1, Salmonella and the main problems currently facing
Salmonella is a common pathogen of poultry and belongs to the subspecies of Salmonella enterica. There are more than 2,500 different serotypes or strains of Salmonella in the world. Among them, there are more than 40 species closely related to poultry, and the rest exist in various kinds of animals. This includes livestock, pets, rodents, beasts, reptiles and insects. The main features related to its purification and control can be summarized as:
(1) Salmonella is ubiquitous and widely distributed in various animals and environments.
(2) Salmonella can be present in flocks, but does not necessarily cause disease, which can cause the onset of breeders or chicks when the flock is stressed or vertically transmitted.
(3) Salmonella is more resistant, they can survive in the environment for a long time, can survive on eggs for more than 200 days, and survive in dust for 3 years. It is very difficult to effectively disinfect the positive house. In the “Binzhou Egg Quality Assurance Programâ€, there was a 50% failure rate when no large amount of formaldehyde fumigation was used.
(4) It is effective for vaccines specially prepared for specific types of Salmonella, but this vaccine has no effect on other serotypes, and there are partial cross-protection effects between different serotypes, but it cannot be completely protected.
(5) Although some antibiotics have certain effects on Salmonella, antibiotics cannot completely remove Salmonella from the body and can only slow down its transmission or detoxification.
In the early 20th century, the two serotypes of A. sinensis and Avian typhoid were important endemic diseases in European and American flocks, but by the mid-20th century, the disease was purified in commercial chicken flocks in the United States, mainly due to its “National Poultry Improvement Program (NPIP). At present, the introduction of breeding chickens in foreign countries, poultry white carp and poultry typhoid are also well controlled, but in local breeds or domestic breeding flocks, the disease also occurs from time to time. At the same time, another major pathogen currently faced at home and abroad is poultry paratyphoid---S. enteritidis, which causes serious damage. Studies have shown that chickens that are positive in S. Enteritidis (SE) have an average of 2 per 10,000 eggs. Three contain SE, although this positive rate is not high, but if the hatchery contaminates 1 day old chicks or vertical infection and spreads between chicks, it will cause unlimited amplification effect, which will ultimately affect product quality and later production performance. Salmonella enteritidis is also one of the important pathogens causing food poisoning. In the 1980s, human food poisoning incidents frequently occurred. The main pathogens were Salmonella enteritidis and Salmonella typhimurium. The current serotype of Salmonella enteritidis accounts for the annual food poisoning incident in France. One-third of the Salmonella infection is the second largest source of contamination in Europe following Campylobacter infection.
2, the spread of Salmonella
To control Salmonella, it is important to understand how chickens are infected by Salmonella. the transmission of Salmonella is one of the most effective means of controlling Salmonella. At present, the following general methods of infection are considered:
(1) The chicken is transmitted to the chick by the fertilized egg vertically or via the egg. This is the main route for the transmission of chicken white mites, poultry typhoid and S. Enteritidis.
(2) Salmonella also spreads non-perpendicularly. When the surface of the eggshell is contaminated by Salmonella, Salmonella enters the egg through the eggshell and infects the developing chicken embryo. When it is hatched, Salmonella is transmitted to other chickens.
(3) The third mode of transmission of Salmonella is to spread Salmonella from one flock to another through an intermediate host or pathogen carrier. The communicator can be a beetle, flies and mice in a positive house. The investigation found that mice were the main pathogens in the SE-infected laying flocks.
(4) The fourth mode of transmission of Salmonella is lateral transmission. Transversely spread, any object that is likely to carry Salmonella is included in the flock, including: drinking water, litter, contaminated daily necessities, and feed. From the current data, drinking water is rarely a source of transmission, but the pollution of water sources will be unimaginable. Feed is a major threat, and studies have shown that animal proteins are more susceptible to contamination, while plant proteins, such as soybean meal, are less contaminated. Granular materials and chemically treated feeds to reduce or eliminate Salmonella also reduce the risk of Salmonella contamination.
3, the control of Salmonella
In view of the characteristics of Salmonella and the spread of infected chickens, it is not an easy task to completely solve all Salmonella infections. Through successful foreign control experience, we also know that it is possible to completely eradicate and purify several serotypes of Salmonella. Chicken white pheasant and typhoid fever are examples. Most of the other Salmonella species can only be reduced in number, as is the case of Salmonella paratyphi A, which mainly lives in the intestines. From the current successful experience at home and abroad, the main control measures for Salmonella include:
(1) Sanitation and disinfection
Before the introduction of new breeders, all houses and utensils, and the chicken farm environment must be cleaned and disinfected, especially if the previous breeder was positive for Salmonella. In a positive house, it is more difficult to remove the pollution, thoroughly cleaned and disinfected and fumigation with formaldehyde is most effective. The effectiveness of the disinfection effect can be verified by rigorous bacteriological testing, and Salmonella sampling should not be detected. Some commonly used items, such as egg trays and block screens, are sometimes contaminated with Salmonella and need to be disinfected.
