in that recovery from either infection leads to immunity to occasionally with sequelae. Death, if it occurs, is normallyboth diseases (due to a heat stable, common soluble anti- due to secondary bacterial pneumonia, encephalitis, or cir-gen); whereas, immunization with killed organisms induces culatory failure. The illness may relapse, especially in casesonly homologous protection, where antibiotic therapy is begun too soon or the course is

Differential diagnosis of endemic typhus is complicated as too brief. Since broad-spectrum antibiotics are rickettsiosta-most reactions are analogous to those seen with epidemic tic in action, total recovery depends upon a suppression oftyphus. Using specific, washed antigens, however, pre- rickettsial growth until the patient develops protective immun-dominating antibodies are directed against R. typhi rather ity. The response following administration of antibiotics isthan R. prowazeki. In guinea pigs rickettsiae of epidemic more rapid in scrub typhus than in other rickettsiel diseases.typhus produce a mild disease, detected primarily by a rise Hence, if antibodies do not develop, the patient is suscepti-in body temperature, while endemic typhus rickettsiae pro- ble to reinfection or recrudescence. Occasionally patientsduce severe testicular lesions and marked swelling of the relapse and require a second course of antibiotic therapyscrotum ("tunica reaction"). Endemic typhus rickettsiae may (especially in those treated early). Signifficanty, recoveredbe maintained indefinitely by passage in white rats. individuals are fully susceptible to infection with heterolog-

Endemic typhus is distributed worldwide, most frequently ous strains. Prevention of scrub typhus is predicated onIn locales where rats are present, and in this county Is most control of the mite by thorough clearing of land then apry-prevalent In the southeastem states. Persons of all ages are ing with mlticides such as dieldrin or lindane.

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Pedersen

R. tsutsugamushi generally appears as a diplococcus or it does not share antigens with other rickettsiae, andshort rod, 0.4 by 0.8 to 2.0 /m, which may appear bipolar. It Coxiella immune animals are not resistant to other ric-is relatively labile; has a slow rate of replication in the cyto- kettsiae.plasm of infected cells; and induces interferon production in C. burnetii is a highly pleomorphic intracellular parasite,vitro. Unlike the typhus and spotted fever group organisms, typically occurring as a small bipolar rod 0.3 by 0.8 ,~m, butthese rickettsiae do not demonstrate intragroup reactivity also appearing as a diplobacillus, a lanceolate rod or a coc-but are unique by virtue of their antigenic heterogeneity. cus. It replicates preferentially in vacuoles of the host cellRepresentative prototypes include the Karp (New Guinea), rather than in cytoplasm or nucleus. It is susceptible to di-Gilliam (Malaya) and Kato (Japan) strains. In addition, 2 gestion by lysozyme but not by trypsin, highly resistant toother immunotypes, the Fan and Chon strains were iden- the adverse effects of chemical and physical agents, andtified in Thailand; other antigenically distinct strains probably can survive for inordinately long periods in the dried or fro-exist. The full diversity among scrub typhus rickettsiae is not zen states. C. burnetii grows in the cytoplasm but not theknown. This strain specific reactivity accounts for the limited nucleus of infected cells. It grows very well in yolk sacs ofapplication of the CF test for diagnostic purposes. As previ- chick embryos and in a variety of cell cultures. The hostously indicated, individuals infected by one strain remain range of C. burnetii is extremely broad. In nature, it infectssusceptible to infection with other strains, and due to this at least 40 species of ticks, other arthropods, birds, bats,diversity, a satisfactory vaccine has not been prepared for and many species of mammals, notably ungulates, rodents,complete protection against scrub typhus. The Weil-Felix and marsupials. Experimentally, mice, hamsters, andresponse in scrub typhus is to the Proteus OX-K (Kinsbury) guinea pigs are susceptible to infection with C. bumetii.strain (Table 2). Agglutinins are found by the end of the 2nd The phenomenon of "phase variation" was described byweek. No OX-2 or OX-19 antibodies develop. Although the Stoker and Fiset in 1956. Freshly isolated strains of C. bur-Weil-Felix OX-K reaction is often positive, it may be nega- netii are characteristically in phase I; however, upon adapta-tive even in persons from whom R. tsutsugamushi is iso- tion to chick embryo yolk sacs in the laboratory they arelated. Serologic diagr 3sis is based on a 4-fold or greater converted to phase II. Any phase II strain may be convertedrise in OX-K agglutinins. While the CF test is not generally back to phase I by a single passage in a susceptible animalemployed, indirect immunofluorescence and neutralization (e.g., guinea pig). Laboratory animals respond to eithertests are specific and reliable for identification. Serologic phase of infecting C. bumeti by first producing phase II an-studies indicate that there is a substantial incidence of sub- tibodies, then at about 30 days produce antibodies whichclinical infection, especially in endemic foci. react with both phase I and phase II. Humans rarely pro-

