Department of Animal Pathology (INVESAGA Group), Veterinary Faculty, University of Santiago de Compostela, Lugo, Spain.
Veterinary Department, Kenya Wildlife Service, Nairobi, Kenya.
Parasit Vectors. 2020 Mar 18;13(1):145. doi: 10.1186/s13071-020-04017-1.
The dynamics of helminth infection in African elephant populations are poorly known. We examined the effects of age, sex, social structure and the normalized difference vegetation index (NDVI) as primary drivers of infection patterns within and between elephant populations.
Coprological methods were used to identify helminths and determine infection patterns in distinct elephant populations in Maasai Mara National Reserve, Tsavo East National Park, Amboseli National Park and Laikipia-Samburu Ecosystem. Gaussian finite mixture cluster analyses of egg dimensions were used to classify helminth eggs according to genera. Generalized linear models (GLM) and Chi-square analyses were used to test for variation in helminth infection patterns and to identify drivers in elephant populations.
Helminth prevalence varied significantly between the studied populations. Nematode prevalence (96.3%) was over twice as high as that of trematodes (39.1%) in elephants. Trematode prevalence but not nematode prevalence varied between populations. Although we found no associations between helminth infection and elephant social groups (male vs family groups), the median helminth egg output (eggs per gram, epg) did vary between social groups: family groups had significantly higher median epg than solitary males or males in bachelor groups. Young males in mixed sex family groups had lower epg than females when controlling for population and age; these differences, however, were not statistically significant. The average NDVI over a three-month period varied between study locations. Cluster analyses based on egg measurements revealed the presence of Protofasciola sp., Brumptia sp., Murshidia sp., Quilonia sp. and Mammomonogamus sp. GLM analyses showed that the mean epg was positively influenced by a three-month cumulative mean NDVI and by social group; female social groups had higher epg than male groups. GLM analyses also revealed that epg varied between elephant populations: Samburu-Laikipia elephants had a higher and Tsavo elephants a lower epg than Amboseli elephants.
Elephants had infection patterns characterized by within- and between-population variation in prevalence and worm burden. Sociality and NDVI were the major drivers of epg but not of helminth prevalence. Gastrointestinal parasites can have a negative impact on the health of wild elephants, especially during resource scarcity. Thus, our results will be important when deciding intervention strategies.
非洲象种群中寄生虫感染的动态变化尚不清楚。我们研究了年龄、性别、社会结构和归一化差异植被指数（NDVI）作为主要驱动因素，以确定不同象群内部和之间的感染模式。
我们使用粪便分析法在马赛马拉国家保护区、东察沃国家公园、安博塞利国家公园和莱基皮亚-萨伯鲁生态系统中，对不同的大象种群进行寄生虫检测，以确定感染模式。利用虫卵尺寸的高斯有限混合聚类分析，根据属对寄生虫卵进行分类。使用广义线性模型（GLM）和卡方检验，检验寄生虫感染模式的变化，并确定大象种群中的驱动因素。
研究人群中的寄生虫患病率存在显著差异。线虫的患病率（96.3%）是吸虫的两倍多（39.1%）。吸虫的患病率而不是线虫的患病率在不同的种群之间有所不同。虽然我们没有发现寄生虫感染与大象社会群体（雄性与家庭群体）之间的关联，但寄生虫卵输出量（每克卵数，epg）确实在社会群体之间有所不同：家庭群体的 epg 中位数明显高于单身雄性或单身雄性群体。在控制人口和年龄的情况下，混合性别家庭群体中的年轻雄性的 epg 低于雌性；然而，这些差异并不具有统计学意义。三个月期间的平均 NDVI 在研究地点之间有所不同。基于卵测量的聚类分析显示存在 Protofasciola sp.、Brumptia sp.、Murshidia sp.、Quilonia sp. 和 Mammomonogamus sp.。GLM 分析表明，epg 受三个月累积平均 NDVI 和社会群体的正向影响；雌性社会群体的 epg 高于雄性群体。GLM 分析还表明，epg 在不同的大象种群之间存在差异：萨伯鲁-莱基皮亚大象的 epg 高于安博塞利大象，而察沃大象的 epg 低于安博塞利大象。
大象的感染模式表现为流行率和虫负荷的种群内和种群间的变化。社会性和 NDVI 是 epg 的主要驱动因素，但不是寄生虫流行率的主要驱动因素。胃肠道寄生虫会对野生大象的健康产生负面影响，特别是在资源匮乏时期。因此，当决定干预策略时，我们的研究结果将是重要的参考。
