Urban Malaria – where can we find it?

In Nairobi’s Korogocho slum Yazoume Ye and colleagues looked for evidence of malaria parasites among 1,069 residents. Among those with data, 16.9% had a recent fever episode. Half were treated, primarily with sulphadoxine-pyrimethamine or amodiaquine, while four received artemether-lumefantrine. Ironically, “Three were positive for Plasmodium falciparum using RDT; however, all were confirmed negative on microscopy. Microscopic examination of all 953 readable slides showed zero prevalence.”

These results were similar to a study we did in low income neighborhoods of Lagos in 1998 screening only children between 6 months and 5 years of age [Afr. J. Med. med Sci (2001) 30, suppl. 7-15].  Blood film investigation of 916 children yielded a parasite prevalence of 0.9%.  Knockdown and night landing collections of mosquitoes in houses in these neighborhoods found no anopheles species. Very low densities of A. gambiae larvae were found in breeding sites.

urban-ag-dscn4842.JPGThese findings should not have surprised us since as far back as 1946, researchers had found that urban Lagos was too dirty to host the more finicky anopheles (Muirhead Thomson RC. Studies on Anopheles gambiae and A. melas in and around Lagos. Bulletin of Entomological Research. 1946; 38: 527-558).  Those cases we did find may have resulted from Lagosians visiting their relatives in the village during a recent wedding or funeral ceremony.

We do know that urban environments are not free from malaria, but one needs to identify anopheles-friendly sites and then look for focal transmission sites around those.  Urban agriculture (see photo from Bamako), flower gardens in higher income areas and some of the less dense urban peripheral settlements might be places to look.  This shows the need to plan urban malaria control with full understanding of the micro-ecologies of an urban setting.

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