Web Seminar Questions

Questions to Prof Tom Humphrey

Please find below the questions and answers from the Web seminar Controlling Salmonella in Poultry. Please click on the question to show or hide the answer.

Are there vaccines against Salmonella Gallinarum / Pullorum?

It is my understanding that there are vaccines against the above mentioned Salmonellas.
Company comment: Nobilis SG9R is a live vaccines for the prevention of Salmonella Gallinarum.

What will be the result of vaccinating an infected flock? Is it viable?
(Broiler Parent stocks)

Vaccinating the birds with inactivated vaccines will provide them with protection against the Salmonella strains which are present in the vaccines and will also provide passive protection for the chicks as antibodies will be transferred in egg yolk.

Use of aviguard as an aid in salmonella control?

This treatment can offer some degree of protection but should not be relied on as the only control measure.

Is it possible to explain the importance of Alphitobius diaperinus?

These insects have been shown to harbour Samonella and there is the possibility that they can allow the carry over of the pathogen from one flock to the next.

What are the most appropriate samples to conduct monitoring in breeders that does not involve removal of birds?

Dust is an excellent example to determine if Salmonella is present in the house. However this may require confirmation by analysis of samples from some birds.

What exactly are the benefits of killed vaccines as opposed to live?

With killed vaccines one can be certain that birds have received the dose of vaccines.

How would you differentiate the vaccine strain from field strain if you isolated salmonella from a farm and you didn't know if the flocks were vaccinated or not?

It is my understanding that some vaccine strains carry a marker or can be differentiated from wild type isolates.

Which isolation technique is do you think the best for salmonella? How would you overcome the disadvantages of MSRV to isolate S. Pullorum and Gallinarum?

There are so many techniques that may be used that it would be difficult to give specific advise. However in my laboratory in Bristol we use BPW followed by RV broth for environmental samples.

Is it imperative that my parent stock are vaccinated against salmonella in case I am feeding fish meal Dagaa type to my broiler parent stock?
Does fish meal contain any strain of Salmonella?

To combine the answer to the above two questions. It is quite probable that fishmeal will contain Salmonella. While those serovars that are found are not often Enteritidis or Typhimurum, it is possible that they might be there or that other potential invasive Salmonella might need be present. In these circumstances control strategies might be needed and certainly consideration should be given to vaccination.

How do you age monitoring in lay?

Company comment: Monitoring in lay in the EU is done by booth swabs or by checking manure from the manure scrapers. This occurs every 15 weeks. Next to that one time per flock dust samples are collected.

Would a SE and STm infection in a flock be a potential concern for the chicken meat?
Thinking from a "food borne diseases" aspect. In my opinion, the risk is minimal. The eggs are more involved.

Under cooked or not well prepared chicken meat in an internationally important vehicle for both SE and ST. Both can be invasive in broiler chickens and both SE and ST have been recovered from chicken muscle tissue. Broilers chickens need protection from these serovars. In the UK this was achieved by culling infected broiler breeders but vaccinating these birds would also be an option.

How can we monitor vaccine titer? Which method?

Company comment: Most inactivated vaccines can be monitored by serology

How do you treat salmonella contamination in feed?

In the UK this is done by re-processing. Company comment: Some countries use acids or heat treat the feed in the feedmill.

What is the approximate timeframe of cortico-steroidal presence in the layer hen after stressors have been ablated?

The compounds are quite labile and will fall within 24-48 hours of stress removal.

The animal is injected either by IM or SC and the major group of antibodies produced are IgG (IgY). The amount of IgA is limited and there is little cell mediated immunity. The IgG is not the major antibody in the gut, yet these vaccines work. Do what to you propose is the contributing factor for immunity?

Immunity will be a mix of innate and adaptive responses. Thus there will be enhanced cycotokine response to limit invasive and increased circulation antibody levels to minimize the effects invasion should this occur.

As you explained during your presentation, the first stages of the laying period are one of the most critical and increase stress and susceptibility to Salmonella infection, but we also know that there is an innate susceptibility, and the young chicks between 1 day to about 4-5 weeks of age are also very susceptible to Salmonella infection.
Increased susceptibility of very young birds makes the vulnerable to environmental contamination of salmonella and if this infection occurs at young age the presentation of salmonella  may occur lately only at start of the laying period.
Vaccination of inactivated vaccines only, will not be able to protect the young chicks against gut infection and further oviduct infection.
Live Salmonella vaccines occupy the receptors in the intestinal wall and may act not only as inducers of immunity, but mainly (probably) by competitive exclusion.
If this assumption is true, don't you think that at very early ages between 1 day to 5 weeks of age it would be better to provide a live vaccine and at point of lay to give an inactivated vaccine in order to increase the levels of specific antibodies that will help in the reduction of salmonella in the oviduct??
In my experience, before the microflora of the chicks is completely developed (up to 3 weeks), the first salmonella entering the enteric system is the one that will occupy most of the receptors and will act in fact as a competitive exclusion, so providing protection during the first days of age is critical.

It is my view that live vaccines do not work by blocking receptors but by the immune mechanisms discussed above.