Risk Factors for the Presence of High-Level Shedders ofEscherichia coliO157 on Scottish Farms

Abstract

Escherichia coli O157 infections are the cause of sporadic or epidemic cases of often bloody diarrhea that can progress to hemolytic uremic syndrome (HUS), a systematic microvascular syndrome with predominately renal and neurological complications. HUS is responsible for most deaths associated with E. coli O157 infection. From March 2002 to February 2004, approximately 13,000 fecal pat samples from 481 farms with finishing/ store cattle throughout Scotland were examined for the presence of E. coli O157. A total of 441 fecal pats from 91 farms tested positive for E. coli O157. From the positive samples, a point estimate for high-level shedders was identified using mixture distribution analysis on counts of E. coli O157. Models were developed based on the confidence interval surrounding this point estimate (high-level shedder, greater than 10 3 or greater than 10 4 CFU g ؊1 feces). The mean prevalence on high-level-shedding farms was higher than that on low-levelshedding farms. The presence of a high-level shedder on a farm was found to be associated with a high proportion of low-level shedding, consistent with the possibility of a higher level of transmission. Analysis of risk factors associated with the presence of a high-level shedder on a farm suggested the importance of the pathogen and individual host rather than the farm environment. The proportion of high-level shedders of phage 21/28 was higher than expected by chance. Management-related risk factors that were identified included the type of cattle (female breeding cattle) and cattle stress (movement and weaning), as opposed to environmental factors, such as water supply and feed.Verocytotoxin-producing Escherichia coli (VTEC), such as E. coli O157, is an important zoonotic agent with worldwide distribution. E. coli O157 may cause sporadic or epidemic cases of often bloody diarrhea that can progress to hemorrhagic colitis, thrombotic thrombocytopenic purpura, and hemolytic uremic syndrome (HUS) (21). HUS is a systematic microvascular syndrome that is initiated by secreted shiga toxins, with predominately renal and neurological complications, which are responsible for most deaths associated with E. coli O157 infection, particularly among elderly patients (22). Infection with E. coli O157 is a leading cause of acute renal failure in children (8). The incidence of E. coli O157 infection in Scotland is substantially higher than elsewhere in Great Britain (28) Healthy cattle shed E. coli O157 in their feces (9,17,35), and this pathogen is present in most cattle operations (48). Cattle are the main reservoir host for E. coli O157 and other VTEC in the developed world (1) and play a significant role in the epidemiology of human infections (13). Outbreaks are attributed to consumption of contaminated food and water, animal contact, and person-to-person transmission (51). However, case control studies of sporadic infections, which account for the majority of cases of E. coli O157 infection in Scotland, have indicated direct contact with animals, their feces, and/...

Identification and Characterization of a Peculiar vtx2 -Converting Phage Frequently Present in Verocytotoxin-Producing Escherichia coli O157 Isolated from Human Infections

“…The ⌽8-specific PCR assay was also used to analyze 30 VTEC O157 strains isolated in the United Kingdom and belonging to PT21/28, the PTs most frequently observed among the strains isolated from human infections in that country (3,20). In agreement with the high frequency observed among the Italian human isolates, most of the PT21/28 strains investigated (28 out of 30) were positive in the cro-cI PCR.…”

“…The results of this PCR screening (Table 4) showed the presence of a ⌽8-specific cro-cI region in 81.6% of the human isolates, whereas only 60% of the animal strains were positive in the assay (P Ͻ 0,001). These results suggest that the presence of ⌽8-like phages is predominant among the VTEC O157 strains causing human infections, regardless of the PTs they belong to.The ⌽8-specific PCR assay was also used to analyze 30 VTEC O157 strains isolated in the United Kingdom and belonging to PT21/28, the PTs most frequently observed among the strains isolated from human infections in that country (3,20). In agreement with the high frequency observed among the Italian human isolates, most of the PT21/28 strains investigated (28 out of 30) were positive in the cro-cI PCR.…”

“…VTEC O157 can be found as a component of the intestinal microflora in numerous animal species, but domestic ruminants, especially cattle, have been identified as its main reservoir (2). The presence of VTEC O157 in the intestinal content of cattle may cause the contamination of food of bovine origin at the slaughterhouse (3,4). Moreover, healthy cattle shed VTEC O157 in their feces, contaminating the farm environment and favoring its persistence in the herd (5)(6)(7).…”

Strain-Dependent Cellular Immune Responses in Cattle following Escherichia coli O157:H7 Colonization

“…In the United Kingdom, PT21/28 strains are associated with higher levels of shedding in cattle than PT32 strains (66) and represent the predominant isolates from human HUS cases (67). In addition, PT21/28 strains are more likely to possess both Stx2a and Stx2c genes, whereas bovine PT32 strains are more likely to possess the Stx2c genes only (68).…”

Concentrated Animal Wastes as Urban Land Pollutants: A Case Study of Liarages in Some Southern Nigeria’s Urban Agglomerations

“…Although soil degradation, urban air and water pollution and rapid urbanization are well documented environmental problems in Nigeria, the growing number of liarages in major urban agglomerations in recent times could be exacerbating the scope of environmental problems particularly in the densely populated state capitals or major commercial cities across Nigeria. Nitrate-N in manure and fertilizer runoff can act as endocrine disruptor [4], and thus could impact fish and amphibians in nearby and distant surface waters and wetlands. Although these negative impact of animal waste have been well documented in advanced countries such as the Unites States [5], there is paucity of local data or research on this growing problem particularly with respect to the extent of the contamination of the various environmental media-Soil/land, air, surface and groundwater in Nigeria.…”