The host range of R. tsutsugamushi is broad. The animal duce phase I antibodies. Phase I and phase II rickettsiaeof choice for laboratory studies is the white mouse. Seven to can be differentiated by buoyant density. In addition, theeight days post-infection ruffling of fur is observed, the ab- phase I antigenic component can be extracted from C. bur-domen swells, edema occurs and death ensues at about 14 neii with trichloroacetic acid leaving particulate rickettsiae indays. Rickettsiae can be found in any affected tissue by im- phase II. It appears probable that the phase I antigen ispression smears, but the spleen is the organ of choice for superficially situated in the cell wall and is associated withpassage material. Strains of R. tsutsugamushi vary widely pathogenicity while phase II antigen may be more deeplyin their virulence for mice; identification of strains may be seated.performed by cross neutralization tests in mice. Cotton and 0 fever is rarely a fatal disease. The incubation periodwhite rats are also susceptible to infection. Chick embryos ranges from 10 to 17 days, and the onset is sudden withare normally killed six to ten days after inoculation, without fever (101 to 104°F), chills, malaise, anorexia, myalgia andpathognomonic lesions. The "toxic effect" for mice has been a characteristic severe frontal headache. The degree ofdemonstrated only with the Gilliam strain, pulmonary involvement varies considerably and patients

may develop pneumonitis; however, 0 fever is generally a[5.] Q Fever systemic disease accompanied by rickettsemia. Recovery

0 fever, caused by Coxiella burneti, is an acute systemic usually takes place rapidly without complications; although,disease first described by Derrick (1937) in abbatoir workers severe weight loss, hepatic involvement, abortion or con-in Brisbane, Australia. The causative agent was simulta- genital malformation can be observed. Rickettsiae may per-enously isolated in Montana by Davis and Cox (1938) and sist in tissues and chronic 0 fever may induce subacute en-has subsequently been shown to have a worldwide distribu- docarditis with concomitant microcolonies of C. bumei inton. This organism was encountered on a large scale by heart valve tissue. This form of disease is invariably fatal.American military personnel during World War II In the A diagnosis of 0 fever in man is established by isolationMediterranean area ("Balkan grippe") and has been impi- of the organism from blood, sputum or lung, or demonstra-cated as the causative agent in several epidemic outbreaks. tion of antibodies in serum. The infection is best confirmed

C. burnetli differs from other rickettsiae in several re- in guinea pigs or embyronated eggs. Guinea pigs inoculatedspects: (1) it does not require an arthropod vector to main- intraperitonealy develop temperatures >40°C after a vari-tain itself successfully in nature and is generally transmitted able prodromal period. Passage material Is usually blood orto man by aerosol, (2) it is unusually stable outside of host spleen suspension. These animals develop specific an-cells, (3) disease in man is usually characterized by tibodles within 14 to 30 days. Approximately 50% of chickpneumonitla without rash, (4) it does not elicit agglutinins for embryos Inoculated with C. bume die within 7 to 11 days.Proteus OX strains (Well-Felix reaction), and (5) It does not Antibodies against C. burrme am quite spefic and a riseelicit a "toxic" reaction in experimental animals. In addition, In titer between paired serum samples is evidence of current

