Nonpoint Pollution From Animal Sources and Shellfish Sanitation

Many of the microorganisms pathogenic to both animals and man are transmitted via the fecal-oral route. Most of these pathogens could conceivably be transmitted through a shellfish vector. Bacteria potentially transmitted from animal to man via shellfish include most of the salmonellae, Yersinia enterocolitica , Yersinia pseudotuberculosis , Escherichia coli O157:H7, Campylobacter jejuni , and Listeria monocytogenes . The protozoa most likely to be transmitted this way are Giardia lamblia and Cryptosporidium spp. Because the enteric viruses are highly species-specific, they are not likely to be transmitted from animals to humans. There are environmental data showing that bacterial pathogens shed by both domestic and wild animals have been isolated from shellfish. However, there is little epidemiological evidence that illness outbreaks have been caused by shellfish harvested from waters polluted by animals. Unfortunately, epidemiological observations are of limited value because most illnesses are probably not recorded. In addition, more than half of the recorded outbreaks are of unknown etiology, and more than half of the shellfish implicated in illness outbreaks cannot be traced to their points of origin. More lenient bacteriological standards should not be established for waters affected only by animal pollution until health effects studies have been performed, and an indicator that differentiates between human and nonhuman fecal pollution is available. Most of the pollution that originates from domestic animals could be eliminated by simple and inexpensive measures.