肠道血吸虫病的爆发:马拉维的未来是什么?

Malawi is endemic for urogenital schistosomiasis, however reports of intestinal schistosomiasis have pointed to the emergence of Schistosoma mansoni in the area. In this blog, researchers from the Liverpool School of Tropical Medicine confirm that an outbreak of intestinal schistosomiasis is occuring in the Mangochi District and discuss the epidemiological and public health implications in Malawi.

我们的最近的调查在马拉维学童中,儿童已经发生了马拉维湖曼戈奇地区的肠道细菌病爆发。

血吸虫病

血吸虫病,,,,of which there are two forms, intestinal and urogenital, is aneglected tropical disease负责整个撒哈拉以南非洲的大量发病率和死亡率。

The perpetual infection cycle that exists in many aquatic habitats and in key disease hotspots, such the communities surrounding Lake Malawi, is hard to break, and the balance between each form of the disease is changing significantly. Control initiatives help to break disease transmission, often through mass drug administration (MDA) of praziquantel withinpreventive chemotherapy策略。但是,淡水体内或周围的生态发展可能导致血吸虫病的意外变化,从出现到暴发和慢性流行性。

Urogenital schistosomiasis,,,,classically caused by theSchistosoma haematobium寄生虫,在马拉维湖流行多年,作为兼容的蜗牛种群Bulinusspp. are found along its shoreline. Accordingly, the mainstay control method of the Malawian National Control Programme has been annual MDA in schools situated in high-risk transmission zones.

相比之下,在意外发现了另一种蜗牛宿主物种之后,Biomphalaria pfeifferi,,,,alongside first confirmation of localS. mansonitransmission (responsible for intestinal schistosomiasis) in Mangochi District (southern tip of Lake Malawi)in 2018(阅读以前Bugbitten博客),现在存在着与两种形式的血吸虫病相关的传播和发病率增加的威胁。

我们的investigationevidenced a significant increase in both urogenital and intestinal schistosomiasis at two schools surveyed a year previously. Moreover, both forms of schistosomiasis were detected at all further ten schools surveyed, with the balance of infection biased towards intestinal schistosomiasis. The available evidence firmly demonstrates that intestinal schistosomiasis, once considered non-endemic in Lake Malawi, has transitioned from emergence to outbreak, and could perhaps eventually become the dominant form locally.

Implications for morbidity in Malawian children

Frank morbidity markers of schistosomiasis, such as red urine (haematuria fromS. haematobium),在像这样的流行地区的学龄儿童中显然是显而易见的。在低收入环境中打破传输周期所需的水,卫生和卫生措施通常不存在。

Adding to these levels of haematuria, we have noticed that co-infection withS. mansoni似乎增加了这种病理。芒果地区的泌尿生殖器发病率持续存在 - 在我们2019年的调查中,所有从一所特定学校(Ndembo)采样的所有三十个儿童对尿液量油量的微尿素呈阳性,表明慢性尿路炎症。同时,faecal-occult bloodtesting was used to highlight morbidity in intestinal schistosomiasis. Our findings show that the general prevalence of blood in stool cannot now be overlooked, nor the additional impactS. mansonihas on increasing inflammation.

Links between both of these early morbidity markers and their associated forms of schistosomiasis are already widely reported in endemic areas and were detected in our study. They likely predict that more cryptic disease, as best detected by ultrasonography (e.g. liver fibrosis), is already underlying and set to become more apparent in these communities in future.

Another important aspect of the dynamics ofS. haematobiumandS. mansoni共同感染是成年人蠕虫本身的行为,它们可能出现在异位卵形位点。例如,当一种棘小斑点被侵入另一个种类的地方时,可能会出现跨特异性蠕虫对,例如S. mansonieggs in the urine (see photo) orS. haematobiumeggs in the stool.

Schistosoma mansoniandS. haematobiumova in the urine (photograph: Bright Mainga).

Previous schistosomiasis outbreaks and threat from novel schistosomes

曼戈奇湖地区的当前局势与1980年代后期的塞内加尔河流域相似。以前非流行S. mansoni,最初的第一次感染后发生了爆发reported at Richard-Toll,,,,not long after the building of the Diama dam. The transition from emergence to outbreak occurred rapidly.

More recently, the emergence of schistosomiasis in Corsica in 2014, as described ina BugBitten post,,,,was an example of how hybridising schistosomes can pose a significant threat to public health. The island, located off the coast of Southern France, sawS. haematobiumparasites hybridise withS. Bovis,牲畜寄生虫。值得注意的是新的杂种螺旋体组合也出现在马拉维湖的曼戈奇区海岸线上questioning the species integrityofS. haematobiumitself.

Next steps

以前的爆发,例如塞内加尔和科西嘉岛的暴发,突显了及时的公共卫生干预的重要性。尽管WASH措施可以提供长期解决方案,但这些方法在大湖海岸线上非常具有挑战性。简而言之,不存在安全的水设施和足够的厕所,并且改善疾病控制会很慢。

因此,最初的建议包括加强预防性化疗(每年两次或更高的社区获取),以及增加监视(包括疾病)以查明高危传播区。牲畜的监视对于推动我们对马拉维杂交螺旋体动力学的理解也可能至关重要。

不幸的是,2019年冠状病毒病的毁灭性时机(COVID-19)大流行导致了MDA计划被搁置。尽管Covid-19危机姿势对公共卫生的威胁更加直接,但我们希望及时获得预防治疗的机会。

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