Fichet-Calvet E, Jomâa I, Ben Ismail R, Ashford R W
Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, U.K.
Ann Trop Med Parasitol. 2003 Sep;97(6):593-603. doi: 10.1179/000349803225001517.
The causative agent of cutaneous leishmaniasis, Leishmania major, was studied in a Tunisian population of the fat sand rat, Psammomys obesus. Seasonal changes in the abundances of parasite and host were monitored in a longitudinal field survey lasting 21 months. Overall, 566 P. obesus, collected during 10 trapping sessions between May 1995 and January 1997, were examined. Analysis of prevalence, using logistic regression, revealed that extrinsic factors, such as season and climatic conditions, and intrinsic factors, such as host age, have a combined effect. Leishmania major showed a seasonal pattern, with most transmission occurring in late summer and in autumn, when prevalences were 7.5- and 6.6-fold higher, respectively, than in spring. Prevalence peaked, at 70%, in September 1995 and then decreased to 0% in June 1996. The same temporal fluctuation was observed during the second study year, albeit among prevalences that were relatively low because of unusually dry conditions. Prevalence was highly dependent on the age of the P. obesus, and season and age acted in synergy so that the rodents were highly infected in late summer and in autumn. Prevalence was not correlated with the relative density of the P. obesus and also appeared independent of gender. Although the ear lesions observed on 378 sand rats during a 1-year survey were closely associated with Leishmania infection, such lesions were not good predictors of infection, as 35% of the rodents found to be infected had no visible lesions on their ears. The prevalences of Leishmania infection observed in this study, among P. obesus living in monospecific colonies, were generally lower than those observed in other studies of P. obesus. It seems possible that P. obesus living in monospecific colonies could have a lesser role in propagating the parasite than those living in plurispecific colonies of rodents, and act as an 'epidemiological sink'.
在突尼斯肥胖沙鼠（Psammomys obesus）种群中对皮肤利什曼病的病原体硕大利什曼原虫（Leishmania major）进行了研究。在一项持续21个月的纵向野外调查中监测了寄生虫和宿主数量的季节性变化。总体而言，对1995年5月至1997年1月期间10次诱捕活动中捕获的566只肥胖沙鼠进行了检查。使用逻辑回归分析患病率发现，外在因素如季节和气候条件以及内在因素如宿主年龄具有综合作用。硕大利什曼原虫呈现出季节性模式，大多数传播发生在夏末和秋季，此时患病率分别比春季高7.5倍和6.6倍。患病率在1995年9月达到峰值70%，然后在1996年6月降至0%。在第二个研究年度观察到相同的时间波动，尽管由于异常干燥的条件患病率相对较低。患病率高度依赖于肥胖沙鼠的年龄，季节和年龄协同作用，使得啮齿动物在夏末和秋季感染率很高。患病率与肥胖沙鼠的相对密度无关，并且似乎也与性别无关。尽管在为期1年的调查中在378只沙鼠身上观察到的耳部病变与利什曼原虫感染密切相关，但这些病变并不是感染的良好预测指标，因为发现35%被感染的啮齿动物耳部没有可见病变。在本研究中观察到的生活在单物种群落中的肥胖沙鼠的利什曼原虫感染率普遍低于在其他肥胖沙鼠研究中观察到的感染率。生活在单物种群落中的肥胖沙鼠在传播寄生虫方面的作用可能比生活在多物种啮齿动物群落中的肥胖沙鼠小，并充当“流行病学汇”。
