Porcine attaching-effacing E. coli strains are very similar to those that cause diarrhea in human infants, and are known as enteropathogenic E. coli. Because many strains of E. coli isolated from animals are nonpathogenic, it is important to identify the virulence factors produced by ETEC or EPEC strains, or the genes that encode those factors, to establish the etiology of diarrhea. Age-associated resistance develops gradually and becomes more-or-less complete by 2 weeks of piglet life.2-4 Interestingly, age-acquired resistance of calves to K99+ E. coli occurs very rapidly and is complete by 48 hours of age.5 Pigs are resistant to infection by F18+ E. coli at birth, but become susceptible after several weeks of life.6 Inheritable resistance to colibacillosis Department of Veterinary Science, South Dakota State University; Brookings, South Dakota 57007-1396 This diagnostic note has not been peer refereed. 7-9 Inherent resistance to, attachment of, and susceptibility to K88+ and F18+ E. coli are autosomal recessive traits. 9 Enterotoxigenic E. coli-expressing K88 and F18 account for essentially all postweaning colibacillosis in pigs.2,10,11 K88+ E. coli is believed to be responsible for a majority of neonatal colibacillosis cases as well.12 Recent studies suggest that about 50% of pigs in common breeds inherit resistance to K88+ organisms. Selective breeding for resistance to K88+ and perhaps F18+ E. coli could have a significant economic impact on the swine industry. High concentrations of E. coli in pure or nearly pure culture in the ileum are indicative of colibacillosis. Abundant growth of E. coli of a single colony type is indicative of colibacillosis. Laboratory methods In addition to the above mentioned methods for estimating the concentration of E. coli in the intestine, determining whether such organisms adhere to epithelial cell brush borders is useful in diagnosing colibacillosis. 16 Examination of anti-fimbriae antibody- Swine Health and Production – September and October, 1999 stained intestinal sections reveals the fimbriae, if any are expressed by the E. coli, provides an estimate of the concentration of the organisms, and shows whether they adhere to the epithelium. Cases involving attaching-effacing E. coli or E. coli-expressing uncharacterized adhesive fimbriae will be missed. Another approach to the characterization of E. coli strains isolated from diarrheic pigs is genetic. These tests do not determine whether a gene is actually encoding a specific virulence factor, only whether a specific segment of DNA is present in the E. coli strain being tested. Wilson RA, Francis DH. Fimbriae and enterotoxins associated with E. coli serotypes isolated from clinical cases of porcine colibacillosis. Rutter JM, Burrows MR, Sellwood R, Gibbons RA. A genetic basis for resistance to enteric disease caused by E. coli.
The Rise of MRSA in Pigs and the Health Risk to Humans
Numerous researchers in other countries have been reporting results on the prevalence of methicillin-resistant Staphylococcus aureus in pigs and the risk of human contraction. No U.S. agency or institution has tested MRSA patients to identify whether they carry the strain, according to the Union of Concerned Scientists, a science-based nonprofit concerned with environmental issues. Researchers with the epidemiology department at the University of Iowa conducted the first test of U.S. swine for MRSA, the bacterium responsible for 94,360 infections and 18,650 deaths in the United States in 2005, a year in which MRSA killed more people than AIDs. Of the 200 pigs tested in the Ohio study, 70 percent carried a strain of MRSA, ST398, which is known to affect humans. The researchers, led by Tara Smith, an assistant professor at the University of Iowa College of Public Health, led the research team that found almost half of 20 workers on local pig farms carried the same strain of MRSA, suggesting the strain has moved up the food chain. MRSA infections come in two forms – hospital acquired, HA-MRSA, and community acquired, CA-MRSA. People with weakened immune systems and the elderly are at most risk of HA-MRSA, according to the Mayo Clinic. CA-MRSA is responsible for serious skin and soft tissue infections and for a serious form of pneumonia. At least three people in Scotland are known to have contracted the ST398 strain, and experts are speculating that they probably contracted it from handling or eating meat. MRSA has been found in swine in Denmark, Belgium, the Netherlands and Germany and in other farm animals such as chickens and cattle. The strain – which has caused skin infections and rare heart and bone problems in humans – is believed to have spread among pigs that were fed antibiotics to spur growth and protect them from disease. “The recent wave of MRSA-related illnesses and deaths among otherwise healthy students and athletes is very troubling. We need to determine as soon as possible whether some of those illnesses and deaths are traceable to the overuse of antibiotics on swine farms,” said Margaret Mellon, director of Union of Concerned Scientist’s Food and Environment Program in a prepared statement. The U.S. testing of swine for MRSA would – under better circumstances – fall under the purview of the U.S. Department of Agriculture but that agency is already under heavy fire for its negligent monitoring of cattle for bovine spongiform encephalopathy, commonly referred to as “Mad cow disease” and other pathogens. A USDA official told the Seattle Intelligencer last month that the agency didn’t have a test for screening imported pork. No other federal agency, including the Food and Drug Administration, has shared any results of screening tests. The National Pork Board has said the accumulating data on MRSA and pork is “Scare-mongering” and that there is “No need to avoid pork consumption or worry that pigs could make you sick as a result of MRSA.”.