Comparison of PCR with other tests for early diagnosis of canine ehrlichiosis

Abstract

The purpose of the study was to compare the sensitivity of PCR with those of cell culture reisolation of Ehrlichia canis, the indirect fluorescent antibody test (IFA), and Western immunoblotting (WI) in the early diagnosis of canine ehrlichiosis. Five German shepherd dogs were intravenously inoculated with 107 E. canis-infected DH82 cells. Blood was collected on alternate days during a 2-week postinoculation period. Mononuclear cell fractions were harvested and used for E. canis reisolation and DNA extraction for PCR. The plasma was used for assaying antibodies against E. canis. By PCR, the 16S rRNA gene of E. canis was detected in the mononuclear cell specimens collected as early as day 4 to 10 postexposure (PE). E. canis was reisolated from the blood starting on day 2 PE from all five dogs. The indirect fluorescent antibody test and Western immunoblotting could detect E. canis antibodies as early as 2 to 8 days PE. Cell culture reisolation proved to be the most sensitive and definitive for early diagnosis of ehrlichiosis, but it is not very convenient, since it takes a long time (14 to 34 days) to show up positive. The sensitivity of PCR is comparable to or slightly less than that of other established methods; however, the convenience, quickness, and direct nature of detecting E. canis DNA is expected to make PCR more useful for clinical diagnosis.

Prevalence of ehrlichial infection among dogs and ticks in Northeastern Brazil

“…Some authors have argued for the utilization of a combination of IFAT and PCR in diagnosing canine ehrlichiosis, pointing out that these tests are more sensitive and are able to detect the infection in different stages (IQBAL; CHAICHANASIRIWITHAYA; RIKIHISA, 1994;WEN et al, 1997).…”

Specific amplification of Ehrlichia platys DNA from blood specimens by two-step PCR

“…Since morulae are most prevalent in the first episode of thrombocytopenia and may be present only intermittently thereafter, and since the appearance of parasitized platelets is cyclic in nature (3,6), diagnosing CICT by demonstration of E. platys within platelets is unreliable, especially in the chronic stage of the disease. The IFA, which evaluates titer of specific antibodies against E. platys in serum, has been used widely; however, this method suffers from a lack of reliability in terms of assessing current status (8). Furthermore, serologic diagnosis is limited by the fact that successful cultivation of E. platys has never been reported, and the antigens for IFA are not readily available.…”

“…The recently introduced technique of PCR has great potential for improving the ability to diagnose infectious diseases caused by obligate intracellular bacteria. It has been employed to detect various kinds of rickettsial agents of humans and animals (1,2,8,14). A disadvantage of PCR-based DNA detection is the need to confirm the authenticity of the amplified products either by Southern blot hybridization, by DNA sequencing, or by restriction endonuclease cleavage patterns.…”

Consensus Statement on Ehrlichial Disease of Small Animals from the Infectious Disease Study Group of the ACVIM*

“…PCR tests may yield positive results within 4-10 days of exposure to E canis in experimental studies. 53,54 Whereas PCR can become positive in experimentally infected dogs before seroconversion, sensitivity in naturally infected animals currently is unknown. In untreated animals, positive PCR results confirm infection by an ehrlichial species, whereas positive serologic test results only confirm exposure.…”