The Epidemiology of Tick-transmitted Zoonotic Disease

1
The Epidemiology of Tick-transmitted Zoonotic
Disease
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

• 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.

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.

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