A molecular survey of farmed and edible snails for the presence of human enteric viruses: Tracking of the possible environmental sources of microbial mollusc contamination

Abstract

Snails have been grown or harvested for human consumption for centuries. Similarly to tissues or meat of other food animals, snail meat should be free from microbiological hazards including viruses. The aim of the study was to investigate the presence of human enteric viruses (hepatitis A and E virus, norovirus genogroup I, II and human adenovirus) in farmed and free-living snails intended for human consumption. In order to find the possible sources of snail contamination with viruses, the quality management system operating in the most widely-adopted snail farming system in Poland was reviewed. Additionally, the process hygiene criteria were checked through testing of snail meat and soil samples for bacterial contamination. Snails of genus Cornu and Helix were collected from two heliciculture farms and a purchase point. They were subjected to bacteriological (n = 180) and viral examination (n = 60). In the case of soil samples (n = 8) they were taken from different areas along the breeding cycle of the snails. For virus detection several real-time PCR protocols with an incorporated target-specific internal amplification control (IAC) were used. Determinations of the total aerobic bacteria count (TBC), number of Enterobacteriaceae (ENC) and enterococci (ECC) were performed using the international reference methods. Human enteric viruses were not detected in any of the tested snail samples. TBC for raw snail meat ranged from 5.1 up to 6.6 log cfu/g and ENC values did not exceed 4.8 log cfu/g. The ECC counts were below 2.0 log cfu/g. The overall microbiological status of snail meat indicated good hygiene and appropriate environmental conditions being maintained during snail breeding. TBC for soil samples was in the range of 6.0–7.7 log cfu/g indicating a low or moderate level of contamination. Only the soil samples from the plots used at the fattening stage were characterised by high ECC content increasing the risk of virus occurrence. In contrary to the sporadic finding of ECC, the ubiquitous presence of bacteria from the Enterobacteriaceae family in all types of soil samples was shown. A good microbial quality of snail meat resulted from the implemented GMP/GHP programmes and food safety management practices. This strategy appeared sufficient in reduction of microbiological risk and in prevention of virus contamination in snails. The study showed that the risk of foodborne virus infection due to consumption of snails and related products is considered negligible.