Evidence of anthrax virulence genes in Bacillus aerius and human exposure in largest abattoir in Lagos, Nigeria.

Background: The anthrax virulence determinants, protective antigens (pag) and poly-D-γ-glutamate capsule (cap) genes have only been reported in 'cereus' group of Bacillus spp reflecting their genetic similarity. Human exposure to these virulence genes, which is through the uptake of the bacterial spores, can have serious public health implications. The study was designed to investigate the presence and burden of anthrax toxins-producing Bacillus spp. and human exposure in the largest abattoir in Lagos, Nigeria.

Methods: Soil samples collected from 3 abattoir-associated sites and blood drawn from abattoir workers and related persons were all processed in biosafety containment (BSL 3) following standard procedures. The identification of the Bacillus spp was done by combination of phenotypic and 16 S rRNA sequencing. The virulence genes were PCR detected following standard protocols. The clear human plasma was used for qualitative measurement of pag immunoglobulin G (PA-IgG) in indirect ELISA. Descriptive analysis and Chi-square test were used to describe the characteristics/distribution of Bacillus spp and relationship between exposure and risk factors.

Results: In total, forty-five soil and 89 human blood samples were collected and analyzed. Bacillus isolates (n = 26), belonging to 8 different spp were recovered from the soil samples. The pag and cap genes were concurrently amplified in three (3) strains of B. aerius (PQ269640, PQ269658, PQ269665) out of the seven isolated across the 3 sites while B. anthracis (n = 4) isolated from two sites amplified only the cap gene. All the B. cereus isolated in this study did not harbour any of the genes. Eighteen (20.2%) of the plasma samples were positive for the anthrax IgG (O.D. ≥ 0.23), male: female (8:1). The positive participants were mainly within the age bracket 30 yrs and ≥ 60 years and were significantly different from the negative (p = 0.01) while the dealing in, living with animals, previous handling of sick/dead animals have no significant differences between the PA- IgG positive and negative.

Conclusion: The non-cereus B. aerius (PQ269640, PQ269658, PQ269665) recovered from the soil harboured the anthrax virulence genes (pag, cap) and there was past exposure of abattoir workers, cattle dealers to anthrax toxins.