Yellow fever protection test surveys in the French Cameroons, French equatorial Africa, the Belgian Congo, and Angola

Abstract 1. 1. The results of the yellow fever protection test survey covering the examination of 4,828 specimens in 108 towns of the French Cameroons, French Equatorial Africa, the Belgian Congo, and Angola are presented. 2. 2. Except in the interior of French Equatorial Africa, the percentages of positive sera obtained in these colonies were much lower than in those situated in West Africa proper and previously reported upon. This difference is probably due to the fact that conditions in this region are relatively unfavourable to the maintenance of yellow fever infection. 3. 3. Though extensive epidemics of yellow fever have occurred both recently and in the past in some parts, endemicity seems to be excluded throughout this entire region. 4. 4. 1,643 specimens were collected from children and adults in thirty-seven towns located in the interior and in the coastal area of French Equatorial Africa, and 18·4 percent, were positive. Though yellow fever has never been reported from this colony, the findings in the interior demonstrated that extensive epidemics of the disease have been present within recent years as well as in the more distant past. That no barrier against the invasion of yellow fever infection towards East Africa exists in this region is evidenced by the fact that high percentages of positives with the sera of both children and adults were secured in many towns in the interior, including several situated near the border of the Anglo-Egyptian Sudan. The findings in the coastal area of French Equatorial Africa indicate that though some yellow fever has been present there in the past the incidence during recent years has been practically negligible. 5. 5. Among 496 specimens from children and adults collected in nine towns in the French Cameroons, only 3·6 percent, were positive. The sera of children were almost completely negative, and specimens from adults from only two towns showed a fair percentage of positives. The completely negative findings with the sera of children and adult residents of Douala and the very low positives in general with the sera of children suggest that this region was not responsible for the introduction of yellow fever infection into the interior of French Equatorial Africa. 6. 6. The survey in the Belgian Congo included the examination of 1,740 specimens collected in forty-three towns, and 8·8 percent, of these were positive. The findings in the lower Bas Congo indicate that the epidemic of 1927-28 involved some towns in that region besides Boma and Matadi, where the disease was recognized. The epidemic was not particularly extensive, however, as the Mayumbe appears to have escaped and the findings in Leopoldville and the interior of the Belgian Congo do not indicate that the infection gained any foothold there. Though the latter region has experienced some yellow fever in the past, it would seem to have escaped almost completely during recent years. The results in towns along both sides of the Congo and Oubangui Rivers suggest the possibility that infection was carried into the interior of French Equatorial Africa through river traffic. 7. 7. The practically negative findings in the south and south-eastern portions of the Belgian Congo and throughout all of Angola indicate that the limits of yellow fever invasion in these directions have been reached.