Rocky Mountain Spotted Fever

Rocky Mountain Spotted Fever (RMSF) is a rickettsial disease that can infect both dogs and humans. This disease spreads by ticks and caused by a small gram-negative obligate intracellular parasite named Rickettsia rickettsii. In many cases, the dog will be healthy within 2 weeks, but seeking veterinary care is recommended if you suspect that your dog suffers from Rocky Mountain Spotted Fever because severe cases can be deadly if left untreated.

Rocky Mountain spotted fever is most common during the period of the year when ticks are active. A majority of the infected dogs are less than 3 years old and have been living in or visiting habitats where ticks can be found.

 

Transmission

The disease is transmitted to dogs via a number of hard-bodied ticks. A majority of the cases in dogs are caused by ticks from the genus Dermacentor, but Amblyomma americanum and Rhipicephalus sanguineous have also been shown to carry Rickettsia rickettsii.

Symptoms

• Fever in the 102.6-104.9º F
• Hemorrhages on exposed mucosal surfaces
• Vasculitis that leads to oedema in the extremities- e.g. swollen ears, prepuce and scrotum
• A red rash
• Joint swelling
• Dyspnea
• Myalgia
• Meningoencephalitis that causes neurological symptoms, e.g. vestibular ataxia    

Incubation period of Rickettsia rickettsii is just 2 days to over 2 weeks. After the incubation period, the organism will enter the circulatory system of the dog, and proceed to invade the endothelial cells of the venules and capillaries where the organisms can start multiplying rapidly. Eventually, this can lead to vasculitis, oedema, vascular collapse, shock and haemorrhage. Brain, heart, kidneys and skin are usually the most damaged parts of the dog's body.

Treatment

• The antibiotic treatment should start within 24-48 hours of onset of clinical signs. If the dog is suffering from an advanced form of RMSF, it might not respond to antibiotics treatment.
• Fluid therapy should however be used with caution due to the risk of pulmonary and cerebral oedema.
• Two of the most commonly used antibiotics are tetracycline and doxycycline. Tetracycline is normally administered three times per day, 22-30 mg per kg body weight.
• Doxycycline is given only twice a day, and no more than 10-20 mg per kg body weight.
• Chloramphenicol is also the drug of choice for pregnant bitches and it also can be given to puppies at the rate of 15-30 mg per kg body weight three times per day.
• In older dogs, enrofloxacin is also effective, 3 mg /kg body weight given twice a daily.
• Retinal hemorrhage, chorioretinitis and other serious lesions can require systemic corticosteroid administration.

Prevention

• Check the dog for ticks several times a day and remove them.
• Anti-tick treatments can be used to discourage ticks. Fiprinol and Permethrin are effective against ticks.
• Use of an anti-tick collar.
• Limit the dog's access to tick infested habitats, at least during the warm season when ticks are active.
• There is no Rocky Mountain spotted fever vaccine.