64 J#. inmrA d08. 1 1Mamgbawd 'm

Rickettsial Diseases

disease. It should be noted that serologic studies suggest to progeny via ova. Man is normally infected by rubbingthat in many instances infection is inapparent. The most louse feces into a bite wound.widely used diagnostic techniques involve agglutination and After a highly variable incubation period, disease in mandirect CF. The microagglutination test with stained antigen begins suddenly with violent headache, dizziness,appears to be more specific and more sensitive than the generalized aches and pains in the long bones (e.g., shimCF. In addition, agglutinins appear earlier (1st to 2nd week) and thighs) and retroorbita pain. A discrete roseolar rashthan CF antibodies (2nd to 4th week). Corpuscular phase I appears with fever, but subsides after about 30 hours. Chillsantigens are used in the CF and agglutination tests; how- and fever tend to subside and recur in repeated cycles of 3ever, phase II antigens are used in the CF test only, since to 5 days' duration ("five-day fever" from Latin: quintus).they tend to agglutinate spontaneously and are therefore The illness may persist for months or, rarely, in excess ofunsatisfactory for the agglutination technique. Other one year. The disease is not normally fatal and ricketsmteserologic procedures which have recently been introduced can be terminated by use of tetracyclines. The illness is oneinclude radioisotope precipitation of antibody and identifica- which occurs during warfare, natural disaster, or other oc-tion by fluorescence microscopy. casions when personal hygiene is poor and louse infestation

Chloramphenicol and tetracyclines are the drugs of occurs. The presently available insecticides coupled withchoice for 0 fever; however, there is evidence of relapses antibiotic therapy make it unlikely that this disease will recurand primary illness resistant to antibiotic therapy. Therefore, in serious epidemics.these drugs are not as effective in the treatment of Q fever The Well-Felix test is negative in Trench fever (Table 2).as they are for other rickettsial diseases. However, specific CF antigens have been prepared from R.

0 fever is primarily a zoonosis, which is typically an inap- quintana cultivated on blood agar. A toxic effect is unknown.parent infection of domestic livestock (cattle, sheep, goats). The standard method of laboratory confirmation has tradi-Man is incidental to the maintenance of disease and is acci- tionally been to allow healthy lice to feed on a patient, thendentally infected. While 0 fever may be transmitted in na- examine louse feces for R. quintana and inoculate mon-ture by ticks, human disease is normally acquired by inhala- keys.tion, and may be the result of occupational exposure. Overt- [7.] Serologic Diagnosisly healthy animals can shed large numbers of rickettsiae in Unless equipped with adequate protective facilities diag-milk, urine, feces, and placentae. In addition, rickettsiae nostic laboratories should not routinely attempt animal in-may reside in wool, feather, and straw. The infectious dose oculations necessary for definitive identification, as the iso-for man may be as small as one microorganism. While C. lation of rickettsial organisms involves hazards to technicalburnetii infects many species of animals and birds, it appar- personnel. Serologic methods are simpler and safer thanently causes frank disease only in man and guinea pigs. isolation procedures and are, therefore, the preferred diag-Control of human disease is predicated on the use of nostic approach used by most laboratories. In general, aspecific vaccines made from killed rickettsiae. Unfortunately, demonstration of a significant rise in antibody (fourfold in-the available products have undesirable side effects eliciting crease) between acute serum collected early in the coursereactions at the site of injection. A live, attenuated vaccine of disease and convalescent serum, collected 10 to 21 daysstrain (M-44) has been developed in the Soviet Union; how- later is presumptive evidence of infection. Antibodies to theever, this product elicits mild disease and available evi- etiologic agent normally appear during the 2nd week of ill-dence indicates that the organism may persist in tissues. ness and peak during or after recovery. Serologic tests may(6.1 Trench Fever be used to dotect antibodies elicited to: (1) ether soluble,

This disease was first recognized during World War I group antigens which have broad characteristics for each ofwhen approximately one million cases were reported. The the major rickettsial groups, and (2) type specific antigens,disease reappeared in small outbreaks In Japan and Poland associated with the rickettsial cell which differentiateduring the 1920's and 1930's, then in epidemic form on the species and strains within species. The types of serologicRussian front during World War II. Strains of the causative tests which may be performed by a diagnostic laboratory willagent Rochalimeea quintana have recently been identified be described in the following paragraphs. For a comprehen-in Tunisia and Mexico. The causative organisms are coc- sive discussion of each the reader is referred to recent pub-coid or coccobacillary 0.2 to 0.5 jpm wide and up to 1.5 14m lications by Elisberg and Ormsbee.in length. They are often seen in pairs and tend to exhibit IA.] The Well-Felix (WF) test is based on the agglutina-bipolar staining. With the exception of rhesus monkeys, tion of Proteus vulgaris strains OX-2, OX-19, and OX-K bynone of the usual laboratory animals are susceptible to dis- antibodies formed in response to infection with rickettsiae ofease. Attempts to grow R. quintana in the embyronated egg the typhus and spotted fever groups. Castaneda (1945)and cell cultures have usually failed. found that the agglutination of Proteus bacilli by antirickett-

