#14,140
For nearly two months we've been following an unusual avian flu story out of Belgium regarding the emergence and spread of an LPAI H3N1 virus that has demonstrated remarkable morbidity and mortality in poultry (see Belgium: Non-Reportable LPAI H3N1 In Poultry).
As only H5 and H7 LPAI viruses are considered serious threats (see OIE Terrestrial Animal Code Article 10.4.1.), these outbreaks have fallen into a regulatory grey area, and a coordinated response has been slow in coming.Conventional wisdom has long held that LPAI H3 viruses aren't supposed to produce significant illness in poultry, and for some weeks the idea has been floated that a co-infection, or some other non-viral factor, was behind the high (up to 50%) mortality rate in laying hens.
In yesterday's ESA report on LPAI H3N1, the authors asserted:
The virus type H3 influenza is typically a bird virus that is completely harmless to humans and the food chain. It has all the characteristics of a low pathogenic virus, which means that the virus itself can not be held responsible for the symptoms or mortality in poultry. Of course, it may, however, help to strengthen the symptoms caused by other pathogens ( point on the AFSCA site 06.12.2019 ).Today, however, the Netherland's AVINED has published their own analysis which shows this LPAI H3N1 virus is perfectly capable of producing elevated morbidity and mortality in poultry without a co-infection.
Two reports, after which I'll have a postscript:
State of affairs H3N1 (update June 19, 2019)
The H3N1 situation in Belgium is and remains a concern. There are currently around 70 H3N1 cases detected. The outbreaks are concentrated in West Flanders, but there are a few cases in East Flanders and a single infection in the provinces of Antwerp and Liège. In addition, an H3N1 case has been found in northern France and Luxembourg. In the meantime, not only production animals, but also young rearing hens have been infected.
Tackling the spread of the virus in Belgium remains difficult because H3N1 is not a legally required virus. That is why the European Commission has not given permission to financially support poultry farmers with the set-up fund for the culling of flocks. It has been learned from the Belgian Boerenbond that agreements have been made between the Belgian government and Brussels about possible compensation for clearing infected companies. In particular, it is important that any reimbursements are compatible with Brussels state aid rules. It will take some time before it becomes clear how Belgium will handle culls and reimbursements. AVINED is in consultation with the Ministry of LNV about the relevance of these agreements for the Netherlands.
H3N1 examination laying hens: major damage and loss without co-infections
Commissioned by the AVINED advisory committee for poultry health care, the GD is conducting a study of the low pathogenic H3N1 strain and the symptoms of disease in laying hens of 35 weeks. The interim results show that this low pathogenic H3N1 strain does not need any other germs to cause major damage in laying animals. The clinical picture, the sectional pictures and the production decrease in these laying hens (SPF - specific pathogen free) correspond to the picture that is seen in the field.
The GD notes that the results are disturbing and that it indicates that the virus can cause major damage without other infections. This means that the original idea of trying to prevent additional infections will not work properly. All the more reason to put a lot of effort into preventing the introduction of this virus. A short report of interim results can be found here.
The GD also organized a meeting for those involved in the poultry sector on 12 June 2019, during which an update was given about the H3N1 situation in Belgium and the actions in the Netherlands. A summary will soon be available on the GD site.
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Translated excerpts from the Interim report (mentioned above) follow:
Intermediate report GD of the results of the H3N1 infection of laying SPF hens
Summary
The interim results of the H3N1 infection experiment in laying hens of 35 weeks show that this low pathogenic H3N1 strain does not need other pathogens to cause major damage in laying animals. The clinical picture, the sectional images and the decrease in production of these laying SPF hens correspond with the image that is seen in the field.
Introduction
In Belgium, more than 70 companies have now been infected with the avian influenza strain H3N1. In the official test for determining whether an AI strain is high or low pathogen, the virus is injected into the bloodstream of young chickens, the so-called intravenous pathogenicity test (IVPI).
