USACHPPM’s Human Tick Test Kit
Combating an Eight-Legged Enemy
DOD Human Tick Test Kit Program:
A ‘First Alert’
Although worldwide, mosquitoes rank as the number-one vectors of human disease (led by malaria with 200-500 million cases per year), in the United States ticks are the major culprits. There are 10 tick-borne illnesses of concern in the U.S.: Lyme disease (LD), Rocky Mountain spotted fever (RMSF), human monocytic ehrlichiosis (HME), human granulocytic ehrlichiosis (HGE), babesiosis, relapsing fever, tularemia, Colorado tick fever, Powassan encephalitis, and tick paralysis. Lyme disease accounts for the bulk of the cases (16,273 reported to the Centers for Disease Control and Prevention in 1999, and over 150,000 cases since 1982). Even though the other diseases are less prevalent, they can nevertheless be very serious and sometimes fatal. For example, in 1999, a soldier died after contracting HME during routine training exercises at a CONUS Army installation.
To help combat the tick-borne disease health
threat, the Entomological Sciences Program (ESP) of the U.S. Army Center for
Health Promotion and Preventive Medicine (USACHPPM) provides a free tick
identification and testing service for Department of Defense health clinics in
CONUS. This service is known as the DOD Human Tick Test Kit Program, and it
serves as a ‘first alert’ for tick-bite patients and their health care
providers. The service is free!
Tick attached to human skin
The ESP uses DNA technology known as polymerase chain reaction (PCR) to analyze ticks for evidence of infection with the agents of four tick-borne diseases: LD (Borrelia burgdorferi), RMSF (Rickettsia rickettsii), HME (Ehrlichia chaffeensis) and HGE (unnamed ehrlichia, closely related to Ehrlichia phagocytophila, a pathogen of sheep and cattle, and currently designated ‘agent of HGE’). Live, as well as dead, ticks are tested. In addition, relative tick engorgement level is also noted: the longer a tick is attached, the more engorged (filled with blood) it becomes, and the greater the risk that transmission will occur if the tick is infected. Therefore, potential disease risk increases with engorgement level.
Results of tick I.D. and engorgement level are telephonically reported back to the clinic within 1 day of receipt at ESP; results of analysis are likewise telephonically reported, usually within a week. The original CHPPM Form 321-R is then returned to the clinic with all of the laboratory results annotated on side two of the form. CHPPM Form 321-R can serve as documentation of the tick-bite incident for the patient’s medical record.
In CY 2000, 80 DOD health clinics submitted 3,431 ticks to the ESP. Of these, 84 (22.2%) of the blacklegged ticks were positive for LD, 36 (1.4%) of the lone star ticks were positive for HME, 16 (4.2%) of the blacklegged ticks were positive for HGE, none of the American dog ticks were positive for RMSF, and 6 (1.6%) of the blacklegged ticks were positive for both LD and HGE (see Table). Note that specific tick species were only analyzed for those pathogens for which they are known to be confirmed competent vectors (e.g. American dog ticks were only tested for the agent of RMSF; they do not transmit the other pathogens). Although lone star ticks were analyzed for B. burgdorferi, studies have not shown them to be effective vectors of this pathogen. However, a syndrome resembling Lyme disease has been associated with some bites by lone star ticks, primarily in the southeastern and south central states. It is currently unknown what organism is responsible for those symptoms (perhaps an as yet unidentified strain of B. burgdorferi, or another species of Borrelia entirely; this remains the subject of ongoing controversy and research).
Overall, three tick species remain the most common human biters, particularly in the eastern half of the U.S.: Ixodes scapularis (blacklegged tick, more commonly known as the ‘deer’ tick), Amblyomma americanum (lone star tick), and Dermacentor variabilis (American dog tick). However, depending upon the geographic area of the country, bites are also incurred by other species, including Ixodes pacificus (western blacklegged tick), Dermacentor maculatum (Gulf Coast tick), and Rhipicephalus sanguineus (brown dog tick), among others.