© Crown copyright 2018
This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: email@example.com.
Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.
This publication is available at https://www.gov.uk/government/publications/avian-influenza-ah5n6-risk-assessment/avian-influenza-ah5n6-risk-assessment
H5N6 risk assessment
There are at least 2 different lineages of highly pathogenic avian influenza (HPAI) A(H5N6) circulating in poultry. The Asian lineage strains of HPAI H5N6 have been responsible for outbreaks in poultry in China and South East Asia since 2014 and are associated with severe human disease.
During 2017, a second lineage of HPAI H5N6, a reassortant of H5N8 was identified in birds in Korea, Japan and across Europe. The reassortant strain is considered unrelated to the Asian lineage and has not been associated with human cases.
Epidemiology in birds and humans
Asian lineage H5N6
Since 2014, HPAI A(H5N6) has been responsible for widespread outbreaks in birds across China, Japan and South East Asia and in 2018 significant outbreaks have been reported from Mainland China, Japan, South Korea, Taiwan, Hong Kong and Vietnam. The Philippines has also reported H5N6 in poultry (1). The virus is highly pathogenic in birds and has been isolated from both poultry and wild birds.
In April 2014, the World Health Organization (WHO) first reported a case of human infection with avian influenza A(H5N6) from China. As of 14 January 2019, a total of 23 human cases of infection with avian influenza A(H5N6) have been reported from 10 different provinces across mainland China (2). 4 of these cases were in children, 2 of whom had only mild illness. Of the remaining 19 adult cases, all had a severe illness and at least 15 were fatal.
The majority of human cases of HPAI A(H5N6) in mainland China are known to have had contact with birds or their environments prior to becoming ill and there is currently no evidence of human-to-human transmission. WHO considers that the H5 avian influenza viruses have not acquired the ability to transmit easily among humans and therefore the risk of sustained human-to-human transmission is low at present (2).
On 3 March 2017, Greece reported the first detection of HPAI A(H5N6) outside of Asia in a backyard flock. Genetic analysis of this virus by the European Reference Laboratory for avian influenza concluded that that the virus is distinct from the strain currently circulating in Asia and is actually a reassortant of European H5N8 viruses (3).
This reassortant has caused outbreaks in poultry in Korea, Japan and Europe (Netherlands). There have also been detections in wild birds across Europe (Switzerland, Netherlands, Germany, Sweden) and in the UK. There are currently no human cases associated with this reassortant lineage of H5N6; however, it is acknowledged that the overall data on human exposures is still accumulating.
Asian lineage H5N6
The potential risk to human health from Asian lineage HPAI A(H5N6) relates to:
- lack of population immunity to H5 haemagglutinin (HA). The emergence of this virus involved the evolution of the H5 HA of highly pathogenic avian influenza (HPAI) A(H5N1) viruses, for which it is known that there is little population immunity to the HA
- neuraminidase immunity may contribute to protection but there is likely to be little population immunity to the N6 neuraminidase subtype
- the internal genes of this virus are derived from the progenitor of the A(H5N1) virus and include sequence correlates of mammalian adaptation and virulence
Furthermore, the internal genes of A(H5N1) viruses have frequently become re-assorted with other subtypes of avian influenza viruses since the emergence of A(H5N1) and the internal gene cassette of influenza A(H5N6) has the potential to support recombination events to produce viruses which are even more suited to adaptation and transmission in humans.
The World Organisation for Animal Health (OIE)/Food and Agriculture Organization/EU Reference Laboratory for Avian Influenza at the Animal and Plant Health Agency has conducted a detailed genetic analysis of a small number of H5N6 HPAI viruses detected in both Europe and Asia. The strains can be differentiated from those strains associated with zoonotic infection in Asia. Furthermore, they do not currently carry any virulence markers strongly associated with human infection risk. In addition, there have been no reported human infections with this particular genetic sub-lineage of H5N6 HPAI to date.
