In our previous article we discussed what happens when Salmonella pullorum (SP) and Salmonella gallinarum (SG) enter layer enterprises. We saw that, whilst SP affects mainly replacement pullets, SG may infect birds of all ages; both SP and SG are able to cause considerable economic losses. We also learned that SG and SP cannot be completely eliminated from an infected flock, and consequently the disease will periodically recur. Based on those premises, it was agreed that the main objective should be to be to keep layer flocks free of SG and SP by implementing an appropriate prevention program.

In this article we will further discuss different prevention strategies and the reasons behind each one of them. The reader should remember that a salmonellosis prevention program should be implemented with the help of a veterinary professional. Therefore, contact your vet before making any changes in biosecurity and/or vaccination programs.

Why does Salmonella keep coming back?

One of the main problems observed in flocks infected with SG or SP is that the infection keeps coming back. Such recurrence responds to the ability of Salmonella to escape the immune system of the birds by “hiding” inside a specific immune cell, the macrophage. One of the functions of macrophages is to trap pathogens and destroy them. However, SG and SP can avoid destruction and remain “dormant” inside such cells. When certain factors depress the bird’s immune system, the dormant salmonella becomes active again, multiplies, and gets shed into the environment by carrier chickens. As a consequence, the amount of salmonella in the environment increases, infecting new birds and restarting the cycle of disease.

Therefore, when SG or SP are diagnosed in a flock, a proportion of the birds will be infected for life. In such conditions, the management of the flock becomes very difficult, and the losses due to mortality and drop in production are usually important and recurrent.

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How to protect my birds against SG and SP?

Protection against SG and SP infection is achieved by implementing a combination of measures targeting the chicken, the environment, and the bacterium. In the following sections we discuss a list of possible control measures. You should work in collaboration with your veterinary advisor to create a prevention plan that suits the situation at your farm.

Main steps towards prevention

Get pullets from reputable sources:

All main Zambian hatcheries have successfully established robust Salmonella prevention programs in their breeder flocks. The main suppliers of point-of-lay birds are also working together with their vet consultants to keep their farms free from SG and SP. Buying birds from reliable sources reduces the risk of infection.

Do not mix flocks of different age and/or different origin. Multi-age farms always present a higher risk, since SG and SP can pass from older to younger birds.

Implement a good cleaning, disinfection, and down-time program between flocks.

Salmonella can remain in the environment for prolonged periods, so it is important that houses are properly prepared for the arrival of new flocks. Discuss a cleaning, disinfection, and down-time program with your vet. Such programs should not only focus on the correct choice and application of cleaning agents and disinfectants. They should also include the laboratory verification that such procedures have been successfully conducted (e.g. by bacteria cultures from samples taken from different areas in the poultry house).

Reduce the exposure of your birds to potential sources of Salmonella.

  • Keep the facilities free of rats, since they can help spreading SG and SP. Use bait boxes placed in strategic points of the farm. Keep weekly control of the bait boxes, recording their location and the level of activity observed in each one of them. Rodents are highly intelligent animals, so they can learn to avoid these traps. If your records show that rats have not been visiting a given bait box, it is time to change it to a new location.
  • Control insects. Darkling beetles and flies, for example, are known for being vectors of foodborne pathogens, including Salmonella.
  • Avoid contact with wild birds by making your poultry houses bird-proof.
  • Source your feed from reliable feed mills. Currently, the main feed mills in Zambia conduct salmonella monitoring and control programs. Also, keep your feed shed free from rodents, insects, and other pests.
  • Offer safe drinking water. Evaluate the levels of bacteria in water periodically, including Salmonella, using a reliable laboratory. Chlorination of water is a good preventative tool.
  • Reduce the chances of SG and SP entering your farm on shoes, clothing, vehicles, etc. Implementation of measures such as compulsory showering and changing of clothes, application of an inside and outside boot system, proper disinfection of incoming vehicles, restriction in the number of visitors and incoming vehicles, disinfection of incoming instruments, can be of significant help.
  • Dispose manure and mortalities appropriately; both are potential sources of infection. Your vet will recommend the most appropriate ways to do it.

How do I check if the measures implemented are successful?

To assess the success of your salmonella control program, you can implement periodical environmental sampling for culture, detection, and typing of salmonella. In automated poultry houses, different surfaces such as feeders, feed hoppers, conveyor belts, etc., may be swabbed. When birds are kept on the floor, litter samples may be taken by walking throughout the house with especial boot covers. Farm workers can also be sampled for salmonella detection. Your vet will be able to explain this in more depth.

Can I vaccinate pullets against SG and SP?

Yes, vaccination plays an important role in preventing SG and SP infections. However, as mentioned before, we cannot expect good protection if their application is not supported by proper biosecurity and management measures. Phibro has created an integral control program against SG, SP, and other Salmonella serovars, based on the administration of the live vaccine Phivax SLE (in early in life), followed by the inoculation of an inactivated vaccine (Salmin Plus) later in rearing (Table 1).

Salmin Plus is Phibro’s latest Salmonella inactivated vaccine. It contains one strain of Salmonella typhimurium (from Salmonella serogroup B), two strains of Salmonella enteritidis (from Serogroup D), and one strain of Salmonella infantis (from Serogroup C). This is the first vaccine in the market to include a strain of the serogroup C, increasing the spectrum of protection.

Salmin Plus helps to prevent vertical and horizontal transmission of salmonella from group B, C, and D among birds, thus protecting the final consumer (humans) from food borne salmonellosis produced when bacteria of such serogroups contaminates food products. Furthermore, since Salmonella enteritidis belongs to serogroup D together with SG and SP, Salmin Plus can also cross-protect the birds against SG and SP.

Finally, Salmin Plus has been developed using advanced vaccine technology. Its novel adjuvant produces minor tissue damage in comparison with other water-in-oil inactivated vaccines. As a result, it can be injected intramuscularly without major inflammation or post-vaccine reactions. This makes vaccine application much easier and quicker than with inactivated vaccines that need subcutaneous application.

As usual, please, consult your veterinarian about the vaccination strategy that best fits the situation at your farm.

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