Tuesday, July 11, 2017

ESA Epidemiological Update: HPAI H5 Clade 2.3.4.4 Viruses In Europe














#12,609


While this past winter's massive HPAI H5 epizootic in Europe has been over for most countries for several months, during June and early July, we saw a small resurgence of  outbreaks in poultry and wild birds in a swath across Luxembourg, Belgium, and just barely into northern France (see Belgium Reports Another Outbreak of HPAI H5N8).
In addition, the UK, Finland, Italy, and the Netherlands all reported single outbreaks.
Yesterday France's ESA (Epidemiosurveillance Santé Animale) released a brief epidemiological report on these summer outbreaks in both English and French. First the report, then I'll return with a bit more.

Epidemiological situation of HPAI viruses from clade 2.3.4.4 in Europe: situation as of 3rd July 2017
Soumis par Alizé MERCIER le 10. juillet 2017 - 16:11.
International Animal Health Epidemic Intelligence (VSI) team – ESA Platform – France
Sources: Data updated on 2nd July 2017 (included) ADNS/FAO/OIE, DGAL (General Directorate of Food – French Ministry of Agriculture), ProMED, MAF (French Ministry of Agriculture and Food) press release from 30th June 2017

This is a translation of a published report. The French version of this report is available here.


From 1st June 2017 to 2nd July 2017 (included), 17 cases and outbreaks of H5 subtype highly pathogenic avian influenza (HPAI) were notified in seven European countries : Luxembourg, the United-Kingdom, Italy, Finland, France, Belgium and the Netherlands (Table 1, Figure 1). H5N8 and H5N5 viruses have been identified.

Table 1: Number of HPAI cases and outbreaks notified in Europe from 1st June to 2nd July 2017 in domestic, captive or wild birds (sources : OIE/ADNS/DGAL)




In addition to these 17 outbreaks, three HPAI outbreaks were reported on 21st June in Belgium in a poultry farm and in captive birds, without further information regarding the subtype (H5 or other). Due to lack of information, these outbreaks will not be considered in this report.

The epidemiological situation of HPAI viruses from clade 2.3.4.4 in Europe from October 2016 to May 2017 is detailed in the last situation report published on the ESA Platform website on 31st May (link).

LIKELY EPIDEMIOLOGICAL LINKS BETWEEN OUTBREAKS IN BELGIUM, LUXEMBOURG AND FRANCE


The HP H5 virus was identified in Belgium near the Luxembourg border on 1stJune 2017, then seven other cases and outbreaks were notified from 14th to 27th June, mainly in amateur breeders of ornamental birds (source: MAF).

The virus was then identified in Luxembourg for the first time, with four cases in captive birds confirmed on 2nd and 3rd June 2017 (with no further information regarding subtype).

France confirmed the presence of the H5N8 virus on 30th June in a poultry farm located in Brillon, in the North of the country. This outbreak is likely linked to chicks and pigeons bought on a market in Tournay, Belgium. The poultry farm is located 15km from an outbreak notified on 23rd June in a commercial poultry farm in Tournai, Belgium (source: MAF). Control measures were implemented to avoid further spread of the virus, and a temporary control zone which spans over 3km around the suspected farm was set up on 27th June.

THE H5N5 VIRUS FROM CLADE 2.3.4.4 STILL PRESENT

The HP H5N5 virus is still circulating in Europe. On 1st June, the Netherlands declared a case of HPAI H5N5 in two wild geese (Anser anser domesticus).

THE H5N8 VIRUS FROM CLADE 2.3.4.4 IN ASIA AND AFRICA

The HP H5N8 virus is also circulating outside of Europe. In Asia, health authorities in South Korea have temporarily banned the transport of poultry across the country on 7th June in an effort to contain the new H5N8 epizooty. In Africa, the virus has recently been notified for the first time in South Africa, Zimbabwe (which confirmed its first outbreak in a poultry farm on 17th May), and the Democratic Republic of Congo (where three outbreaks were notified end of May in the Ituri region bordering Uganda where the H5N8 virus is also circulating) (sources: OIE, FAO, ProMED).




Figure 1. Map of HPAI outbreaks and cases notified in Europe from 1st June 2017 to 2nd July 2017 included (sources : ADNS/DGAL)


Article au format PDF:  2017-07-03_Note-IAHP-Europe_EN.pdf


While the upshot of this report - that HPAI H5 continues to circulate at low levels in Europe - seems fairly obvious, this is a decided change from the behavior of HPAI H5 viruses in past summers.

After HPAI H5's epizootic in North America (and its brief appearance in Europe) during the winter of 2014-2015, the virus unexpectedly vanished in wild and migratory birds on both continents (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl) and failed to return the following winter.  
This lack of persistence in wild birds led leading researchers to conclude that  migratory birds are not a reservoir for highly pathogenic flu viruses.

The lead author, Dr. Robert Webster explained. "Existing immunity in wild birds is one of the possible explanations that may explain why highly pathogenic influenza A viruses do not become established in wild bird populations."
Short term infection is another matter, as migratory birds have been linked to the carriage, and spread, of HPAI viruses (see HPAI H5N1 Clade 2.3.2.1c Virus in Migratory Birds, Novel H5N1 Reassortment Detected In Migratory Birds - China, etc.).
But the HPAI H5 virus that returned to Europe last fall had reinvented itself during its summer vacation in China and Russia by reassorting with other viruses (see EID Journal: Reassorted HPAI H5N8 Clade 2.3.4.4. - Germany 2016), sparking Europe's largest avian epizootic on record. 

In addition to being far more virulent in wild and migratory birds (see Europe: Unusual Mortality Among WIld Birds From H5N8)., it also displayed the ability to infect a much wider range of birds (see ESA list of 78 species).
The $64 question - as yet unanswered - is whether the recent evolutionary changes to Europe's H5N8 virus have moved it towards a strain that can sustain itself in the migratory waterfowl population.
It is a possibility hinted at obliquely in last November's  EID Journal: HPAI A(H5Nx) Viruses With Altered H5 Receptor-Binding Specificity, where researchers postulated:
`Altered receptor-binding properties might affect the balance between HA and NA, enable the virus to acquire different NA subtypes, and might result in altered host range and spreading.'
The persistence of HPAI H5N8 in wild birds well into the summer - even at the relatively low levels reported in June - would appear to be another sign that the virus is becoming better adapted to carriage by migratory birds.

While we know the HPAI H5 virus still circulates in some European birds, the big unknown is what the virus is doing (if anything) in the northern migratory bird breeding areas of Siberia and the Arctic.   
It could be weakening, or dying out, as birds develop immunity.  Or it could be growing stronger. It might even be reassorting into new subtypes.
There is simply too little real-time surveillance, and too many moving parts, to know with any certainty. The only thing we can say with confidence, is that we are only about 3 months away from finding out, when next fall's migration begins to arrive in Europe and North America.

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