Subclinical Anthrax Exposure in Railroad Workers Following Soil Disruption in an Endemic Region: A Seroprevalence...

During construction of the Baku-Tbilisi-Kars railroad between Kars City in Türkiye and Tbilisi in Georgia, blasting operations in an anthrax-endemic region disrupted a burial pit containing carcasses of cattle that had died of anthrax. Railroad workers expressed concerns that release of this material could result in them developing anthrax infection. We therefore undertook a seroprevalence study six months later to seek evidence of exposure to Bacillus anthracis spores. We used an optimised Enzyme-Linked Immunosorbent Assay (ELISA) to screen serum for antigen-specific IgG antibodies to the anthrax toxin subunits Protective Antigen (PA) and Lethal Factor (LF). Stepwise linear regressions and t-tests were performed to compare results from railroad workers (n = 64) with a group of long-term Kars City residents (urban dwellers, n = 16), who had no history of possible contact with anthrax antigens. Anti-PA IgG concentrations were higher (p = 0.038) in railroad workers than in urban dwellers, but anti-LF IgG concentrations did not differ (p = 0.932) between the two groups. The anti-PA response is known to be dominant, and the difference was small. The lack of LF response did not preclude an antibody response to B. anthracis. Following the blasting operations, no cases of anthrax infection occurred in either railroad workers or villagers living nearby, suggesting that the spore exposure (evidenced by higher antibody titres) was at levels insufficient to initiate clinical infection. The elevated PA-specific antibody responses in railroad workers compared with urban dwellers might be consistent with the former having had previous subclinical exposure to B. anthracis. In anthrax-endemic regions, therefore, construction activities that involve blasting or large-scale excavation may pose risks of occupational exposure to Bacillus anthracis spores.