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The Comoros Islands are situated off the coast of East Africa, at the northern entrance of the channel of Mozambique. Contemporary Comoros society displays linguistic, cultural and religious features that are indicators of interactions between African, Middle Eastern and Southeast Asian (SEA) populations. Influences came from the north, brought by the Arab and Persian traders whose maritime routes extended to Madagascar by 700-900 AD. Influences also came from the Far East, with the long-distance colonisation by Austronesian seafarers that reached Madagascar 1500 years ago. Indeed, strong genetic evidence for a SEA, but not a Middle Eastern, contribution has been found on Madagascar, but no genetic trace of either migration has been shown to exist in mainland Africa. Studying genetic diversity on the Comoros Islands could therefore provide new insights into human movement in the Indian Ocean. Here, we describe Y chromosomal and mitochondrial genetic variation in 577 Comorian islanders. We have defined 28 Y chromosomal and 9 mitochondrial lineages. We show the Comoros population to be a genetic mosaic, the result of tripartite gene flow from Africa, the Middle East and Southeast Asia. A distinctive profile of African haplogroups, shared with Madagascar, may be characteristic of coastal sub-Saharan East Africa. Finally, the absence of any maternal contribution from Western Eurasia strongly implicates male-dominated trade and religion as the drivers of gene flow from the North. The Comoros provides a first view of the genetic makeup of coastal East Africa. [ABSTRACT FROM AUTHOR]

From January to April 2005, an epidemic of chikungunya virus (CHIKV) illness occurred in the Union of Comoros. Entomological studies were undertaken during the peak of the outbreak, from March 11 to March 31, aimed at identifying the primary vector(s) involved in transmission so that appropriate public health measures could be implemented. Adult mosquitoes were collected by backpack aspiration and human landing collection in homes and neighborhoods of clinically ill patients. Water-holding containers were inspected for presence of mosquito larvae. Adult mosquitoes were analyzed by RT-PCR and cultivation in cells for the presence of CHIK virus and/or nucleic acid. A total of 2,326 mosquitoes were collected and processed in 199 pools. The collection consisted of 62.8% Aedes aegypti, 25.5% Culex species, and 10.7% Aedes simpsoni complex, Eretmapodites spp and Anopheles spp. Seven mosquito pools were found to be positive for CHIKV RNA and 1 isolate was obtained. The single CHIKV mosquito isolate was from a pool of Aedes aegypti and the minimum infection rate (MIR) for this species was 4.0, suggesting that Ae. aegypti was the principal vector responsible for the outbreak. This was supported by high container (31.1%), household (68%), and Breteau (126) indices, with discarded tires (58.8%) and small cooking and water storage vessels (31.1%) registering the highest container indices.

An outbreak of Chikungunya virus (CHIKV) illness associated with high fever combined with prolonged and severe arthralgias occurred on Grande Comore Island from January through May 2005; 5,202 cases were reported. A seroprevalence study was conducted to define the extent of transmission on the island. We conducted a cross-sectional survey using a multistage sampling technique. A total of 481 households were sampled. In each household, one resident was selected randomly for interview and blood collection. We administered questionnaires and tested 331 sera for CHIKV-specific IgM and IgG antibodies by capture enzyme-linked immunosorbent assay. Infection with CHIKV infection (seropositivity) was defined as presence of IgG and/or IgM antibodies to CHIKV. A total of 331 (69%) of 481 survey participants consented to blood collection. Antibodies to CHIKV were detected in 63% of sera; IgM antibodies were found in 60% of specimens and IgG antibodies were detected in 27% of specimens. Extrapolation of the findings to the entire Grande Comore population suggested that nearly 215,000 people were infected with CHIKV during the outbreak. A total of 79% of the seropositive persons were hospitalized or stayed at home in bed for a mean of 6 days (range = 1-30 days); 52% missed work or school for a mean of 7 days (range = 1-40 days). The findings suggest that CHIKV was broadly transmitted during the outbreak with a high attack rate. Although not fatal during this outbreak, CHIKV infection caused significant morbidity and decreased economic productivity.