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15 Mar 2017

Preliminary #Assessment–#Outbreaks of #H7N9 #avian #influenza in #poultry in the #USA, 13th March 2017 (DEFRA, edited)


Title: Preliminary #Assessment–#Outbreaks of #H7N9 #avian #influenza in #poultry in the #USA, 13th March 2017.

Subject: Avian Influenza, H7N9 subtype (North American lineage), poultry epizootics in the US.

Source: Department of Agriculture, UK, full PDF file: (LINK).

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Department for Environment, Food and Rural Affairs Animal & Plant Health / Agency Veterinary & Science Policy / Advice Team - International Disease Monitoring

Preliminary Outbreak Assessment - Outbreaks of H7N9 avian influenza in poultry in the USA, 13th March 2017


Ref: VITT/1200


HPAI in USA Disease – Report

The USA has reported an outbreak of H7N9 HPAI in a commercial chicken broiler breeder flock in Lincoln County in the State of Tennessee (OIE, 2017a; see map).

A small increase in mortality (700 of 74,000) was reported and tests confirmed HPAI. All birds have been culled and destroyed and disease control measures are in place, including a 10 mile (16 km) surveillance zone.

This is the first outbreak of HPAI in the USA this year.

The National Veterinary Services Laboratory (NVSL) has confirmed this is a North American wild bird lineage, based on full genome sequencing and is not related to the Asian H7N9 LPAI / HPAI strain currently circulating in China (USDA, 2017).

As part of routine surveillance at point of slaughter, H7N9 LPAI virus was also detected in a broiler breeder chicken flock also in Tennessee (Giles County) and the flock was depopulated (OIE, 2017b). Again, the origin of the virus was a North American wild bird lineage.

In other reports, the USA has also detected H5N2 LPAI in a commercial turkey flock in Wisconsin (Barron County). This was a North American wild bird virus and is not related to the EA/AM H5N2 HPAI clade viruses which caused multiple cases in 2015 (OIE, 2017c).


Situation Assessment

Tennessee and Wisconsin States are within the Mississippi Flyway for migratory wild birds. Therefore occasional incursions into poultry farms are not entirely unexpected. However, since the 2014-2015 epizootic in the USA, lessons were identified and an updated HPAI preparedness and response plan has been issued (APHIS, 2016).

Export certificates for poultry and poultry products (under Commission Regulation 798/2008/EC) have been suspended from the counties of Lincoln, Franklin and Moore in Tennessee and Madison and Jackson counties in Alabama. However, under regionalization agreements, consignments from other regions are accepted for export to the EU, including the UK.

It is possible that the H7N9 HPAI virus was the result of an incursion of LPAI virus into the flock and consequent mutation into a highly pathogenic strain. It will be interesting to see if there is any evidence of this occurring.

In Asia, the H7N9 virus which has been circulating in South East China for five years in poultry was recently sequenced from several poultry, environmental and human samples in Guangdong Province and Taiwan.

Mutations in the HA gene suggested these strains could be highly pathogenic in gallinaceous poultry. If this were correct, it would mean surveillance could be targeted at clinical reports in poultry and allow controls to be put in place more readily.

The European Centre for Disease Control has confirmed these mutations are not linked to any increase in affinity to mammalian cells and therefore no increase pathogenicity or spread in humans (FAO, 2017; ECDC, 2017).



We will continue to monitor the situation and work with our partners to ensure we continue to trade safely. We would like to remind all poultry keepers and attending veterinarians to maintain high standards of biosecurity, remain vigilant and report any suspect clinical signs promptly.



International Disease Monitoring Team



  1. APHIS (2016) 2016 HPAI Preparedness and Response Plan.
  2. ECDC (2017) Mutation of avian influenza A(H7N9): now pathogenic for poultry but risk of human to human transmission remains low. t=a3216f4c-f040-4f51-9f77-a96046dbfd72&ID=808
  3. FAO (2017) H7N9 Situation Update. Date 08/03/2017
  4. OIE (2017a) Immediate Notification OIE Ref 23139. Date 06/03/2017.
  5. OIE (2017b) Immediate Notification OIE Ref 23161. Date 09/03/2017
  6. OIE (2017c) Immediate Notification OIE Ref 23189. Date 10/03/2017
  7. USDA (2017) USDA issues update on Highly Pathogenic Avian Influenza in Tennessee.


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Keywords: UK; Updates; USA; Tennessee; Avian Influenza; H5N2; H7N9; Wisconsin; Poultry.