Epidemiology of salmonellosis
Of the known Salmonella, only S. Typhi and S. Paratyphi A cause the disease only in humans - typhoid and paratyphoid A. All other Salmonella are pathogenic also for animals. The primary source of salmonella are animals: cattle, swine, waterfowl, chickens, sinantropic rodents and a large number of other animals. Diseases of animals caused by salmonella are divided into 3 main groups: primary salmonellosis, secondary salmonellosis and enteritis of cattle. Primary salmonellosis (paratyphoid calves, typhoid pigs, chicken typhus, dysentery of chickens, etc.) are caused by certain pathogens and occur with a characteristic clinic. Secondary salmonellosis occurs under conditions when the animal's organism is sharply weakened as a result of some causes (often of various diseases); they are not associated with specific types of salmonella in certain animals, are caused by their various serotypes, but most often S. Typhimuriwn.
Cattle enteritis is characterized by a specific clinical picture and in this respect is similar to primary salmonella. However, enteritis in this case is a secondary manifestation, the primary role is played by various predisposing circumstances. Its causative agents are most often S. Enteritidis and S. Typhimurium.
The most dangerous sources of foodborne toxic infections are animals suffering from secondary salmonella and enteritis of cattle. A large role in the epidemiology of salmonellosis is played by waterfowl and their eggs, as well as chickens, their eggs and other poultry products. Salmonella can enter the egg directly during its development, but can easily penetrate through intact shells. Outbreaks of toxic infections are most often associated with eating meat contaminated with salmonella, up to 70-75%, including up to 30% of slaughtered meat. Forced slaughter is often subjected to animals that are in an agonizing state. In weakened animals, salmonella easily penetrate from the intestine into the blood, and through it into the muscles, causing lifetime infection of the meat. The share of eggs and poultry products accounts for more than 10%, milk and dairy products - about 10%, and fish products - about 3-5% of all outbreaks of salmonella.
Modern epidemiology of salmonellosis is characterized by a constant increase in the incidence of people and animals and an increase in the number of serotypes of salmonella that cause these diseases. From 1984 to 1988, the number of cases of salmonellosis in England increased 6-fold. However, WHO experts believe that the true number of cases of salmonellosis remains unknown. In their opinion, no more than 5-10% of infected people are detected. One of the main reasons for the increase in the incidence of salmonellosis is the infection of food products during their production as a result of the widespread distribution of salmonella in environmental objects and in processing plants, where animals come in whose salmonellosis flows in a latent form. One of the main reasons for the wide circulation of Salmonella among animals is the use of food containing processed by-products of animal origin and very often infected with Salmonella.
Despite the constant increase in the number of serotypes of salmonellae isolated from humans and animals, up to 98% of all cases of salmonellosis are due to Salmonella of groups A, B, C, D and E, primarily S. Typhimurium and 5. Enteritidis (up to 70- 80% of cases of diseases).
Another important feature of the modern epidemiology of salmonellosis is the establishment of the role of man as a source of infection with salmonella. Infection of a person from a sick or bacterial carrier is possible not only through food in which salmonella finds good conditions for reproduction, but also by contact-household means. This method of infection leads to a wide spread of asymptomatic bacterial transport.
A major water epidemic of salmonella infection in Riverside (USA) in 1965, caused by S. Typhimurium (ill about 16 thousand people), showed that infection with salmonella is possible not only through food, but also through water.
The increase in the etiological role of S. Enteritidis, the activation of the food pathway for transmission of infectious agents with the predominance of the role of poultry and poultry products, the increase in the number of group diseases, including nosocomial infections, the increase in the incidence among children under 14 years (more than 60 % of all cases of diseases).
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