Asian lineage H5N6
Areas of the world affected by the Asian lineage of avian influenza A(H5N6) include China and anywhere with outbreaks within the last 12 months: Update on avian influenza in animals (types H5 and H7)
- the risk of influenza A(H5N6) infection to UK residents within the UK is very low
- the risk of influenza A(H5N6) infection to UK residents who are travelling to China or affected areas with confirmed outbreaks and incidents in avian species is very low
- the level of risk of influenza A(H5N6) infection in those who arrive in the UK from China or affected areas and meet the case definition for novel avian influenza infection is low but warrants testing
- the probability that a cluster of cases of severe respiratory illness in the UK is due to influenza A(H5N6) is very low, but warrants testing. A history of travel to China or other affected areas and close contact with either avian species or a confirmed human case or a history of direct exposure to a confirmed H5N6 incident in avian species in the UK, would increase the likelihood of influenza A(H5N6)
- if there is good compliance with guidance on infection control measures, the risk to healthcare workers caring for cases of influenza A(H5N6) in the UK is very low; however, severe respiratory illness in healthcare workers caring for cases of influenza A(H5N6) requires testing
- the risk to contacts of laboratory confirmed human or avian cases of influenza A(H5N6) infection is low but warrants follow up in the 10 days following exposure and urgent investigation of any new febrile or respiratory illness
In addition, there have been sporadic incidents and outbreaks in the UK related to the reassortant lineage of the virus.
Risk to the general public
- the risk of HPAI A(H5N6) infection to UK residents in the UK is very low
- the risk to people who have handled dead birds that are subsequently confirmed as infected with HPAI A(H5N6) may be higher, but is still considered to be low
Risk to people occupationally exposed
There have been no reported cases of human infection among farm workers, or those involved in the culling, clean-up and disposal of infected birds during previously reported HPAI A(H5N6) incidents. However, there is a theoretical risk of human infections due to occupational exposure, and a precautionary approach is advised:
- the risk to persons occupationally exposed to HPAI A(H5N6) is slightly higher than for the general public but is considered to be low
- when appropriate interventions are implemented, such as use of full PPE, this risk is considered to be very low
Until further information is available, Public Health England (PHE) recommends a precautionary approach for people exposed during incidents, which includes the use of appropriate Personal Protective Equipment (PPE), antiviral prophylaxis where indicated, and active public health follow-up.
The Health and Safety Executive (HSE) provide guidance on the appropriate PPE for people who are occupationally exposed.
Advice for the general public
The general public are advised not to touch or pick-up birds that are dead, or appear to be sick or dying.
The Department for Environment, Food and Rural Affairs (DEFRA) provide advice on reporting dead wild birds.
No specific restrictions are advised for most people. However, people who are undergoing public health follow-up following a confirmed exposure to H5N6 are advised not to travel for the purposes of ensuring rapid access to care and investigations.
To help reduce the risk of infection, the National Travel Health Network and Centre (NaTHNaC) advised travellers visiting China or other areas affected by the Asian lineage of H5N6 to:
- avoid close or direct contact with live poultry
- avoid visiting live bird and animal markets (including ‘wet’ markets) and poultry farms
- avoid contact with surfaces contaminated with animal faeces
- avoid untreated bird feathers and other animal and bird waste
- do not eat or handle undercooked or raw poultry, egg or duck dishes
- do not pick up or touch dead or dying birds
- do not attempt to bring any poultry products back to the UK
- maintain good personal hygiene with regular hand washing with soap
- use alcohol-based hand rubs
Travellers to China or other affected areas should be alert to the development of signs and symptoms of influenza for 10 days following their return. It is most likely that anyone developing a mild respiratory tract illness during this time is suffering from seasonal influenza or some other commonly circulating respiratory infection. However, if they become concerned about the severity of their symptoms, they should seek appropriate medical advice and inform the treating clinician of their travel history.
Advice for clinicians and health professionals
Clinicians should retain a high level of suspicion of influenza A(H5N6) when managing patients with:
- suspected influenza or confirmed Influenza A (unsubtyped) or
- confirmed influenza A (unsubtypable as seasonal H3 or H1N1 pdm09)
And one of the following:
- a history of travel to China or one of the affected areas and contact with
- avian species in the 10 days before symptom onset
- a history of travel to China or one of the affected areas and contact with a confirmed human case of influenza A(H5N6) or a human case of severe unexplained respiratory illness resulting in death, in the last 10 days before symptom onset
- any history of exposure to a laboratory confirmed H5N6 incident in avian species
Clinicians should also remember to consider testing for influenza A(H5N1) and influenza A(H7N9) in patients with an appropriate similar travel history. Clinicians should also remember to consider testing for other avian influenza viruses in patients with an appropriate similar travel history.
Guidance on the public health management of possible human cases of novel avian influenza and their contacts is available online.
The local PHE Public Health Laboratory can provide advice on arranging testing for possible cases of influenza A due to H5/H7.
(2) WHO: Influenza at the human-animal interface, 25 January 2018