Human spotted fever rickettsial infections

Emerging Infectious Diseases,  April, 2005  by George B. Schoeler,  Cecilia Moron,  Allen Richards,  Patrick J. Blair,  James G. Olson

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The signs and symptoms of patients with confirmed spotted fever who came to the treatment facility included fever and malaise (100%), chills (94%), weakness (94%), shortness of breath (94%), prostration (81%), arthralgia (62%), abdominal pain (62%), cough (56%), nausea (56%), and runny nose (56%). None of the patients died, and most patients had a relatively mild febrile illness. There were no clear clinical differences in patients with confirmed cases of spotted fever compared with febrile patients who did not have spotted fever.

Evidence of SFG rickettsial infection was observed in samples taken from febrile patients in Cusco, Junin, and Piura departments. The etiologic agent or agents responsible for the spotted fever illnesses remain unknown. Appropriate samples from these patients were not available for isolation or molecular identification by a polymerase chain reaction.

Conclusions

Host inflammation may partly contribute to the pathogenic sequelae with intra-endothelial cell infection in more severe SFG infection (9). Patients infected with R. akari typically experience a mild and or asymptomatic disease characterized by low-grade fever, sweats, headache, and a vesicular eruption over the trunk and extremities (10). R. akari is maintained transovarially in the mite vector and transmitted to humans by the house mouse mite (Liponyssoides sanguineus). Infections have generally been reported among higher risk populations such as intravenous drug users (11), or within the densely populated inner city (12). Less is known about the susceptibility of rural agrarian populations. The concentration of humans in close proximity to house mice and their mites are factors that could contribute to an increase in rickettsialpox in the region. Sporadic cases of rickettsialpox may be confused with chickenpox, a common illness associated vesicular rash. However, none of the confirmed SFG rickettsia-infected patients had vesicular rashes typical of rickettsialpox.

Cat flea typhus, caused by R. felis, is a mild disease similar to murine typhus (13). Typical clinical findings include fever, headache, and occasional rash. The clinical manifestations of patients infected with SFG rickettsiae are similar to those described for cat flea typhus. However, recent discoveries of novel rickettsioses caused by distinct SFG rickettsiae in Europe, Africa, Australia, Asia, and North America during the last 25 years (14,15) suggest that the infections reported in this study may be the results of a novel SFG rickettsial agent. Future work is needed to identify the agent involved and to clearly link clinical signs and symptoms with diagnoses.

The higher frequency of cases in women suggests occupational exposure since in these areas of Peru women are generally more involved with domestic activities near the home. Possibilities for increased exposure of women may include more frequent work in the fields, thus exposing them to arthropod vectors; closer contact with domestic animals that may be involved in maintaining the SFG rickettsial agent (although no evidence was collected to support this); or exposure to house mouse mites in the home. Serologic evidence suggests that SFG rickettsiae were responsible for causing febrile illnesses in these 4 study sites of Peru, which demonstrates that SFG rickettsia result in human disease in Peru. Further studies are needed to document the species of SFG rickettsiae and to determine the vectors of these rickettsial infections. In addition, epidemiologic studies are needed to identify the risk factors, document the clinical spectrum, and suggest public health recommendations for prevention.