Human malaria in the highlands of Yemen

It is unclear why febrile patients in the highlands of Yemen are much more likely to be found to have malarial infection than their counterparts from the coastal plains and foothills. Although it is possible that malarial transmission is relatively intense in the highlands, it seems more likely that, compared with those who live at lower altitudes, those who live in the highlands are less immune to malaria, and therefore more likely to develop febrile illness following malarial infection. Whatever the cause of the symptomatic malarial infection commonly found in the highlands of Yemen, it is a matter of serious concern that should be addressed in the national strategy to control malaria. Human malaria is the most common vectorborne disease in Yemen, with an annual incidence of about 900,000 cases and approximately 60% of the total population considered to be at risk of the disease (WHO, 2009a). Plasmodium falciparum accounts for 95% of the cases and, although Anopheles arabiensis is the predominant vector, An. culicifacies plays an important role in malarial transmission in the coastal areas of Yemen and another known vector species, An. sergenti, has been reported in the mountainous hinterland and highland areas (Anon., 2002; WHO, 2005; Alkadi