The occurrence of Mansonella perstans among residents of Calabar metropolis in Cross River State of Nigeria.

The occurrence of Mansonella perstans was studied among people who had resided in Calabar metropolis for at least one year prior to the time of this study, which lasted from February to August, 2011. One thousand residents, comprising 530 males and 470 females, with an age range of 4 to 59 years, participated in the study, after an informed consent. Two millilitres of venous blood were collected at day time into EDTA bottles. The blood samples were processed by diluting 1ml of blood in 9 mls of 1% formalin and centrifuging the preparation at 3,000 revolutions per minute for 5 minutes. Deposits were left as blood smears on clean slides and after air-drying, were stained with 3% Giemsa solution for microscopy. Overall, the prevalence of Mansonella perstans was 2% (20 vs 1,000). The prevalence of the parasite among the females was 2.1% (10 vs 470) and males 1.9% (10 vs 530). Microfilaraemia only occurred among subjects aged between 25 and 45 years. The results of this study suggest that loiasis, which earned Calabar an unenviable mention in early medical literature, is no longer very prevalent in the area. Instead, a low prevalence of mansonelliasis occurs, in tandem with the existence of sparse farmlands of banana and plantain. Old stems of these crops provide suitable habitats for Culicoides species, which transmit Mansonella perstans.