The human body louse Pediculus humanus var. corporis slal serum could be explained on the basis of an antigentransmits the disease to man. R. quintana grows within the common to both organisms. Antigens and standard antiseralumen of the louse gut rather than within intestinal epithelial are commercially available and this test is capable of estab-cells. This fact, together with the finding that the organisms lishing a useful presumptive diagnosis. The procedure ismay be cultivated on blood agar place them in a genus available as both a tube and slide test. Unfortunately, theapart from other rickettsiae. reaction is nonspecific; with this technique it is not possible

Once a louse has been infected it excretes infectious par- to differentiate between epidemic typhus, murine typhus and1tices in feces for the remainder of its life. The louse does RMSF. In addition, positive reactions have been obtained Innot die as a result of Infection and rickettsiae are not passed patients with nonrickettslal diseases, while some patients

A AVf. Mea. fmehlm.Mmsh AP, ISi as

Pedersen

never produce Proteus agglutinins. These antibodies have a titer specific antiserum, while the indirect IF technique is nottendency to disappear in late convalescence and, therefore, quite as simple, but is more flexible. Unfortunately, slidethe WF test cannot be used for epidemiologic studies of preparations of antigen (preferably infected tissues) are notpast infections in a given area. WF agglutinins may not ap- commercially available; however, slides prepared in the lab-pear during the first week of illness but are usually present oratory can be fixed in acetone and preserved at -70°Cby the 14th day. They may be delayed by vigorous early indefinitely. Recently, a microimmunofluorescencetreatment with antibiotics. Since OX-19 agglutinins as high technique has been described which is both practical andas 1:80 occasionally appear in healthy persons, the lowest reliable. (he test is more sensitive than the CF test andtiter considered significant in a single serum specimen is detects antibodies as early as 5 to 7 days after onset of1:160, while in paired sera a 4-fold rise is required. Reac- illness and apparently after CF antibodies have disap-tions normally encountered in the WF test are presented in peared. Briefly, slides containing 25-50 Al "spots" of fixedTable 2. antigen are flooded with antiserum and then examined by

the indirect fluorescent antibody (IFA) method. Using humanlB.] The complement fixation (CF) test is more specific or primate antisera we have found excellent correlation be-

than the Weil-Felix reaction for the detection and identifica- tween the IFA and MA tests.ion of rickettsial antibodies. However, the CF test can pro- [E.) Chang, et at. (1953, 1954) described a hemaggluti-duce erroneous and misleading information unless details nation technique in which alkaline extracts of typhus andare rigorously and faithfully followed for reliable and repro- spotted fever group rickettsiae could be used to sensitizeducible results. Antibodies to both group and typespecific human or sheep erythrocytes which could then be aggluti-antigen may be detected by the CF test. This test is imprac- nated by convalescent human sera. The group specifictical for diagnosis of scrub typhus due to the multiplicity of erythrocyte sensitizing substance (ESS) is stable and con-strains. CF antigens are commercially available for phase II tains proteins and carbohydrate. It may be distinct from theQ fever, typhus and spotted fever groups. CF antigen, rickettsial agglutinogen and Proteus common

1C.] Rickettsial agglutination tests with highly purified antigen. Shirai, et al (1975) have recently described an indi-antigens are lifore species-specific than the CF test. The rect hemagglutination (IHA) test using gluteraldehyde-testmay be performed by either macro (tube) or micro (slide stabilized sheep erythrocytes treated with group-specificor Micn;titer) methods. The microagglutination (MA) test de- ESS obtained from R. rickettsii. While this technique is ap-sc ed by Fiset, et al. (1969) is highly sensitive in detecting parently not as sensitive as IFA, the method is simpler thanantibody; the good reproducibility of results is a strong rec- CF and results compare favorably with CF and Weil-Felixommendation forits general use when appropriate antigens tests.are available. The major drawback of the test is the lack of IF.] In 1911 Ricketts reported that spotted fever immunitycommercially available antigens normally prepared from could be passively transferred by convalescent serum toembryo cells or infected yolk sac tissues. In addition, phase normal animals. According to Parker's protection or neut-I C. bimetii cannot big used in the agglutination test be- ralization test, a serum sample from a patient is added tocause of their tendency to aggregate spontaneously. In the blood taken from infected guinea pigs, and then injected in-

