Avian Influenza Technical Summary of previous trends and future expectations regarding the UK Poultry Industry and H5 Strain Avian Influenza

Poultry Health and Welfare Group Conference on Avian Influenza Issues 13th July 2022

David Hodson Jnr, Rosehill Agricultural Trading Company

The following information is from a technical briefing from Professor Ian Brown – APHA head of Virology and Director of EU International Reference Library for Avian Influenza and Newcastle Disease. He is the lead of the H5 strain research team, and he is renowned as the world’s leading expert on the epidemiology and pathogenicity of Avian Influenza.

Summary of Current Situation

There has been a 450% increase in the detected cases of AI within the UK bords, this has been driven principally by the wild bird populations but the dramatic increase in infected premises is theorized to stem from H5N1 superior pathogenicity compared to both H5N8 and H5NX (only 315 cases of H5NX). The H5N1 virus has evolved to become superior at the virus’s primary tasks, which is to reach the maximum number of new hosts by not killing the current carrier. Canadian Geese, Gizzards and Seagulls are all relatively resilient hosts to the virus. As a reference point, worldwide in 2016-2017 there were 2781 cases across 29 countries and in 21-22 there have 5299 cases across 36 countries. So far 61 species have been infected across 78 countries with this strain, including foxes, a seal and in a single case, a gentleman that kept ducks who was said to have “strange habits”.  For the first time the weight of infection has been so great that the wild bird populations have spread the virus into the Arctic regions, then to Greenland and finally to the US coast. This will mean that when the birds migrate there will not only be the traditional challenge to the East Coast of the UK, but also a second wave on infection coming from the west Scottish region. This will form a pincer movement of disease to challenge the UK industry. 

In 2021 we had 71 commercial premises infected with Avian influenza, of which 24 were commercial laying units. The spread of infection areas has fallen broadly into line with wild bird migration routes, with the key entry points to the UK being the hotspots of infection. The most shocking piece of information was that there has no relevant increase in migratory wild bird numbers, what we have instead is a much higher infectivity of the virus. A single dropping from an infected host will hold 1000’s of infective doses. Ian referred to the behaviour of viruses being “A battle of the fittest” in which the primary virus in a population is the one which sheds virus at the highest rate and will infect with the smallest dose while surviving in the environment for the greatest duration. 

H5N8 represent the mother strain of this challenge, with there being 200 genomes sequenced to date. The strain is broadly similar to that which challenged central Asia throughout 2021. The ability of the APHA to process samples has allowed the tracking of the genetic mutations which have occurred and in turn, allows outbreaks to be tracked down to other outbreaks in different regions. The ability of the APHA to sequence Avian Influenza has been improved to the point whereby in 5 days its possible to know the unique identity of the virus. Herein lies the importance of immediately reporting suspected outbreaks. Not only will the control zones allow for a decrease of threat to the surrounding areas by several orders of magnitude, but it also allows the investigative work to understand the virus identity that may be present.  

Routes of Infection for UK Commercial Sites

Ian spoke of the power we have to control he viral spread by implement vigorous biosecurity protocols, there is a scale of .1-1 which is called the predictive risk scale, which is also referred to as low, medium and high. In 2021 the following classification was made through assessment of the risk to UK commercial poultry units; 

• Threat of Infection for Wild birds – medium 
• High standard biosecurity commercial unit – low 
• Low standard biosecurity commercial unit – medium

This part is critical, as we have the perfect storm of a virus which is 4.5 times greater in ability to infect combined with an enormous increase in the amount of contact area between commercial birds and wild birds due to the great expanse in poultry holding premises.

Imagine, the scenario of a site where biosecurity is not fully understood. Whereby a broken piece of guttering leads to a puddle of standing water developing where a stock man parks his car. The water is infected with faeces from wild birds which has washed down from the roof. The stockman treads into the water (which is a virus soup for all intents and purposes) and then proceeds to enter the control room and without changing footwear and walks into the bird area. The virus will then take hold and in turn this will lead to an enormous financially destructive case occurring. 

The diseases principle means of infection is via the aerosol route, which requires bird to bird contact. Secondary to this is contact with infected faeces. At 4⸰C H5N1 will survive for 9.5 days per log of virus titre, in practical terms this equates to faeces being infective for 5-6 weeks in the winter months. An infected premises will become infected via the following routes that Ian defined; 

1. Through the farm gate (it will be brought onto the site via human movement) 
2. Through the hedge (wild birds having physical contact with commercial poultry) 
3. From the sky (faeces coming into contact with the birds via the range, biosecurity lapses or airborne fomites which are defined as physical objects contaminated with virus)

In the future Lion code, there will be sections covering the prevention of standing water within the range and around the poultry unit. Standing water is referred to as “virus soup” for its capability to spread infection quickly, either through humans moving the virus on footwear or through birds drinking. 

It seems we face a challenge which is constructed of the combined threat of a highly infectious virus, which can survive robustly in the environment and has the combined ability to survive in certain wild bird populations while being lethal to domesticated poultry. 

There is significant crossover in the risk factors for salmonella infection and for avian influenza. Biosecurity is king of prevention and the greater the attention to detail that can be placed on this, the greater the chance of evasion. Wild rodent populations provide both an incubator for disease and a significant method of spread. In the case of Salmonella Enteritidis and Salmonella Typhimurium, the rodents will spread the disease via urination and defecation in the food troughs, water line cups and in the bedding. The combined risk for AI lies in the rodents being pecked or consumed by wild birds, or the chickens within the shed.

How to Prevent Avian Influenza

While the primary method of prevent the outbreak will always be the strict control of biosecurity, we operate in a new environment for commercial whereby there has been a dramatic increase in free range holdings over the last 10 years. The range represents a significant risk of infection, as does the failure to implement wheel washes, foot dips and footwear changes. The safety of a poultry business is reliant on education of the teams that care for the birds and for the managerial level that have the ability to invest in the correct areas to mitigate risk. 

Andy Paterson identified the director of the company as the key person who will dictate company culture with regards to Biosecurity. There is a requirement to lead by example and set the standard from the top down of how important it is to control the threat. 

The key points a company should invest in are as follows; 

1. Education of the entire company, from logistics, to maintenance, to those with direct contact with birds. 
2. Building infrastructure, the presence of moss on a roof, damaged guttering, standing water or the lack of a concrete pad outside access points all represent a high degree of risk. 
3. The correct sanitising products for foot dips, wheel washes and cleanout. It is not enough to use the correct product, but it must be used at the correct concentration and foot dips must be changed with a frequency that ensures the chemical is still viable. 
4. Range management, standing water represents the greatest risk for a multitude of reasons, first it allows a contact point between wild and domesticated birds, secondly it provides a reservoir and transfer point due to faeces being present in the water. 

The key point that the afternoon of talks left me with was that, although we face an enormous challenge, we also have the ability to make the viruses sole purpose of infection as difficult as possible. If your business becomes infected despite your most stringent efforts to prevent this from happening, as with all great challenges, we must take the learnings from it and stay one step ahead.