On 18 February 2021, the National IHR Focal Point for the Russian Federation notified WHO of 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 farm workers who participated in a response operation to contain an avian influenza A(H5N8) outbreak detected in a poultry farm in Astrakhan Oblast in the Russian Federation. The laboratory confirmation of the seven specimens were performed by the State Research Centre for Virology and Biotechnology VECTOR (WHO H5 Reference Laboratory). The age of seven positive cases ranged between 29 to 60 years and five were female.
Between 3 and 11 December, a total of 101 000 of 900 000 egg laying hens on the farm died. This high mortality rate prompted an investigation. Samples were collected from these birds and an initial detection of avian influenza A(H5N8) was performed by the Russian regional veterinary laboratory. On 11 December, the outbreak was confirmed by the World Organisation for Animal Health (OIE) Reference laboratory, and the Federal Centre for Animal Health (FGBI-ARRIAH), in Vladimir, the Russian Federation. Outbreak containment operations started immediately and continued for several days due to the large size of the poultry farm.
The cases remained asymptomatic for the whole follow up duration (several weeks). Follow-up nasopharyngeal swabs were collected during medical observation period and were tested negative for avian influenza A(H5N8). No obvious clinical manifestations were reported from any farm workers under medical surveillance, their family members, or other close contacts of the seven cases. Additionally, acute and convalescent sera was collected from the seven positive human cases for serological testing. The results were suggestive of recent infection.
Influenza A(H5N8) viruses isolated from this poultry outbreak in Astrakhan belonged to clade 22.214.171.124b of avian influenza A(H5Nx) viruses. In 2020, avian influenza A (H5N8) viruses were also detected in poultry or wild birds in Bulgaria, the Czech Republic, Egypt, Germany, Hungary, Iraq, Japan, Kazakhstan, the Netherlands, Poland, Romania, the United Kingdom, and the Russian Federation.
Public health response
On receiving the initial signal of a probable outbreak of highly pathogenic avian influenza (HPAI) at the poultry farm on 3 December 2020, the national authorities took immediate measures including cessation of poultry production cycles, and product transportation from the affected farm.
Between 11 and 18 December, several measures including culling and disposing of poultry, eggs, litter and disinfection of contaminated premises were taken as part of outbreak response activities
During and after the culling of all the poultry, nasopharyngeal swabs and serum samples were collected from poultry farm workers and personnel involved in outbreak response at the farm. The surveillance activities, both within and outside of the containment area, was intensified. A total of 24 close contacts of the confirmed cases have been identified and traced. In total, 150 individuals were monitored for clinical indication of respiratory disease and received antiviral prophylaxis therapy. No symptoms were reported among these individuals.
Whole Genome Sequencing of avian influenza A (H5N8) viruses isolated from poultry and from one of the seven human cases was performed and were uploaded to the Global Initiative on Sharing All Influenza Data (GISAID) database on 20 February 2021. Genetic and phenotypic characterization of the virus is ongoing.
WHO is following up with the public health authorities in the Russian Federation, including implementation of public health measures warranted by such events, and with the WHO Global Influenza Surveillance and Response System (GISRS) on further analysis and assessment of the virus materials and serum samples. On 20 February, a special briefing by the head of the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing was organized for the state Russian media to inform the public about these cases and the implications.
WHO risk assessment
Since 2004, avian influenza A(H5) viruses have spread from Asia to Europe via wild birds. The genetic clade 126.96.36.199 H5 viruses have often reassorted among other avian influenza viruses, resulting in avian influenza A(H5N1), A(H5N2), A(H5N3), A(H5N5), A(H5N6) and A(H5N8) viruses, some of which have been detected in birds in many countries .
In the Russian Federation, avian influenza A(H5N8) of clade 188.8.131.52 was isolated for the first time in 2014 in a wild bird in the northern region of Russian Far East.
As mentioned earlier, all the seven cases with PCR-positive results were clinically asymptomatic. All close contacts of these cases were clinically monitored, and no one showed signs of clinical illness. Infections with avian influenza viruses of the same clade (H5 clade 184.108.40.206) have been reported from China since 2014 in people with exposure to infected birds. The likelihood of human infections with influenza A(H5N8) viruses has been considered to be low.
Further genetic and antigenic characterization and information on seroconversion among contacts of the positive cases is required to fully assess the risk.
The development of zoonotic influenza candidate vaccine viruses for potential use in human vaccines, coordinated by WHO, remains an essential component of the overall global strategy for influenza pandemic preparedness.
Based on currently available information, the risk of human-to-human transmission remains low.
These cases do not change the current WHO recommendations on public health measures and surveillance of animal and seasonal human influenza, which should continue to be implemented. Respiratory transmission occurs mainly by droplets, disseminated by unprotected coughs and sneezes. Short-distance airborne transmission of influenza viruses may occur, particularly in crowded enclosed spaces. Hand contamination, direct inoculation of virus, exposure to infected birds or virus-contaminated materials or environments are potential sources of infection.
When avian influenza viruses are circulating in an area, the people involved in specific, high-risk tasks such as sampling sick birds, culling and disposing of infected birds, eggs, litter and cleaning of contaminated premises should be trained on how to protect themselves, and on proper use of personal protective equipment (PPE) . People involved in these tasks should be registered and monitored closely by local health authorities for seven days following the last day of contact with poultry or their environments.
Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses that may affect human (or animal) health and timely virus sharing for risk assessment.
Thorough investigation of all potential novel influenza human infections is warranted. All human infections caused by a novel influenza subtype are notifiable under the International Health Regulations (IHR), and State Parties to the IHR are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by new influenza A subtype with the potential to cause a pandemic (please see case definitions for diseases requiring notification under the IHR ). Evidence of illness is not required.
In the case of a confirmed or suspected human infection, a thorough epidemiologic investigation of history of exposure to animals, of travel, and contact tracing should be conducted, even while awaiting the confirmatory laboratory results. The epidemiologic investigation should include early identification of unusual respiratory events that could signal person-to-person transmission of the novel virus. Clinical samples collected from the time and place that the case occurred should be tested and sent to a WHO Collaboration Center for further characterization.
Travelers to countries with known outbreaks of avian influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or contact with any surfaces that appear to be contaminated with animal feces. Travelers should also wash their hands often with soap and water. Travelers should follow good food safety and good food hygiene practices.