Tick season is here, and apparently in full effect this season. I was told by a patient yesterday that she knows of at least five cases of Rocky Mountain Spotted Fever that have been diagnosed this week. Here is some info about the disease contracted from a tick bite:
Rickettsia rickettsii (Rocky Mountain Spotted Fever)
1. Epidemiology
Rocky Mountain Spotted Fever is the most common rickettsial disease in the United States with 400 - 700 cases occurring annually.
While the disease was originally described in the Rocky Mountain states, it is now most common in the South Central states, including South Carolina.
The organism is transmitted by the bite of an infected tick with most infections occurring from April through September because of more frequent human contact with ticks at this time of the year. The Rickettsia in the tick are in a dormant state and must be activated by the warm blood meal. They are then released into the saliva of the tick. Thus, prolonged exposure (24 - 48 hrs) to an infected tick must occur before the organisms can infect the human host. The principal reservoir for R. rickettsii is the ixodid (hard) tick in which transovarian passage occurs. Wild rodents can become infected and act as a reservoir for the bacteria but they are not considered to be the main reservoir.
2. Clinical syndromes
Rocky Mountain spotted fever begins with the abrupt onset of fever, chills headache and myalgia usually 2 - 12 days after the tick bite. Patients may not recall being bitten by a tick. Rash usually (90% of cases) appears 2 - 3 days later. The rash begins on the hands and feet and spreads centripetally towards the trunk. Rash on the palms and soles is common. Initially, the rash is maculopapular but in the later stages may become petechial and hemorrhagic
Complications from widespread vasculitis can include gastrointestinal symptoms, respiratory failure, seizures, coma and acute renal failure. Complications occur most frequently in cases in which the rash does not develop, since treatment is usually delayed. Mortality rate in untreated patients is 20%.
3. Laboratory diagnosis
Initial diagnosis should be made on clinical grounds and treatment should not be delayed until laboratory confirmation is obtained. A fluorescent antibody test to detect antigen in skin punch biopsies is the fastest way to confirm a diagnosis. However, this test is available only in reference laboratories. PCR based methods are also available but limited to reference laboratories. The Weil-Felix test, which is an agglutination test to detect antibodies that cross react with Proteus vulgaris, is no longer recommended. The primary laboratory diagnostic tool is serology. Indirect fluorescent antibody tests and latex agglutination tests are available for serological diagnosis of Rocky Mountain spotted fever.
4. Treatment, prevention and control
R. rickettsii is susceptible to tetracyclines and chloramphenicol. Prompt treatment is necessary since morbidity and mortality increases if treatment is delayed. No vaccine is available. Prevention of tick bites (protective clothing, insect repellents, etc.) and prompt removal of ticks are the best preventative measures. It is not feasible to attempt to control the tick reservoir
If someone I knew contracted RMSF, I would highly recommend a consistent dosage of Silver Shield.
-Dr. Mason