Hello. I'm Dr Chris Paddock, with the Rickettsial Zoonoses Branch at the Centers for Disease Control and Prevention (CDC). I am speaking with you as part of the CDC Expert Commentary series on Medscape about the 2016 updated guidelines for the diagnosis, treatment, and management of tickborne rickettsial diseases endemic to the United States. The guidelines address several of these bacterial infections, including Rocky Mountain spotted fever, Rickettsia parkeri rickettsioses, Rickettsia 364D rickettsiosis, human anaplasmosis, and diseases caused by three distinct Ehrlichia species. These guidelines will provide you with the latest information about the epidemiology, clinical characteristics, laboratory diagnosis, treatment, and prevention of these infections, which range from moderately severe to life-threatening.
Here's the good news: Doxycycline is the drug of choice to treat all tickborne rickettsial diseases in children and adults. Yes, you heard me correctly— doxycycline is safe for use in young children to treat rickettsial infections. For this reason, early recognition and prompt initiation of doxycycline are crucial to preventing adverse clinical outcomes or death.
The signs and symptoms of tickborne rickettsial diseases during the first few days of illness are typically nonspecific; they are shared by many other infectious and some noninfectious conditions. Early manifestations often include fever, headache, malaise, and myalgia. Rash is a classic finding in Rocky Mountain spotted fever and R parkeri rickettsiosis, but it is generally not identified until the third or fourth day of the illness, and is less commonly observed in ehrlichiosis or anaplasmosis. R parkeri rickettsiosis and Rickettsia species 364D rickettsiosis are distinct in that these infections are associated with an inoculation eschar at the site of tick attachment (Figure).
Figure. Inoculation eschars at the site of tick attachment in a patient infected with R parkeri. Courtesy of Centers for Disease Control and Prevention.
Ehrlichiosis and anaplasmosis are often characterized by leukopenia, thrombocytopenia, and mildly elevated levels of hepatic transaminases. Rocky Mountain spotted fever, and ehrlichiosis caused by Ehrlichia chaffeensis, are the most severe of these infections, and a delay in therapy of more than 5 days may lead to severe manifestations, including acute renal failure, pulmonary or cerebral edema, shock, myocarditis, and death. Untreated Rocky Mountain spotted fever can be a highly lethal disease, with a case-fatality rate that exceeds 20%.
The clinical diagnosis of tickborne rickettsial diseases is challenging, but is enhanced by clinician awareness of the seasonality and distribution of these infections. The tick species that transmit these infections are most active starting in spring, summer, and into early fall. Confirmatory laboratory assays are crucial to corroborate clinical diagnoses and to provide accurate surveillance data for tickborne rickettsial diseases, but doxycycline therapy should always be initiated on the basis of clinical suspicion, and never delayed for the result of a confirmatory test.
The reference standard for the diagnosis of tickborne rickettsial diseases is the indirect immunofluorescence antibody assay. This test is most effective when paired serum samples are evaluated in tandem, with the initial specimen obtained as soon as possible after the onset of illness, and the second sample collected 2-4 weeks after recovery from the illness. A fourfold or greater rise in antibody titer provides confirmation of infection.
Serology of tickborne rickettsial diseases is typically group-specific and generally cannot be used to ascribe a species-specific etiology. Polymerase chain reaction (PCR) assays of DNA extracted from whole blood collected during the acute illness is a superior method to confirm ehrlichiosis and anaplasmosis, but is a less sensitive diagnostic assay for Rocky Mountain spotted fever. Biopsy specimens of rash or eschar lesions provide the best samples for PCR for spotted fever group rickettsioses.
Doxycycline is the drug of choice for treatment of all tickborne rickettsial diseases in children and adults. Empirical therapy should be initiated as soon as possible—as soon as rickettsial disease is suspected—and should not be delayed pending the appearance of clinical signs (such as rash) or the return of laboratory test results. Treatment is most effective at preventing severe illness and death if given within the first 5 days of symptoms. Recent studies have shown that short courses of doxycycline, such as those used to treat rickettsial infections, do not cause dental staining or enamel hypoplasia in children under the age of 8 years.
It is important that healthcare professionals emphasize to their patients that no vaccine is licensed for the prevention of tickborne rickettsial diseases in the United States. Patients should be educated that the best way to prevent getting a tickborne infection is to prevent being bitten by ticks. People who will be exposed to ticks should wear protective clothing, such as pants and long-sleeved shirts, and apply DEET repellent. Following exposure to tick-infested environments, people should take a shower and examine for and promptly remove any attached ticks.
To review the complete guidelines and the full recommendations, and for more information on the diagnosis, treatment, management, and prevention of tickborne rickettsioses, please review the resources listed on this page. Thank you.
Christopher Paddock, MD, MPHTM, is a medical officer and directs the Reference Diagnostic and Microbiology Laboratories for the Rickettsial Zoonoses Branch at the CDC's National Center for Emerging and Zoonotic Infectious Diseases. Dr Paddock received his MD and MPHTM degrees at Tulane University in New Orleans, Louisiana, in 1990. He completed his residency in anatomical pathology and laboratory medicine at the University of California, San Francisco, in 1995. His joined CDC in 1996 as a medical officer, served as a pathologist for 11 years with CDC's Infectious Diseases Pathology Branch, and has authored or coauthored approximately 170 scientific publications and 20 book chapters. His research interests include clinical, diagnostic, and epidemiologic aspects of rickettsial diseases.
Public Information from the CDC and Medscape
Cite this: The Very Latest on Tickborne Rickettsial Diseases: Updated Guidelines for Patient Diagnosis and Management - Medscape - May 23, 2016.