Edward R. Atwill

Escherichia coli O157:H7 in Feral Swine near Spinach Fields and Cattle, Central California Coast

We investigated involvement of feral swine in contamination of agricultural fields and surface waterways with Escherichia coli O157:H7 after a nationwide outbreak traced to bagged spinach from California. Isolates from feral swine, cattle, surface water, sediment, and soil at 1 ranch were matched to the outbreak strain.

Host adaptation and host-parasite co-evolution in Cryptosporidium: implications for taxonomy and public health.

To assess the genetic diversity and evolution of Cryptosporidium parasites, the partial ssrRNA, actin, and 70kDa heat shock protein (HSP70) genes of 15 new Cryptosporidium parasites were sequenced. Sequence data were analysed together with those previously obtained from other Cryptosporidium parasites (10 Cryptosporidium spp. and eight Cryptosporidium genotypes). Results of this multi-locus genetic characterisation indicate that host adaptation is a general phenomenon in the genus Cryptosporidium, because specific genotypes were usually associated with specific groups of animals. On the other hand, host-parasite co-evolution is also common in Cryptosporidium, as closely related hosts usually had related Cryptosporidium parasites. Results of phylogenetic analyses suggest that the Cryptosporidium parvum bovine genotype and Cryptosporidium meleagridis were originally parasites of rodents and mammals, respectively, but have subsequently expanded their host ranges to include humans. Understanding the evolution of Cryptosporidium species is important not only for clarification of the taxonomy of the parasites but also for assessment of the public health significance of Cryptosporidium parasites from animals.

An examination of risk factors associated with beef cattle shedding pathogens of potential zoonotic concern

The prevalence of three waterborne zoonotic pathogens (Campylobacter sp., Giardia sp. and Cryptosporidium parvum) in rectal faecal samples from a random sample of adult beef cattle was determined. Management factors that may be associated with shedding of these organisms were examined. For Campylobacter sp. prevalence was 5.0%, and the number of females on the farm was positively associated with the proportion that tested positive. For Giardia sp. prevalence was 6.5%, and none of the management factors examined was significantly associated with the proportion in a herd testing positive. C. parvum was identified in 1.1% of samples. The length of calving season and whether any procedures were performed on the calves in the first 2 days of life were positively associated with the proportion that tested positive. We conclude that this sample of adult beef cattle represent a relatively limited threat to water supplies and subsequent disease transmission to humans from these pathogens.

Occurrence of generic Escherichia coli, E. coli O157 and Salmonella spp. in water and sediment from leafy green produce farms and streams on the Central California coast.

Irrigation with water of poor microbiological quality can elevate levels of bacteria on produce. This study aimed to identify climate and management variables associated with generic Escherichia coli in irrigation water on leafy green produce farms and to measure the prevalence of E. coli O157 and Salmonella spp. in irrigation and non-irrigation water sources on these farms. Water and sediment samples collected from various points along irrigation systems, as well as from streams and ponds on farms on the Central California coast between May 27th, 2008 and October 26th, 2010 were cultured for generic E. coli (MPN/100 mL or cfu 100 g) (n=436), E. coli O157 (n=437), and (n=163) Salmonella. Variables were based on growers management practices, landscape features in proximity to samples (e.g., distance to roads and ranches/livestock), and climate data accessed from an online database. Negative binomial regression models were constructed to test associations between generic E. coli (MPN/100 mL) in water from farms and variables. Arithmetic mean concentration of E. coli for water, not including those from Moore swabs, and sediment samples, was 7.1×10(2) MPN/100 mL and 1.0×10(4) cfu/100 g, respectively. Matched by collection day, E. coli concentration in sediment (cfu/100 g) was typically 10- to 1000-fold higher than the overlying water (MPN/100 mL) for these irrigation systems. Generic E. coli concentration (MPN/100 mL) increased by 60.1% for each 1m/s increase in wind speed and decreased by 3% for each 10 m increase in the distance between the sample location and rangeland. Moore swabs detected a higher proportion of E. coli O157 (13.8%) positive water samples compared to grab samples (1.8%); 1.7% of sediment samples had detectable levels of this pathogen. Interestingly, season was not significantly associated with E. coli O157 presence in water or sediments from produce farms or water sources with public access. Salmonella was detected in 6% (6/96) water and 4.3% (3/67) sediment samples. Generic E. coli concentration was not significantly associated with the presence of either E. coli O157 or Salmonella in water or sediment samples, suggesting that, for this 2.5-year period and geographical location, generic E. coli would likely be an unreliable indicator bacteria for predicting the presence of these food- and waterborne pathogens in a key produce production environment.

