ANALYSIS - Dr Guillermo Zavala, the world-renowned poultry disease expert, gave a presentation during the 4th Merial Global Avian Forum on the current situation with vector vaccines, and also led a workshop on emerging (and re-emerging) poultry diseases. Nuria Martínez Herráez, editor of ThePoultrySite's Spanish sister site ElSitioAvícola, interviewed Dr Zavala to find out more about vaccination and bird health.
French company Merial recently held their Forum in Barcelona, Spain. From 26 to 29 April, international experts presented information on the control and effective prevention of poultry diseases to more than 500 delegates from 70 countries.
ThePoultrySite: Which lines of investigation are at the forefront of avian vaccination? What role do vector vaccines play in current lines of investigation?
Dr Zavala: In the vaccination field, there is still a great deal of research into recombinant vaccines, to develop products which can be used to immunise birds against multiple diseases using the fewest injections possible, so the bird is handled as little as possible.
Vector vaccines are still at the forefront of investigation due to this very goal of vaccinating against several diseases with one single vaccination. That is one of the lines of investigation.
Another, which is still mainly carried out by academic institutions rather than vaccine companies, looks at how the immune response can be modulated. And, of course, a great deal of work is going into developing vaccines that ensure food safety (including Salmonella and Campylobacter).
ThePoultrySite: In 2015, the US poultry industry suffered the worst blow in its history, with the outbreak of highly pathogenic avian influenza that killed more than 48 million birds, mostly layers (although it also affected turkey production). Why do misgivings about vaccinating against avian influenza remain, and why is there a range of opinions for and against, amongst US poultry producers?
Dr Guillermo Zavala: Firstly, you have to consider who was affected by the outbreak: the layer and turkey industries were the worst affected, not the broiler producers. You also have to consider that the broiler sector is the largest exporter in the poultry business.
If the turkey or layer industry starts to vaccinate, then the broiler industry can’t export (even though they themselves don’t vaccinate).
So the main reason for not vaccinating is that importing countries see vaccination as a sign that a country has lost control of its problems. This loss of confidence by the importing country is the reason that poultry are not vaccinated.
ThePoultrySite: Which avian diseases are best controlled by vaccination and why?
Dr Guillermo Zavala: Actually, there are many. Diseases which mainly stimulate antibody-mediated immunity are the best ones to control with vaccination, but this doesn't mean that vaccination can’t be successful against diseases which are controlled more by cell-mediated immunity.
In reality, current vaccines provide very good protection against most diseases.
There are some exceptions, because it is difficult to develop and maintain a product that is effective against all the variants that a pathogen might possess. For example, it is impossible to put fifteen different pathogens in a vaccine vial if there are fifteen variants of a particular pathogen.
So there are generally very good vaccinations for diseases which are caused by a single, principal germ.
ThePoultrySite: Which emerging diseases should concern the global poultry industry most and why?
Dr Guillermo Zavala: Avian influenza, without a doubt. Also diseases which pose a threat to food safety; they are not emerging diseases as such, but the concern caused by them is emerging.
There is also the perception, real or imagined, that antibiotic resistance is increasing, so pressure is brought to bear to stop using antibiotics that are also important in human health. But this is also an emerging worry, rather than an emerging problem, and a lot of this is related to perception.
So what are the real emerging diseases? Many of the diseases caused by the changes that the industry is undergoing, such as removing hens from cages and housing them in barns, and also parasitic diseases, which hadn’t been seen for many years.
ThePoultrySite: Regarding these industry changes, what avian health problems are likely to be caused by the move away from caged hens?
Dr Guillermo Zavala: That depends on the final product. For example, there are hens’ eggs produced without cages; organic eggs; free-range eggs produced without cages; eggs that are both organic and free-range produced without cages, and so on.
If hens are confined in some way, regardless of whether this is in a cage or not, most of their problems will be intestinal or caused by physical trauma, because they move around more and these issues are bound to arise (they knock themselves more, and there is more competition). Some genetic lines also have problems with feather pecking and cannibalism.
Hens that are given access to the outdoors are also much more susceptible to everything, including respiratory and intestinal diseases, and avian influenza. However, the final product is worth considerably more money, so there is a niche opportunity for everything and that’s why I say that it’s all down to the final product.
Free-range hens will be exposed to the pathogens they come across outside, in the pasture. However, hens confined in barns will not be exposed to these pathogens.
So, most of the problems that we are seeing now, and that we will continue to see, are generally intestinal problems, as well as some behavioural issues (such as pecking).
ThePoultrySite: While we are on the subject of the changes occurring in the poultry sector at the moment, what can the industry do to cope with the restrictions on antibiotic use?
Dr Guillermo Zavala: Well, we can’t turn the clocks back. Legislation and consumer pressure will continue to increase and we can’t go against this.
This is another subject altogether, which has nothing to do with vaccination, but in reality it is not the end consumer who is driving all these changes, but activist groups and, as a result, supermarket and restaurant chains, etc., who want to align themselves with a philosophy which suits their image: they don’t want to be seen as businesses which condone animal welfare problems.
So it’s easier for these chains to publicise their ingredients as compatible with good practice and high animal welfare, free of antibiotics etc. That’s how they promote it to their customers and share-holders, but it wasn’t the consumers who demanded it. But that’s another topic altogether.
Nevertheless, we are talking about the end result, so what will the industry have to do?
It will have to adapt, to invest thousands of millions of dollars, that’s billions of dollars, to transform an industry which currently produces a dozen eggs which are sold to the consumer for USD 1.80.
That cost will eventually have to be passed on to the end consumer. And the end consumer still doesn’t know this. The consumer is also unaware that, as soon as you remove hens from cages, they have to be medicated more, if that’s even possible, and they die more.
The consumer also doesn’t know that a hen that isn’t in a cage will eat more feed. This feed is mostly made up of soya and grain and we will need a bigger land area, more water, more transportation etc. to produce the 15 per cent more soya and grain required.
Ultimately, a bigger carbon footprint will produce the same number of eggs, at three or four times the cost. This is what end consumers don’t realise. They’ve only been told that the egg on the menu has been produced without cages, by happy hens.
But, in the end, the industry will have to adapt. It will have to make the changes necessary to keep operating and there will be those who can afford to invest, and those who will have to leave the market, that’s the reality.
Now, those who survive will have to adopt very strict management and biosecurity measures, excellent nutrition, use more and more products of 100 per cent vegetable origin in their feed, reduce stress on the hens to a minimum so they don’t fall ill, and vaccinate more, given that they won’t be able to medicate.
In summary, what can be done to prevent diseases? Good management, good nutrition, biosecurity and vaccination.
About Dr Guillermo Zavala
Dr Guillermo Zavala is a poultry consultant. Of Mexican origin, Zavala has lived in the United States for many years and is an expert on avian diseases.
He has presented at more than 175 conferences across the five continents since 2001, and has also published over 30 articles in scientific journals and co-authored chapters on avian retroviruses and immunosuppressive viruses in reference books.
He was adjunct professor of Avian Health and Medicine at the University of Georgia (Atlanta, USA) and is currently the founder and owner of Avian Health International, LLC, a company which offers poultry consulting in many countries in the Americas, Europe, Australia and Asia.