Yellow fever in the Gambia. I, Historical / by G.M. Findlay and T.H. Davey.

  • Findlay, G. M.
Date:
1936
Catalogue details

Licence: In copyright

Credit: Yellow fever in the Gambia. I, Historical / by G.M. Findlay and T.H. Davey. Source: Wellcome Collection.

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    abundance in the sea of cod and mackerel. Only further research can show whether periodic variations in mosquito populations also exhibit the influence of this cycle. Discussion. The history here recounted of outbreaks of epidemic disease in the Gambia would seem at first sight merely to add further evidence to that so skilfully marshalled by Carter (1932) in favour of the African origin of yellow fever. Since the publication of Carter’s book, however, many new facts have accumu¬ lated which render the problem of the original home of yellow fever still more complicated. The following facts are in favour of the African origin of yellow fever :— (i) As a result of the survey of Africa by the mouse protection test, Africans with immune bodies to yellow fever have been found as far east as the Bahr el Ghazal Province of the Anglo-Egyptian Sudan. There is evidence that the disease is not of recent introduction in this region. (ii) The mild reaction of Africans to yellow fever suggests a long period of exposure to infection during which the more susceptible members of the indigenous population have been slowly eliminated and a racial resistance has been gradually acquired. (iii) The failure of African monkeys to react to yellow fever virus by the development of clinical symptoms or pathological lesions also suggests a long period of exposure to infection. (iv) Aedes aegypti is almost certainly an Old World mosquito since there are many parts of South America to which it has not yet penetrated. On the other hand : (i) Yellow fever has occurred in mountainous regions in South America far removed from the eastern seaboard. (ii) A mild reaction to infection is not always met with in Africans since in certain outbreaks their mortality has been high. Inapparent infections are by no means rare in South Americans of mixed European and Indian descent while, as laboratory infections have shown, even persons of pure European descent may suffer from yellow fever in a very mild form. (iii) Monkeys from East Africa where yellow fever has never been known to occur are no more susceptible than those from West Africa. West African monkeys are also relatively insusceptible to an East African virus, Rift Valley fever, to which they have never been exposed (Findlay, 1933). (iv) Although there are many areas in South America where Aedes aegypti is absent yet the disease is effectively transmitted in these regions by indigenous South American mosquitoes such possibly as Aedes scapularis. It is possible that a true explanation of the origin of yellow fever may eventually be found in the existence of an Old and a New World strain of yellow fever virus. The Old World strain, that transmitted by Aedes aegypti, has