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Arthropod Disease

Arthropod Disease . Surbhi Modi, MD, MPH Preventive Medicine Resident Emory University School of Medicine September 20, 2007. OBJECTIVES . Understand the role of arthropods in human disease Recognize arthropods implicated in important human diseases Describe important vector-borne diseases.

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Arthropod Disease

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  1. Arthropod Disease Surbhi Modi, MD, MPH Preventive Medicine Resident Emory University School of Medicine September 20, 2007

  2. OBJECTIVES • Understand the role of arthropods in human disease • Recognize arthropods implicated in important human diseases • Describe important vector-borne diseases

  3. WHAT ARE “ARTHROPODS”? • Largest phylum of animals – 80% of described animal species are arthropods • Include insects, spiders, crustaceans

  4. MEDICAL ENTOMOLOGY • Direct parasitism or injury • Indirect injury as disease vectors

  5. DIRECT DISEASE AGENTS

  6. SCABIES • Caused by the mite Sarcoptes scabei • Mites burrow under the skin – takes <3 minutes • Linear burrows that contain mites & their eggs • Especially in the webbing between fingers and the folds of the wrists • Genital lesions common • Spread by skin-skin contact • Secondary infections • Norwegian scabies

  7. SCABIES

  8. SCABIES • Clinical diagnosis, but can confirm by microscopy • Treatment: • Ivermectin • Lindane, Permethrin, Crotamiton • Prevent Re-infection • Treat ALL family & close contacts • Clean environment • Warn patients that itching may continue for 2 – 4 weeks after treatment initiated

  9. BROWN RECLUSE SPIDER BITES • Found in midwest & south-central US • “Reclusive” nature • Found inside shoes, clothing, attics, cardboard boxes, etc. • Be careful of misdiagnosis!

  10. BROWN RECLUSE SPIDER BITES • Painless bite • Followed by erythema, swelling, tenderness

  11. BROWN RECLUSE SPIDER BITE • Skin necrosis • Sphingomyelinase D • Rare systemic reactions • Routine treatment • Dapsone? • Antivenom not widely available

  12. BLACK WIDOW SPIDER BITES • Found throughout US & worldwide • “Red hourglass” • Neurotoxic venom • Pain but NO necrosis • Abdominal rigidity • Rx = antivenom

  13. OTHER ARTHROPODS DIRECTLY CAUSING DISEASE • Allergic reactions • Bites/Stings • Dust mites/Cockroaches • Myiasis

  14. ARTHROPODS AS VECTORS

  15. VECTOR-BORNE DISEASES • MAJOR VECTORS: • MOSQUITOS • TICKS • FLEAS

  16. MOSQUITO-BORNE DISEASES

  17. DENGUE FEVER • Dengue virus is a flavivirus • Transmitted by aedes mosquitoes • Composed of single-stranded RNA • Has 4 serotypes (DEN-1, 2, 3, 4)

  18. TRANSMISSION OF DENGUE VIRUS

  19. CDC Dengue Map

  20. DENGUE IN THE UNITED STATES • Small risk for dengue outbreaks in US – endemic & among travelers • Treatment: • Supportive care: fluids, rest, antipyretics • Monitor blood pressure, hematocrit, platelet count, level of consciousness

  21. YELLOW FEVER • Flavivirus transmitted by Aedes mosquito • Illness varies from flu-like to severe hemorrhagic fever • Case fatality rate of up to 20%

  22. YELLOW FEVER DISTRIBUTION Endemic areas: Africa/South America

  23. YELLOW FEVER VACCINE • Effective vaccine is available • Side effects are generally mild, flu-like symptoms • Rare occurrence of serious complications – encephalitis, yellow fever vaccine-associated viscerotropic disease (YEL-AVD)

  24. WEST NILE VIRUS • WNV isolated in Uganda in 1937 • First identified in the US in 1999 • Important public health problem in US • Recent fatality in GA from WNV Culex mosquito laying eggs

  25. WEST NILE VIRUS: EPIDEMIOLOGY • Peak incidence: August – September • Transmission occurs primarily via bite of infected mosquito • Mosquitoes are infected by feeding on infected birds • Secondary modes of transmission : • Organ transplant • Blood transfusion • Breastmilk/transplacental • Occupational exposure

  26. WEST NILE VIRUS • Clinical suspicion is key to making early diagnosis • 80% never develop clinical symptoms • Mild Disease: West Nile Fever • Severe Disease: West Nile Meningitis, West Nile Encephalitis, and West Nile Poliomyelitis

  27. WEST NILE VIRUS • Supportive treatment • Clinical trials for alpha-interferon • WNV is on the list of nationally notifiable arboviral encephalitides • GA also investigates dead birds

  28. OTHER MOSQUITO-BORNE ILLNESSES • Malaria • Lymphatic filariasis • Rift Valley fever • Other encephalitides: • Eastern equine encephalitis • St. Louis encephalitis • Western equine encephalitis • Japanese encephalitis

  29. PREVENTION OF MOSQUITO-BORNE ILLNESS • Primary prevention relies on measures to decrease mosquito bites • Insect repellants: Permethrin, DEET, Picaridin, Oil of lemon eucalyptus • Protective clothing • Environmental control

  30. TICK-BORNE DISEASES

  31. TULAREMIA • Pathogen: Francisella tularensis • ≥ 10 organisms can cause disease • Vector: Deer flies, Dermacentor & Amblyomma ticks • Occurs throughout N. America & Europe

  32. TULAREMIA • Multiple clinical syndromes • Clinical course: febrile, flu-like attack • Cutaneous form is most common • Inhalational form is most likely route for BT attack • Vaccine under FDA review • Treatment = streptomycin

  33. LYME DISEASE • Pathogen: Borrelia burgdorferi • Vector: Black-legged or Deer Tick (Ixodes) • Occurs throughout the US but majority of cases in the Northeast and Great Lakes area • Most common vector-borne infxn in US

  34. LYME DISEASE • Stage 1: Early Localized • Stage 2: Early Disseminated • Stage 3: Late Chronic • Clinical Diagnosis • Treatment: doxycycline

  35. SOUTHERN TICK-ASSOCIATED RASH ILLNESS • Pathogen: Borrelia Lonestari?? • Vector: Lone Star Tick (Amblyomma americanum) • Southern US & along coast to Maine

  36. STARI • Erythema migrans • No arthritis, neurological or chronic symptoms • True incidence unknown

  37. OTHER TICK-BORNE DISEASES • Rocky Mountain Spotted Fever • Ehrlichiosis • Babesiosis • Relapsing Fever • Colorado Tick Fever • Tick-Borne Relapsing Fever • Tick Typhus

  38. PREVENTION OF TICK-BORNE DISEASE • Proper clothing • Combination of skin & clothing repellant • Avoid grassy areas with shrubs • Perform daily skin checks for ticks

  39. FLEA-BORNE DISEASES

  40. PLAGUE • Pathogen: Yersinia pestis • Vector: Oriental rat fleas (Xenopsylla cheopsis) • Occurs worldwide: 1000 – 3000 cases annually

  41. PLAGUE • Most common form = bubonic plague (swollen, tender lymph nodes) • Pneumonic plague: high fever, cough, hemoptysis, difficulty breathing • 50 - 60% case fatality without abx • Treatment: streptomycin • 2nd line: gentamicin, tetracyclines

  42. THANK YOU!

  43. SOURCES • The Physician’s Guide to Arthropods of Medical Importance • Introduction to Medical Entomology • www.cdc.gov • www.who.int • http://www.wikipedia.org/ (For all the great pictures!)

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