1. The Epidemiology of Tick-transmitted Zoonotic Disease
Lecture 4
VM 544 Preventive Veterinary Medicine
Dr. Paul Bartlett
Dr. Paul Bartlett

2. Kenji Sato catching flies – Organic dairy farm study in the Kickapoo River Valley of Wisconsin

3. Grazing organic dairy cows. Kickapoo River Valley,Wisconsin

4. 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.

5. 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.

6. 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.

7. 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.

8. 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

9. Ehrlichia
There are two ehrlichioses causing disease in humans. 500 cases of both have been reported since 1985.

10. 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

11. 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)     

12. 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.

13. Colorado Tick Fever
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.

14. 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.

15. photo provided courtesy of Rocky Mountain Laboratories, NIAID, NIH, Hamilton, Montana)

16. Reported cases of Rocky Mountain spotted fever in the United States, 1942-1996

17. Seasonal distribution of reported cases of Rocky Mountain spotted fever, 1993-1996

18. RMSF – Geographical Distribution

19. Number of reported cases of Rocky Mountain spotted fever by state and region, 1994-1998
                                                                                                  

20. Late (petechial) rash on palm and forearm
Early (macular) rash on sole of foot

21. 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

22. 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.
Untreated cases can have a 13-25% fatality rate while treated cases have about a 5% fatality rate. The fatality rate increases with length of time between onset of symptoms and antibiotic treatment. Illinois Professor – fatality.
There is no vaccine available in the US
Treatment: Tetracycline (doxycycline) or Chloramphenicol

23. 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
Wild animals
Wild rodents, rabbits, and other small mammals are often reservoirs of infection
Large mammals are not a reservoir because they have the lower levels of the agent in their blood.
Ticks can themselves be a reservoir of infection by transmitting the agent through transovarian or transtadial transmission