Download The Epidemiology of Tick-transmitted Zoonotic Disease

The Epidemiology of
Tick-transmitted
Zoonotic Disease
Dr. Paul Bartlett
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Kenji Sato catching flies – Organic dairy farm
study in the Kickapoo River Valley of Wisconsin
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Grazing organic dairy cows.
Kickapoo River Valley,Wisconsin
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Introduction
• 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.
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Prevention
• Long pants and long sleeves should be
worn when hiking or in tick infested areas
• Insect repellent spray should be used on
skin and clothing
• 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.
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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 disease.
• Tick control in domestic animals is a important
public health consideration and can be
accomplished through dips, powers, and
sprays.
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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 bite.
• Ticks should be removed using tweezers or
fingers protected by a gloves or a tissue.
• Grasp the tick firmly and pull slowly and steadily
– Give him a choice of taking it (head) along or
leaving it behind. Pull slowly. Give him time to
think about it.
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Lyme and Lyme-Like Disease
• Lyme Disease- Dr. Stobierski will talk about this
• Lyme-Like Disease - CDC is currently
investigating
– Unknown infectious agent or it may be an atypical
type of immunologic reaction to the tick proteins
– 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.
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Lone Star tick
Ehrlichia
• There are two ehrlichioses causing
disease in humans. 500 cases of both
have been reported since 1985.
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Ehrlichiolses
• Human Monocytic
Ehrlichiosis (HME) infects mononuclear
phagocytes
– Etiological agentEhrlichia chaffeensis
– Vector- Lone Star tick
Amblyomma
americanuum
– Seen in Southeastern
and South central US
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Ehrlichiolses
• 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
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(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.
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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.
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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.
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photo provided courtesy of Rocky Mountain
Laboratories, NIAID, NIH, Hamilton, Montana)
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Reported cases of Rocky Mountain spotted
fever in the United States, 1942-1996
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Seasonal distribution of reported cases of
Rocky Mountain spotted fever, 1993-1996
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RMSF – Geographical Distribution
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Number of reported cases of Rocky Mountain
spotted fever by state and region, 1994-1998
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Early
(macular)
rash on
sole of foot
Late
(petechial)
rash on
palm and
forearm
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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
host.
American Dog tick
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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.
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RMSF in Animals
• Dogs
– Most of the time the disease is sub-clinical.
Sentinals.
– 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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