Volume 29, Issue 5
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



An entomological survey was conducted in the Gambia in January 1979, during the last phase of a yellow fever (YF) outbreak which began during the previous rainy season. In the dry conditions which prevailed in January, was the only YF vector present. Two YF virus strains were isolated from females of this mosquito species caught in a village of western Gambia, where active human cases were documented. The breeding sites were exclusively of the domestic type. Larval indices varied greatly from place to place, but generally appeared to correlate with the incidence of disease. A better understanding of the conditions that prevailed at the onset and during the early phase of the epidemic will require further entomological investigations. Nevertheless, it appears probable that initial transmission was by sylvatic vectors such as the group and possibly others such as , and . As the outbreak progressed, interhuman transmission by also occurred, and this mixed epidemiological pattern later gave way to transmission by only when sylvatic vector populations declined in the dry season. We speculate that a prolongation of the rainy season during 1976–1978 was important in the origin of the outbreak. The relationship of this epidemic to the established focus of sylvatic YF in southeastern Senegal is discussed. The Gambian outbreak is considered the result of a recent northwesterly extension of the YF Emergence Zone.


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