Zoonotic Influenza

Authored by
Staff
Last reviewed
April 10, 2021

Zoonotic Influenza Viruses

The WHO says Zoonotic influenza refers to a disease caused by animal influenza viruses that cross the animal–human divide to infect people. People can be infected with influenza viruses that are usually circulating in animals, such as avian influenza virus subtypes A(H5N1) and A(H9N2) and swine influenza virus subtypes A(H1N1) and (H3N2).

Even though these viruses may be named the same subtype as viruses found in humans, all of these animal viruses are distinct from human influenza viruses and do not easily transmit between humans. 

Avian Influenza

Avian influenza is the disease caused by influenza type A viruses in animals. These viruses occur naturally among birds and domestic poultry. Whenever avian influenza viruses are circulating, there is a risk for sporadic infection and small clusters of human cases due to exposure to infected poultry or contaminated environments, says the U.S. CDC.

Humans do not normally contract Avian flu viruses; however, human infections have occurred and are very lethal.  Globally, from January 2003 to February 2021, there were 862 cases of human infection with avian influenza A(H5N1) virus reported from 17 countries. Of these cases, 455 were fatal (CFR of 53%), reported the WHO.

Swine Influenza

The first swine influenza virus was found in pigs in 1918. Research points to a possible avian origin of the virus that was then transmitted to pigs. There are different swine influenza virus subtypes and strains, some of which have been known to infect other animal species, including (rarely) humans.

When animal influenza viruses infect their natural animal host, they are named for that host, as in avian influenza viruses, swine influenza viruses, equine influenza viruses, etc. As such, the term “swine flu” refers to swine influenza viruses infecting swine.

African swine fever is a highly contagious and deadly viral disease affecting domestic and feral swine of all ages. The U.S. Department of Agriculture says it is not a threat to human health and cannot be transmitted from pigs to humans. And it is not a food safety issue. 

Zoonotic Influenza News

April 9, 2021 - Nigerian authorities have reported outbreaks of influenza A(H5N1) in poultry and human cases of influenza A(H5) during 2021. As of 28 March, outbreaks of highly pathogenic avian influenza (HPAI) H5N1 in poultry have been reported in 30 farms from seven states in Nigeria. In addition, the ECDC reported 13 blood samples have been collected from the very-close human contacts of birds in Bauchi (5), Gombe (5), and Plateau (3) states.

April 7, 2021 - The first human case of avian influenza A(H5N6) virus infection has been reported in Laos. A five-year-old boy developed symptoms on 28 February 2021, was hospitalized, and recovered. He had exposure to poultry, which also tested positive for A (H5N6). No further cases were detected.

March 30, 2021 - An Avian Influenza Prevention Zone (AIPZ) is in force across the whole of England. In light of the two most recent cases of avian influenza and following an urgent review of the risk of avian influenza to both wild and kept birds: the housing measures component of the Avian Influenza Prevention Zone (AIPZ) will still be lifted at 11:59 pm on the 31 March 2021; the AIPZ requiring enhanced biosecurity will remain in force until further notice but Wednesday 31 March 2021 will be the last day poultry and other captive birds will need to be housed (housing restrictions end at 11:59 pm on 31 March 2021); bird gatherings will remain prohibited.

March 26, 2021 - The US Centers for Disease Control and Prevention (CDC) today reported a variant H1N1 (H1N1v) case involving a North Carolina resident who had daily contact with pigs. This person was infected with an influenza A(H1N1) variant (A(H1N1)v) virus in 2020. While this variant virus infection was not identified until 2021, it represents the first influenza A(H1N1)v virus identified from a specimen collected in the USA in 2020. No influenza A(H1N1)v virus infections have been identified in specimens collected in 2021 thus far.

March 25, 2021 - In a federal notification issued, the United States Department of Agriculture's Animal and Plant Health Inspection Service said India has been on the list of regions “we consider to be affected” with African Swine Fever.

March 22, 2021 - The Hong Kong Centre for Health Protection of the Department of Health announced it is closely monitoring a human case of avian influenza A(H5N6) in Guangxi and again urged the public to maintain strict personal food environmental hygiene locally and during travel. The case involved a 50-year-old man living in Hechi in Guangxi. He developed symptoms on February 16, 2021, and was admitted for treatment on February 17th due to severe pneumonia. The patient passed away on March 2nd. From 2014 to date, 30 human cases of avian influenza A(H5N6) have been reported by Mainland health authorities.

March 19, 2021 - European countries reported wild bird outbreaks involving various strains, including H5N5 in the Czech Republic, H5 in Sweden, and H5N4 in the Netherlands.

March 15, 2021 - According to the World Organization for Animal Health, veterinary officials in the UK reported highly pathogenic H5N8 avian influenza in (5) seals and a fox that died at a wildlife rescue center in Surrey county. This location is where mute swans died from the virus in November 2020.

March 10, 2021 - Sweden reported an H5N5 outbreak at a poultry farm in Trelleborg that began on March 2, 2021. The farm culled about 3,000 of 18,000 susceptible birds. The country's last H5N5 outbreak in poultry was reported in November 2020. A protection zone (3km) and a surveillance zone (10 km) have been put in place around the infected farm, and all other restrictions and necessary measures according to Directive 2005/94/EC were applied.

March 8, 2021 - Kuwait reported a highly pathogenic H5N8 avian flu outbreak in poultry. Kuwait's reported its last H5N8 outbreak in November 2020.

March 3, 2021 - The WHO published Antigenic and genetic characteristics of zoonotic influenza viruses and candidate vaccine viruses developed for potential use in human vaccines. This summary provides a review on the zoonotic influenza virus activity and virus characterization and describes the current status of the development of candidate vaccine viruses for pandemic preparedness purposes. It is meant to guide national authorities and vaccine companies on selecting candidate viruses for use in vaccine development.

March 1, 2021 - To date, five avian influenza A(H9N2) cases were reported from China in 2021. A total of 43 cases of human infection with avian influenza A(H9N2) in China have been reported since December 2015.

February 25, 2021 - The WHO reported a total of 239 cases of human infection with avian influenza A(H5N1) virus had been reported from four countries within the Western Pacific Region since January 2003 (Table 1). Of these cases, 134 were fatal, resulting in a case fatality rate (CFR) of 56%. The last case was reported from Lao PDR, with an onset date of 13 October 2020 (one case, no death).

February 18, 2021 - The National IHR Focal Point for the Russian Federation notified the WHO of the detection of avian influenza A(H5N8) in seven human clinical specimens. These are the first reported detection of avian influenza A(H5N8) in humans. Positive clinical specimens were collected from poultry farmworkers who participated in a response operation to contain an avian influenza A(H5N8) outbreak detected in a poultry farm in Astrakhan Oblast, the Russian Federation.