S...... M'tst formalin killed, purified rickettsial antigen suspen- traperitoneally into normal guinea pigs. If protective an-sions are standardized to contain approximately 1 mg of tibodies are present in the serum of the patient, guinea pigsrickettsiae/ml. Antigen and antibody in microtiter plates are will be protected from disease. The technique is expensiveincubated at room temperature for 18 hours after which time in terms of animals, laboratory space, and time, and can be25 AI of 0.02% (W/V) acridine orange is added. Agglutina- hazardous.tion results are recorded at 24 hours. It has been reported [G.] In the "toxin" neutralization test the "toxic" effect ofthat rickettsial agglutinins appear earlier and persist longer the typhus and spotted fever groups can be abated by mix-than CF antibodies. The capillary agglutination test, employ- ing rickettsial suspensions with protective antiserum prior toing hematoxylin stained C. bumelf, recently was developed injection. This test is still used for the standard assay ofas a seroepidemiologic tool to detect 0 fever antibody in epidemic typhus vaccine. Neutralization of either toxicity orserum, milk, or other opaque fluids. infectivity depends on antibodies to the type specific anti-

10.1 Immunofluorescence (IF) methods have been used gen.for the detection of rickettsial antigens in cells and for dem- [H.J In addition, in vitro measurements for neutralizingonstration of rickettsial antibodies in serum. The direct antibody may be performed using tissue culture. Convates-technique using fluorescein-labeled antibody has been most cent serum will bind to, but not neutralize, spotted fever rick-successfully used for the observation of rickettsiae in ar- ettsiae. However, infectious complexes are neutralized bythropod vectors (e.g., hemolymph), infected tissues and cell the addition of anti-immunoglobulin and subsequent incuba-cultures. The indirect method involves the initial reaction of ion. This indirect plaque reduction technique is not gener-specific antibody with antigen; this complex is then reacted ally recommended for the routine clinical laboratory detec-with fluorescein-conjugated secondary antiserum against ion of rickettsial antibody.the specific species of antibody used In the test (e.g., an- 11.1 While a radioisotope precipitation (RIP) techniquetihuman). This is the technique generally used for the detec- has been described for 0 fever serology, this procedure hastion of antibodies in serum specimens, and is the most rei- not been adequately adapted to diagnosis of other rickettsialable test available for the diagnosis of scrub typhus. In addi- diseases. Basically, antigen labeled with isotope is sen-tion, the test can distinguish between sera from murine and sitized with suspect serum, then incubated with appropriateepidemic typhus patients. The direct IF technique Is simpe secondary antiglobuhn. This suspension Is differentially can-and relatively inexpensive but requires quantities of high- trifuged, the precipitate and the supematant counted, and

J. AMe.. imd. fmbmIl.Mwed,-I1md, I iSI

Rickettsial Diseasesthe radioactivity in both determined. The amount of isotope Self-Assessment Quizprecipitated is an indication of the antibody activity. Questions[J.] Serum opsonizing activity has been studied using a

radiometabolic assay. Briefly, peripheral polymorphonuclear 1. What are the rickettsial diseases endemic to Northleukocytes (neutrophils) are separated from blood by dex- America, and what are the respective etiologic agents?tran sedimentation. Serum, inactivated rickettsial antigen, 2. Describe those characteristics which lead to the clas-balanced salt solution and 1 1

4CI glucose are incubated in the sification of rickettsiae as bacteria.presence of hyamine hydroxide. After opsonization, leuko- 3. In what way do rickettsia resemble viruses?cytes are added, released 14CO, is measured and opsoniz- 4. What are the antibiotics of choice for the treatment ofing activity is equated to hexose monophosphate shunt acti- rickettsial diseases?vation in terms of '4C0 2 released from the oxidation of [14C) 5. How are species of the genus Rickettsia primarilyglucose by the polymorphonuclear cells. Opsonizing an- transmitted?tibodies have been demonstrated in infections with typhus 6. How is Coxiella burnetii normally transmitted?and spotted fever group rickettsiae. 7. Species of Rickettsia grow only in actively growing host

