Release of live baitfish by recreational anglers drives fish pathogen introduction risk.

Emerging diseases of wildlife are an existential threat to biodiversity, and human-mediated movements of live animals are a primary vector of their spread. Wildlife disease risk analyses offer an appealing alternative to precautionary approaches because they allow for explicit quantification of uncertainties and consideration of tradeoffs. Such considerations become particularly important in high-frequency invasion pathways with hundreds of thousands of individual vectors, where even low pathogen prevalence can lead to substantial risk. The purpose of this study was to examine the landscape-level dynamics of human behavior-mediated pathogen introduction risk in the context of a high-frequency invasion pathway. One such pathway is the use and release of live fish used as bait by recreational anglers. We used a stochastic risk assessment model parameterized by angler survey data from Minnesota, USA, to simulate one year of fishing in Minnesota and estimate the total number of risky trips for each of three pathogens: viral hemorrhagic septicemia virus, the microsporidian parasite Ovipleistophora ovariae, and the Asian fish tapeworm Schizocotyle acheilognathi. We assessed the number of introductions under four scenarios: current/baseline conditions, outbreak conditions (increased pathogen prevalence), source-focused control measures (decreased pathogen prevalence), and angler-focused control measures (decreased rates of release). We found that hundreds of thousands of introduction events can occur per year, even for regulated pathogens at low pathogen prevalence. Reducing the rate of illegal baitfish release had significant impact on risky trips in scenarios where a high number of anglers were involved, but was less impactful in circumstances with limited outbreaks and fewer affected anglers. In contrast, reducing pathogen prevalence in the source populations of baitfish had relatively little impact. In order to make meaningful changes in pathogen introduction risk, managers should focus efforts on containing local outbreaks and reducing illegal baitfish release to reduce pathogen introduction risk. Our study also demonstrates the risk associated with high-frequency invasion pathways and the importance of incorporating human behaviors into wildlife disease models and risk assessments.

Pooled surveillance testing for asymptomatic SARS-CoV-2 infections at a Veterinary Teaching Hospital College, University of Minnesota, December 2020-April 2021.

To evaluate the use of asymptomatic surveillance, we implemented a surveillance program for asymptomatic SARS-CoV-2 infection in a voluntary sample of individuals at the College of Veterinary Medicine at the University of Minnesota. Self-collected anterior nasal samples were tested using real time reverse transcription-polymerase chain reaction (RT-PCR), in a 5:1 pooled testing strategy, twice weekly for 18 weeks. Positive pools were deconvoluted into individual tests, revealing an observed prevalence of 0.07% (3/4,525). Pooled testing allowed for large scale testing with an estimated cost savings of 79.3% and modeling demonstrated this testing strategy prevented up to 2 workplace transmission events, averting up to 4 clinical cases. At the study endpoint, antibody testing revealed 80.7% of participants had detectable vaccine antibody levels while 9.6% of participants had detectable antibodies to natural infection.

Assessing transmission of lymphatic filariasis using parasitologic, serologic, and entomologic tools after mass drug administration in American Samoa.

Assessing the interruption of lymphatic filariasis transmission after annual mass drug administration (MDA) requires a better understanding of how to interpret results obtained with the available diagnostic tools. We conducted parasitologic, serologic, and entomologic surveys in three villages in American Samoa after sentinel site surveys suggested filarial antigen prevalence was < 1% after five annual MDAs with diethylcarbamazine and albendazole. Antigen and antifilarial antibody prevalence ranged from 3.7% to 4.6% and from 12.5% to 14.9%, respectively, by village. Only one person was microfilaria positive. Although no children less than 10 years of age were antigen positive, antifilarial antibody prevalence in this age group was 5.1% and antibody-positive children were detected in all three villages. Wuchereria bancrofti-infected mosquitoes were also detected in all three villages. Thus, monitoring of infections in mosquitoes and antifilarial antibody levels in children may serve as indicators of local transmission and be useful for making decisions about program endpoints.

Variation in virulence among clades of Escherichia coli O157:H7 associated with disease outbreaks.

