The Epidemiology of Tick-transmitted Zoonotic Disease - PowerPoint PPT Presentation

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The Epidemiology of Tick-transmitted Zoonotic Disease


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Title: The Epidemiology of Tick-transmitted Zoonotic Disease

The Epidemiology of Tick-transmitted Zoonotic
Dr. Paul Bartlett
Kenji Sato catching flies Organic dairy farm
study in the Kickapoo River Valley of Wisconsin
Grazing organic dairy cows. Kickapoo River
  • In the USA, ticks can carry tularemia, Rocky
    Mountain Spotted Fever (RMSF), Lyme Disease,
    Colorado tick fever, Q fever, and tick-borne
    relapsing fever.
  • These diseases can be transmitted to humans or
    animals through the bite of an infected tick
  • Even though the bite wounds are small, tick bites
    should be avoided because of the possibility of
    the transmission of disease.

  • Long pants and long sleeves should be worn when
    hiking or in tick infested areas
  • Insect repellent spray should be used on skin and
  • Pant legs should be tucked into socks to prevent
    tick attachment
  • Tick checks should be preformed every 3 hours
    when in infested areas
  • This is especially important because transmission
    of some tick borne diseases can be prevented by
    prompt removal of the tick.

Why are Veterinarians Involved?
  • Wild animals are typically the natural
    reservoirs, but domestic animals can bring
    infected ticks into the homes of humans where
    people can become exposed.
  • In this way domestic animals serve as the vector
    of the vector for human tick transmitted
  • Tick control in domestic animals is a important
    public health consideration and can be
    accomplished through dips, powers, and sprays.

Removal of the Attached Tick
  • The key in tick removal is to avoid crushing the
    tick so that its body fluids will not contact
    your skin or the hole in your skin made by the
  • Ticks should be removed using tweezers or fingers
    protected by a gloves or a tissue.
  • Grasp the tick firmly and pull slowly and
  • Give him a choice of taking it (head) along or
    leaving it behind. Pull slowly. Give him time to
    think about it.

Lyme and Lyme-Like Disease
  • Lyme Disease- Dr. Stobierski will talk about this
  • Lyme-Like Disease - CDC is currently
  • Unknown infectious agent or it may be an atypical
    type of immunologic reaction to the tick
  • Tends to be associated with the tick Amblyomma
    americanum (Lone Star tick)
  • Cases often present with an erythema migrans-like
    rash without a fever
  • This disease responds well to
  • antibiotics.

Lone Star tick
  • There are two ehrlichioses causing disease in
    humans. 500 cases of both have been reported
    since 1985.

  • Human Monocytic Ehrlichiosis (HME) - infects
    mononuclear phagocytes
  • Etiological agent- Ehrlichia chaffeensis
  • Vector- Lone Star tick Amblyomma americanuum
  • Seen in Southeastern and South central US

  • Human Granulocytic Ehrlichiosis (HGE) - infects
    granulocytes (neutrophils)
  • Unknown etiological agent (maybe E. equi)
  • Vector- Black-legged ticks
  • Usually more severe and acute than HME and
    sometimes with a fatal febrile syndrome

Blacklegged tick (Ixodes scapularis)  
Western blacklegged tick (Ixodes pacificus)     
Human Erlichiolses (cont)
  • They are clinically indistinguishable and cause
    fever, renal failure, respiratory in sufficiency,
    CNS problems, headache, myalgia, nausea, vomiting
    and infrequently a rash. Can look similar
    clinically to RMSF with out the rash
  • 500 cases reported in US since 1985
  • Co-infections with HGE, Babesia microti, other
    Babesia, and Lyme disease can be serious.

Colorado Tick Fever
  • 200 - 300 cases of this disease occur each year
    in the mountainous areas of the Northwestern US.
  • The disease is characterized by fever, chills,
    headache, and muscle pain.
  • It is usually mild in adults but can be sever in
    approximately 15 of effected children.

Rocky Mountain Spotted Fever (New World Spotted
Fever) (Tick-borne typhus)
  • There are about 1,000 cases of RMSF reported each
    year in the US.
  • Most cases of RMSF occur in the South Atlantic
    States of Virginia, Tennessee, Georgia, North and
    South Carolina.
  • The victims are most often young males who
    contract the disease between April and September.
  • Rickettsia rickettsii is the etiological agent
    for the disease.

photo provided courtesy of Rocky Mountain
Laboratories, NIAID, NIH, Hamilton, Montana)
Reported cases of Rocky Mountain spotted fever in
the United States, 1942-1996
Seasonal distribution of reported cases of Rocky
Mountain spotted fever, 1993-1996
RMSF Geographical Distribution
Number of reported cases of Rocky Mountain
spotted fever by state and region, 1994-1998
Late (petechial) rash on palm and forearm
Early (macular) rash on sole of foot
Vectors for RMSF
  • Dermacentor andersonia is the vector in the
    western part of the US
  • The American Dog tick (Dermacentor variabilis) is
    the vector in the southeast part of the US.
  • Larva and nymphs feed on wild rodents while the
    adults feed of larger mammals and possibly humans
    or domestic dogs.
  • Upon attachment, a 5 to 20 hour

    reactivation time is required
    before the agent
    can enter the

American Dog tick
RMSF in Humans
  • Incubation period is 2-12 days
  • Symptoms include sudden onset, high fever,
    nausea, vomiting, headache, chills, muscle pain
    in the lower back and legs.
  • A diagnostic maculopapular rash can be
    seen in 50 of the
    patients and usually
    starts at the wrist and ankles and
    moves to the trunk. It often

    involves the soles and palms.

RMSF in Animals
  • Dogs
  • Most of the time the disease is sub-clinical.
  • Some dogs can have fever, anorexia, vomiting,
    diarrhea, depression, conjunctivitis, mucopurlent
    oculonasal discharge, cough and petechial or
    ecchymotic hemmorrages on the ocular, oral, and
    genital mucous membranes.
  • Humans are sometimes infected by removing ticks
    from pet dogs
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