Dogs : Canine Monocytic Ehrlichiosis

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 a tick-borne disease caused by rickettsia Ehrlichia canis, a small Gram-negative, coccoid bacterium. Ehrlichia canis is transmitted by the brown dog-tick Rhipicephalus sanguineus. The disease has been reported to occur in Asia, Africa, Europe, and America. To date, no effective vaccine has been developed and tick control remains the most effective preventive measure.

The course of ehrlichiosis can be divided into three phases: acute, subclinical, and chronic, each one being characterized by specific signs. Signs of the acute phase may include depression, lethargy, fever, enlarged lymph nodes, and occasional bleeding under skin and in the internal eye that may result in retinal detachment and blindness. Other clinical signs may include vomiting, clear or pus-filled discharge form the eyes 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 subsequently proceed to the chronic phase characterized by bacterial and protozoan infections, pneumonia, kidney failure, arthritis, prolonged bleeding during estrus, inability to conceive, abortion, and neonatal death.

 Neurological signs may occur during the acute and chronic disease. These include signs of meningoencephalitis, such as arched back, severe neck or back pain, loss of movement coordination, cranial nerve damage and convulsions. Some dogs may develop polymyositis.

Diagnosis of canine monocytic ehrlichiosis is based on clinical signs and laboratory tests. Presently the indirect immunofluorescent antibody (IFA) test is the most acceptable serological test, although dot-blot enzyme linked immunoassay (ELISA) procedures have been shown to be sensitive for the detection of antibodies to E. canis. 

The presence of antibody titers at a dilution greater than 1:40 is considered positive. In the acute stage of the disease titers may increase rapidly. Doxycycline for a period of at least three weeks in conjunction with imidocarb dipropionate is the treatment of choice. Doxycycline is frequently used alone where imidocarb is unavailable or not approved for use. Other drugs can also be effective. In severe cases blood transfusions are given.