Zooprophylaxis, artefact or reality? A paired-cohort study of the effect of passive zooprophylaxis on malaria in The Gambia.

The World Health Organization has recommended the use of cattle for zooprophylaxis as a protective measure against malaria since 1982. However, concern has been raised about this practice, since some studies have shown that the presence of cattle may instead increase malaria prevalence. This study was designed to investigate the effect of passive zooprophylaxis on malaria in an area of moderate seasonal transmission in The Gambia, West Africa. The study was based on a paired-cohort of 204 children aged < 7 years, sleeping < 20 m or > 50 m from cattle, and surveys were done from 14 October to 2 December 1997. Entomological investigations showed that the presence of cattle did not alter the risk of malaria transmission in nearby houses. There was also no significant difference in the prevalence of Plasmodium falciparum between the 2 groups. Although the presence of cattle appeared to be protective against high parasitaemia, cattle were also associated with greater wealth of the children's families. Conditional logistic regression analysis showed that the decreased risk of high parasitaemia in the group with cattle present was an artefact associated with the higher general wealth of the cattle owners. We concluded that zooprophylaxis is not an effective intervention method against malaria in settings similar to The Gambia.