None — Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is a disease caused by infection with the bacterium, Rickettsia richettsii (R. richettsii). The bacterium is transmitted through the bite of an infected tick. On average, about one percent of ticks in the U.S. carry the bacteria. In the Western part of the U.S. the most common carrier is the Rocky Mountain wood tick (Dermacentor andersoni). The American dog tick (Dermacentor variabilis) is the most common carrier tick in the Eastern part of the U.S.
RMSF isn't very common. The Centers for Disease Control and Prevention estimates just 1,200 cases occur the U.S. every year. More than 50 percent of reported cases have occurred in Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, West Virginia and Washington, DC. Peak incidence occurs from April through September.
People who are infected with RMSF develop symptoms within 3 to 14 days of the tick bite. Initially, a patient may have chills, fever, nausea, severe headache, muscle pain, confusion and a lack of appetite. About two-thirds of people with RMSF develop a rash, typically beginning a few days after the onset of fever, and often starting on the wrists and ankles. Later, patients may develop stomach ache, joint pain, diarrhea and thirst. Those who develop severe illness usually need to be hospitalized. Potential complication of RMSF include: brain damage, organ failure, clotting problems, meningitis, pneumonia and shock. The condition is treated with tetracycline-based antibiotics and supportive care.
RMSF in Dogs
Dogs that spend time outdoors in tick-infested areas are at risk for acquiring RMSF. Symptoms may develop in 4 to 5 days and can include a high fever, blood spots on the lips, gums or other mucous membranes and leg swelling. Later, or during recovery, the damaged skin and tissue on the legs may slough. Other signs of infection may include: abdominal pain, lack of appetite, depression or other altered mental state, cough and circling or head tilting (indications of balance problems).
In the U.S. most dogs with RMSF are seen by veterinarians from March through October. For an unknown reason, the condition is more commonly seen in dogs three and under. German Shepherds have the highest rate of incidence, while English Springer Spaniels tend to have the most severe disease.
Pets as Sentinels of Human Illness
Pets who are sick can sometimes provide clues about the cause of symptoms in humans. For example, RMSF isn't very common in humans, so doctors may not suspect the illness in sick patients. However, if a pet has been diagnosed with the condition, that can be a good clue for diagnosis in an owner who develops similar symptoms.
Jennifer Adler, V.M.D., specialist in Veterinary Internal Medicine Specialist at the Center for Animal Referral and Emergency Services (CARES) Animal Hospital in Langhorne, PA, says since pets and humans share the same spaces, a pet can also be a sentinel for other types of environmentally-related human illnesses, such as Lyme disease or water contamination.
Adler notes, RMSF is not naturally transmitted from one animal or species to another. In the rare instance in which both a dog and owner are infected by RMSF, the infections were most likely acquired while walking in a tick-infested environment.
For general information on Rocky Mountain Spotted Fever or other tick-borne diseases in humans or pets:
American Veterinary Medical Association Centers for Disease Control and Prevention
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