H9N2 sub-strain of avian influenza is classified as a Low Pathogenic Avian Influenza (LPAI), which means that it does not require reporting to the World Animal Health Organization (O.I.E. in the past). It also means that it does not require the culling of all birds affected, as is the case with High Pathogenic strains, such as H5 and H7. The direct reason for the difference is that the H9N2 virus does not cause catastrophic death rates like the HPAI viruses, and yet it is a growing concern to poultry growers, as well as to regulatory authorities.
H9N2 first appeared in domestic chickens in 1966 in South Korea and at the same time in the USA in turkeys. There are two major lineages of the H9N2 genome since then – the American (North and South American lineage) and the Eurasian lineage. H9N2 has spread since the 1960's to practically all of Asia and to large parts of the Middle East, and parts of Europe and Africa. Great parts of the chicken industry on these continents have become enzootic.
Map demonstrating the spread of detected H9N2 virus
The virus has also affected periodically turkey, quail, pheasant and partridge farms. The economic damage caused by H9 LPAI is considerable and at times devastating. In addition to the direct loss from mortality, other effects are due to secondary infections, cost of therapeutical treatment and poor performance. The damage to layer and breeder flocks can be extreme, as the hens may not return to their potential production even after recovery.
Public health authorities keep a close watch on H9 LPAI for some good reasons. This virus carries a potential to become more pathogenic by itself. It has inherited some genes from swine and may do so in the future from other species as well, adapting the ability to infect humans (there have been some 59 cases of human infections recorded). Other animal species are known to be infected or carry the virus, such as minks. H9N2 has been implicated to contribute some genes to HPAI viruses, such as H5N1.
H9N2, like other Influenza strains, is to be found in its natural reservoir of waterfowl and shore birds. It is also detected in domestic ducks. These birds do not show any illness and are not affected clinically but serve as a constant source and contact.
Obviously, LPAI, like many other pathogens, is a hazard to any commercial poultry operation and is one more factor to be considered in the biosecurity planning. Fortunately, there are inactivated oil-based vaccines against H9N2 viruses available. The closer the isolate used in the vaccine manufacturing to the one currently found in the field; the better protection can be expected. In the Eurasian lineage of the virus there are 3 sub-lineages (h9.2 – h9.4) and some Clades and subclades. Therefore, vaccines should contain isolates which represent their geographic regions. Each organization must choose its own up-dated vaccine as things develop.
One thing is a constant in any biosecurity plan – beside the basic hygiene, isolation and off-limits to visitors, preventive vaccination against all current pathogens is a most sensitive link in the chain. Dose volume accuracy and the assurance that all birds are receiving the complete vaccine dose, are the baseline to an effective vaccination program.
However, mass injection of vaccine to large flocks poses a significant challenge and often the problems we confront are detected only after they occurred. Worn out needles, injecting from emptied vaccine containers, in-accurate dose and other crucial factors can lead to suboptimal titer levels, lack of uniformity of titers and reduced flock immunity.
Field trial results demonstration non-controlled Vs. controlled injection
The results three weeks post-vaccination show a clear advantage to the controlled injection birds:
All these and other causes of misapplication can be easily prevented using pHi-Tech™, the new poultry vaccination management system, developed by Phibro. This breakthrough technology enables accurate administration of vaccine in every shot and provides real-time alerting for misapplications, enabling the operator to re-administer the injection. During the vaccination process, the system collects data which is transferred and stored to the cloud, providing managers with essential tools for monitoring performance and making data-driven decisions for improving the vaccination process.
This article was composed by Dr. Amnon Michael, DVM and Veterinary Consultant at Phibro Animal Health Corporation, and published in the 'Asian Poultry Magazine' on April 26 2021.