Socio-environmental variables and transmission risk of lymphatic filariasis in central and northern Mozambique

Lymphatic filariasis (LF) is endemic in Mozambique, where it is caused by Wuchereria bancrofti with Culex quinquefasciatus as the main vector. It affects approximately 10% of the population (2 million) with about 16 million at risk. Prevalence rates in 40 out of 65 districts that together comprise the four endemic provinces Niassa, Cabo Delgado, Nampula and Zambezia were analysed with the aim of elucidating the socio-environmental variables influencing the transmission. The levels of prevalence were divided into six ranks and certain climatic, environmental and social factors were considered independent variables. A climadiagram was created and the LF risk and the water budget-based index were calculated for each district. Factors influencing the risk of the overall transmission and that of the provincial levels were established by discriminant analysis. The results show that LF transmission increased with mean maximum temperature and decreased with altitude. The almost constant annual temperature (especially in the tropical area), altitude, general economic conditions and predominant crop production (rice) were found to be responsible for the abundance and presence of the vector. However, despite the presence of the vector in the hinterland, presence and survival of the parasite were not found to be favoured there. The transmission risk was found to be highest in Zambezia, and consequently also the prevalence, while the situation in Niassa was the opposite. The conclusion is that temperature, altitude and the development/poverty index (particularly in the urban areas) have to be considered as transmission risk factors for LF in Mozambique. The extent of rice culturing probably also plays a role with respect to this infection.