Bovine Visceral schistosomosis caused by S. indicum is a neglected tropical disease in southeast Asia. This was first discovered in horse, donkey and sheep in north India ( Montgomery, 1906). It has also been recorded in cattle, buffaloes, goat and camel. The record of this infection in erstwhile Madras province is not uncommon though infrequent (Rao, 1939;Alwar, 1950). Banerjee et al. (1972) also reported a clinical case of the infection in crossbred Holstein bull in West Bengal based on coprological examination.. In Northern states of India such as Haryana, Himachal Pradesh, Punjab and Rajasthan the incidence rate of S. indicum in cattle was around 2.3% as per the study conducted by Chaudhri et al, (2007) and it was also noted that the infection of S. indicum was more widespread than that of S. spindale. Central Indian states also showed this infection in cattle (Giri et al. 2018).Cherian and D’Souza (2009) reported the prevalence of S. indicum infection from faecal samples of small ruminants in Karnataka. Prevalence of S. indicum in cattle also reported from Kerala (Chirayath, 2007; Divya et al., 2012)
A study conducted by Jeyathilakan et al. (2008) wherein 114 cattle mesenteries collected from same slaughter house in Chennai,Tamil Nadu, were examined among which the prevalence of S. spindale was about 30.7% but there was no S. indicum infection found in cattle, even though common intermediate host Indoplanorbis exustus prevalent in Tamil Nadu. The present abattoir study conducted in Chennai revealed the occurrence of S.indicum in Nellore breed of cattle migrated from neighboring Andhra Pradesh state. Identification of Schistosoma spp causing bovine visceral schistosomosis under microscopy can be done by examination of characteristic morphology of ova upon coprological survey but visual appraisal of the affected animal does not aid in diagnosing this condition since the infected animal shows symptoms overlapping with other debilitating diseases. PCR based on 16sRNA gene and sequence analysis has been used for accurate confirmation of the species. Karnataka isolate of S.indicum showed no specific amplification (Manohara et al., 2019)
S. indicum Bangladesh isolate showed 99. 30% identity to the Tamil Nadu isolate. The phylogenetic tree was constructed based on character based method. The pylogenetic tree based analysis indicated that there could have existed a common ancestor for S. indicum of India and S. cf. indicum W528 Nepal isolate. The common ancestor of Tamil Nadu, India and Nepal isolate could have originated from S. spindale of Thailand and Sri Lankan isolate. Gene sequence of Indian isolate of S.indicum was so far not compared with other country isolates ( Jones et al., 2020). However, the earlier report revealed S. indicum from India forms a separate clade along with S. spindale of UK origin.
Livestock sector farmers of Tamil Nadu are unaware of this infection which is prevalent in most of the South Indian states except Tamil Nadu. It was also found that the infection of S. indicum was so far not reported from domestic cattle population of Tamil Nadu. This report also showed this infection in slaughtered migrant Nellore cattle breed from neighbouring states of India. The infection was seen more among the adult males and occurred mainly during the monsoons. Further studies are required so that in depth knowledge about epidemiology and bionomics of this infection in other parts of Tamil Nadu can help us to know the clarity of prevalence and take strategic preventive measures in better way.