Human anthrax in India in recent times: A systematic review & risk mapping

The disease anthrax occurs generally in herbivores and the causative organism (Bacillus anthracis) infects humans who come in contact with infected animals or their products. The persistence of anthrax spores for decades and its lethality contribute to its biowarfare potential. We conducted this systematic review along with risk mapping to investigate the spatio-temporal distribution, clinico-epidemiological, socio-behavioural and programmatic issues pertaining to anthrax in India over the last two decades. Peer reviewed quantitative and qualitative studies and grey literature comprising weekly reports of the ‘Integrated Disease Surveillance Program’ (IDSP), were accessed for extracting data. IDSP data were used for geo-referencing of the villages of anthrax cases; Pseudo-absence was generated to fit a Bayesian Additive Regression Trees (BART) model to develop anthrax risk map. The case fatality rate of cutaneous anthrax ranged from 2% to 38%, while the gastrointestinal and inhalational types were 100% fatal. Our synthesis revealed that human anthrax outbreaks in India were clustered around the eastern coastal regions. The states of Odisha, West Bengal, Andhra Pradesh and Jharkhand reported maximum number of outbreaks. Odisha reported a maximum number of 439 human anthrax cases since 2009, of which Koraput district contributed to 200 cases (46%). While handling or consumption of infected animal product were proximal drivers of these events, poverty, lack of awareness, traditional beliefs and local practices served as facilitatory factors. Other structural determinants were wild life-livestock interface, historical forest loss, soil pH, soil-water balance, organic carbon content, temperature, rainfall and humidity. The programmatic issues identified through this review were lack of active surveillance, non-availability of diagnostic facility at the periphery, delayed reporting, absence of routine livestock vaccination and lack of adequate veterinary services. Interventions based on One-health approach in the country merit immediate policy and program attention; high risk zones for anthrax identified during present investigation, should be prioritized.