Mono-parasite infection versus co-infections in Tanzania: the need to revise our research focus.

Parasitic infectious agents in endemic African countries including Tanzania rarely occurs in isolation and co-infections within a single host in populations are norms rather than exceptions (Brooker et al., 2007; Mazigo et al., 2010a; Mboera et al., 2011). Coinfection refers to a situation in which an individual harbours two or more infections from different species simultaneously, where as mono-infection refers to a situation in which an individual harbours only one infection from a single species (Brooker et al., 2007). Several factors determines the wide geographical distributions of helminth and protozoan parasites and they include climate, environment, socio-economic status, human behaviour and host-specific factors such as genetics, host physiology, host immunological status and population dynamics (Mwangi et al., 2007). In general, multiple parasitic infections in single host tend to cause more severe morbidities as compared to single infections. For example, the consequence of coinfections of malaria and hookworm is anaemia (Brooker et al., 2006). Recent studies have shown that helminth infections may alter host susceptibility to clinical malaria (Druilhe & Tall, 2005). Similarly, malaria may also exacerbate the consequences of helminth infections (Mwangi et al., 2007; Mboera et al., 2011). In school-age children infection with Schistosoma mansoni is commonly associated with hepatomegaly and splenomegaly as a result of eosinophilic inflammatory and granulomatous reactions against parasite eggs trapped in host tissues (Gryseels et al., 2006). Similarly, atypical immune responses to repeated or chronic Plasmodium falciparum infection are also an important cause of hepatomegaly and splenomegaly in the tropics (Grobusch & Kremsner, 2005). On the other hand, parasitic infections in sub Saharan Africa are known to interact with viral infections such as HIV-1 and cause severe morbidities in coinfected individuals (Walson et al., 2008). Despite the fact that parasitic co-infections are known to occur and cause multiple morbidities, yet most parasitic diseases are still studied individually and data on prevalence, morbidity and mortality associated with multiple parasitic infections in Tanzania are limited (Mazigo et al., 2010a; Mboera et al., 2011). Importantly, even the planning for prevention and control activities are designed to focus on single infection. This lack of research information on parasitic co-infections in Tanzania hinders the ability to accurately assess the disease burden attributable to individual infections