Changing livestock vaccination policy alters the epidemiology of human anthrax, Georgia, 2000-2013

Abstract

Anthrax is a widely spread zoonotic disease found on nearly every continent. To control the disease in humans and animals, annual livestock vaccination is recommended. However, in 2007, the country of Georgia ended its policy of compulsory annual livestock anthrax vaccination. Our objective was to assess how the epidemiology of human anthrax has evolved from 2000-2013 in Georgia, in the wake of this cessation. We used passive surveillance data on epidemiological surveys of human anthrax case patients. Risk factors and rates of self-reported sources of infection were compared, before and after the change in livestock vaccination policy. We mapped ethnicity-adjusted incidence during the two periods and assessed changes in the spatial pattern of risk. The overall risk of human anthrax increased >5-fold, from 0.7 cases per 100,000 in 2000 to 3.7 cases per 100,000 by 2013. Ethnic disparities in risk became pronounced; from 2000 to 2013, incidence increased >60-fold in Azerbaijanis from 0.35 to 21.1 cases/100,000 Azerbaijanis compared to 0.61 to 1.9 cases/100,000 among ethnic Georgians. Food-borne exposures from purchasing meat increased from 11% in 2000-2006 to 21% in 2007-2013. Spatial analyses revealed a shift from a random pattern of reporting pre-policy change to clustering among district municipalities following the change in policy. Our findings indicate there were unintended human health consequences associated with changing livestock vaccination policy. Following a reduction in the immunizations administered, there was a major shift in the epidemiology of human anthrax in Georgia. Current infection risk is now highest among ethnic minorities. Increased reporting among individuals uncharacteristically at risk for anthrax from foodborne exposures suggests spillover from modes of agricultural production. Given the importance of human-livestock health linkages, careful evaluations of policy need to be undertaken before changes to animal vaccination are made.

Keywords: Anthrax; Epidemiology; Human; Livestock; One health; Policy; Vaccine.