Reasons for the potential spread of avian influenza include which of the following? | Jannah Arnav Eamonn

Situation at a glance

Public health authorities in Spain reported the detection of influenza A(H5N1) in two poultry workers on a single farm, following an outbreak in poultry confirmed on 20 September. Given the potential impact on public health, a multisector response including measures for control, prevention, and early detection was initiated in the poultry farm. The detection of influenza A(H5N1) in these individuals was likely due to exposure to infected poultry or contaminated environments. No evidence of human-to-human transmission of influenza A(H5N1) virus in this event has been identified to date.

Description of the case

On 27 September 2022, the Ministry of Public Health of Spain notified WHO of a case of influenza A(H5N1) in an individual working at a poultry farm in the province of Guadalajara. An outbreak of avian influenza A(H5N1) in poultry had been confirmed on the farm on 20 September. Nasopharyngeal samples were subsequently collected from all 12 farm workers on 23 September and influenza A(H5N1) virus was detected in a sample from one of the workers (a 19-year-old male) on 27 September. He remained in isolation until 28 September when a second sample tested negative by RT-PCR. On 28 September, samples from one close contact of the case were collected, which tested negative for avian influenza by RT-PCR.

Following response measures on the farm, all workers were tested again on 13 October. Influenza A(H5N1) virus was detected in a nasopharyngeal sample from another worker (a 27-year-old male involved in the control measures including cleaning and disinfection whilst wearing personal protection equipment) on 13 October. He had initially tested negative during the first round of testing on 23 September. He remained in isolation until 22 October when a second sample tested negative by RT-PCR. Two close contacts of his were identified and tested negative on respiratory sampling.

Both cases did not have any symptoms. Samples were tested using RT-PCR at the National Microbiology Center.   

Epidemiology of disease

Zoonotic influenza infections in humans may range from asymptomatic or mild upper respiratory infection (fever and cough) to rapid progression to severe pneumonia, acute respiratory distress syndrome, shock and even death.

Human cases of infection with avian influenza viruses are usually the result of direct or indirect exposure to infected live or dead poultry or contaminated environments.

From 2003 to 21 October 2022, a total of 868 human cases of infection with influenza A(H5N1), including these two cases, and 456 deaths have been reported globally from 21 countries. A total of three human cases of infection with influenza A (H5N1), one case from the United Kingdom in 2021 and two cases from Spain in 2022 have been reported in Europe to date.

Public health response

• Coordination and response: A multisector response including measures for control, prevention, and early detection have been carried out in poultry farms according to the Practical Operations Manual of the Ministry of Agriculture, Fisheries and Food.
• Surveillance: A follow-up response including passive and active surveillance of exposed workers and close contacts has been initiated. Excluding the reported cases, all other individuals who were exposed at the affected poultry farm were monitored for seven days following the last day of exposure to infection and have not developed any symptoms.
• Laboratory: Virus characterization, and serological studies are in process. The samples from both cases were sent on 24 October 2022 to the WHO Collaborating Centre for Reference and Research on Influenza at the Crick Worldwide Influenza Centre in London, the United Kingdom of Great Britain and Northern Ireland.
• Infection prevention and control: In the affected farms, measures related to the control of the outbreak have been undertaken, including on-site slaughter of the birds, the destruction of contaminated materials that could carry the virus, and the cleaning and disinfection of the facilities. All participants involved in the culling process wore personal protective equipment.

WHO risk assessment

Individuals are at risk of becoming infected with avian influenza viruses if they are exposed to infected birds or virus-contaminated fomites or environments.

Whenever avian influenza viruses are circulating in poultry, there is a risk for sporadic infection and small clusters of human cases due to exposure to infected poultry or contaminated environments. Therefore, sporadic human cases are not unexpected. The detection of influenza A(H5) virus in nasopharyngeal/oropharyngeal samples collected from individuals in close contact with infected poultry or other birds, whether the individuals are symptomatic or not, is not unexpected. Good quality serological investigations may be useful in differentiating infection from contamination in these cases and allow for a better assessment of the risk of human infection.  There was no evidence of human-to-human transmission in this event.

