Tonate virus infection in French Guiana: clinical aspects and seroepidemiologic study.

Two recent cases of human infection with Tonate virus, one of which was a fatal case of encephalitis, have renewed interest in these viruses in French Guiana. The clinical aspects of confirmed and probable cases of infection with this virus indicate that it has pathogenic properties in humans similar to those of other viruses of the Venezuelan equine encephalitis complex. To determine the prevalence of antibodies to Tonate virus in the various ethnic groups and areas of French Guiana, 3,516 human sera were tested with a hemagglutination inhibition test. Of these, 11.9% were positive for the virus, but significant differences in seroprevalence were found by age, with an increase with age. After adjustment for age, significant differences were found between places of residence. The prevalence of antibody to Tonate virus was higher in savannah areas, especially in the Bas Maroni (odds ratio [OR] = 22.2, 95% confidence interval [CI] = 15.2-32.4) and Bas Oyapock areas (OR = 13.4; 95% CI = 9.8-18.4). The ethnic differences observed in this study were due mainly to differences in place of residence, except that whites were significantly less frequently infected than other ethnic groups. This study indicates that Tonate virus infection is highly prevalent in French Guiana, especially in savannah areas.

Determination of natural versus laboratory human infection with Mayaro virus by molecular analysis.

A laboratory worker developed clinical signs of infection with Mayaro virus (Togaviridae), an arbovirus of South and Central America, 6 days after preparation of Mayaro viral antigen and 10 days after a trip to a rain forest. There was no evidence of skin lesions during the antigen preparation, and level 3 containment safety measures were followed. Therefore, molecular characterization of the virus was undertaken to identify the source of infection. RT-PCR and DNA sequence comparisons proved the infection was with the laboratory strain. Airborne Mayaro virus contamination is thus a hazard to laboratory personnel.

Mayaro virus fever in French Guiana: isolation, identification, and seroprevalence.

This paper reports the first isolation of Mayaro (MAY) virus from a patient infected in French Guiana. The identification was initially performed using immunofluorescent antibody testing with specific mouse antibody, and confirmed by plaque-reduction neutralization testing and reverse transcription-polymerase chain reaction. To determine if MAY virus infection is widespread in French Guiana, a serosurvey was performed to determine the prevalence of antibody to this virus in various ethnic groups and areas of French Guiana. Human sera (n = 1,962) were screened using the hemagglutination inhibition (HI) test. To determine whether MAY virus circulates in the rain forest, a serosurvey in monkey populations was performed. Monkey sera (n = 150) were also screened for antibody to MAY virus using HI testing. Of the human sera tested, 6.3% were positive for anti-MAY virus antibodies. Significant differences in MAY virus seroprevalence between different age groups were observed. Seroprevalence rates increased with age, with a large increase in people 10-19 years of age in comparison with those less than 10 years of age. After adjustment for age, significant differences were also found between places of residence. The prevalence of anti-MAY virus antibody was higher in people living in contact with the forest, especially in the Haut Oyapock area (odds ratio [OR] = 97.7, 95% confidence interval [CI] = 48.2-197.9) and along the Maroni River (OR = 39.7, 95% CI = 20.6-76.6). The ethnic differences observed in this study were probably due to differences in residence. Among monkeys, higher seroprevalence rates were found in Alouatta seniculus (66.0%) than in Saguinus midas (18.2%). Among Alouatta, the seroprevalence increased significantly with weight (and therefore with age). This study indicates that MAY virus is present in French Guiana, and human infections occur in areas where people live near the tropical rain forest.

Immunoglobulin A-specific capture enzyme-linked immunosorbent assay for diagnosis of dengue fever.

Dengue fever (DF) is usually diagnosed by testing for dengue virus immunoglobulin M (IgM) by a capture enzyme-linked immunosorbent assay (ELISA) (MAC-ELISA). However, IgM can last for months, and its presence might reflect a previous infection. We have tested the use of anti-dengue virus IgA capture ELISA (AAC-ELISA) for the diagnosis of DF by comparing the results of MAC-ELISAs and AAC-ELISAs for 178 serum samples taken from patients with confirmed cases of DF. IgM appears more rapidly (mean delay of positivity, 3.8 days after the onset of DF) than IgA (4.6 days) but lasts longer; the peak IgA titer is obtained on day 8. The specificity and the positive predictive value of AAC-ELISA are 100%; its sensitivity and negative predictive value (NPV) are also 100% between days 6 and 25 after the onset of DF, but they decrease drastically when data for tests conducted with specimens from the first days of infection are included, because the IgA titers, like the IgM titers, have not yet risen. AAC-ELISA is a simple method that can be performed together with MAC-ELISA and that can help in interpreting DF serology.