What Is Rocky Mountain Spotted Fever (RMSF)

Rocky Mountain spotted fever (RMSF), which is caused by the bacteria Rickettsia rickettsii, is the most severe tick-borne rickettsial illness in the United States. The highest incidence of RMSF is reported from the southeastern and south-central regions. In 2008, Tennessee had the fourth highest number of reported cases in the United States.The rate of reported RMSF was 3.75 cases/100,000 population in Tennessee, nearly 4.5 times the nationally reported rate of 0.84 cases/100,000 population. Spatial clusters of increased illness severity and death were also identified among persons with RMSF in western Tennessee in a study of 2001–2005 national surveillance data.

ELISA For Rocky Mountain Spotted Fever (RMSF)

During the study period, the focus of RMSF testing shifted away from indirect immunofluorescent assay (IFA) immunoglobulin (Ig)G assays, concomitant with a 2004 change in the case definition that included qualitative assays (ELISA) for categorization of probable cases. While only 2.8% of cases reported in 2001 were based on ELISA testing, this percentage increased to a mean of 38.3% for 2005–2007 (. Although the specific assay used was not always provided, at least 11% of cases reported using assays that detected IgM antibodies. Use of polymerase chain reaction (PCR), culture, or immunochemical stains for RMSF diagnosis was noted for less than 0.5% of reported cases.

Rocky Mountain Spotted Fever(RMSF) Symptoms

Rickettsia rickettsii is transmitted by the American dog tick, Dermacentor variabilis, which is common in the southeastern United States. Symptoms commonly include fever, headache, myalgia, and rash. Although patients occasionally present on the first day of symptoms with an influenza-like illness accompanied by various rashes, the distinguishing maculopapular to petechial rash often is not apparent until several days after symptom onset. Notably, 10–20% of patients have no rash.The early nonspecific presentation can cause delays in diagnosis and treatment. The median delay between first visiting a health care provider and starting antibiotics has been reported to be five days.This delay in treatment can result in severe outcomes, including death or long-term neurologic deficits. Treatment with inappropriate antibiotics also increases the risk of death. Doxycycline is the recommended treatment of children and adults. The American Academy of Pediatrics (AAP) describes doxycycline as a first-line treatment of suspected RMSF in children of all ages .

Rocky Mountain Spotted Fever(RMSF)In Dogs

In August 2007 and March 2008, the Los Angeles County Veterinary Public Health and Rabies Control Program (LACVPH) was notified about two ill dogs on the same property suspected of having Rocky Mountain spotted fever, a rare condition in the area. Both dogs were seropositive to spotted fever group rickettsiae (SFGR), as established by testing at the commercial laboratory, and had a heavy infestation with the brown dog tick Rh. sanguineus. The LACVPH reviewed the clinical history, treatment outcome, and commercial laboratory testing results of these dogs. Whole blood treated with EDTA and serum were collected from both case dogs and from two housemate apparently healthy dogs and submitted to the Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention (CDC) (Atlanta, GA) for further testing. Ticks were also collected from the property and dogs and submitted to the CDC for testing. The owner was advised on tick control and prevention measures.

ELISA For Rocky Mountain Spotted Fever (RMSF) Related Studies

1.Emily Mosites et al.(2009).Knowledge, Attitudes, and Practices Regarding Rocky Mountain Spotted Fever among Healthcare Providers, Tennessee.Am J Trop Med Hyg. 88(1):162-6.

2.Emily Beeler et ai.(2011).A Focus of Dogs and Rickettsia massiliae–Infected Rhipicephalus sanguineus in California.Am J Trop Med Hyg.84(2):244-9.

3.John J. Openshaw et al.(2010).Rocky Mountain Spotted Fever in the United States, 2000–2007: Interpreting Contemporary Increases in Incidence.Am J Trop Med Hyg . 83 no. 1