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Salmonella – general issues 6 - Positive Action Publications Ltd

Salmonella – general issues 6 - Positive Action Publications Ltd

Salmonella – general issues 6 - Positive Action Publications

Hatchery Microbiology issues6 Salmonella general In this Hatchery Microbiology we are going to focus on salmonella. Salmonella is a zoonotic pathogen, that is, it can spread from animals to man (zoonotic) and it is capable of causing disease (pathogen). Since salmonella is a zoonotic pathogen we are concerned about it for two reasons it can cause disease in poultry and because it can cause disease (food poisoning) in man. Damage from S. enteritidis In the late 1980s and early 1990s S. enteritidis was a very important cause of food poisoning in man and much of this infection came from poultry products, namely eggs and poultry meat. This became public knowledge and did the poultry sector a lot of harm because of depressed consumption of poultry products following adverse publicity in the newspapers and on television. Thus, as well as actually causing cases of food poisoning, the adverse publicity associated with salmonella lost business. Even today, there are some consumers who will not eat poultry products because they perceive them, albeit wrongly, as dangerous. Salmonella is a Gram negative bacillus that is closely related to organisms such as E. coli, proteus and citrobacter. Similarities to colisepticaemia This point is interesting because, when salmonella causes disease in birds it often shows a post mortem picture very similar to that seen with E. coli (yolk sac infection, pericarditis, perihepatitis, septicaemia and the like). There are over 2,500 types or serotypes of salmonella, yet at any one time those causing the vast majority of cases of human food poisoning in a country will usually be not more than 10, and many of these are not common in poultry. Thus, the vast majority of serotypes are of little consequence when it comes to humans. When it comes to diseases in poultry the actual number is less. S. pullorum and S. gallinarum cause specific diseases known as pullorum disease and fowl typhoid respectively. The only other two serotypes involved in poultry diseases are S. enteritidis and S. typhimurium. In many ways these two serotypes are the most important because of their dual role in poultry and human disease. S. pullorum and S. gallinarum do not have a role in human disease (food poisoning). The fact that so many serotypes are, in reality, of little consequence is good news, but it is also bad news in that there is always the possibility of a new serotype entering poultry production and becoming established. Specific turkey problem This happened with turkeys and S. hadar in the 1970s and with chickens in the late 1980s with S. enteritidis. Of these two, the latter was of greater significance because the S. enteritidis was much more pathogenic to both poultry and man. As a consequence, the whole issue of salmonella has become a major consumer issue and consumers now want all their foods, including poultry products, to be salmonella free. This begs an interesting question and that is, does or could a totally apathogenic (not capable of causing disease) salmonella serotype be a good thing, in that it could naturally exclude a more pathogenic serotype from poultry? Consumer perception Unfortunately, this scenario will never happen in real life because to the consumer ‘salmonella is salmonella is salmonella’, that is, all salmonella serotypes are now viewed similarly. So, why is salmonella more of an issue (or apparently so) in poultry than it is in other farm animals? The answer lies in a combination of factors. Firstly, there are the numbers of birds in a flock that are effectively living in the same environment. If one has salmonella it will very quickly spread to the others via the faecal-oral route. Interestingly, in a battery cage house where birds are kept in small groups and are separated from their faeces, salmonella spreads much more slowly than it does in a deep litter house. Secondly, the way birds are processed in the abattoir facilitates massive salmonella cross Fig. 1. The position of the hatchery. All product passes through it. BREEDER FARMS HATCHERY COMMERCIAL FARMS contamination. Finally, birds produce eggs that can be contaminated by salmonella and eggs can be eaten without being cooked (for example, in mayonnaise or as soft boiled eggs). Historically, another product of animals that was consumed by man without cooking was milk and it caused so many problems in man, including salmonella infection, that in many parts of the world it is now pasteurised before consumption. One way of controlling salmonella infections associated with eggs would be to pasteurise them but this can not be done in the shell and consumers want to buy their eggs as shelled eggs. Vertical transmission So, let us bring salmonella back to the hatchery and the breeder farm. An important property of salmonella is that in a poultry integration it can be transmitted vertically, that is from the hen to her progeny. A few serotypes such as S. pullorum, S. gallinarum and S. enteritidis can do this inside the egg by becoming a systemic infection in the bird and then localising in the ova in the ovary, which then become the yolks of the eggs or by infecting the upper oviduct and becoming incorporated in the inner albumen of the eggs. These three salmonella serotypes and others also contaminate the shell and are either drawn into the egg and contaminate the contents or are released at hatching and contaminate the hatcher environment. This latter scenario certainly occurs when salmonella bacteria have been retained in the shell pore behind a plug of debris, such as faecal material, that has protected them against washing, disinfection and/or fumigation. Thus, if we have a salmonella infected breeder flock it can regularly or intermittently infect its own progeny. The nature of hatchers and the hatchery environment is such that should this situation be present Continued on page 26 International Hatchery Practice — Volume 18 Number 6 25

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