Animal Waste, Water Quality and Human Health

92Animal Waste, Water Quality and Human Healthof Campy. jejuni strains from Lancashire, UK, and concluded that 96.6% of humanclinical infections could be attributed to farm livestock, 2.3% were from wildanimals and only 1.1% from environmental sources. Among domestic animals,56% of the clinical isolates could be attributed to chicken, 35% to cattle, 4.3% tosheep and only 0.8% to pigs. This and other MLST studies have shown thatundercooked poultry is the most important source of Campylobacter associatedwith human disease and that cattle and sheep are an important secondary sourcesof this human pathogen (Sheppard et al. 2009). They also suggest that specificSTs are host-adapted and may be useful in determining the host animal sourcesof campylobacters associated with disease in humans (Colles et al. 2008).While multiple Campy. jejuni STs can occur in the same herd, spatial clusteringof specific genotypes of Campy. jejuni is also observed within the same herd and forherds within one km of each other (Kwan et al. 2008). However, there is noevidence of geospatial clustering of bovine Campylobacter genotypes beyondthis distance; rather, a number of relatively cattle-specific Campy. jejunigenotypes can be found in herds present in distant geographical regions (Rotariuet al. 2009). These data suggest that, 1) many genotypes can co-exist in thesame herd, 2) there is a limited amount of inter-herd and cattle-independent (viavectors such as flies, wildlife, wind) transmission of the organism, and 3) certaingenotypes appear to be relatively host-specific and are widespread in the cattlepopulation. It is possible that the limited geospatial movement of certainCampylobacter genotypes is related to their high susceptibility to harshenvironmental conditions such as desiccation and may also be related tohost-specificity. Studies performed on Campy. jejuni isolates from surface waterin New Zealand suggest that many of these water genotypes originating fromwild birds and others belong to novel STs of unknown origin (Carter et al.2009). While water-associated STs are not commonly associated with humanclinical infections, Kärenlampi et al. (2007) reported that in Finland new andunassigned STs of Campy. jejuni were associated with illness followingswimming in natural waters. Therefore, it is possible that Campy. jejuni fromwater are less frequently associated with human enteric disease simply as aresult of less frequent exposure, rather than because they are less virulent thanthose from foods such as poultry. However, more research is required to betterdefine the routes of transmission and relative virulence of different genotypes.3.3.3 Salmonella entericaMore than 2500 serotypes of Salmonella enterica have been described and theorganism can be isolated from a wide variety of host species, including humans,livestock, companion animals, reptiles, avian species, and mammalian wildlife.