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