Ehrlichia canis - Microscopic exam and Molecular diagnosis (PCR)

Information 22-09-2015.

Ehrlichia canis is an intracellular gram - negative bacteria of the genus Ehrlichia, the Anaplasmataceae family, causing canine monocytic ehrlichiosis. Geographically, this pathogen is primarily located in the US, South America, Asia and Africa. Ehrlichia canis primarily affects dogs, wolves and other canids, but can also infect cats and people.

The life cycle of this microorganism involves intermediate host where mature, arthropod vectors usually infected ticks (specifically Dermacentor variabilis and Rhipicephalus sanguineus), who acquire the infection during feeding in the stages of larvae or nymphs of ticks. For a new feed infect a new host. After infection, Ehrlichia canis infects macrophages, and these subsequently colonize the spleen, liver and lymph nodes. The organism multiplies in circulating monocytes and subsequently in the mononuclear phagocytic cells of the whole organism. Infected monocytes bind to vascular endothelial cells and initiate a vasculitis and infection of subendothelial cells. Inside the cells, this microorganism form intracellular pools (morulae) , which are transitory.

In Ehrlichia canis infected after an incubation period of 1 to 3 weeks, animals clinical signs associated with infection manifest, although some infected animals can remain asymptomatic for months. Usually, the duration of clinical signs of the disease is 2 months. In most cases, the animals recover without treatment, depending on the response of the immune system of the animal. Three manifestations usually enrolled clinicopathological stages.

• Acute phase. In this first phase, they may manifest signs include fever, anorexia, lethargy, lymphadenopathy, splenomegaly, leukopenia, thrombocytopenia and non - regenerative anemia. The acute phase of the disease is largely due to a vasculitis. Usually, most of the affected dogs recover at this stage. However, in other cases, infected animals progress to the subacute and chronic phase.

• Subacute phase. Affected animals may have hipergammaglobulinemia, thrombocytopenia and anemia. In these cases, the disease can last for months or even years.

• FaseFase chronic. Associated signs and symptoms may include ocular and meningeal involvement, pancytopenia, bone marrow suppression and bleeding. Mortality can be elevated in cases progress to the chronic phase.

Other signs and symptoms may include associated uveitis, retinal hemorrhages and central nervous system disease CNS. In addition, animals in the acute and subacute stage may have a typical cell lymphocytosis granularity lymphocytic leukemia.

Recommended tests for diagnosis:

The diagnosis is based on microscopic identification of clusters of intracellular bacteria (morulae) that can be observed in blood smears; in detecting antibodies; or detecting DNA by molecular diagnostic methods (PCR).

Microscopic examination looking for groups (morulae) does not guarantee identification, because the groups are transitory, and the sensitivity of this test is very low. On the other hand, serological tests, and require time to have developed antibodies to identify the genus Ehrlichia to cause infection but not the species. Furthermore, detection of antibodies by ELISA does not distinguish between current and previous exposure infection. As a result, molecular diagnosis as the most sensitive and specific for Ehrlichia canis identification method is recommended. Molecular diagnostic methods help confirm the causal agent, reduce the time needed to confirm the clinical diagnosis, help tell if a dog is free from infection, and thereby reduce the risk of human infection.

Tests in IVAMI:

• Microscopic examination for bacteria grouped observation intracellular (morulae) in neutrophils.
• Molecular diagnosis (PCR), to detect Ehrlichia canis DNA.

Recommended sample:

• Whole blood collected in EDTA or ACD (1 to 2 mL), synovial fluid, or possible tick own transmitter.

Preservation and shipment of sample:

• Refrigerated (preferred) for less than 2 days (essential for microscopic examination).
• Frozen: over 2 days (for molecular diagnostic tests only).

Delivery term:

• Microscopic examination: 24 hours.
• Molecular diagnosis (PCR): 24 to 48 hours.

Cost of the test:

Consult ivami@ivami.com