1K.] Assays of immunity by cell-mediated responses have tissue such as laboratory , embryoniconly recently come under close scrutiny. Comparatively little or tissueinformation exists conceming rie cell-associated immune 8. List five serologic techniques which may be used asresponse to rickettsial diseases. Coonrod and Shepard indicators of rickettsial disease.have examined the lymphocyte transformation response of 9. Rocky Mountain spotted fever rickettsiae are trans-human peripheral blood leukocytes to rickettsial antigen. mitted to man by the bite of infected , Rickett-Using a modification of the method of Bach and Hirschhorn sial pox rickettsiae by , epidemic typhus rickett-(1964) [3H] thymidine uptake was demonstrated in the siae by , and endemic typhus rickettsiae bystimulated lymphocytes of individuals previously affectedwith RMSF. Inhibition of macrophage migration (MIF) has 10. What is the epidemiolo .. ".n...f Brill Zinsseralso been demonstrated in animals previously infected with disease? | L E -R. rickettsii. The technique of Harnngton and Stastny hasbeen in the immobilization of the movement of polymor-phonuclear cells. Lymphocyte transformation has the dem-onstrated advantage that several data points may be ob-tained from the same animal, while in contrast, animals Ef -'must generally be killed to obtain peritoneal macrophages Mfor use in the MIF test. S2

Recommended Supplemental Reading -

1. Brezina, R., Murray, E. S., Tarizzo, M. L., and K. Bgel. Rick- A Wswumettsiae and rickettsial diseases. Bull. W.H.O. 49 (1973) 433-442. 1. The rickettsial diseases endemic to North America in-

2. Davis, B. D., Dulbecco, R., Eisen, H. N., Ginsberg, H. S., and clude: Rocky Mountain spotted fever (Rickettsia rickeftsii),Wood, W. B., Jr. (Editors). Microbiology, Second edition. Rickettsial pox (R. akari), Brill Zinsser disease (R. pro-Harper & Row Publishers, Inc. Hagerstown, Md., 1973, pp.897-913. wazeldi) endemic typhus (R. typhi) and Q fever (Coxiella

3. Eliaberg, B. L, and Bozeman, F. M. Rjckettsieae (sic). Diag- bumedi).nostic Procedures for Viral and Rickettsial Infections, Fourth 2. Both have similar morphology, contain DNA and RNA,edition. Edited by Lennette, E. H., Schmidt, N. J. American contain muramic acid and diaminopimelic acid in cell walls,Public Health Association, New York, 1969, pp. 826-868.

4. Horsfal, F. L, Jr., and Tamm, I. (Editors). Wra! and Ricketsial possess metabolic enzymes, divide by binary fission andInfectfons of Man, Fourth edition. J. B. Uppincott Co., Philadel- growth is inhibited by antibacterial compounds.phia, 1965. pp. 10569-1183. 3. Both are obligate intracellular parasites.

5. Joldik, W. K., and Smith, D. T. Zinsser Microbiology, Fifteenth 4. Broad spectrum tetracyclines and chloramphenicol.edition. Appleton-Century-Crofts, Now York, 1972, pp. 671- 5. Species of Rickettsia are transmitted from arthropod to664.

6. Ormsbee, R. A. Rickettsiae (as organisms) Ann. Rev. Mj- arthropod via infected ova; mammal to arthropod via in-crobOl. 23 (1969) 275-292. fected blood; arthropod to mammal via direct inoculation.

7. Ormsbee, R. A. Rickettsiae. Manual of Clinical Microbiology, 6. Coxlella bumeti (0 fever) is normally transmitted viaSecond edition. Edited by Lomette, E. H., Spaulding, E. H., infectious aerosols.Truant, J. P. American Society for Microbiology, Washington,1974. pp. 806-815. 7. Animals, eggs, culture.

8. Rhodes, A. J., and Van Rooyen, C. E. Textbook of Wroogy, 8. Weil Felix test, complement fixation, agglutination,Fifth edition. Williams & Wilkins, Baltimore, 1968. pp. 851-922. Immunofluorescence, hemagglutination, neutralization,

9. Smadel. J. E. Status of the ricketteloses in the United States. precipitation, radiometaboic assay.Ann. In~. Mod. 51 (19) 421-435. 9. Ticks, mites, lice, fleas.

10. Weiss, E. Growth and physiology o rickett e. Bacterlo. Rev. 9. csm ies ice fla37 (1973) 259-283. 10. Human carriers with a latent infection may constitute a

11. Woodward, T. E. A historical account of the rickeUttel dieass reservoir for overt disease outbreaks.wfll a discussion of unsoted pobie. J. Ifect. &/s. 127(1973) 683-594.

12. Zinseer, H. Rate, Lc and /atory. Lit, Brown and Co., Bos-- ton, 1935.

A, Amer. Afud. feeiWI.Im ,,, s87