Credit Defra
# 10,374
The announcement earlier this week of highly pathogenic H7N7 Reported At Emsland Poultry Farm comes on the heels of several low path (LPAI) H7N7 detections in recent months in Germany, the Netherlands, and the UK. Of particular interest, this latest HPAI outbreak was detected less than a kilometer away from a farm that had reported LPAI H7N7 less than 3 weeks ago.
LPAI H7 viruses are often found in wild and migratory birds, and are viewed as the principal vector of the virus to domesticated poultry.
The concern with these LPAI H5 and H7 viruses is that when they are not controlled - they have the potential to mutate into highly pathogenic strains. HPAI viruses have been generated in the lab by repeated passage of LPAI viruses through chickens (cite FAO) but exactly how and why this occurs naturally is poorly understood (see JVI Emergence of a Highly Pathogenic Avian Influenza Virus from a Low Pathogenic Progenitor). .
While it hasn’t been documented often, the risk is considered great enough that all LPAI H5 and H7 outbreaks must be reported to the OIE, and immediate steps must be taken to contain and eradicate the virus.
All of which brings us to a Defra preliminary analysis of last week’s HPAI H7N7 outbreak, that has buried in it sneak peek from a yet-to-be published report about the UK’s most recent HPAI H7N7 outbreak.
. . on the 6th July, the UK reported an outbreak of H7N7 HPAI in laying hens. Investigations into this outbreak have revealed a mutation event occurred within the poultry premises, following an incursion of LPAI. The most likely source of infection was contact with wild birds, given the presence on the farm of nesting wild waterfowl and two ponds
As this report points out, this is a rare event:
In the last 10 years, there have been only four such documented events of mutation from LPAI to HPAI occurring all within chicken layers in Europe: UK in 2008, Spain in 2009 (SCoFCAH, 2010), Italy in 2013 and UK in 2015; all involved H7N7.
The question – still under investigation - is whether this latest HPAI H7N7 outbreak in Germany has any connection with the LPAI outbreak earlier this month on a farm a kilometer away.
If it turns out to be true - and we have really had two such `rare’ events in the span of a couple of weeks - it then begs the question as to whether these sorts of LPAI to HPAI `conversions’ are becoming more common . . .and why?.
Preliminary Outbreak Assessment
Highly Pathogenic Avian Influenza H7N7 in poultry in Germany29 July 2015 Ref: VITT/1200 HPAI H7N7 in Germany
Disease Report Germany has reported an outbreak of highly pathogenic avian influenza, H7N7 in poultry in North West Germany (Lower Saxony) (European Commission, 2015; OIE, 2015). The holding was comprised of over 10,000 laying hens and clinical signs were first reported on 24/7/2015. Disease control measures are in place, including 3km and 10km protection and surveillance zones in line with Directive 2005/94/EC. The birds have been depopulated.The outbreak was located less that 1km from a premises which had reported H7N7 LPAI on June 11th 2015 and this new IP tested negative in the course of disease investigations into LPAI. Further analyses may reveal the relationship if any between the two events.
Situation assessment In the last few months there have been several reported outbreaks of H7N7 avian influenza viruses in poultry in Europe. The UK had a low pathogenicity strain in February, Netherlands had two outbreaks of LPAI in March and April while Germany had two outbreaks of LPAI in both March and June. The June outbreak in Germany was in the same region as the latest HPAI incident.
Meanwhile on the 6th July, the UK reported an outbreak of H7N7 HPAI in laying hens. Investigations into this outbreak have revealed a mutation event occurred within the poultry premises, following an incursion of LPAI. The most likely source of infection was contact with wild birds, given the presence on the farm of nesting wild waterfowl and two ponds. The full epidemiology report will be available soon at www.gov.uk
It is of no surprise that H7 LPAI viruses have been detected this year, as these viruses are continually circulating in wild waterfowl and therefore there is a constant low risk of incursion of these viruses into poultry. However, the mutation of LPAI to HPAI viruses is a rare event.
Several factors may drive these mutation events: a “jump” from Anseriform birds into Galliform poultry; adaptation to Galliform poultry; repeated passage through the poultry; spread within the poultry (free range birds as opposed to caged birds where mixing between birds is reduced) that acquire LPAI virus immunity that then acts to exert selective pressure and possibly the age of the birds.
In the last 10 years, there have been only four such documented events of mutation from LPAI to HPAI ccurring all within chicken layers in Europe: UK in 2008, Spain in 2009 (SCoFCAH, 2010), Italy in 2013 and UK in 2015; all involved H7N7. In the case of the UK mutation event in 2008, mallard ducks present at the premises and in contact with free range laying hens seemed to be the source for the LPAI incursion with subsequent mutation following sustained transmission within the flock. In Spain, the incursion of LPAI was believed to be from wild waterfowl on a nearby reservoir which was the water source for the farm and the mutation consequently occurred in one of four sheds of laying hens (SCoFCAH, 2010). In Italy the virus was introduced to free range hens as LPAI and mutated to HPAI during transmission within the flock.
It remains to be seen if the same event has occurred in Germany, but given the circulation of LPAI demonstrated recently, this would seem highly probable. Surveillance sampling in the event of an outbreak only gives a level of confidence for finding over a certain prevalence, therefore occasionally there may be a possibility that additional cases which have gone undetected if incursion at the time of sampling is relatively new.
