Canine ehrlichiosis is a bacterial disease caused by infectious bacteria from the Ehrlichia genus. Though this disease happens everywhere, it is more common in tropical regions. With global warming, the expansion of tick habitats and the prevalence of cross-border tourism, the chances of the disease spreading to non-endemic areas have increased.
How is a dog infected with Ehrlichia?
Ehrlichiosis is a disease that develops in dogs after being bitten by an infected tick. Disease transmission can occur in as little as three to six hours after the tick attaches, therefore prompt tick removal is crucial. Ehrlichia canis (E. canis) is the most common species of the Ehrlichia genus involved in ehrlichiosis in dogs, but other species of the organism will occasionally be found.
What are the Symptoms of ehrlichiosis?
There are three phases to ehrlichiosis caused by E. canis, acute, sub-clinical and chronic. Each phase of this disease has differing or no symptoms at all.
Acute phase occurs 1 to 3 weeks after the host is bitten by the infected tick. The Ehrlichia organism is replicating in this time period and attaching to white blood cell. Symptoms for this phases of the disease include fever, lymph node swelling, limping and stiffness, reluctance to walk, reduced appetite, tiredness, coughing and breathing difficulty, and abnormal bruising and bleeding.
Dogs will generally move from the acute to the sub-clinical phase after about 1-4 weeks. In the sub-clinical phase, the organism is present but is not causing any outward signs of disease. The bacteria hide in the spleen where it can remain for months or years. Dogs that are infected sub-clinically may eliminate the organisms or may progress to the next stage, chronic ehrlichiosis.
Not all dogs ever progress from the sub-clinical phase to the chronic phase, but when they do, the symptoms become much more serious. Up to 60% of dogs infected chronically with Ehrlichia canis will have abnormal bleeding due to reduced platelet numbers.
Antibody Testing
The presence of antibodies to E. canis is the basis of the serology test. Ehrlichia antibodies can be detected by serology tests, such as ELISA or rapid test. It may be difficult to diagnose infected dogs during the very early stages of infection. The immune system usually takes two to three weeks to respond to the presence of the organism and develop antibodies. In addition, antibodies against Ehrlichia species might remain elevated for many months after disease has resolved.
Real-time PCR testing
Real-time PCR testing detects the presence of Ehrlichia DNA using whole blood samples. The test is most sensitive in the first week of illness and decreases in sensitivity following the administration of appropriate antibiotics (within 48 hours). This test can also determine the species of Ehrlichia infecting dogs. Although a positive PCR result is helpful, a negative result does not rule out the diagnosis, and treatment should not be withheld due to a negative result.
Sample collection tips for Qmini real-time PCR
Collecting more than 200 μl of blood sample, transfer to EDTA anticoagulant tube, and mix thoroughly. Then, transfer 200 μl of whole blood from EDTA tube into the sterile tube containing preservation and mix well for nucleic acid extraction.