Escherichia coli O157:H7, a toxin-producing food and waterborne bacterial pathogen, has been linked to large outbreaks of gastrointestinal illness for more than two decades. E. coli O157 causes a wide range of clinical illness that varies by outbreak, although factors that contribute to variation in disease severity are poorly understood. Several recent outbreaks involving O157 contamination of fresh produce (e.g., spinach) were associated with more severe disease, as defined by higher hemolytic uremic syndrome and hospitalization frequencies, suggesting that increased virulence has evolved. To test this hypothesis, we developed a system that detects SNPs in 96 loci and applied it to >500 E. coli O157 clinical strains. Phylogenetic analyses identified 39 SNP genotypes that differ at 20% of SNP loci and are separated into nine distinct clades. Differences were observed between clades in the frequency and distribution of Shiga toxin genes and in the type of clinical disease reported. Patients with hemolytic uremic syndrome were significantly more likely to be infected with clade 8 strains, which have increased in frequency over the past 5 years. Genome sequencing of a spinach outbreak strain, a member of clade 8, also revealed substantial genomic differences. These findings suggest that an emergent subpopulation of the clade 8 lineage has acquired critical factors that contribute to more severe disease. The ability to detect and rapidly genotype O157 strains belonging to such lineages is important and will have a significant impact on both disease diagnosis and treatment guidelines.

Influence of antibiotic selection on genetic composition of Escherichia coli populations from conventional and organic dairy farms.

The widespread agricultural use of antimicrobials has long been considered a crucial influence on the prevalence of resistant genes and bacterial strains. It has been suggested that antibiotic applications in agricultural settings are a driving force for the development of antimicrobial resistance, and epidemiologic evidence supports the view that there is a direct link between resistant human pathogens, retail produce, farm animals, and farm environments. Despite such concerns, little is understood about the population processes underlying the emergence and spread of antibiotic resistance and the reversibility of resistance when antibiotic selective pressure is removed. In this study, hierarchical log-linear modeling was used to assess the association between farm type (conventional versus organic), age of cattle (calf versus cow), bacterial phenotype (resistant versus susceptible), and the genetic composition of Escherichia coli populations (E. coli Reference Collection [ECOR] phylogroup A, B1, B2, or D) among 678 susceptible and resistant strains from a previously published study of 60 matched dairy farms (30 conventional and 30 organic) in Wisconsin. The analysis provides evidence for clonal resistance (ampicillin resistance) and genetic hitchhiking (tetracycline resistance [Tet(r)]), estimated the rate of compositional change from conventional farming to organic farming (mean, 8 years; range, 3 to 15 years), and discovered a significant association between low multidrug resistance, organic farms, and strains of the numerically dominant phylogroup B1. These data suggest that organic farming practices not only change the frequency of resistant strains but also impact the overall population genetic composition of the resident E. coli flora. In addition, the results support the hypothesis that the current prevalence of Tet(r) loci on dairy farms has little to do with the use of this antibiotic.

Genetic diversity and population structure of Escherichia coli isolated from freshwater beaches.

Escherichia coli is an important member of the gastrointestinal tract of humans and warm-blooded animals (primary habitat). In the external environment outside the host (secondary habitat), it is often considered to be only a transient member of the microbiota found in water and soil, although recent evidence suggests that some strains can persist in temperate soils and freshwater beaches. Here we quantified the population genetic structure of E. coli from a longitudinal collection of environmental strains isolated from six freshwater beaches along Lake Huron and the St. Clair River in Michigan. Multilocus enzyme electrophoresis (MLEE) and multilocus sequence typing (MLST) revealed extensive genetic diversity among 185 E. coli isolates with an average of 40 alleles per locus. Despite evidence for extensive recombination generating new alleles and genotypic diversity, several genotypes marked by distinct MLEE and MLST profiles were repeatedly recovered from separate sites at different times. A PCR-based phylogrouping technique showed that the persistent, naturalized E. coli belonged to the B1 group. These results support the hypothesis that persistent genotypes have an adaptive advantage in the secondary habitat outside the host.