background, taxonomy, history morphology, distribution ...psmith3/teaching/490-21.pdf ·...

Background, Taxonomy, HistoryMorphology, Distribution, Life CycleTransmission, Symptoms, DiagnosisTreatment/PreventionSummary (Scabies vs. Chiggers)

Human scabies iscaused by aninfestation of the skinby human itch miteSarcoptes scabieivar. hominis (CDC)

One of the firstmicroorganismslinked to humandisease

Figure 1. Sarcoptes scabiei

Sarcoptes Scabiei

Obligate humanparasite

Entire life cycle inhumans

Usually foundbetween fingersand on the wrist

Figure 2. Characteristic welts ofscabies

Sarcoptes scabieiKingdom: AnimaliaPhylum: ArthropodaClass: ArachnidaSubclass: AcariFamily: Sacroptidae

Natural History of Scabies

Aristotle (384-322BC)Previously attributed to “corrupt

blood”Crusca Academy (1623)›Pellicello

Natural History of Scabies

Dr. Giovan Cosimo Bonomo (1663-1696) Discovered the etiological agent, affirmed

that it laid eggs and suggested itstransmission.

Figure 3. Bonomo’s drawings,International Journal ofDermatology

Morphology of Sarcoptes scabiei

Round, sac-likeeyeless mites

Female Sacroptesscabiei are 0.30-0.45mm long and0.25-0.35mm wide

Figure 4. Microscopic view ofSarcoptes scabiei

Distribution of Scabies

Figure 5. Worldwide distribution of Scabies

Usually found inimmunocompromised, leprosy andmentally retarded patients.

Large parasite load in the epidermisDeep scaly lesionsRecurrence is very high

Figure 6. A 24 yr old with widespreadNorwegian Scabies.

Direct skin to skin contactCrowded living areasFomitesSexually

It can be asymptomatic, 2-6weeks before symptoms develop

Pruritus at nightPimple-like rashTiny burrows on skin

Complaint of pruritusObservation of burrowsSkin biopsy

The larvae stageof the mite familytrombiculidae

The only form thatis parasitic

There arenumerous species

Figure 7. A chigger

Taxonomy

Trombicula alfreddugesi Kingdom: Animalia Phylum: Arthropoda Class: Arachnida Subclass: Acari Family: Trombiculidae

They are found worldwide Different species native to different

regions. North America: Trombicula alfreddugesi In the United States, they are found

mostly in the south, southeast & Midwest.

Morphology of Chiggers

Larvae stagehas 3 pairs oflegs

Adult has 4 pairsof legs

Orange, yellowor red

Figure 8. Larvae and Adult form

Figure 9. Life cycle of Chiggers

They penetrate thin skin, folded &wrinkled skin

It injects a salivary secretion into theskin

The skin reacts by forming a tube-likestructure called a stylostome

The feeding process can last up to 3or 4 days.

Skin itches due to a reaction to thestylostome

Figure 10. Formation of stylostome.

Intense itching & red welts

Figure 11. Characteristic red welts of chiggers.

Described by the Chinese over 2000yrs ago

Caused by a Orientia tsutsugamushiTrombicula akamushi and T.

deliensisRodents serve as reservoirs

Skin rashHeadacheLoss of appetiteSwelling of lymph glandsMuscular aches and pains

Figure 12. Eschar on skin surface.

Weil-Felix TestFluorescent Antibody TestPCR

Treatment & Prevention

Application ofbenzocaine,hydrocortisone,calamine lotion orother anti-itch lotions.

Doxycycline orChloramphenicol

Avoid areas ofinfestation

Premethrin cream Lindane lotion Ivermectin Benzyl benzoate and

Ivermectin Keep surroudings

clean

Chiggers Scabies

Scabies burrow into the skin whilechiggers do not.

Scabies can be transmitted from personto person while chiggers cannot.

The scabies mite completes its entire lifecycle on humans while chiggers do not.

ReferencesGiovan Cosimo Bonomo (1663-1696)http://www.dermato.med.br/hds/bibliography/1998giovan-cosimo-bonomo.htmChiggershttp://ohioline.osu.edu/hyg-fact/2000/2100.htmlChiggershttp://mdc.mo.gov/nathis/arthopo/chiggers/Chiggershttp://www.nyc.gov/html/doh/html/ehs/ehschig.shtmlDonabedian, H. and U. Khazan. 1992. Norwegian Scabies in a Patient with AIDS. Clinical Infectious Diseases. 14:

162-164.Ewing, H.E. 1944. The Trombiculid Mites (Chigger Mites) and Their Relation to Disease. The Journal of Parasitology

30: 339-365.Lofttin, H. 1955. Beat Chiggers and Ticks. The Science News-Letter 68: 42-43.Mathisen, G.E. 1998. Editorial Response: Of Mites and Men: Lessons in Scabies for the infectious Disease Clinician.

Clinical Infectious Diseases 27: 646-648.Phillip, B. C. 1949. Scrub Typhus or Tsutsugamushi Disease. The Scientific Monthly 69: 281-289.Rickettsial Infectionshttp://wwwn.cdc.gov/travel/yellowbook/ch4/rickettsial.aspxScabies picturehttp://www.scabieshotline.org/images/scabies-hand.jpgScrub Typhushttp://history.amedd.army.mil/booksdocs/vietnam/GenMedVN/CH07.htmSarcoptes scabieihttp://www.stanford.edu/group/parasites/ParaSites2009/LeighaWinters_Scabies/LeighaWinters_Scabies.htm,Wendel, K. and A. Rompalo. 2002. Scabies and Pediculosis Pubis: An update of Treatment Regimens and General

Review. Clinical Infectious Diseases 35: 146-151.