Rocky Mountain Spotted Fever in Dogs
Canine Ehrlichiosis and Anaplasmosis continued...
Ticks acquire the rickettsia by feeding on an infected host. A variety of
wild and domestic animals serve as reservoirs. Because of its chronic nature,
cases of ehrlichiosis are seen year-round, not just during the tick season.
The disease occurs in three phases. During the acute phase, the dog develops
fever, depression, loss of appetite, shortness of breath, enlarged lymph nodes,
and, occasionally, signs of encephalitis. These symptoms may suggest Rocky
Mountain spotted fever, Lyme disease, or canine distemper.
Two to four weeks after the onset of the acute phase, the dog enters a
subclinical phase that lasts weeks to months. Some dogs eliminate the infection
during the subclinical phase; others progress to the chronic phase. There
appears to be a breed disposition for developing
chronic ehrlichiosis; German Shepherd Dogs and Doberman Pinschers, for example,
are at increased risk.
During the chronic phase, which appears one to four months after the tick
bite, the disease attacks the dog’s bone marrow and immune
system, producing weight loss, fever, anemia, a hemorrhagic syndrome with spontaneous
bleeding and nose bleeds, swelling of the limbs, and various neurological
signs. These signs may suggest leukemia. Infections of E. ewingii usually show
arthritis as well.
A serologic blood test (IFA) is sensitive for E. canis. However, the test
may not be positive until two to three weeks after the tick bite. A new ELISA
test has been developed that checks for Lyme disease, ehrlichiosis,
anaplasmosis, and heartworm.
Treatment: Tetracycline and doxycycline are highly effective against
rickettsiae, and should be given for at least one month. Improvement in the
acute phase begins within one to two days. Supportive treatment involves
intravenous fluids and blood transfusions. The outlook for recovery is
excellent if treatment is started before the dog develops bone marrow
Prevention: Tick control is the mainstay of prevention. Ticks do not infect
dogs until they have been attached for 5 to 20 hours. Therefore, examining pets
who have been roaming in tick-infested areas, and promptly removing ticks, can
prevent many infections.