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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

Arthropod Disease

Surbhi Modi, MD, MPH

Preventive Medicine Resident

Emory University School of Medicine

September 20, 2007


Objectives
OBJECTIVES

  • Understand the role of arthropods in human disease

  • Recognize arthropods implicated in important human diseases

  • Describe important vector-borne diseases


What are arthropods
WHAT ARE “ARTHROPODS”?

  • Largest phylum of animals – 80% of described animal species are arthropods

  • Include insects, spiders, crustaceans


Medical entomology
MEDICAL ENTOMOLOGY

  • Direct parasitism or injury

  • Indirect injury as disease vectors



Scabies
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



Scabies2
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


Brown recluse spider bites
BROWN RECLUSE SPIDER BITES

  • Found in midwest & south-central US

  • “Reclusive” nature

  • Found inside shoes, clothing, attics, cardboard boxes, etc.

  • Be careful of misdiagnosis!


Brown recluse spider bites1
BROWN RECLUSE SPIDER BITES

  • Painless bite

  • Followed by erythema, swelling, tenderness


Brown recluse spider bite
BROWN RECLUSE SPIDER BITE

  • Skin necrosis

  • Sphingomyelinase D

  • Rare systemic reactions

  • Routine treatment

  • Dapsone?

  • Antivenom not widely available


Black widow spider bites
BLACK WIDOW SPIDER BITES

  • Found throughout US & worldwide

  • “Red hourglass”

  • Neurotoxic venom

  • Pain but NO necrosis

  • Abdominal rigidity

  • Rx = antivenom


Other arthropods directly causing disease
OTHER ARTHROPODS DIRECTLY CAUSING DISEASE

  • Allergic reactions

    • Bites/Stings

    • Dust mites/Cockroaches

  • Myiasis



Vector borne diseases
VECTOR-BORNE DISEASES

  • MAJOR VECTORS:

    • MOSQUITOS

    • TICKS

    • FLEAS



Dengue fever
DENGUE FEVER

  • Dengue virus is a flavivirus

  • Transmitted by aedes mosquitoes

  • Composed of single-stranded RNA

  • Has 4 serotypes (DEN-1, 2, 3, 4)




Dengue in the united states
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


Yellow fever
YELLOW FEVER

  • Flavivirus transmitted by Aedes mosquito

  • Illness varies from flu-like to severe hemorrhagic fever

  • Case fatality rate of up to 20%


Yellow fever distribution
YELLOW FEVER DISTRIBUTION

Endemic areas: Africa/South America


Yellow fever vaccine
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)


West nile virus
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


West nile virus epidemiology
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


West nile virus1
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


West nile virus2
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


Other mosquito borne illnesses
OTHER MOSQUITO-BORNE ILLNESSES

  • Malaria

  • Lymphatic filariasis

  • Rift Valley fever

  • Other encephalitides:

    • Eastern equine encephalitis

    • St. Louis encephalitis

    • Western equine encephalitis

    • Japanese encephalitis


Prevention of mosquito borne illness
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



Tularemia
TULAREMIA

  • Pathogen: Francisella tularensis

  • ≥ 10 organisms can cause disease

  • Vector: Deer flies, Dermacentor & Amblyomma ticks

  • Occurs throughout N. America & Europe


Tularemia1
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


Lyme disease
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


Lyme disease1
LYME DISEASE

  • Stage 1: Early Localized

  • Stage 2: Early Disseminated

  • Stage 3: Late Chronic

  • Clinical Diagnosis

  • Treatment: doxycycline


Southern tick associated rash illness
SOUTHERN TICK-ASSOCIATED RASH ILLNESS

  • Pathogen: Borrelia Lonestari??

  • Vector: Lone Star Tick (Amblyomma americanum)

  • Southern US & along coast to Maine


Stari
STARI

  • Erythema migrans

  • No arthritis, neurological or chronic symptoms

  • True incidence unknown


Other tick borne diseases
OTHER TICK-BORNE DISEASES

  • Rocky Mountain Spotted Fever

  • Ehrlichiosis

  • Babesiosis

  • Relapsing Fever

  • Colorado Tick Fever

  • Tick-Borne Relapsing Fever

  • Tick Typhus


Prevention of tick borne disease
PREVENTION OF TICK-BORNE DISEASE

  • Proper clothing

  • Combination of skin & clothing repellant

  • Avoid grassy areas with shrubs

  • Perform daily skin checks for ticks



Plague
PLAGUE

  • Pathogen: Yersinia pestis

  • Vector: Oriental rat fleas (Xenopsylla cheopsis)

  • Occurs worldwide: 1000 – 3000 cases annually


Plague1
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



Sources
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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