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Before H7N9 emerged in China in 2013, avian H5N1 was the king of the novel flu contenders, going back to early in the last decade (see chart above). In late 2014 and the first half of 2015 - after several years of slow decline - it staged a major comeback in Egypt (see EID Journal: H5N1 In Egypt)..
Since then, however, H5N1 has reportedly only infected a handful of humans.I say reportedly because there remain many areas in the world where the virus circulates, but influenza testing and sub-typing is rarely - if ever - performed (see 2013's Nepal: Human H5N1 Testing (Or Lack Thereof).
After a year-long drought in cases, in early May we learned of a fatal H5N1 infection in Nepal (see WHO SEARO Statement On Nepal H5N1 Case), which occurred in March.The World Health Organization has published their latest Summary and Risk assessment on novel influenza, which provides details on the recently reported H5N1 case in Nepal and Oman's first reported human infection with H9N2.
Influenza at the human-animal interface
Summary and assessment, 10 April to 10 May 2019
New infections 1 : Since the previous update on 9 April 2019, new human infections with avian influenza A(H5N1) and A(H9N2) viruses were reported.
Risk assessment: The overall public health risk from currently known influenza viruses at the human-animal interface has not changed, and the likelihood of sustained human-to-human transmission of these viruses remains low. Further human infections with viruses of animal origin are expected.
IHR compliance: All human infections caused by a new influenza subtype are required to be reported under the International Health Regulations (IHR, 2005). 2 This includes any influenza A virus that has demonstrated the capacity to infect a human and its haemagglutinin gene (or protein) is not a mutated form of those, i.e. A(H1) or A(H3), circulating widely in the human population. Information from these notifications is critical to inform risk assessments for influenza at the human-animal interface.
Avian Influenza Viruses
Current situation:
Avian influenza A(H5) viruses
Since the last update on 9 April 2019, one new laboratory-confirmed human case of influenza A(H5N1) virus infection was reported to WHO from Nepal on 30 April 2019.
The patient was a 19 -year-old male resident of Kathmandu who had illness onset on 17 March 2019. He was hospitalized on 23 March. A throat swab sample was collected for laboratory testing. Antiviral treatment was initiated on 25 March. The patient passed away on 29 March.
The detection of influenza A(H5N1) in the sample from the case was confirmed at the WHO Collaborating Centre (CC) in Tokyo, Japan (National Institute of Infectious Diseases). Further characterization of the virus is underway.
Among other response actions, a detailed epidemiological investigation was completed. The investigation indicated that the most likely source of exposure of the case to the virus occurred at a live bird market. No symptomatic contacts of the case were detected. Multiple detections of influenza A(H5N1) in domestic birds in Nepal since February 2019 have been reported to the World Organisation for Animal Health (OIE).
Since 2003, a total of 861 laboratory-confirmed cases of human infection with avian influenza A(H5N1) virus, including 455 deaths, have been reported to WHO from 17 countries (see Figure 1). This is the first human case of A(H5N1) virus infection reported from Nepal.
Risk Assessment:
1. What is the likelihood that additional human cases of infection with avian influenza A(H5) viruses will occur?
The overall risk assessment is unchanged. Most human cases were exposed to A(H5) viruses through contact with infected poultry or contaminated environments, including live poultry markets. Since the viruses continue to be detected in animals and environments, further human cases can be expected.
2. What is the likelihood of human-to-human transmission of avian influenza A(H5) viruses?
Even though small clusters of A(H5) virus infections have been reported previously including those involving healthcare workers, current epidemiological and virological evidence suggests that influenza A(H5) viruses have not acquired the ability of sustained transmission among humans, thus the likelihood is low.
3. What is the risk of international spread of avian influenza A(H5) viruses by travellers?
Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as evidence suggests these viruses have not acquired the ability to transmit easily among humans.
Avian influenza A(H9N2) viruses
Since the last update on 9 April 2019, one new laboratory-confirmed human case of influenza A(H9N2) virus infection was reported to WHO from Oman on 24 April 2019.
A 13-month-old female from living in Oman developed illness on 17 March 2019 and was hospitalized on 22 March. Following treatment, the case recovered and was discharged on 1 April.(Continue . . . .)
The detection of influenza A(H9N2) virus in a nasopharyngeal sample from the case was confirmed at the WHO CC in the USA (Centers for Disease Control and Prevention). Further characterization of the virus is underway. The case may have had indirect exposure to chickens. No further human cases were reported among the close contacts. Avian influenza A(H9N2) viruses are enzootic in poultry in Asia.
This is the first confirmed human case of infection with an avian influenza virus reported from Oman.
Despite relatively few documented human infections (see FluTrackers List) - and having a reputation for causing generally less severe human illness than its avian H5 & H7 cousins - LPAI H9N2 is still considered an important player in the avian flu world.
- H9N2 has become widespread - even ubiquitous - among poultry across Europe and the Middle East
- Serological studies suggest human infection is far more common than standard surveillance would have us believe (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan)
- H9N2 reassorts easily with other viruses, and its internal genes are often found inside many HPAI viruses (including H5N1, H5N6, and H7N9) - (see The Lancet's Poultry carrying H9N2 act as incubators for novel human avian influenza viruses)
- H9N2 viruses continue to accrue evolutionary changes, which include mammalian adaptations, and increased binding to human receptor cells (see PLoS Path: Genetics, Receptor Binding, and Transmissibility Of Avian H9N2).
