Ehrlichia risticii - Microscopic exam and molecular diagnosics (PCR)


Ehrlichia risticii (now Neorickettsia risticii) is a Gram - negative bacteria of the genus Neorickettsia, family Anaplasmataceae. Geographically, this pathogen is primarily located in the US and Canada, although outbreaks have also been identified in Europe. Ehrlichia risticii affects horses, causing Potomac horse fever, also known as equine monocytic ehrlichiosis, a potentially fatal febrile illness.

The life cycle of this organism involves an intermediate host where mature, usually arthropod vectors such as ticks, aquatic insects such as caddisflies, mayfly and dragonflies, or flukes. Transmission horses, typically occurs through the bite of arthropods, ingestion of larvae flukes by ingesting water, or by inhalation of infected insects through the air. Ehrlichia risticii Once located in the body of the horse, this parasite colonizes the epithelial cells of the intestines, blood monocytes, and macrophages in lymphoid tissues and others.

Clinical signs associated with Ehrlichia risticii generally occur between 10 and 18 days after infection and include gastrointestinal problems such as diarrhea, fever, depression, anorexia, lethargy, lack of appetite and dehydration. Often loas affected animals develop laminitis several days after the onset of diarrhea. Other symptoms associated with the disease include leukopenia, congestion of the mucous membranes and hypercoagulability. In pregnant mares, infection with this organism can cause abortions. In developing laminitis horses, usually 3 to 5 days after the onset of diarrhea, the outcome can be fatal.

Recommended tests for diagnosis:


The diagnosis is based on detecting antibodies, or by detecting its DNA molecular diagnostic methods (PCR).

Serologic tests, and require time to have developed antibodies to identify the genus Ehrlichia to cause infection but not the species. As a result, the molecular diagnosis as the most sensitive for the identification of Ehrlichia risticii method is recommended.

Tests in IVAMI:


  • Molecular diagnosis (PCR), to detect Ehrlichia risticii DNA.

Recommended sample:


  • EDTA whole blood collected (1 to 2 mL).
  • dregs

It is recommended to perform the assay in both blood sample and faeces, since the presence of the organism in the blood and feces do not necessarily coincide.


Preservation and shipment of sample:


  • Refrigerated (preferred) for less than 2 days.
  • 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: