18 May 2023

5 minute read

By: Zoetis Global Poultry

How significant a problem is Newcastle disease (ND) for poultry producers in Southeast and South Asia?

CKM: ND has been an ongoing problem for poultry producers in Southeast Asia and South Asia, where, in contrast to the US, ND virus (NDV) is endemic. The symptoms and lesions induced by NDV vary, but without timely and appropriate interventions, significant losses are inevitable.

Problems can be particularly acute in the region as a result of NDV genotype VII, which was first reported in the early 1990s and is now said to be the most prominent virus strain in almost all Asian countries. This genotype can be divided further into sub-genotypes, some of which are extremely velogenic (aggressive and dangerous). In unvaccinated birds, an outbreak of virulent NDV genotype VII can cause high morbidity and mortality, reaching 100% in commercial broilers, layers and breeders.

What ND-control options are available for producers in these regions?

CKM: As usual with viral diseases, it takes attention to a number of factors to achieve satisfactory control. Biosecurity and good farm-management practices are a big part of that, but to keep flocks protected, a reliably efficacious and safe vaccine is essential. Vaccination against ND is common across Asia, wherever commercial poultry production takes place. Live and inactivated ND vaccines are available, and more recently, recombinant vector vaccines were introduced to these markets.

How effective are available ND vaccines at controlling disease?

CKM: In theory, the fact that NDV has only one serotype means that any well-constructed vaccine should provide cross-protection against different genotypes. However, the identification of new genotypes over the last few decades highlights that NDV is constantly evolving, and some of these genotypes, including genotype VII, ask for a stronger immunity to avoid ND outbreaks. The fact is the current ND control by vaccination in Asia is not about disease eradication but rather to reduce clinical signs and prevent economic losses.

Conventional vaccines use either low-virulence live viruses or inactivated ND viruses, but these approaches have shortcomings. With live ND vaccines, immunity is often not very long-lasting and repeated vaccinations are needed, and there is concern about vaccine reactions as well. Inactivated vaccines are labor-intensive to administer and relatively higher cost.

In Southeast and South Asia, we’ve also seen that the combination of new, virulent field strains and interference from maternal antibodies are resulting in limited or delayed protection with some ND vaccines.

What about recombinant vector vaccines? How does the protection they offer compare to conventional ND vaccines?

CKM: Recombinant vector vaccines offer a number of important advantages with respect to conventional ND vaccines. Ones based on herpesvirus of turkey (HVT), such as Poulvac Procerta HVT-ND, have the added benefit of protecting against Marek’s disease (MD). They’re also known to be safe and there is little interference from maternal antibodies.[i]

HVT is known to be a good vector because it’s not virulent in the chicken, yet it provides long-lasting immunity.[ii] Rigorous testing has shown that Poulvac® Procerta® HVT-ND, when administered in ovo or subcutaneously at hatch, can protect commercial poultry against ND and MD from 19 days of age right through the production process.[iii]

The effects of such protection are clear: better overall flock health and better bodyweight gain and performance.

How well does Poulvac Procerta HVT-ND cross-protect against the various NDV genotypes?

CKM: The HVT “backbone” of Poulvac Procerta HVT-ND vectors the NDV fusion (F) protein, which is the antigen that protects against ND. This particular insertion has been shown to stimulate strong immunity and provide good cross-protection against numerous genotypes of NDV.

The original development work for the vaccine was done in the US, where the vaccine proved highly effective against prevalent strains. However, given that Asia has much more severe problems with ND and different genotypes in circulation, Asian poultry producers rightfully asked for more evidence that the vaccine provides the necessary cross-protection against NDV genotype VII. We therefore conducted Phase 3b studies — after regulatory submission but before product launch — in Malaysia, Egypt and Thailand.

What evidence of protection against this virulent genotype has come out of this work?

CKM: The studies in Asia and the Middle East offer additional data from completely independent sources, demonstrating the vaccine’s effectiveness against genotype VII — and, in particular, against different sub-genotypes that are seen in these regions.

Research carried out in Malaysia[iv] showed that Poulvac Procerta HVT-ND can be used as a standalone option to protect against genotype VIIh, regardless of whether it is administered in ovo or subcutaneously.

It’s important to acknowledge, though, that based on their previous experiences with vector vaccines and their current level of field challenge, many producers believe that a vector vaccine alone is not sufficient to protect their flocks. With that in mind, the research in Thailand[v] worked with a realistic scenario of co-administration of the vector vaccine alongside either a live, or live and inactivated vaccines. It was demonstrated that these are both safe and successful approaches to reduce production losses and mortality when faced with a genotype VIId challenge.

Finally, work in Egypt[vi] showed that the addition of the vector vaccine to programs using live and/or killed vaccines considerably improved protection against the local isolate, NDV genotype VII.1.1.

On to the basics: How is the vaccine administered?

CKM: One of its practical advantages is that Poulvac Procerta HVT-ND can be administered either via in ovo vaccination at 18 to 19 days of incubation or subcutaneous at day of age. What we have found in the recent studies is that you’re likely to get very high levels of protection from either route.

In Asia, as I’ve previously mentioned, producers often use a strategy of a vector vaccine with either a live or killed vaccine, or both, depending on the level of challenge faced in the field. So, should they seek peace of mind through such a co-administration approach, this is also possible, with no effects on performance.

Based on the challenge studies’ results carried out with velogenic NDV and virulent infectious bursal disease virus (IBDV), the vaccine can also be administered alongside Poulvac® Bursaplex® or Poulvac® Magniplex, meaning it’s possible to design a simple strategy for protection against IBDV[vii] — another predominant viral condition affecting poultry — alongside ND. This is an important convenience benefit as they are fully compatible when administered together either in ovo or subcutaneously.

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