Calodium hepaticum (syn. Capillaria hepatica) infection in synanthropic small mammals (rodents and shrews) in Northeastern India: Zoonotic and One Health implications

Rapid urbanization has increased overlap between human and synanthropic rodent habitats. This intensifies human-animal-environment interactions and facilitates the emergence and re-emergence of zoonotic diseases, highlighting the importance of the "One Health" concept. Calodium hepaticum (syn. Capillaria hepatica) is a neglected zoonotic parasite where rodents serve as the principal reservoirs. Human infections are often asymptomatic, but they can also cause liver failure and death in severe cases, with definitive diagnosis requiring liver biopsy. This study was conducted in Meghalaya, Northeastern India, where 173 rodents and shrews representing seven species were captured from synanthropic environments, with B. bengalensis comprising the largest proportion of captured animals (49.13%), followed by B. indica (17.34%), S. murinus (14.45%), M. musculus (8.67%), R. rattus (4.63%), M. booduga (4.05%), and R. norvegicus (1.73%). Liver samples were examined using gross pathology, histopathology, parasitological, and molecular methods, including 18S rRNA gene sequencing and phylogenetic analysis. Histopathological examination revealed non-embryonated barrel-shaped eggs in hepatic tissues, while molecular analysis confirmed the identity of C. hepaticum. Based on molecular detection, the overall prevalence of C. hepaticum was 36.99% (64/173; 95% CI: 30.16-44.44). Species-level prevalence was highest in Bandicota indica (80%; 95% CI: 62.69-90.49), followed by Mus booduga (57.14%; 95% CI: 25.05-84.18), B. bengalensis (31.76%; 95% CI: 22.84-42.27), and M. musculus (26.67%; 95% CI: 10.90-51.95), with lower rates in S. murinus (16%; 95% CI: 6.40-34.65) and R. rattus (12.50%; 95% CI: 2.24-47.09). Given the high prevalence observed, appropriate rodent control and carcass disposal should be encouraged to minimize the potential risk of environmental contamination, as eggs may be released during decomposition, predation, or cannibalism and subsequently embryonate in soil, becoming infective to humans or other susceptible hosts.