Potential for Spread of Some Bacterial and Protozoan Pathogens via Abattoir VVastes Applied on Agricultural Land

Twenty-eight commercial abattoirs were surveyed for practices related to, and quantitative levels of pathogens in, wastes to be applied on agricultural land. The abattoir wastes applied on agricultural land comprise two main groups, effluent-based wastes and animal-based wastes. The effluent-based wastes include three main types: separated solids, sludge and water. Mixing sludge and blood is a regular practice at poultry-only abattoirs. Animal-based wastes include two main sub-groups: digestive tract content-based and blood-based. All red meat abattoirs surveyed apply some of these wastes to land, and 37 such wastes were counted. In all wastes tested (lairage, lairage/stomach content, stomach content, blood and effluent), the average incidence of the most commonly isolated viable bacterial pathogen, Campylobacter, was 5.7%. The pathogen was found in effluent and blood from poultry abattoirs (12.5%, each) and in lairage and blood from red meat abattoirs (8.3%, each). Listeria monocytogenes was found in only 1.1 % of all waste samples (4.2% in lairage waste), and not in any sample from poultry abattoirs. Salmonella and E. coli 0 157 were not isolated from any of the abattoir waste samples. A number of possible explanations exist for these relatively low levels of the bacterial pathogens in abattoir wastes, including pathogens dying off in wastes, low shedding rates by the animals,"dilution" of contaminated wastes with non-contaminated wastes (e.g., blood) and/or water, non-detection of pathogens present in small numbers by quantitative (non-enrichment) methods, and effects on isolation of the stressed status of pathogen cells.The overall incidence of the protozoan pathogens Giardia and Cryptosporidium (viability not assessed) in red meat abattoir wastes was around 52.5% and 40%, respectively. The waste type most frequently contaminated with protozoan pathogens was lairage waste, followed by effluent. In lairage wastes from single-species abattoirs, the incidence of Giardia and Cryptosporidium was higher at sheep and pig abattoirs than at cattle abattoirs. Also, the incidence of both protozoan pathogens was higher in lairage wastes at three three-species abattoirs, as the throughput was higher. On the other hand, the sampling season did not show any significant effect on either overall incidences of Giardia or Cryptosporidium or their average total counts/g in abattoir wastes. Because of the highly variable nature of abattoir wastes and the limited numbers of samples tested, a direct extrapolation of these microbiological results to all abattoirs is not appropriate.