Seasonal variation in the prevalence of malaria and vector species in Northern Namibia

Abstract

The prevalence of malaria parasite, Plasmodium falciparum and the abundance of malaria vector species were studied in selected areas of northern Namibia during the wet and the dry seasons. Female mosquitoes were collected using exit window traps. Blood smears were prepared and body temperatures recorded from suspected malaria patients in order to determine the prevalence of malaria parasites and confirm clinical malaria through microscopic examination. The study revealed that Anopheles (Cellia) arabiensis was the most common (84.4%) of the malaria vector species collected. Other vector species included Anopheles funestus (5.0%) and non-malaria vector species (10.6%). Anopheles (Cellia) arabiensis were more prevalent and significantly more abundant during the wet (85.1%) than the dry (14.9%) season. The opposite was true for A. funestus (35.1% in the wet and 64.9% in the dry season). There was no significant difference between the number of patients diagnosed with malaria and those with no malaria during the wet and the dry seasons (2 = 0.55, df = 1, P>0.05). Furthermore, 72.1% of patients with fever tested negative for P. falciparum when clinical diagnosis was employed. Results reveal that diagnosis of malaria using fever is inaccurate compared to microscopic examination of blood smears. This leads to over-diagnosis of the prevalence of malaria and consequent wastage of malaria drugs on patients who do not have clinical malaria. The use of microscopic examination should therefore be promoted to improve diagnosis of malaria and hence facilitate treatment of patients with malaria.