In highly pathogenic strains, almost all animals die in a few days in this IVPI test. With the H3N1 strain there were hardly any phenomena in the IVPI test, the strain is officially a low pathogenic AI strain, which you would expect with an H3N1. Although this strain is clearly low pathogenic in the official test in young animals, the symptoms in the field are serious in many cases.
The vast majority of infections in Belgium concern laying hens and meat breeding animals. The couples show production drops of up to 100% and the mortality can rise to tens of percent (up to 60%). The big question is what explains the difference between the laboratory findings and those in the field. Are other factors involved? For example, other pathogens such as E.coli or IB.
It is known that combinations of low pathogenic AI strains with other pathogens can greatly increase the damage. With the support of Avined, GD has infected a group of 36 laying SPF hens of 35 weeks of age with the H3N1 strain isolated from a Belgian pair of laying animals with a large production decline and strong outages. SPF hens have been used to ensure that no other germs are involved.
The H3N1 virus is administered through an eye drop so that the virus will spread naturally in the animal. To be able to follow this spread within the animal (where does it start, where is it, what excretion can you expect)? animals were withdrawn from the study at 2, 4 and 7 days after the infection in order to examine the various organs. At 3 weeks after the infection, the study is terminated and the blood is collected from the animals.
Although the study does not run for another week and the test results are only partly known, the intermediate results are already very informative. In the first 7 days after the infection there was nothing to be seen on the animals, the egg production also remained stable.
In the second week, some of the hens became seriously ill, 58% of the animals died or had to be euthanized in order to prevent unnecessary suffering. The section showed that the sick animals often had a severe peritoneal infection sustained. Egg production among survivors who have not shown any external symptoms has dropped to 9%.
The interim results of this study show that this low pathogenic H3N1 strain does not need any other germs to cause major damage in laying animals. The clinical picture, the sectional images and the production decrease with these laying SPF hens correspond to the image that is seen in the field. Officially, this strain remains a low pathogenic strain, but this is a code for this virus that leads to a serious underestimation of the pathogenic potential.One of the traps we tend to fall into - particularly when dealing with complex systems and rapidly evolving pathogens - is the belief that what was considered true yesterday, will still hold true tomorrow.
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- Until 15 years ago, the Chikungunya virus was limited to central and eastern Africa. Then a mutation allowed it to be carried by the Aedes Albopictus `Asian tiger’ mosquito (see A Single Mutation in Chikungunya Virus Affects Vector Specificity and Epidemic Potential), allowing it to quickly cut a swath across the Indian ocean and into the Pacific, and beyond.
- Prior to 2013, no one thought that an LPAI H7 virus could ever match HPAI H5N1 as our top avian flu pandemic threat. That is, until LPAI H7N9 emerged in China.
- In early 2014, when the first reports of Ebola emerged from West Africa, conventional wisdom was that the virus was too virulent to spread widely, and that it would `burn itself out'. Two years and 30,000 cases later, we knew better.
- Until 2015, the notion that an arbovirus - transmitted by mosquitoes - could cause an epidemic of severe birth defects was unheard of. And then Zika came along, with tragic consequences.
A high impact LPAI H3N1 virus (in poultry), while perhaps not as dramatic as the examples listed above, is another reminder how nature can throw us a curve ball. And why long-held beliefs must occasionally be re-examined in light of new evidence.
How much of an impact this LPAI H3 virus will have is still unknown. It may prove to be little more than a curious footnote in the history of avian influenza, or it could be a harbinger of things to come.But it does reinforce the warning given by the WHO about avian influenza viruses in 2015:
Warning: be prepared for surprises
Though the world is better prepared for the next pandemic than ever before, it remains highly vulnerable, especially to a pandemic that causes severe disease. Nothing about influenza is predictable, including where the next pandemic might emerge and which virus might be responsible. The world was fortunate that the 2009 pandemic was relatively mild, but such good fortune is no precedent.
Four years may have passed, but the threat remains.
