Rocky Mountain Spotted Fever in Dogs
Rocky Mountain Spotted Fever (RMSF)
Rocky Mountain Spotted Fever (RMSF)
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Rocky Mountain Spotted Fever is a tick borne disease caused by the organism Rickettsia rickettsii.
Severity is mild to moderate to severe
Requires a diagnosis by a veterinarian
Resolves within days to weeks with proper treatment
Treatable by a veterinarian
Effective tick control products should be regularly used, avoid areas where ticks may be found
Transmission does not directly occur between animals or animals to people.
Diagnosis requires a physical examination and blood tests
Dogs that are outside and exposed to ticks are most commonly affected.
There are two stages of Rocky Mountain Spotted Fever: Subclinical and Acute.
In the subclinical stage, dogs are infected, but do not show outward signs of the disease. These cases may have laboratory test abnormalities. These dogs typically recover quickly.
In the acute stage, dogs may have a variety of clinical signs, which can mimic many other diseases. These include a loss of appetite, fever, depression, pain in the muscles and joints, swollen lymph nodes, and edema (fluid accumulation) in the face and legs. Some animals develop pneumonia or heart arrhythmias, which can lead to sudden death. Some dogs have gastrointestinal signs such as vomiting and diarrhea. Most dogs have neurological signs (dizziness, depression, stupor, seizures) and these can sometimes become very severe. Many dogs develop hemorrhages in the retina of the eye, and may also have blood in the stool or nose bleeds. Renal (kidney) failure can also occur in these cases. Most of these signs appear 2 to 14 days after the tick bite. In these cases, they may have slight anemia (low red blood cells), a low number of platelets (platelets help blood to clot), and increased liver enzymes as measured by a blood chemistry panel. Some dogs develop ulcerations of the mucous membranes and extremities.
Several blood tests are available which test for the dog's antibodies (proteins produced to fight off the infection) to R. rickettsii. Since we need to look for a change in the antibody levels, usually two tests will be done 2 weeks apart and the results compared. Dogs with an active infection will show a significant rise in the amount of antibody present. A test is also available which detects antigens (protein parts) of R. rickettsii. This test can become positive as early as 4 days after the tick bite. This test is not a blood test, but a small biopsy of the skin at the site of the tick bite.
Dogs with Rocky Mountain Spotted Fever mayhave a low white blood cell count early in the course of infection, and then the cell numbers may increase. During the most severe phase of the disease, the white blood cell counts may again drop, along with the red blood cell counts and platelet numbers. Other organs may be damaged, so liver enzymes, and kidney function tests may be at abnormal levels.
Rocky Mountain Spotted Fever is caused by Rickettsia rickettsii. It is one of many rickettsia organisms, which on the evolutionary scale are between bacteria and viruses. R. rickettsii is transmitted from animal to animal through the bite of the American dog tick (Dermacentor variabilis) and the Rocky Mountain spotted fever tick Dermacentor andersoni. The tick has various life stages, several of which feed on animals. Any of these stages could be infected with R. rickettsii and transmit Rocky Mountain Spotted Fever. The tick must be attached to a host for a minimum of 5-20 hours for transmission of R. rickettsii to occur. Since it is transmitted by ticks, most cases of Rocky Mountain Spotted Fever occur during the tick season from April to September.
Some dogs can develop severe disease and must be hospitalized to treat shock or severe nervous system symptoms. German Shepherds and certain lines of English Springer Spaniels tend to have a more severe form of the disease.
The antibiotics tetracycline, doxycycline, or enrofloxacin are commonly prescribed to treat Rocky Mountain Spotted Fever. Treatment usually lasts for 14-21 days and it is important to finish all medications as directed by the veterinarian.
A general practitioner veterinarian can diagnose and treat most cases of Rocky Mountain Spotted fever.
Treatment costs will depend on the size of the dog. Antibiotics may cost between $75 and $250 for a 3 week course of treatment. Costs will increase significantly if hospitalization and intensive care is required.
If treated within the first several days, most dogs will recover completely - some dogs actually show improvement within hours of starting the antibiotics. Dogs who have severe damage to their nervous systems may not recover completely. It appears that dogs who have had Rocky Mountain spotted fever and recovered are immune to reinfection for years.
Dogs with Rocky Mountain Spotted Fever should be closely monitored until the condition has resolved. . The dog will need to have follow-up examination and blood-work, especially if there were abnormal values on initial blood testing.
In regions where Rocky Mountain Spotted Fever is prevalent, tick control is the key way to prevent the disease. An effective tick control product should be regularly used, tall grass should be avoided, and dogs should be frequently inspected for ticks. Because rodents play a role in the life cycle of the Dermacentor ticks, rodent control is important as well.
People can become infected through a tick bite or the contents of a tick, therefore it is important to wear protective gloves when removing ticks.
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