Longitudinal survey of Loa loa filariasis in southern Cameroon: long-term stability and factors influencing individual microfilarial status.

A longitudinal, one-year survey of Loa loa infection was carried out in an endemic area of southern Cameroon. Parasitologic samplings (calibrated thick blood smears) were performed every two months to study the evolution of loiasis infection at both the population and the individual level. The mean number of measurements by subject was 3.8 (range 1-6). At the population level, prevalence of infection and microfilarial load were found to be very stable over time. This observation is consistent with the existence of an important reserve of parasitic material available for vectors and the maintenance of high levels of transmission. At the individual level, both the microfilarial status (microfilaremic/nonmicrofilaremic) and the level of parasitemia showed a remarkable stability over time. Age was the relevant factor that influenced the individual microfilarial status in the whole population. When only microfilaremic individuals were taken into account, age did not influence the level of microfilaremia, suggesting that loiasis could be considered as a noncumulative disease. The stability of individual microfilarial status and the pattern of infection variations observed with age support the view that genetic factors might be involved in host defense mechanisms against loiasis infection.