P
KWENTION OF FOODBORNE DISEASES
It was just over a century ago that American veterinarians Salmon and Smith isolated an organism now known as SaZmoneZZa ChoZeraesuis and thus discovered a large and important group of bacteria, the Salmonelleae. This group is now known to comprise more than 2,200 serotypes capable of infecting humans as well as mammals, birds, reptiles, and insects, and new antigenic types are still being identified.
Salmonellosis is a zoonosis-an ani- mal disease that can be transmitted to humans. Human salmonellosis is now a global problem, representing 60 to 80% of all reported cases of foodborne
disease in countries where surveillance systems for such diseases are in place. The disease causes illness and even death in humans, as well as economic losses in the animal and food industries. In the United States, almost 40,000 cases of human salmonellosis are reported annually by physicians, but epide- miologists believe that the actual number of persons infected each year with salmonella from food products of animal origin could be as high as four mil- lion. Extrapolation of one study indicated that more than 18,000 hospitaliza- tions and 500 deaths annually may be associated with salmonellosis in the United States. This translates into a cost of about US$1.2 billion per year.
The cost of salmonellosis in terms of animal loss can be even higher than the public health cost. For example, according to a survey conducted in the early 198Os, salmonellosis infection in cattle in the Federal Republic of Germany cost around US865 million, which was more than the cost attributed to human salmonella infection (approxi- mately US$61 million) at that time. Veterinarians have been quite successful in combatting cases of salmonella infection in animals with obvious clinical symptoms. However, the problem is complicated significantly by seemingly healthy animal carriers. These animals harbor salmonella but show no clini- cal symptoms of the disease, thus providing a hidden source of infection.
Since salmonella is primarily an ani- mal pathogen, all animals play an important role in the epidemiologic cycle of human infection. Raw food of animal origin and contaminated food of vegetable origin are the major sources of human salmonella infection.
Between 1976 and 1986, reported
cases of illness caused by the serotype SadmoneZZa en~eeritidis increased more than sixfold in the northeastern United States. In almost 80% of the out- breaks of food poisoning in that area from January 1985 to May 1987 in which the vehicle could be identified, the implicated food was raw or inade- quately cooked Grade A shell eggs or foods containing such eggs. This find- ing raises the possibility of transovarian contamination of the eggs, and is distinct from past problems of salmonellosis associated with cracked or soiled eggs, which are contaminated from the environment. ’
Both the existence of healthy animal carriers and evidence of transovarian transmission of the pathogen in fowl
I St. Louis, M. E. et al. The emergence of grade A eggs as a major source of JaCmoneLla enter&& infec-
would suggest that salmonella contamination of certain foods is beyond con- trol and that food safety measures, such as pasteurization of milk and egg products, are the only effective weapons against infection. However, since cases of postpasteurization contamination do occur, probably due to salmo- nella present in the environment, environmental decontamination must be carried out in conjunction with food decontamination.
In the last few decades, the dispersal in the environment of animal salmonellae has been facilitated by the crea- tion of large-scale industrial animal farms in both developed and developing countries. The environment becomes contaminated not only by airborne spread of infection, but to a large extent by the great quantities of manure and slurry (particularly from cattle and pig farms) that leak into rivers and underground water. Lack of proper sanitary measures during animal rearing, transportation, slaughter, and processing also contribute to the spread of sal- monellae to the environment, to food, and eventually to man.
There is some evidence that the emer- gence of antibiotic-resistant salmonella infection in humans is linked to the heavy use of antibiotics on farms, particularly their unregulated use for growth promotion and therapeutic purposes.
Due to extensive international trade in animal feed, live animals, raw animal materials, and animal products, the problem of zoonotic foodborne dieases, such as salmonellosis, is not limited to one country or continent. Therefore, proper veterinary control in the im- portation and exportation of such goods is of paramount importance in pre- venting the spread of infection.
The World Health Organization and its regional office, the Pan American Health Organization, have accumu- lated international knowledge and experience on the main technical mea- sures for the control of salmonella infection. They include decontamination of animal feed, vaccination of animals against salmonellosis, use of competi- tive intestinal flora to suppress salmonella infection in young animals, the raising of pathogen-free animals, and good animal husbandry practices (in- cluding cleaning and disinfection of surroundings, decontamination of ma- nure, proper milking and egg collection, and hygienic slaughtering and pro- cessing of food animals).
These measures are effective in pre- venting the spread of animal-borne salmonella infection by attacking its source. They complement food-safety processes (pasteurization, smoking or salting, and thorough cooking of foods that may be contaminated) and other public health activities, such as education of consumers, food distributors, and inspectors. Moreover, these measures aid in prevention and control of other diseases transmitted to humans by animals or food of animal origin.
