Ngonseu E, Greer G J, Mimpfoundi R
Projet Bilharziose, IMPM, Yaoundé, Cameroun.
Ann Soc Belg Med Trop. 1991 Dec;71(4):295-306.
The population dynamics of Bulinus globosus was followed at seasonal and perennial habitats in three villages in the Extreme North Province, Cameroon, known to have high prevalences of Schistosoma haematobium. The study covered 2 rainy and 1 dry season between June 1987 to November 1988. Of several environmental factors monitored, only rainfall and the resulting changes in water level were strongly correlated with changes in snail density, and even then only when values were at their extremes. In seasonal pools, adult snails emerge from estivation and begin laying eggs shortly after the first rains. A decline in the number of larger snails 3 to 6 weeks later suggests a die off of the founding population. In general, the population density increases modestly during the rainy season and then rapidly declines after torrential rains have ended in September or October. Adults are again dominate just before the habitats dry up. In seasonal streams, population densities fluctuate dramatically in association with rainfall and subsequent flooding, and populations stabilize only after the torrential rains have ceased. Unlike populations in temporary ponds, young snails constituted a large percentage of the population very late in the season. In perennial habitats, seasonal fluctuations in population density were related to manipulation of water levels in a rice irrigation scheme. The lowest densities occurred when the water levels were at their most extreme levels, between November and April. But declines in the population densities often preceded significant changes in the water level, indicating that this factor alone is not responsible for these declines. Of the B. globosus shedding schistosome cercariae, more than 90% were infected with S. haematobium and the remainder with S. bovis. Of 153 infected B. globosus, 87% were found in seasonal habitats. In those sites the first infected snails were found in July but the large numbers were not present until late August and September. Infected snails declined rapidly before the final decline in the general population of B. globosus in November and December. In perennial habitats, infected snails were most common in May and June, just before and early in the rainy season. These findings may prove useful in developing more effective schistosomiasis control measures in sahelian climates.
在喀麦隆极北省的三个村庄，对球拟沼螺的种群动态进行了跟踪研究，这些村庄的埃及血吸虫患病率很高。研究涵盖了1987年6月至1988年11月期间的两个雨季和一个旱季。在监测的几个环境因素中，只有降雨量以及由此导致的水位变化与蜗牛密度的变化密切相关，而且即便如此，也只有在数值处于极端水平时才会如此。在季节性水塘中，成年蜗牛从夏眠中苏醒，在第一场雨后不久就开始产卵。3至6周后，较大蜗牛数量的减少表明初始种群出现死亡。总体而言，种群密度在雨季适度增加，然后在9月或10月暴雨结束后迅速下降。在栖息地干涸之前，成年蜗牛再次占据主导地位。在季节性溪流中，种群密度随着降雨和随后的洪水而剧烈波动，只有在暴雨停止后种群才会稳定下来。与临时池塘中的种群不同，幼螺在季节后期在种群中占很大比例。在常年栖息地，种群密度的季节性波动与水稻灌溉计划中的水位调控有关。最低密度出现在11月至4月水位最极端的时候。但种群密度的下降往往先于水位的显著变化，这表明仅这一因素并不能解释这些下降。在排出血吸虫尾蚴的球拟沼螺中，超过90%感染了埃及血吸虫，其余感染了牛血吸虫。在153只感染的球拟沼螺中，87%发现于季节性栖息地。在这些地点，7月首次发现感染蜗牛，但直到8月下旬和9月才出现大量感染蜗牛。在11月和12月球拟沼螺总体数量最终下降之前，感染蜗牛数量迅速减少。在常年栖息地，感染蜗牛在5月和6月最为常见，就在雨季来临前和雨季初期。这些发现可能有助于在萨赫勒气候地区制定更有效的血吸虫病控制措施。
