Risk factors for anthrax in livestock: findings from one health outbreak investigations in Bangladesh.

Abstract

BACKGROUND: Anthrax remains endemic in Bangladesh, causing recurring outbreaks in livestock and humans despite vaccination programs. Although environmental persistence of Bacillus anthracis is recognized, evidence on modifiable animal- and farm-level practices that contribute to livestock anthrax is limited. This study aimed to identify animal-level and farm-level risk factors associated with anthrax in livestock in endemic areas of Bangladesh, addressing gaps in understanding how husbandry practices and farm management contribute to disease transmission. METHODS: Geographically matched animal case–control studies of ruminants were conducted in Bangladeshi subdistricts reporting human cutaneous anthrax cases from October 2012 to December 2016. A total of 103 cattle, goats, and buffalo were recruited from 81 case farms, while 1,098 ruminants were recruited from 553 control farms. Data on animal characteristics, feeding and grazing practices, vaccination status, and farm management behaviors were collected using structured questionnaires and analyzed using conditional logistic regression. RESULTS: At the animal level, communal grazing (adjusted matched odds ratio [mOR]: 2.67, 95% CI: 1.48–4.82), feeding freshly harvested hybrid grass (cultivated fodder) within three days of illness onset (adjusted mOR: 6.07, 95% CI: 1.71–21.42), and failure to vaccinate livestock (adjusted mOR: 0.06, 95% CI: 0.02–0.14) were strongly associated with infection. At the farm level, practices that disturbed or imported potentially contaminated soil, including scraping topsoil from animal sheds (adjusted mOR: 10.8, 95% CI: 3.02–38.63), routine collection of soil from cultivable land for shed maintenance (adjusted mOR: 6.49, 95% CI: 1.73–24.33), and on-farm slaughtering of animals (adjusted mOR: 3.09, 95% CI: 1.30–7.16), significantly increased anthrax risk. These findings highlight behavioral and management practices that facilitate exposure to B. anthracis spores. CONCLUSIONS: Our findings demonstrate that environmental disturbances, animal husbandry and farm management practices, alongside low vaccine coverage, intersect to sustain anthrax transmission in livestock in Bangladesh. Strengthening immunity through large-scale vaccination programs, coupled with improved animal grazing, soil husbandry, farm management, and slaughter practices, could significantly reduce animal anthrax and prevent human spillover in endemic settings such as Bangladesh.