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Canine Monocytic Ehrlichiosis (CME)
The etiologic agent of canine monocytic ehrlichiosis (CME), previously known as canine rickettsiosis, canine hemorrhagic fever, tracker dog disease, canine tick typhus, Nairobi bleeding disorder and tropical canine pancytopenia, is the rickettsia Ehrlichia canis. It is a small-gram negative, coccoid bacterium. Ehrlichia canis is mainly transmitted by the brown dog-tick Rhipicephalus sanguineus and has also recently been shown to be transmitted experimentally by the tick Dermacenter variabilis. It has been reported to occur in Asia, Africa, Europe and America. Infection occurs when the infected tick ingests a blood meal and salivary secretions contaminate the feeding site. Once the dog is infected the course of ehrlichiosis can be divided into three phases: acute, subclinical, and chronic.
SIGNS Naturally occurring CME may be manifested by a wide variety of clinical signs. The clinical signs in the acute phase may occasionally be mild and may include depression, lethargy, mild weight loss, loss of appetite, fever, and enlarged lymph nodes. There also may be bleeding under skin. Eyes may look cloudy and may have brown spots. Internal eye bleeding resulting in retinal detachment may occur and lead to blindness.
Other clinical signs may include vomiting, clear or pus-filled discharge form the eys and nose, lameness, loss of movement coordination and difficulty breathing. Ticks are commonly found on dogs during this stage. In most cases, the clinical signs will resolve without treatment. Dogs that do not successfully eliminate the parasite following the acute stage may remain in this stage and may subsequently proceed to the chronic phase of CME.
The common clinical signs of the chronic disease are weakness, depression, anorexia, chronic weight loss, pale mucous membranes, fever and swelling of the limbs, especially of the hind limbs and the scrotum. Bleeding from the gums and under skin is common. Secondary bacterial and protozoal infections, pneumonia, kidney failure, and arthritis may occur during chronic severe disease. Some reproductive disorders have also been associated with chronic CME including; prolonged bleeding during estrus, inability to conceive, abortion and neonatal death. Polymyositis has also been associated with CME. Neurological signs may occur during the acute and chronic disease. These include signs of meningoencephalitis, e.g. arched back, severe neck or back pain, loss of movement coordination, cranial nerve deficits and convulsions. Neurological signs may be attributed to bleedings, and inflammation of the blood vessels.
DIAGNOSIS Diagnosis of CME is based on clinical signs and confirmation by laboratory tests. Presently the indirect immunofluorescent antibody (IFA) test is the most acceptable serological test, although dot-blot enzyme linked immunoassay (ELISA) procedures developed and were shown to be sensitive for the detection of antibodies to E. canis. The presence of anti-E. canis antibody titers at a dilution greater than 1:40 is considered positive (17). In the acute stage of the disease titers may increase rapidly.
TREATMENT Doxycycline for a period of at least three weeks in conjunction with Imidocarb dipropionate is considered the treatment of choice for CME. Doxycycline is frequently used alone where Imidocarb is unavailable or not approved for use. Other drugs can also be effective against E. canis. Supportive treatment should include multi-vitamin supplements. In severe cases blood transfusions should be given.
PREVENTION To date, no effective anti-E. canis vaccine has been developed and tick control remains the most effective preventive measure.
Adapted from
1. Canine Monocytic Ehrlichiosis - An Overview, T. Waner1, A. Keysary1, H. Bark, E. Sharabani and S. Harruss
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
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