Rocky Mountain spotted fever

Scott Speelziek MS (Dr. Speelziek of Mayo Clinic, Rochester has no relevant financial relationships to disclose.)
Karen L Roos MD FAAN, editor. (Dr. Roos of Indiana University School of Medicine has no relevant financial relationships to disclose.)
Originally released December 13, 1993; last updated June 16, 2016; expires June 16, 2019

This article includes discussion of Rocky Mountain spotted fever, rickettsial disease, Rickettsiae rickettsii infection, Rickettsial spotted fever, RMSF, spotted fever group rickettsiosis, and spotted tick fever. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Rocky Mountain spotted fever is a tickborne illness that often has an initial clinical presentation similar to a viral “flu-like” syndrome. Despite a nonspecific presentation, a prompt clinical diagnosis and initiation of antimicrobial therapy are essential to prevent multiple organ system sequelae. Despite a long history of the disease and effective antibiotic treatment since the 1940s, early opportunities for intervention are often missed, resulting in increased morbidity and mortality. In this article, the author reviews the clinical manifestations, pathophysiology, diagnosis, and recommended treatment. The neurologic manifestations of the disease are emphasized.

Key points

 

• Rocky Mountain spotted fever is a tickborne illness due to infection with the gram-negative coccobacillus, Rickettsia rickettsii.

 

• The primary target of infection is endothelial cells of small and medium blood vessels in multiple organ systems, including the skin, lungs, CNS, and renal systems.

 

• Early symptoms are nonspecific, but Rocky Mountain spotted fever should be suspected in patients with high fever, headache, and a macular rash with a possible tick exposure.

 

• Neurologic symptoms of Rocky Mountain spotted fever are headache, seizures, and altered mental status.

 

• Doxycycline at 2.2 mg/kg BID (max 100 mg BID) is first-line treatment for adults and children of ALL ages and should be started while awaiting laboratory confirmation. Chloramphenicol is second-line therapy for those with hypersensitivity reactions and can be used in pregnant patients.

Historical note and terminology

Rocky Mountain spotted fever as a specific clinical disease has been recognized in the United States for more than 130 years. Originally described in Montana and Idaho in the 1870s, Rocky Mountain spotted fever was described in the literature by Maxey in 1899. Following this work, Wilson and Chowning discovered that wood ticks transmitted the infection. The extensive investigative work of Dr. Howard Taylor Ricketts between 1906 and 1909 led to the isolation of the etiologic infective agent for Rocky Mountain spotted fever, Rickettsia rickettsii (Ricketts 1906; Ricketts and Gomez 1908). Unfortunately, Ricketts contracted typhus while studying it and died from typhus in 1910. In 1919, Wolbach published a report confirming that the bacterium responsible for Rocky Mountain spotted fever was carried by wood ticks, and it was an obligate intracellular species (Wolbach 1919). He subsequently named the bacterium rickettsii in Ricketts's memory. In 1921 the Public Health Service allocated ,000 to establish the Rocky Mountain Laboratory in Hamilton, Montana, for the purpose of studying the spread of Rocky Mountain spotted fever and developing effective eradication and prevention measures. The work done at the Rocky Mountain Laboratory during the subsequent 8 decades has provided basic information and understanding about not only Rocky Mountain spotted fever, but also all other rickettsial diseases that have been identified worldwide since the discovery of R rickettsii (Philip 1990). In 2010, the reporting of Rocky Mountain spotted fever was changed to the broader spotted fever rickettsiosis (Woods 2013). Studies have focused on the use of genetic analysis and genotyping to uncover different clades of the bacterium and its evolution (Merhej et al 2014; Paddock et al 2014).

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