D331 - Ehrlichia spp.

Description:

Canine ehrlichiosis, a tick-borne disease caused by the rickettsia Ehrlichia species, has been acknowledged worldwide as an important infectious disease of dogs and other canids. Historically, infection with Ehrlichia species has generally been considered to be host specific. For example, Ehrlichia canis was thought to infect only dogs and wild carnivores and Ehrlichia chaffeensis was thought to infect only deer and human beings. Recently, an isolate genetically and antigenically similar to Ehrlichia canis was obtained from veterinarians in Venezuela. Similarly, isolates genetically identical to Ehrlichia risticii, the cause of Potomac horse fever, have been obtained from dogs. Recent evidence indicates that a member of the Ehrlichia phagocytophila group, presumably Ehrlichia equi, causes disease manifestations in cats, dogs, horses, and human beings. Ehrlichia chaffeensis, originally isolated and characterized as a cause of human disease, was found to cause disease in dogs. Collectively, these observations suggest that several Ehrlichia species can be transmitted to a variety of hosts in nature E. chaffeensis, as well as Ehrlichia canis, Ehrlichia equi, Ehrlichia ewingii, can cause disease manifestations and clinicopathologic abnormalities in dogs originating from the same geographic region. Infection with any of these species can cause severe disease manifestations that may be clinically, hematologically, and serologically indistin-guishable from each other.

Diagnosis:

Since readily discernible differences in IFA or Western immunoblot seroreactivity patterns to Ehrlichia canis antigens do not appear to differentiate between the infecting species, molecular detection and speciation of ehrlichial DNA is necessary to determine if predictable differences in therapeutic outcomes can be further correlated with an infecting Ehrlichia species. Several factors, including anticipated duration of infection, therapeutic responsiveness (particularly to tetracycline derivatives), and zoonotic potential, emphasize the importance of determining which Ehrlichia species is causing infection and antibody reactivity to Ehrlichia canis antigen in a dog. For example, Ehrlichia canis causes chronic, frequently subclinical infection with the potential for the development of severe life-threatening disease manifestations whereas Ehrlichia ewingii is considered to cause polyarthritis and potentially self-limiting infection. Ehrlichia canis and Ehrlichia chaffeensis may not be eliminated by doxycycline therapy, whereas therapeutic elimination of Ehrlichia ewingii or Ehrlichia equi is an expected outcome.
PCR amplification of ehrlichial DNA is gaining acceptance as an important adjunct to serologic testing for the diagnosis of canine ehrlichiosis. It was concluded that if the result of PCR test is positive or negative, dogs are either infected or not infected, respectively. The PCR with probes specific for Ehrlichia chaffeensis, Ehrlichia canis, Ehrlichia equi, and Ehrlichia ewingii, was shown to be highly specific and sensitive for the detection and differentiation of Ehrlichia species.

Sample:

1. Whole blood (3 ml) in a lavender top (EDTA) tube.
2. Bone marrow samples.

Special Handling:

Store samples at 4°C until pick up or shipment.

Test Code:

D331

1. Harrus et al. (1998) Amplification of Ehrlichial DNA from Dogs 34 Months after Infection with Ehrlichia canis. J. Clin. Microbiol. 36: 73-76.
2. Dawson et al. (1996) Polymerase chain reaction evidence of Ehrlichia chaffeensis, an etiologic agent of human ehrlichiosis, in dogs from southeast Virginia. Am. J. Vet. Res. 57: 1175–1179.
3. Perez et al. (1996). Ehrlichia canis-like agent isolated from a man in Venezuela: antigenic and genetic characterization. J. Clin. Microbiol. 34: 2133–2139.