Deer mice (Peromyscus maniculatus) are abundant and widely distributed rodents in North America that occupy diverse habitats, including agricultural landscapes. Giardia and Cryptosporidium are common parasites in wildlife including deer mice, which may play a role in on-farm contamination of produce. An important step in assessing the risk of produce contamination by Cryptosporidium and Giardia shed by deer mice is to determine the prevalence, levels, and genotypes of (oo)cysts in mouse feces. A total of 63 (30.3%) and 53 (25.5%) of 208 deer mice trapped on 12 farms on the California Central Coast were positive for Cryptosporidium and Giardia, respectively. Of these mice, 41 (19.7%) contained both parasites. The odds of Cryptosporidium shedding were 2.5 to 5 times higher for mice trapped in autumn than for mice trapped in summer or spring. Female mice had a higher prevalence and two- to threefold higher levels of Cryptosporidium and Giardia compared with male mice. Female adults and female juveniles had the highest rates of contamination of the environment with Cryptosporidium and Giardia, respectively. We estimated that 20 infected deer mice inhabiting 1 ha of a typical leafy green produce farm in the study region could shed approximately 5.3 × 108 Cryptosporidium and 10.5 × 108 Giardia, respectively, per day into the environment. The small-subunit rRNA gene loci from a subset of protozoan isolates were sequenced and compared with existing sequences in GenBank. Multiple genotypes of Cryptosporidium and Giardia were found, and BLAST analyses suggest that Giardia and the majority of Cryptosporidium genotypes in deer mice circulate within various rodent populations, but some Cryptosporidium isolates possess zoonotic potential.

ABSTRACT Recent outbreaks of food-borne illness associated with the consumption of produce have increased concern over wildlife reservoirs of food-borne pathogens. Wild rodents are ubiquitous, and those living close to agricultural farms may pose a food safety risk should they shed zoonotic microorganisms in their feces near or on agricultural commodities. Fecal samples from wild rodents trapped on 13 agricultural farms (9 produce, 3 cow-calf operations, and 1 beef cattle feedlot) in Monterey and San Benito Counties, CA, were screened to determine the prevalence and risk factors for shedding of several food-borne pathogens. Deer mice ( Peromyscus maniculatus ) were the most abundant rodent species trapped (72.5%). Cryptosporidium species (26.0%) and Giardia species (24.2%) were the predominant isolates from rodent feces, followed by Salmonella enterica serovars (2.9%) and Escherichia coli O157:H7 (0.2%). Rodent trap success was significantly associated with detection of Salmonella in rodent feces, while farm type was associated with fecal shedding of Cryptosporidium and Giardia . Seasonal shedding patterns were evident, with rodents trapped during the spring and summer months being significantly less likely to be shedding Cryptosporidium oocysts than those trapped during autumn. Higher rodent species diversity tended to correlate with lower fecal microbial prevalence, and most spatiotemporal pathogen clusters involved deer mice. Rodents in the study area posed a minimal risk as environmental reservoirs of E. coli O157:H7, but they may play a role in environmental dissemination of Salmonella and protozoa. Rodent control efforts that potentially reduce biodiversity may increase pathogen shedding, possibly through promotion of intraspecific microbial transmission.

Outbreaks of foodborne illness associated with the consumption of leafy green produce from California and across the United States have heightened the need to identify vertebrate sources of these microbial hazards.Concern has focused on wildlife species that have direct access to the produce production environment and irrigation water supplies.Recent fecal surveys of California wildlife, feral animals, and livestock and companion animals are allowing regulators to compare the food safety risks of such pathogens as E. coli O157:H7 and Salmonella from these various animal species.In order to make valid food safety risk comparisons between wildlife, livestock, and companion animals, a variety of methodological and epidemiological issues need to be addressed in order to avoid substantial biases.For example, the amount of feces tested per animal can vary up to a 1000-fold, substantially biasing the probability of testing positive for large fecal contributors (e.g., cattle) compared to smaller wildlife (e.g., deer mice).Many wildlife species intrude and forage as a group in fields of produce, which can lead to infield defecation, substantially, elevating the risk of microbial contamination compared to many larger animal species that do not have direct access to produce fields due to fencing.This paper highlights the technical challenges of making valid quantitative comparisons of microbial food safety risks from wildlife compared to other domestic animals.

Between 2009 and 2011, fecal samples were collected from ten species of wild rodents in locations adjacent to leafy green blocks in a major produce production region of California.Samples were screened for Cryptosporidium spp.oocysts and Giardia spp.cysts using immunofluorescent microscopy.Five and seven species of wild rodents carried Cryptosporidium spp.and Giardia spp., respectively.In general, 26.0% and 24.2% of the trapped wild rodents were positive for Cryptosporidium spp.and Giardia spp., respectively.Deer mice (Peromyscus manicultus) were the primary trapped species, with 30.3% (63/208) positive for Cryptosporidium spp.and 25.5% (53/208) positive for Giardia spp.