Changes in the distribution of human schistosomiasis in Far North province, Cameroon, since 1986.

Abstract

The most recent, large-scale survey on human urinary schistosomiasis (caused by Schistosoma haematobium) and human intestinal schistosomiasis (caused by S. mansoni) in Cameroon, which was carried out in 1986, revealed that both diseases were endemic throughout Far North province (Ratard et al., 1990). In a survey in 2008–2009, Massenet et al. (2009) found that the prevalences of these diseases in the neighbouring North province were markedly lower than those recorded by Ratard et al. (1990), in the same area, about two decades earlier. Since antischistosomal treatment has never been delivered at community level in North province, the reasons behind this favourable trend were (and remain) unclear. The aim of the present, cross-sectional survey, conducted in 25 primary schools in 2009, was to see if urinary schistosomiasis and intestinal schistosomiasis had shown a similar decline in Far North province, from the prevalences of 35% and 9%, respectively, recorded among schoolchildren in 1986 (Ratard et al., 1990). Lot quality assurance sampling (LQAS) was used, previous studies having shown this to be a cost-effective method of identifying communities that qualify for treatment (Rabarijaona et al., 2003; Brooker et al., 2005). The 25 surveyed schools (see Figure) were those previously investigated, in 1986, by Ratard et al., (1990). In each school, eight boys and seven girls were randomly selected from an exhaustive list of the children aged 9–11 years who were present on the day of the survey. Human infection with S. mansoni or S. haematobium is considered hyper-endemic in a community when eggs are observed in at least 50% of stool or urine samples, respectively. In each study school, for each of these schistosome species, the null hypothesis (H0) that the prevalence of infection was ⩾50% among all the schoolchildren was therefore explored. Using the LQAS method, the null hypothesis was accepted if at least four of the 15 children investigated were observed to be excreting the eggs of the schistosome of interest (this sampling plan gives a 95% probability of the null hypothesis being accepted when the prevalence is ⩾50%, as well as an 80% probability of schistosomiasis being categorized as not hyper-endemic in a school where the prevalence of infection is <20%). The locations of the schools surveyed in the Logone et Chari (1), Mayo Danay (2), Kaele (3), Diamare (4), Mayo Sawa (5) and Mayo Tsanaga (6) departments of Far North province in 2009, showing the schools where Schistosoma haematobium was ... Each subject was given a stool container (including a specimen-collection spoon) and a urine container and asked to collect fresh stool and urine specimens between 10·00 and 15·00 hours. On the day of their collection, the stool specimens were checked for S. mansoni eggs as Kato–Katz smears (Katz et al., 1972) while 10 ml of each urine sample were checked for S. haematobium eggs, by membrane filtration (WHO, 1985). The locations of the 11 schools where S. haematobium infection was considered hyper-endemic are shown in the Figure. None of the surveyed schools was found hyper-endemic for S. mansoni. After aggregation of the collected data, by department (see Table), the recorded prevalences of S. haematobium infection were found to be significantly higher in the Mayo Danay department than in any other department in Far North province (P<0·0001). In 1979, a dam was built in Mayo Danay, to support the large-scale cultivation of irrigated rice, and it may be the resultant lake (Lake Maga), wetlands and irrigation canals that support relatively high levels of S. haematobium transmission in the department. Six of the 11 schools found hyper-endemic for S. haematobium lie within Mayo Danay. The other five such schools are scattered throughout the other departments of Far North province (with low prevalences of S. haematobium infection recorded in neighbouring schools; see Figure). Such heterogeneity in the distribution of schistosomiasis in the province is similar to that observed in North province, in 2008–2009, by Massenet et al. (2009). Comparative results of the 1986 and 2009 examinations of urine samples (from schoolchildren in six departments of Far North province) for the eggs of Schistosoma haematobium Schistosoma mansoni now appears to be relatively rare in Far North province, with no schools considered hyper-endemic for this parasite and only five (1·3%) of the 375 tested children found to be co-infected with S. mansoni and S. haematobium. Although the results of such comparison must be interpreted with care, because the two surveys used different sampling methods, the Table allows the results of the survey in Far North province in 1986 study (Ratard et al., 1990) to be compared with those recorded in 2009 (present study). The mean prevalence of S. haematobium infection detected in the schoolchildren of Far North province in 2009 (33%) was very similar to that recorded in 1986 (35%) but the geographical distribution of such infection appears to have changed markedly between the two surveys. For example, the prevalence of such infection in Mayo Danay department (which, in 1986, was close to the median value for all the other departments of the province) appears to have markedly increased. The mean prevalence of S. mansoni infection among the schoolchildren of Far North province seems to have decreased between the surveys, from 9% in 1986 to 4% in 2009 (P = 0·001), without any delivery of antischistosomal treatment at community level. A similar decrease in the prevalence of schistosomal infection, in the absence of any systematic praziquantel treatment, was found to have occurred in neighbouring North province in 2008–2009 (Massenet et al., 2009). The reason behind the temporal and geographical changes seen in the prevalence of schistosomal infection in northern Cameroon, in the absence of community-level treatment, merit further research.