Chronic Ehrlichiosis

Dogs who spend time around trees are vulnerable to tick-borne diseases like ehrlichiosis

Chronic ehrlichiosis is an advanced stage of infection by the ehrlichia rickettsia, which is transmitted by the brown dog tick and the lone star tick who feed off and transmit an ehrlichia organism into the dog's bloodstream. Every dog the tick bites is exposed to ehrlichia, and has the potential to become infected. Since the disease doesn't show symptoms until it is well-advanced, prevention is the best treatment.

Symptoms

Lethargy is an early warning sign of ehrlichiosis

The acute stage of the disease generally shows no outward signs at all, and can begin as soon as one week after exposure and last for up to a month. Dogs begin showing depression, fever, lethargy and joint pain during the subclinical phase, which can last for years. If the dog's immune system doesn't eliminate the ehrlichia, the disease moves into the chronic phase. Weight loss, anemia, fluid accumulation in the legs and fever can occur, and in severe cases the dog may begin displaying neurological signs such as a head tilt, circling or seizures.

Diagnosis

A blood test can show if a dog has been exposed to ehrlichia

Chronic ehrlichiosis is diagnosed by a combination of physical exam and multiple blood tests. The most common test looks for antibodies, but if the dog is very weak and not producing enough antibodies, the test may come back as a false negative. Additionally, a positive test means the dog has been exposed to the disease, not that it is necessarily infected. Newer tests look for the ehrlichia organism itself, but their inability to distinguish between live and dead organisms means they cannot gauge the extent of the infection. A comprehensive workup would include both tests if ehrlichia is suspected.

Treatment

In severe cases, a blood transfusion may be necessary

There is no cure for ehrlichia once it has reached the chronic stage, and symptoms may return off and on for the rest of the dog's life. Doxycycline is the drug of choice to fight ehrlichia, although results may not be seen for up to a month, and is administered for six to eight weeks. Intravenous fluids will help with dehydration, and severe cases may require a blood transfusion. Corticosteroids may be administered if the dog's immune response to the organism begins to destroy platelets or cause arthritis.

Prognosis

If the infection is too far advanced, the dog may not respond to treatment

Chronic ehrlichiosis has a guarded prognosis. If the infection has progressed to the point where the bone marrow is not producing adequate blood cells, the dog may not respond to treatment.

Prevention

Dogs who spend time among hedges are more likely to be exposed to ticks

A monthly flea and tick preventative will kill any ticks that attach, but you should always examine your dog after he spends time outside. Ticks tend to live on vertical surfaces, such as trees, shrubs and fences and can hide in the dog's ears or between his toes.

References

• Veterinary Clinical Pathology Clerkship Program: An Overview of Canine Ehrlichiosis
• Drs. Foster and Smith: Pet Education - Ehrlichiosis in Dogs
• Working Dogs: Canine Ehrlichiosis