Schistosome Infections: An Indian Perspective
Schistosomiasis is an endemic helminthic disease of human. Schistosomes display considerable biodiversity in habitat, host range, and epidemiology globally. In spite of the noticeable presence of sero-positivity for schistosomal antibody and passage of schistosome eggs in human faeces, Indian subcontinent has always been considered as a low risk region for human schistosomiasis. Several species has been described in India which may have association with human infection and cercarial rash. Although sporadic cases are not uncommon, the status of human schistosomiasis in India is not well investigated. In this review different aspect of schistosomal infection in human in India has been described briefly.

Schistosomiasis is one of the oldest known parasitic infestations described in historical records. It affects about 200 million people worldwide. On an average 85% of these cases are indigenous to African continent. However, it had not caught attention of the scientific community until German scientist Theodor Bilharz first described the presence of adult schistosomes in portal vein of a man at autopsy. Scistosomes are unique member of Class Trematoda. In contrast to other trematodes, these adult worms are dioecious, parasitize venous systems and produce non-operculated eggs. The fork tail cercaria of scistosomes develops in snail and infect human by skin penetration.

While Schistosoma haematobium, S. mansoni, S. guineensis and S. intercalatum are the anthropophilic species widespread in Africa, these are not common in Asia. Instead, S. japonicum, S. mekongi, and S. malayensis are prevalent in Asian countries. Classically schistosomiasis had been a disease of the poor and rural population in tropical countries. However, significant change in its geographical distribution has been observed in recent years. Advancement in health and hygiene as well as snail control measures and chemotherapy has eliminated the threat from several endemic countries. On the contrary, population movement from endemic zones and expansion of natural habitat of snail associated with unplanned establishment of dam and irrigation projects has resulted in emergence of newer endemic foci. The status of human schistosomiasis in India is not well established. India has always been considered as a non-endemic country for human schistosomiasis. The non-existence of intermediate host of anthropophilic schistosomes in India is believed to be the principal reason which precludes the natural lifecycle of these schistosomes in Indian subcontinent. However, at least three endemic foci of human schistosomiasis had been described in India previously and sporadic autochthonous cases and cercarial dermatitis are also not uncommon. Moreover, several unique schistosome species of animals are prevalent in India. The co-existence of several different species of schistosomes may result in newer hybrid strains pathogenic to man and the risk associated with these species as a potential source of human infection needs further research

Video links

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Introduction about Schistosomiasis and Complete Details About Schistosomiasis

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