Ehrlichiosis in dogs

Ehrlichiosis is a disease which is transmitted to animals and humans by ticks. In canine ehrlichiosis, especially the pathogen Ehrlichia (E.) canis plays a role, which is mainly transmitted by the brown dog tick (Rhipicephalus sanguineus) and may lead to canine monocytic ehrlichiosis (CME). E. canis is a gram-negative, obligatory intracellular bacterium which mainly affects the mononuclear cells of the blood. CME occurs in tropical and moderate climates worldwide. The geographical distribution of E. canis increases with the further distribution of the vector tick which is accelerating due to climate change.

CME is a multisystemic disease which can manifest in acute, subclinical or chronic forms. After an incubation period of 1 – 3 weeks, an acute CME manifests amongst others by high fever, lethargy, weight loss, lymphadeno- and splenomegaly and haemorrhages. Frequently, eye damage occurs, which may lead even to complete blindness. Infl ammatory changes or bleeding
in the meninges may cause various CNS symptoms. Usually, after 2 – 4 weeks, the subclinical phase begins, in which the dogs appear to be healthy and without obvious symptoms, even though high titers of E. canis-specifi c IgG antibodies and changes in the blood values are detectable. In some dogs, this is succeeded by a chronic phase. Here the symptoms resemble those of acute CME again, but are often more pronounced.

Antibodies against E. canis can be found in the serum of specifically infected animals after 12 to 14 days. E. canis-specific IgG antibodies persist over months to years. For the serological detection of the antibodies, different techniques are applied, such as ELISA-based test systems or the indirect immunofluorescence test (IIFT), which is considered to be the gold standard. Since in E. canis infections, IgM antibodies are not consistently formed, detection of IgM antibodies is not suitable. Consequently, for the diagnosis of an acute infection, always two blood samples should be analysed at a time interval of 7 to 14 days, whereby a titer increase to the fourfold of the value of the first blood samples indicates an acute infection.

This applies particularly to samples from endemic regions, where a high seroprevalence is present. If the first blood sample is negative, a second sample should be examined after around two weeks in cases of suspected ehrlichiosis, since dogs have not yet formed antibodies in the early phase of infection. A serological differentiation between E. canis and E. chaffeensis is not possible.

• Anti-Ehrlichia canis ELISA Dog (IgG)