Houston Department of Health and Human Services > Epidemiology and Disease Reporting > Epidemiology Corner > Rocky Mountain Spotted Fever

Epidemiology Corner

March 25, 2005

Rocky Mountain Spotted Fever
 
Introduction
Rocky Mountain spotted fever (RMSF) is a disease caused by a type of bacteria that is passed on to humans by a hard tick called the Ixodes tick. Historically, it was first encountered in the year 1896 around the Snake River Valley of Idaho and was originally referred to as the Black Measles. The disease has been detected widely all over the continental United States, Mexico, Central America, southern part of Canada and major parts of South America. The states with the highest incidences of RMSF are North Carolina and Oklahoma.

Male and female Ixodes ticks transmit the organism to vertebrates during feeding by biting. Most patients complain of a history of tick bite; contact with crushed tick tissue, feces and fluids may also lead to an infection. Two types of vectors have been associated with the transmission of the disease. The American dog tick, which feeds on humans, dogs and other medium size animals, is the most commonly identified species associated with human infection. The Rocky Mountain wood tick is also implicated in the disease process. Unlike the Rocky mountain wood tick, the American dog tick is found in Texas.

Mode of transmission
Populations that have frequent exposures to dogs and who live near wooded areas or environments with high grass are all at risk of being infected. The majority of the infections occur between April and September which coincides with the increase in population of the adult type ticks.

Signs and symptoms
Patients generally report to a physician within 5-10 days of a tick bite, initially complaining of severe nausea, vomiting, severe headache, muscle pain and lack of appetite. Since these are largely non specific symptoms, it is an extremely difficult disease to diagnose. Later on, patients often develop a rash, abdominal pain, joint pain and diarrhea. Usually, it is the history of a tick bite, fever and rash that points to the possibilities of a RMSF infection. The rash begins as a small, flat, pink, non-itchy spots on the wrist, forearms and ankle, but turns pale if pressure is applied and becomes elevated on the skin. The characteristic red spotted rash involving the palms or soles is often noted at a later stage of the disease.

Complications of the disease
Untreated RMSF may result in a variety of multi-systemic disorders. It affects the nervous system, respiratory system, gastrointestinal system and renal system. It is generally more fatal in the elderly population. Long term problems following an acute infection include partial paralysis of the lower limbs, gangrene of the toes, fingers, arms, or legs, as well as hearing loss, loss of bladder control and language disorders.

Prevention and control
Limiting contact with ticks is the most effective way of reducing the chance of infection. If there is an exposure to a tick infested environment, removal of tick is an important precautionary measure that has to be taken. The wearing of light colored clothing to enable you to see ticks that are crawling on your clothing is important as well. Also, conducting a body check following exposure to a tick infested environment is advisable. It is also advisable that parents conduct a thorough check on their children for ticks especially their hair once they return from potentially tick infested areas. Dogs and pets should be checked for any tick and prompt removal is recommended.

Treatment
Reporting to a physician immediately if any of the above symptoms occur is important. Good response to prescribed antibiotics by a physician has been widely reported and documented.

For more information visit the Center’s for Disease Control website at http://www.cdc.gov/ncidod/dvrd/rmsf/Index.htm.