Arthropod disease
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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


Direct disease agents

DIRECT DISEASE AGENTS


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


Scabies1

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


Arthropods as vectors

ARTHROPODS AS VECTORS


Vector borne diseases

VECTOR-BORNE DISEASES

  • MAJOR VECTORS:

    • MOSQUITOS

    • TICKS

    • FLEAS


Mosquito borne diseases

MOSQUITO-BORNE DISEASES


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)


Transmission of dengue virus

TRANSMISSION OF DENGUE VIRUS


Arthropod disease

CDC Dengue Map


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


Tick borne diseases

TICK-BORNE DISEASES


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


Flea borne diseases

FLEA-BORNE DISEASES


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


Thank you

THANK YOU!


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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