In the current outbreak of HPAI A(H5N1) on a poultry farm in Spain, both human and animal health agencies have implemented public health measures. Based on the available information, WHO assesses that the risk for the general population posed by this virus is low, and for occupationally exposed persons, it is low to moderate.

WHO advice

The reports of these two influenza A (H5N1) cases do not change the current WHO recommendations on public health measures and surveillance of influenza.

WHO does not advise special traveler screening at points of entry or restrictions with regard to the current situation of influenza viruses at the human-animal interface.

Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect and monitor virological, epidemiological, and clinical changes associated with emerging or circulating influenza viruses that may affect human (or animal) health and timely virus sharing for risk assessment.

When avian influenza viruses are circulating in an area, people involved in high-risk tasks such as sampling sick birds, culling, and disposing of infected birds, eggs, litters and cleaning of contaminated premises should be trained in the proper use of and provided with appropriate personal protective equipment (PPE). All persons 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.

In the case of a confirmed or suspected human infection caused by a novel influenza virus with pandemic potential, including a variant virus, a thorough epidemiologic investigation (even while awaiting the confirmatory laboratory results) of history of exposure to animals, of travel, and contact tracing should be conducted. The epidemiological investigation should include early identification of unusual respiratory events that could signal person-to-person transmission of the novel virus and clinical samples collected from the time and place that the case occurred should be tested and sent to a WHO Collaboration Centre for further characterization.

Currently, there is no vaccine to protect against avian influenza in humans. WHO recommends that all people involved in work with poultry or birds should have a seasonal influenza vaccination to reduce the theoretical risk of a reassortment event.

Travelers to countries with known outbreaks of animal 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 faeces. General precautions include regular hand washing and good food safety and food hygiene practices. 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 this virus has not acquired the ability to transmit easily among humans.

All human infections caused by a novel influenza subtype are notifiable under the International Health Regulations (IHR) and State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic. Evidence of illness is not required for this report.

Further information

• Current technical information including monthly risk assessments at the Human-Animal Interface. Available at: https://www.who.int/teams/global-influenza-programme/avian-influenza
• World Health Organization. Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003-2022, 5 October 2022. Available at: https://www.who.int/publications/m/item/cumulative-number-of-confirmed-human-cases-for-avian-influenza-a(h5n1)-reported-to-who-2003-2022-5-oct-2022
• Case definitions for diseases requiring notification under the IHR (2005). Available at: www.who.int/ihr/Case_Definitions.pdf
• IHR (2005). Available at: https://www.who.int/publications/i/item/9789241580410 
• World Organisation for Animal Health. WAHIS report poultry outbreak in Guadalajara, Spain. https://wahis.woah.org/#/in-review/4570?reportId=157103&fromPage=event-dashboard-url
• Manual for the laboratory diagnosis and virological surveillance of influenza (2011). Available at: https://www.who.int/publications/i/item/manual-for-the-laboratory-diagnosis-and-virological-surveillance-of-influenza
• Terms of Reference for National Influenza Centres of the Global Influenza Surveillance and Response System. Available at:  National Influenza Centres (who.int)
• Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases. Available at: https://apps.who.int/iris/handle/10665/275657
• World Organisation for Animal Health (WOAH). H5N1 Highly Pathogenic Avian Influenza in poultry and wild birds: Winter of 2021/2022 with focus on mass mortality of wild birds in UK and Israel. Available at: https://www.oie.int/app/uploads/2022/03/avian-influenza-0.pdf
• Testing and detection of zoonotic influenza virus infections in humans in the EU/EEA, and occupational safety and health measures for those exposed at work Guidance: https://www.ecdc.europa.eu/en/publications-data/zoonotic-influenza-virus-infections-humans-testing-and-detection(link is external)
• ECDC. 2021-2022 data show largest avian flu epidemic in Europe ever. Available at: https://www.ecdc.europa.eu/en/news-events/2021-2022-data-show-largest-avian-flu-epidemic-europe-ever
• European Food safety authority. Avian influenza overview June – September 2022. https://www.efsa.europa.eu/en/efsajournal/pub/7597

Citable reference: World Health Organization (3 November 2022). Disease Outbreak News; Avian Influenza A (H5N1) – Spain. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON420