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Malaria in the Netherlands

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they are no nearer the breedingplaces of the larvae than others. Here is an instance of such a house, examined through four consecutive years, all that time occupied by the same family. This example, moreover, shows how such a house may become a permanent hotbed of anopheline infection. In this house we detected in the months of:

December 1934 *83 anopheles, 48 infected, 45 sporozoite-carriers Jan.-Feb. 1935 483 „ 68 „ 64 Sept.-Dec. 1935 414 „ 26 „ 10 Aug.-Dec. 1936 191 „ o „ o „

Aug.-Sept. 1937 132 „ 4 „ o

Still, the number of anopheles found in a house does not all depend on the human population, but likewise on the house itself. The following is an example of the influence of the house, independent of the number of people living in it, on the number of anopheles it shelters and the extent of the anopheline infection it is fostering.

In a family of eight members four had malaria in 1935; moreover, there were two parasite-carriers * among them. In 1936 they had two malaria patients and four parasite-carriers. In 1935 52 anopheles were found infected in their house, among 172 captured on three visits; in 1936 none was found infected among 8 anopheles captured on four visits. The family had remained the same, the parasite reservoir had remained the same, but anopheline infection had become extinct for lack of anopheles. Here is a case which contradicts the conclusion we arrived at, that the mosquitoes each year tend to return in large numbers to the same house. But it is no con-

* The importance of "healthy" parasite-carriers as a source of infection for anopheles will be discussed later on (p. 165).