Efficacy of Natural Wetlands to Retain Nutrient, Sediment and Microbial Pollutants

Wetlands can improve water quality through natural processes including sedimentation, nutrient transformations, and microbial and plant uptake. Tailwater from irrigated pastures may contribute to nonpoint source water pollution in the form of sediments, nutrients, and pathogens that degrade downstream water quality. We examined benefits to water quality provided by a natural, flow-through wetland and a degraded, channelized wetland situated within the flood-irrigation agricultural landscape of the Sierra Nevada foothills of Northern California. The non-degraded, reference wetland significantly improved water quality by reducing loads of total suspended sediments, nitrate, and Escherichia coli on average by 77, 60, and 68%, respectively. Retention of total N, total P, and soluble reactive P (SRP) was between 35 and 42% of loads entering the reference wetland. Retention of pollutant loads by the channelized wetland was significantly lower than by the reference wetland for all pollutants except SRP. A net export of sediment and nitrate was observed from the channelized wetland. Decreased irrigation inflow rates significantly improved retention efficiencies for nitrate, E. coli, and sediments in the reference wetland. We suggest that maintenance of these natural wetlands and regulation of inflow rates can be important aspects of a best management plan to improve water quality as water runs off of irrigated pastures.

Capture and Retention of Cryptosporidium parvum Oocysts by Pseudomonas aeruginosa Biofilms

ABSTRACT The association of Cryptosporidium oocysts with biofilm communities can influence the propagation of this pathogen through both environmental systems and water treatment systems. We observed the capture and retention of C. parvum oocysts in Pseudomonas aeruginosa biofilms using laboratory flow cells. Biofilms were developed in two different growth media using two different strains of P. aeruginosa, a wild-type strain (PAO1) and a strain that overproduces the exopolysaccharide alginate (PDO300). Confocal laser-scanning microscopy was used in conjunction with image analysis to assess the structure of the biofilms prior to introducing oocysts into the flow cells. More oocysts were captured by the biofilm-coated surfaces than the abiotic glass surface in both media. There was no significant difference in capture across the two strains of P. aeruginosa biofilm, but the fraction of oocysts captured was positively related to biofilm roughness and surface-area-to-volume ratio. Once captured, oocysts were retained in the biofilm for more than 24 h and were not released after a 40-fold increase in the system flow rate. We believe the capture and retention of oocysts by biofilm communities can impact the environmental transmission of C. parvum, and this interaction should be taken into consideration when predicting the migration of pathogens in the environment.

Prevalence of and risk factors for shedding of Cryptosporidium parvum in Holstein Freisian dairy calves in central México

A total of 31 dairy farms from three states in central México were selected for this study in order to determine the prevalence of and risk factors for Cryptosporidium parvum shedding in young Holstein Freisian calves. Fecal samples were obtained once from each calf for acid-fast staining for detection of C. parvum oocysts. Information on each calf and on each dairys management practices regarding the maternity pen, calf hutches and calf feeding was obtained by personal interview using a standardized questionnaire. Of the 31 dairies, 29 had one or more calves shedding C. parvum oocysts. The overall point prevalence was 25% (128/512). Dairy calves from the states of Hidalgo, Jalisco, and México had overall point prevalences of 28% (51/185), 29% (33/112) and 20% (44/215), respectively. Day of age was strongly associated with the risk of shedding C. parvum oocysts, with a maximum risk of shedding at approximately 15 days of age. Using mixed-effects logistic regression with herd as the random effect, feeding starter grain to calves, sweeping out the maternity pen, and using hay bedding in the maternity pen were significantly associated with increased odds of shedding C. parvum oocysts. We speculate that the association between feeding starter grain to calves and the higher odds of shedding C. parvum is linked to an increased duration rather than a higher incidence density of shedding. In addition, the association between sweeping the maternity pen and the increased odds of shedding C. parvum may be attributable to dairy personnel using the same broom for cleaning calf hutches and the maternity pen, thereby cross-contaminating oocysts from infected to newborn calves.

