Hoping to safeguard the health of farm animals and the people who care for them, diagnosticians at the Cornell University College of Veterinary Medicine are urging farm operators to implement management practices aimed at slowing the spread of SalmonellaTyphimurium, including the antibiotic-resistant bacterium, Typhimurium DT104.

"Salmonella can gain access to the farm via carrier cattle, contaminated feed and water or even from infected wildlife, including birds," said Patrick L. McDonough, a bacteriologist at the Veterinary College's Diagnostic Laboratory. "We see an increased risk of infection in any dairy herd that is buying animals as replacements or that is rapidly expanding, especially when newly added animals are not initially separated from the resident herd and where sick cows are housed near cows that have recently calved. We currently do not know all of the potential risk factors for the contamination of a dairy herd with DT104.

The Cornell Diagnostic Laboratory identified DT104 as the agent responsible for an outbreak of bacterial illness in dairy cattle and humans last year at a Vermont farm. In what the Centers for Disease Control (CDC) now regards as the first proven case of animal-to-human transmission of DT104 in the United States, nearly 10 percent (13) of the Vermont farm's dairy cattle died, nine of 10 family members became seriously ill and one nearly died. CDC investigators suspect the Vermont infections resulted from drinking raw (unpasteurized) milk and contact with sick animals.

DT104 also was found by the Cornell laboratory in samples from other dairy farms, horses, small-animal hospitals and zoological collections in the Northeast. In the United Kingdom, recent cases of DT104 illness in humans have been traced to contaminated meat products, particularly sausage and meat paste. Although there have been no confirmed cases of DT104 food poisoning in the United States -- other than the unpasteurized milk in Vermont -- public health officials fear the disease could spread to the food supply during the slaughterhouse processing of infected cattle.

The results of salmonellosis from DT104 can be similar in cattle or in humans: High fever, rapid dehydration, bloody diarrhea and, if the disease is not treated, death from blood poisoning. The bacteria can survive in a wide variety of conditions and can spread predominantly through feces, although saliva from infected calves, as well as contaminated food and water may contribute to disease spread. Of all the salmonella strains known to infect humans, DT104 is regarded as one of the most likely to cause severe illness.

DT104 is resistant to several common anti-microbial drugs, including ampicillin, chloramphenicol, streptomycin, sulfa and tetracycline, and is showing decreased susceptibility (but not yet clinical resistance) to one of the remaining anti-microbial drug groups in the medical arsenal -- fluoroquinolones. DT104's resistance to specific anti-microbial drugs is one diagnostic marker (called an antibiogram or resistance profile) that is used to "fingerprint" DT104 among more than 2,000 salmonella types.

Veterinarians were just becoming familiar with another relatively new salmonella serotype, Salmonella Dublin, a form that was reported in California before World War II and which finally reached New York and other Eastern states in 1988, McDonough said. "But SalmonellaTyphimurium and DT104 in particular is the emerging type to watch, in part because of its drug-resistance and its virulence," he said. "The worst year for Salmonella Typhimurium cases in our lab was 1996 -- one of the wettest years on record in the Northeast, and Salmonella loves standing water -- but 1997 is not far behind."

Now the Cornell Veterinary Diagnostic Laboratory, which already runs on-farm prevention programs for infectious diseases, such as bovine leukosis, bluetongue and Johne's disease, is hoping to focus concern on salmonellosis, said laboratory Director Donald Lein. Surveillance in part of the state is possible, Lein said, because the laboratory screens samples from 40 dairy farms in the New York City watershed through an ongoing program to ensure environmental safety of drinking water supplies. Another way to trace DT104's potential path through the food supply would be testing at meat-packing plants in the Northeast, where Cornell scientists conducted a 1995-96 study of possible E. coliO157:H7 contamination in slaughtered cattle.

In the meantime, the Cornell diagnosticians are asking farm operators and their veterinarians to be aware that Salmonella Typhimurium DT104 could appear in their herds.

"This disease can occur almost anywhere -- in wild animals, domestic and exotic animals, in pets, in humans and in our food supply -- and it's not clear what the initial source or the present reservoir is for DT104 in the United States," McDonough said. "But we are increasing numbers of farms with salmonellosis including DT104.