Zavala: Scratching the surface of emerging poultry health challenges

By Guillermo Zavala, DVM, PhD, Dipl. ACPV
Avian Health International, LLC

Over many decades, the US poultry industry has been at the forefront of productivity and disease prevention and control. Many poultry pathogens that circulate routinely in other global regions have been kept out of the continental US until recently.

Over the last 20 years, though, the US has lost some ground in productivity and in disease prevention and control. Productivity in broiler breeders has decreased substantially to the point that the cost per hatching egg and chick is now much higher than it was only 10 to 15 years ago. Additionally, hatchability in the US is extremely low compared to many other countries in the same continent.

Broiler production efficiency has also suffered since the implementation of ‘no antibiotic ever’ production, but the efforts to add value to processed broiler meat at further processing plants have helped keep the industry viable. Productivity and livability in commercial egg layers are at an all-time high, but the frequent incursions of highly pathogenic avian influenza (HPAI) have created very significant market disruptions in the egg industry, not to mention the heavy losses in the national hen inventory.

The turkey industry has certainly also been affected by HPAI. In addition, some diseases that were absent in the past are now causing economic losses to breeder, broiler, layer and turkey operations.

Emerging poultry health challenges

HPAI has been, and remains, without a doubt, the most important health problem for the poultry industry in dozens of countries, including the US, over the last 20 to 25 years. Stamping-out strategies against HPAI are less effective than they once were. Countries that have implemented vaccination along with enhanced biosecurity and surveillance have been able to secure their food production in a more predictable manner. The US, however, remains a country that insists on stamping out without vaccination.

Additional health issues that were never a problem in the US, or that had not been a problem for decades and have reemerged, include those listed below:

• Occasional incursions of virulent Newcastle disease (vNDV)
• Avian metapneumovirus (aMPV) subtypes A and B (aMPV-A, aMPV-B)
• Infectious coryza
• Variant avian reovirus
• Inclusion body hepatitis
• Variant infectious bronchitis viruses
• New genotypes of infectious laryngotracheitis virus
• Egg drop syndrome 76
• Spotty liver disease in brown layers (Campylobacter hepaticus)
• Erysipelas (Erysipelothrix rhusiopathiae) in free-range chickens
• Focal duodenal necrosis in layers
• Various myopathies in broiler chickens and other diseases

Double-edged sword

The more powerful the detection tools, the easier it becomes to find pathogens that we were not aware of. Some of the most recent molecular diagnostic tools available to research and diagnostic laboratories are extremely effective at identifying pathogens, commensal microorganisms and viruses.

The advent of these tools, though, exposes a significant disadvantage: The expertise we once had to use classical microbiological methodologies to manage pathogens such as infectious coryza or fowl cholera is almost lost. The tools are excellent, fast and effective, but we are forgetting how to isolate and characterize microorganisms that often cannot be characterized easily using molecular tools.

Future of poultry diagnostics, research

The role of research and diagnostic laboratories at academic institutions, state diagnostic and surveillance laboratories and private industry laboratories is rapidly being reshaped. For example, the vaccine industry is now pushing hard to provide diagnostic services as part of their service package, often at the expense of the clinical sample volumes that used to be directed to academic and independent laboratories.

Additionally, it is quite possible that the independent epidemiological surveillance expertise will gradually be reduced and concentrated in private businesses. Also, various integrators aim to have their own laboratories for routine serology, bacteriology and quality programs.

Perhaps only the laboratories conducting official surveillance of disease agents such as vNDV, HPAI, non-motile Salmonella, Salmonella Enteritidis, S. Typhimurium, Mycoplasma gallisepticum and M. synoviae will remain relatively intact for this specific function. It is my hope that basic and applied research of poultry pathogens and diseases will continue at academic institutions and agricultural stations.

Why the emergence?

Nobody can claim to have a real explanation for the emergence or reemergence of new pathogens and diseases. However, there are some risk factors that cannot and should not be ignored.

For example, egg-layer production complexes are typically designed for efficiency but rarely for disease prevention and control. Also, large-capacity farms are a significant risk that needs consideration before constructing future poultry facilities. Multi-age farms that can house millions of chickens can pose a real challenge and, in a way, are not conducive to effective disease prevention and control.

Production pressure in any type of poultry production should be regarded as a risk factor. Long ago, the broiler industry understood that a very short downtime and high bird density are not compatible with disease control.

Farm density is another issue in some areas where infectious diseases tend to recur. If possible, new farms should be isolated as much as possible.

Continuing education on biosecurity at all levels of any company is critical for disease control. There is certainly an opportunity at all poultry companies to optimize biosecurity awareness.

Preventing, controlling new health problems

Biosecurity, disease surveillance, rapid diagnosis and response, and coordinated collaboration among diagnostic laboratories, allied industry and the poultry industry are essential.

As vaccine and poultry industry laboratories take on a substantial share of surveillance and diagnostic work from the independent laboratories, there will be a gap in epidemiological knowledge and reporting and a partial loss of awareness. It is important that the usual lines of communication are not lost.

It is concerning that the expertise in some fields is being lost or has simply been lost. In particular, if the US breeding industry suffers renewed problems caused by tumor viruses, there will be virtually no one to assist because the expertise and the support are disappearing. There is virtually no one left to work on avian leukosis viruses, and very few scientists work on Marek’s disease or reticuloendotheliosis viruses.

When the experts in classical bacteriological and virological methods retire, all that will be left are powerful molecular tools but little knowledge or criteria on how to apply the results. A classic example is next-generation sequencing (or deep sequencing), a very promising approach in metagenomics. When this exquisite technique is applied to clinical samples, the results are difficult to interpret, explain and use, even for the laboratory that generated them.

The US needs to retain agility to respond to unexpected poultry health challenges. A good example is aMPV: Neither the expertise nor the vaccines were there when aMPV surfaced in the US. Certainly, the response was eventually productive and very positive, but it took longer than it should have. Meanwhile, many other countries had already been vaccinating effectively against aMPV-A and aMPV-B for decades, and aMPV is generally a non-issue elsewhere.

The debate about vaccination against HPAI in the US is still very much alive, while other countries have gained vast experience with vaccines and vaccination and have not had the production disruptions that the US and the EU have experienced.

What I have mentioned in this article only touches the surface of what to consider regarding the very complex subject of attempting to prevent and control future health problems in the poultry industry.

Final thoughts

The vast resources, knowledge and experience the US poultry industry has accumulated over decades have equipped us with the necessary tools to confront any challenge, no matter how large. Younger generations must make every possible attempt to understand and identify potential health problems and apply an effective holistic approach to optimize the early detection, prevention and control of poultry pathogens that can threaten the US poultry industry and the US food supply.

Moving forward, as the research, surveillance and diagnostic laboratory work are being reshaped, it will be critical to maintain active and effective lines of communication between academia, government, industry, and private and independent laboratories if we want to stay on top of epidemiological issues as an industry.

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