Development of a Robust Method for Isolation of Shiga Toxin-Positive Escherichia coli (STEC) from Fecal, Plant, Soil and Water Samples from a Leafy Greens Production Region in California

During a 2.5-year survey of 33 farms and ranches in a major leafy greens production region in California, 13,650 produce, soil, livestock, wildlife, and water samples were tested for Shiga toxin (stx)-producing Escherichia coli (STEC). Overall, 357 and 1,912 samples were positive for E. coli O157:H7 (2.6%) or non-O157 STEC (14.0%), respectively. Isolates differentiated by O-typing ELISA and multilocus variable number tandem repeat analysis (MLVA) resulted in 697 O157:H7 and 3,256 non-O157 STEC isolates saved for further analysis. Cattle (7.1%), feral swine (4.7%), sediment (4.4%), and water (3.3%) samples were positive for E. coli O157:H7; 7/32 birds, 2/145 coyotes, 3/88 samples from elk also were positive. Non-O157 STEC were at approximately 5-fold higher incidence compared to O157 STEC: cattle (37.9%), feral swine (21.4%), birds (2.4%), small mammals (3.5%), deer or elk (8.3%), water (14.0%), sediment (12.3%), produce (0.3%) and soil adjacent to produce (0.6%). stx1, stx2 and stx1/stx2 genes were detected in 63%, 74% and 35% of STEC isolates, respectively. Subtilase, intimin and hemolysin genes were present in 28%, 25% and 79% of non-O157 STEC, respectively; 23% were of the “Top 6″ O-types. The initial method was modified twice during the study revealing evidence of culture bias based on differences in virulence and O-antigen profiles. MLVA typing revealed a diverse collection of O157 and non-O157 STEC strains isolated from multiple locations and sources and O157 STEC strains matching outbreak strains. These results emphasize the importance of multiple approaches for isolation of non-O157 STEC, that livestock and wildlife are common sources of potentially virulent STEC, and evidence of STEC persistence and movement in a leafy greens production environment.

Network Stability Is a Balancing Act of Personality, Power, and Conflict Dynamics in Rhesus Macaque Societies

Stability in biological systems requires evolved mechanisms that promote robustness. Cohesive primate social groups represent one example of a stable biological system, which persist in spite of frequent conflict. Multiple sources of stability likely exist for any biological system and such robustness, or lack thereof, should be reflected and thus detectable in the groups network structure, and likely at multiple levels. Here we show how network structure and group stability are linked to the fundamental characteristics of the individual agents in groups and to the environmental and social contexts in which these individuals interact. Both internal factors (e.g., personality, sex) and external factors (e.g., rank dynamics, sex ratio) were considered from the level of the individual to that of the group to examine the effects of network structure on group stability in a nonhuman primate species. The results yielded three main findings. First, successful third-party intervention behavior is a mechanism of group stability in rhesus macaques in that successful interventions resulted in less wounding in social groups. Second, personality is the primary factor that determines which individuals perform the role of key intervener, via its effect on social power and dominance discrepancy. Finally, individuals with high social power are not only key interveners but also key players in grooming networks and receive reconciliations from a higher diversity of individuals. The results from this study provide sound evidence that individual and group characteristics such as personality and sex ratio influence network structures such as patterns of reconciliation, grooming and conflict intervention that are indicators of network robustness and consequent health and well-being in rhesus macaque societies. Utilizing this network approach has provided greater insight into how behavioral and social processes influence social stability in nonhuman primate groups.

Network structure and prevalence of Cryptosporidium in Belding’s ground squirrels

Although pathogen transmission dynamics are profoundly affected by population social and spatial structure, few studies have empirically demonstrated the population-level implications of such structure in wildlife. In particular, epidemiological models predict that the extent to which contact patterns are clustered decreases a pathogen’s ability to spread throughout an entire population, but this effect has yet to be demonstrated in a natural population. Here, we use network analysis to examine patterns of transmission of an environmentally transmitted parasite, Cryptosporidium spp., in Belding’s ground squirrels (Spermophilus beldingi). We found that the prevalence of Cryptosporidium was negatively correlated with transitivity, a measure of network clustering, and positively correlated with the percentage of juvenile males. Additionally, network transitivity decreased when there were higher percentages of juvenile males; the exploratory behavior demonstrated by juvenile males may have altered the structure of the network by reducing clustering, and low clustering was associated with high prevalence. We suggest that juvenile males are critical in mediating the ability of Cryptosporidium to spread through colonies, and thus may function as “super-spreaders.” Our results demonstrate the utility of a network approach in quantifying mechanistically how differences in contact patterns may lead to system-level differences in infection patterns.