No abstract

The first fatal Rickettsia rickettsii infection was diagnosed in the southwest of Mexico. The patient had fever, erythematous rash, abdominal pain, and severe central nervous system involvement with convulsive crisis. The diagnosis of R. rickettsii infection was established by immunohistochemistry and specific polymerase chain reaction.

In search for the vector of the recently recognized spotted fever rickettsiosis of the Yucatán, ticks, fleas, and lice were collected from vegetation and dogs in localities where seropositive persons had been found. The arthropods were examined by polymerase chain reaction (PCR) using primers for the genus-specific 17-kDa protein gene followed by restriction fragment length polymorphism (RFLP) and DNA sequencing. Eleven (20%) of 54 pools of Ctenocephalides felis fleas contained DNA of Rickettsia felis. None of 219 Amblyomma cajennense, 474 Rhiphicephalus sanguineus, 258 Boophilus sp. ticks, and 33 Poliplax species lice contained DNA of Rickettsia. The identity of the rickettsial DNA was confirmed as R. felis by PCR/RFLP for the citrate synthase and outer membrane protein A genes and by DNA sequencing. The results indicate that the host of R. felis in Yucatán is C. felis and suggest that the spotted fever rickettsiosis that has infected >5% of the population of the Yucatán and can present as a dengue-like illness is likely to be caused by R. felis.

Abstract. Because of the discovery of a spotted fever group rickettsiosis with signs and symptoms similar to dengue fever in Yucatán, Mexico, immunofluorescence assay (IFA) serology was performed on sera from 390 persons selected from a representative geographic distribution of rural Yucatán to detect antibodies reactive with Rickettsia rickettsii, R. akari, a Thai strain (TT-118) that is most closely related to a rickettsia identified in Amblyomma cajennense ticks in southern Texas, and R. typhi. The IFA antibodies at titers Ն 1 : 64 against R. akari were detected in 22 (5.6%) of the samples with the expected cross-reactivity against the other antigens of the spotted fever group. Immunoblotting with antigens of R. akari identified antibodies against antigens of spotted fever group lipopolysaccharides and not against rickettsial outer membrane proteins A and B, which contain the species-specific epitopes. A rickettsiosis most likely caused by a relative of R. akari appears to be both prevalent and widely distributed geographically in Yucatán.Rickettsioses are caused by small, gram-negative, obligately intracellular bacteria of the family Rickettsiaceae. 1 In Mexico during the decades from 1930 to 1950, cases of Rocky Mountain spotted fever were observed in Coahuila, Durango, San Luis Potosi, Sinaloa and Sonora, where the vector was identified to be Rhipicephalus sanguineus. [2][3][4] Additionally, the isolation of a spotted fever group (SFG) rickettsia was reported from Amblyomma cajennense found in Veracruz. 5 Furthermore, a study performed in 1993 in patients from Jalisco and Yucatan who were suspected clinically to have dengue fever, but did not develop antibodies to dengue viruses, showed that 40% of the cases were serologically an endemic rickettsiosis. Those sera contained IgM antibody titers equal to or greater than 1/128 reactive with Rickettsia rickettsii and/or R. akari. 6 Recently, an SFG rickettsia was identified in A. cajennense ticks in southern Texas that is most clearly related to a strain (TT-118) that had been isolated from a pool of larval Rhipicephalus and Ixodes ticks from Thailand. 7,8 DNA sequence analysis subsequently demonstrated that the southern Texas rickettsia and strain TT-118 are both R. honei, the etiologic agent of Flinders Island spotted fever in Australia. 9 Amblyomma cajennense, A. immitator, A. mitens, and Boophilus microphus are the most prevalent ticks encountered in the State of Yucatán. 10 Based on the previous study, the objective of the present work was to determine the prevalence of antibodies to the genus Rickettsia in humans in the State of Yucatán. MATERIALS AND METHODS Sera.The sample was established according to a statistical design using the software Epi-Info 6.02 (Centers for Disease Control and Prevention, Atlanta, GA and World Health Organization, Geneva, Switzerland), based on a previous study. The confidence level was 95%, the standard error was 5%, and the estimated seroprevalence was 50%, the estimate that would require the largest sample size. The study w...

No abstract