(2) Pest control
Pests such as beetles or litter beetles are hosts and vectors for a variety of pathogens (including Salmonella) in poultry. They should be disinfected immediately after the breeder is cleared to prevent them from being transferred or hidden in the next batch of chickens. . It is also necessary to develop an effective control scheme for rats and flies. The main source of Salmonella typhimurium is transmitted between different flocks. The infected mice discharge about 100 faeces per day, and each feces contains several Thousands of SE germs.
(3) Personnel control
All personnel must comply with biosafety regulations. The ability of the farm staff to perform is a key factor in determining the success of the Salmonella control program. They must understand and implement the biosafety standards of the farm and must implement disinfection control measures at all stages. Most of the Salmonella contamination control failures are related to human error.
(4) Feed Hygiene Control
Feed is an extremely important source of Salmonella contamination. Although granulating feed ingredients can kill almost all bacteria in the feed, the feed can be contaminated again in a cooler environment, or through insects and mice in dust and feed mills. Studies have shown that Salmonella in feed mills Pollution is often associated with poor management and poor environmental conditions. Cleaning and disinfection of the production line and the surrounding environment should be routine work and should be disinfected with disinfectants such as organic acids and/or formaldehyde.
(5) Hatchery Health Control
The hatchery is not only a place for hatching eggs, but also a place for the proliferation and spread of Salmonella, especially when there are both Salmonella positive and negative eggs or chickens in the hatchery. Cross-contamination can occur through direct contact, dust, manual work (such as male and female identification and vaccination), or in the transport of chicks. It takes only a short time for the chickens to carry the Salmonella in the feces and contaminate other chickens in the same hatchery. Important measures to reduce the spread of Salmonella in hatching include: disinfection of eggs, avoiding mixed storage of positive and negative eggs, using different incubators, staggering the time of shelling, etc.
Reducing the degree of contamination of Salmonella in hatcheries in the hatchery, it is also effective to use Salmonella to compete for the rejection of probiotics in the hatchery, using competitively repulsive bacterial probiotics in the first few hours of hatchery or chick entry to prevent Salmonella Infect the chicken gut system and prevent it from re-propagating with other tissues or chickens.
(6) Vaccine application
Vaccination is an effective means of controlling Salmonella infection. There are two types of vaccines commonly used: inactivated vaccines and attenuated vaccines, both of which have serotype specificity, so their protective efficacy is limited to Salmonella infection of the same species or the same serotype (eg, belonging to group D) Salmonella typhimurium and Salmonella enteritidis). At the same time, the use of inactivated vaccines is flawed, and after use, the chickens cannot be purified by serology.
(7) Probiotics and other additives
The use of probiotics is becoming more common and has proven to be very effective in preventing Salmonella infections. In a recently completed study, Aulia LF et al. (2011), Soncini R. et al. (2011) and Herich R. et al. (2010) demonstrated that the use of probiotics to prevent S. Enteritidis is very effective. In addition to probiotics, continued use of acidifiers is another alternative to Salmonella prevention programs.
(8) Monitoring of flocks and treatment of Salmonella-positive flocks
Breeding flocks can be routinely monitored by serological-slab agglutination, but prone to false positives, especially after oilseed immunization, the most important and only method of diagnosis is pathogen detection. Regular bacterial isolation, combined with serological test results, will help to understand the infection status and type of flocks, and take targeted prevention and control measures as early as possible. Positive chickens or chickens should be eliminated in time to prevent transmission to negative populations. For breeders, the key to monitoring is the laying period, hatchery and feed mill. The use of antibiotics for Salmonella-positive flocks is a very common approach, but antibiotics do not completely cure Salmonella infections.
4 Conclusion
Salmonella is highly adaptable and widely distributed. It is a difficult task to completely eradicate all Salmonella. It requires multiple control specifications and strict implementation of Good Management Practices (GMP) or Hazardous Key Control Programs. ". For the production of flocks, these good management programs or key points include: hatchery hygiene, competition for bacteria in the chicks, pest control (rats, beetles, flies, etc.), reduction or removal of Salmonella in feed, positive chickens Sterilize, use new litter, use vaccine immunization, etc.; although the use of antibiotics has limitations, the use of key nodes can reduce the detoxification of chickens and improve the quality of chicks.
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