Rocky Mountain Spotted Fever

A highly specific real-time polymerase chain reaction (PCR) assay was developed to detect spotted fever and typhus group rickettsiae using the citrate synthase gene as the target. The assay amplified rickettsial members of the spotted fever and typhus group including Rickettsia akari, R. australis, R. conorii, R. honei, "R. marmionii," R. sibirica, R. rickettsii, R. typhi, and R. prowazekii. The ancestral group rickettsia, R. bellii, did not produce a positive reaction, nor did other members of the order Rickettsiales or any non-rickettsial bacteria. The assay had a sensitivity of one target copy number per reaction as determined by serial dilutions of a plasmid containing a spotted fever group target sequence. This quantitative assay is useful for the enumeration of rickettsiae in clinical specimens and the diagnosis of rickettsial illnesses, when rickettsial numbers are very low.

Fifteen bacterial isolates from spotted fever group rickettsiosis in Brazil were genetically identified as Rickettsia rickettsii. In a phylogenetic analysis with other R. rickettsii isolates from GenBank, the Central/South American isolates showed low polymorphism and formed a clade distinct from two North American clades, with the North American clades having greater in-branch polymorphism.

Tickborne rickettsial diseases (TBRD) continue to cause severe illness and death in otherwise healthy adults and children, despite the availability of low cost, effective antimicrobial therapy. The greatest challenge to clinicians is the difficult diagnostic dilemma posed by these infections early in their clinical course, when antibiotic therapy is most effective. Early signs and symptoms of these illnesses are notoriously nonspecific or mimic benign viral illnesses, making diagnosis difficult. In October 2004, CDC's Viral and Rickettsial Zoonoses Branch, in consultation with 11 clinical and academic specialists of Rocky Mountain spotted fever, human granulocytotropic anaplasmosis, and human monocytotropic ehrlichiosis, developed guidelines to address the need for a consolidated source for the diagnosis and management of TBRD. The preparers focused on the practical aspects of epidemiology, clinical assessment, treatment, and laboratory diagnosis of TBRD. This report will assist...

A lethal case of Brazilian spotted fever (BSF) is presented. Clinical features were initially of gastrointestinal involvement and evolved with progression to septic shock, meningoencephalitis and death on the 6th day of illness. Indirect immunofluorescence assay (IFA) for spotted fever group rickettsia (SFGR) was non-reactive. Diagnosis was confirmed by the polymerase chain reaction (PCR) and the nucleotide sequencing of a fragment of the ompA gene showed 100% homology to Rickettsia rickettsii. BSF has not been reported in the city of Rio de Janeiro in the last three decades, and the present description should alert the clinicians to its presence in urban Rio de Janeiro, and to the differential diagnosis with dengue fever, gastroenteritis, leptospirosis and bacterial septic shock, among others.

Rocky Mountain spotted fever (RMSF) is a tick-borne infection caused by Rickettsia rickettsii. We report a cluster of fatal cases of RMSF in 2007 in Panama, involving a pregnant woman and two children from the same family.  The woman presented with a fever followed by respiratory distress, maculopapular rash, and an eschar at the site from which a tick had been removed.  She died four days after disease onset.  This is the second published report of an eschar in a patient confirmed by PCR to be infected with R. rickettsii.  One month later, the children presented within days of one another with fever and rash and died three and four days after disease onset. The diagnosis was confirmed by immunohistochemistry, PCR and sequencing of the genes of R. rickettsii in tissues obtained at autopsy.

The genome sequence of Rickettsia felis revealed a number of rickettsial genetic anomalies that likely contribute not only to a large genome size relative to other rickettsiae, but also to phenotypic oddities that have confounded the categorization of R. felis as either typhus group (TG) or spotted fever group (SFG) rickettsiae. Most intriguing was the first report from rickettsiae of a conjugative plasmid (pRF) that contains 68 putative open reading frames, several of which are predicted to encode proteins with high similarity to conjugative machinery in other plasmid-containing bacteria. Using phylogeny estimation, we determined the mode of inheritance of pRF genes relative to conserved rickettsial chromosomal genes. Phylogenies of chromosomal genes were in agreement with other published rickettsial trees. However, phylogenies including pRF genes yielded different topologies and suggest a close relationship between pRF and ancestral group (AG) rickettsiae, including the recently c...

Equines play a role in the epidemiology of Brazilian spotted fever (BSF) since they are a primary host for the tick Amblyomma sculptum. We studied the seroprevalence for three species of Rickettsia in equines in four endemic (with human cases) and in four non-endemic areas (no human cases) in the Piracicaba River Basin, São Paulo, Brazil. A serological survey of 504 equines was performed: around 63 animals were sampled in each area and tested through indirect immunofluorescence assay for R. rickettsii, R. parkeri, and R. bellii in 2012-2013. Blood samples were seropositive for 183 equines (36.3%) in which 73 (39.9%) were from non-endemic areas. In the studied sites equines were highly exposed to Rickettsia infection ranging from 6.1% to 54.7%, with Geometric Mean Titers greater in endemic area (p = 0.012). Results suggest that Rickettsia may be more widespread than the surveillance of BSF has detected. These results highlight the need to include data on the seroprevalence of sentine...

Rocky Mountain spotted fever (RMSF) is a tick-borne infection caused by Rickettsia rickettsii. We report a cluster of fatal cases of RMSF in 2007 in Panama, involving a pregnant woman and two children from the same family.  The woman presented with a fever followed by respiratory distress, maculopapular rash, and an eschar at the site from which a tick had been removed.  She died four days after disease onset.  This is the second published report of an eschar in a patient confirmed by PCR to be infected with R. rickettsii.  One month later, the children presented within days of one another with fever and rash and died three and four days after disease onset. The diagnosis was confirmed by immunohistochemistry, PCR and sequencing of the genes of R. rickettsii in tissues obtained at autopsy. 

Tickborne rickettsial diseases (TBRD) continue to cause severe illness and death in otherwise healthy adults and children, despite the availability of low cost, effective antimicrobial therapy. The greatest challenge to clinicians is the difficult diagnostic dilemma posed by these infections early in their clinical course, when antibiotic therapy is most effective. Early signs and symptoms of these illnesses are notoriously nonspecific or mimic benign viral illnesses, making diagnosis difficult. In October 2004, CDC's Viral and Rickettsial Zoonoses Branch, in consultation with 11 clinical and academic specialists of Rocky Mountain spotted fever, human granulocytotropic anaplasmosis, and human monocytotropic ehrlichiosis, developed guidelines to address the need for a consolidated source for the diagnosis and management of TBRD. The preparers focused on the practical aspects of epidemiology, clinical assessment, treatment, and laboratory diagnosis of TBRD. This report will assist...