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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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