Cornell program helps keep New York-produced eggs free from Salmonella

Fearful that a little eggnog or Caesar salad dressing might send you to bed with a Salmonella-related illness? The chances are slight, but they’re even slimmer if your eggs are produced in New York, thanks to the Salmonella Control Program conducted by the Unit of Avian Medicine at Cornell University’s College of Veterinary Medicine.

Funded by the New York State Department of Agriculture and Markets, the Avian Disease Control Program works hand in hand with state poultry producers to minimize the risk of Salmonella enteritidis (SE) infection in eggs. Although SE has been detected in only two flocks of layer chickens in New York State since the surveillance program began in 1989, it is the most significant source of egg-transmitted salmonellosis in parts of the Northeast. Therefore, the Avian Disease Program at Cornell maintains continual surveillance and testing of chicken flocks throughout the state. Benjamin Lucio, D.V.M., Ph.D., the veterinary poultry extension specialist in charge, also provides educational assistance for egg producers to keep their poultry houses free of S. enteritidis.

SE is a bacterium that may be present inside normal-looking eggs, and can cause illness if the eggs are consumed raw or partially cooked. Symptoms appear 12 to 72 hours after eating a contaminated egg and may last four to seven days. The resulting illness, salmonellosis, can include fever, abdominal cramps and diarrhea, and, in rare cases, may cause death among individuals who are very young or old or whose immune system is already compromised. Of the eggs laid by a flock infected with SE, only a very small proportion (two per 10,000) may contain the bacterium. However, when infected eggs, or food containing the eggs, are not handled properly they pose a serious health risk. And any SE-infected eggs in the billion-plus produced in the state every year are too many.

The SE surveillance program is just one among many active programs in the Veterinary College’s Unit of Avian Medicine that focus on preventing and controlling diseases of commercial, backyard, and hobby poultry. In New York State, poultry is the second largest animal industry and fourth largest agricultural industry.

Investigations on S. enteritidis date back to 1988, when it was discovered that clean, unblemished (Grade A) eggs could be infected with SE.  Cornell researchers were among the first to demonstrate that SE is an ovarian infection in hens that occasionally passes on to the eggs. In 1989, they conducted extensive surveys of commercial chicken flocks throughout New York but found none were infected with SE. Since then continuous surveillance has identified only two SE-positive flocks.One was destroyed and the other flock’s eggs were pasteurized to destroy the bacterium.

Early in their studies, Cornell researchers also found that refrigeration followed by adequate cooking destroys SE present in eggs. This research led to egg handling recommendations printed on egg crates to educate people handling eggs from the farm to the table.

Lucio maintains close ties with the major egg producers in the state, not only to test laying hens, but also to help keep grower houses free from SE. He collects samples for testing from chick boxes, egg belts and manure pits, and advises on how to prevent introduction of S. enteritidis into farms by cleaning and disinfecting chicken houses and properly controlling rodents, which play a major role in spreading the bacterium.

“The goal of the program is to detect any evidence of SE in New York State’s poultry. Poultry production in the State is worth some $92 million and provides jobs for many people working on the farms or for poultry-allied industries. SE has to be detected before any infection can spread to humans,” said Lucio. “ hope we never find another positive flock but to make sure, we must provide constant monitoring. At the moment we are covering 70 percent of the eggs produced in New York State. Last year more than 2,000 samples were taken, with expenses being assumed by the poultry producer.

When the Department of Avian and Aquatic Animal Medicine and the Department of Microbiology and Immunology in the College of Veterinary Medicine merged in 1995, the change in organization significantly enhanced the college’s avian disease research and control programs. Currently, seven active faculty members in the Unit of Avian Medicine, one of the few such programs in the nation, conduct diagnostic, disease surveillance, extension and research programs to prevent and control diseases that threaten chickens, turkeys and ducks. With its state-of-the-art poultry isolation building and flocks of specific pathogen-free genetically defined lines of chickens, Cornell is recognized as one of the top avian research institutions in the world.

Last year, for example, the Cornell surveillance programs found avian influenza and chicken infectious anemia in two of the largest commercial chicken flocks in the state. This allowed prompt intervention by the N.Y.S. Department of Agriculture and Markets and the USDA, which prevented further outbreaks.  Even though avian influenza is not a threat to humans, it is a devastating disease for poultry; a 1983 outbreak in Pennsylvania resulted in losses in excess of $500 million.

Faculty members in the Avian Medicine Unit are involved in an array of programs that use the chicken as a research model, including basic research on cancer, immunosuppression, and respiratory diseases.  Their studies have resulted in vaccines for chickens, programs to control and eradicate poultry diseases, and techniques that are now being used for preservation of human chicken pox vaccines.

Among the diseases now under study are chicken infectious anemia and infectious bursal disease, which are immunosuppressive diseases in chickens, as well as infectious bronchitis, infectious laryngotracheitis, avian influenza, coccidiosis, and duck plague.

“The crucial nature of these disease control programs cannot be overemphasized,” asserted Syed Naqi, B.V.Sc., Ph.D., director of the Unit of Avian Medicine.  “The ability to rapidly detect infection is imperative. Without surveillance and prevention, such diseases could devastate flocks and potentially spread to other commercial poultry farms within and beyond the state.”

Basic and applied research are essential for the Veterinary College’s long-term preventive medicine approach to disease control, said Naqi, and form the backbone of the Avian Unit's efforts to assist the poultry industry in controlling disease outbreaks in the field. “Pathogens are in a continual state of evolution, and we need improved and sometimes entirely new methods for control. There is a constant need to develop and deploy new diagnostic tests and control methods,” he said.

S. enteritidis is one of many infectious pathogens in the genus Salmonella, named in 1913 for its discoverer, Daniel E. Salmon. Salmonella are usually motile enterobacteria that can cause food poisoning, gastrointestinal inflammation, typhoid fever, or septicemia in humans and other warm-blooded animals. Salmon entered Cornell as a veterinary student when the university opened in 1868. He earned a B.V.Sc. in 1872 and a D.V.M. in 1876 – the first D.V.M. degree to be awarded by an American university.Salmon became the first chief of the U.S. Bureau of Animal Industry and was a pioneer in the use of inoculation to prevent infectious diseases.