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The Epidemiology of Tick-transmitted Zoonotic Disease

Dr. Paul Bartlett

2Kenji 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.

Lone Star tick

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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 agent-

Ehrlichia 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 (Ixodes pacificus)     

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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