Появление птичьего гриппа A(H9N2) во Вьетнаме требует заблаговременных мер предосторожности

• Анджум Рамиса
• Хан С.Р.
• Сиддики У.А.
• Деван С.М.Р.

Резюме

В связи с недавним выявлением случая птичьего гриппа A(H9N2) во Вьетнаме необходимо оценить масштаб угрозы, которую авиарные вирусы представляют для общественного здоровья. Несмотря на то что заболевший получает необходимое лечение и новых случаев передачи вируса от человека к человеку во Вьетнаме не зафиксировано, ситуация требует пристального внимания. Высокая распространенность вируса среди птиц (особенно во Вьетнаме), способность к межвидовой передаче, постоянная эволюция и накопление мутаций, говорящих о приспособлении к человеческому организму - все это требует заблаговременных мер предосторожности.

Данный случай еще раз подчеркивает опасность вирусов птичьего гриппа, особенно в эндемичных регионах. Хотя H9N2 обычно протекает у людей в легкой форме, мутации могут привести к появлению способности к устойчивой передаче между людьми, что чревато пандемией. Для предотвращения и контроля будущих вспышек критически важно усилить эпидемиологический надзор, отработать протоколы быстрого реагирования и активизировать разработку эффективных вакцин и противовирусных препаратов. Только путем принятия этих мер и укрепления международного сотрудничества мы сможем успешно противостоять угрозам, исходящим от вирусов птичьего гриппа, подобных H9N2.

Ключевые слова: птичий грипп; вирус гриппа А(H9N2); Вьетнам; пандемия; разработка вакцины; зоонозные инфекции; эпидемиологический надзор; генетическое секвенирование; биобезопасность; глобальное сотрудничество

Recently, Vietnam recorded its first human case of avian influenza A (H9N2), a low-pathogenic avian influenza virus (LPAIV) subtype distinct from the more commonly known A (H5N1) virus. The infected individual, who had underlying health conditions, was hospitalized on March 16, 2024, and remains under medical care. Genetic sequencing by the Hospital for Tropical Diseases and Pasteur Institute Ho Chi Minh confirmed the presence of A(H9N2) virus. The Centers for Disease Control and Prevention (CDC) is actively monitoring the situation and collaborating with both local and global partners [1].

Since its discovery in Wisconsin in 1966, the H9N2 subtype has spread widely among poultry populations, causing substantial economic losses. Human infections were first reported in Hong Kong in 1998, with subsequent cases mainly occurring in China and Hong Kong, along with reports from Bangladesh, Pakistan, and Egypt [2-4]. And till now, there have been a total of 99 instances of human avian influenza A (H9N2) infections worldwide, with two fatalities, documented by the WHO since 2015 [1]. From 2019 to 2020, routine surveillance in poultry farms and markets across mainland China yielded 22 isolated H9N2 viruses from chicken populations in seven provinces. Analysis revealed that these viruses showed genetic divergence, forming three distinct branches in the phylogenetic tree, indicating recent evolution. Further examination using hemagglutinin-inhibition assays revealed the emergence of three new antigenic groups among these H9N2 variants [5]. Surprisingly, the bivalent HN/SD vaccine candidate did not effectively protect chickens against these H9N2 viruses, underscoring the critical need for comprehensive analysis of H9N2 strains and vaccine development [5].

Avian influenza typically resides in wild water birds, and infected birds spread the virus through their saliva, mucous, and feces. While rare, humans can get infected when the virus enters their eyes, nose, and mouth, or is breathed in as shown in Fig. 1. These sporadic human infections usually occur in people with direct or close contact with sick or dead birds in areas where the virus is widespread among wildlife. Currently, there’s no evidence that this case in Vietnam is spreading from person to person or poses a threat to the U.S. public [6].

Avian influenza viruses, typically presenting as low-pathogenic strains in birds, are widespread across continents, with particularly high prevalence in Vietnam’s live bird markets. While these viruses usually cause only mild respiratory symptoms or asymptomatic infections in humans, they remain a concern due to their ability to combine with other influenza viruses and create new variants. Although H9N2 viruses generally cause mild illness in birds, they present a risk of cross-species transmission, especially through domestic poultry such as chickens and ducks, which serve as key vectors in viral spread and evolution. Historical cases have shown that these viruses can infect humans, typically resulting in mild respiratory symptoms [3, 5].

The recent case in Vietnam hasn’t altered WHO’s standard health recommendations for influenza surveillance and prevention. The organization maintains that every human infection case requires a comprehensive investigation. WHO advises people to avoid live animal markets and farms where they might contact sick animals or contaminated surfaces, and to practice regular hand hygiene through washing or using sanitizer. WHO has clarified that no additional precautions are necessary for travelers, though all novel influenza subtype infections in humans must be immediately reported. Based on current evidence, the organization sees no need for travel or trade restrictions. The most effective strategy for preventing a potential H9N2 pandemic remains containment at the source of infection [1, 7].

Vaccines are an effective tool against H9N2 infection in poultry. However, developing vaccines for both chickens and ducks is challenging due to variations in their immune responses. Inactivated whole-virus vaccines have shown promise in protecting chickens from clinical symptoms. Yet, the H9N2 virus undergoes antigenic drift, requiring continuous optimization of vaccines to match circulating strains. Vaccines for ducks are limited, with lower antibody responses compared to chickens. This underscores the urgent need for improved vaccines to enhance antibody levels and curb H9N2 spread among ducks [8-10].

Influenza A viruses are the only influenza viruses known to cause flu pandemics (i.e., global epidemics of flu disease). A pandemic can occur when a new and different influenza A virus emerges that infects people, can spread efficiently among people, and against which people have little or no immunity [11]. Studies indicate that avian influenza A viruses, including H5N1 and H9N2, coexist in Southeast Asian poultry, alongside human cases of H7N9, indicating the potential for interspecies transmission and human infections. While evidence suggests that H9N2 viruses can cross species barriers, definitive proof is lacking. Nonetheless, their transmission from poultry to humans, particularly in farms or bird markets, poses significant health risks. Recent research indicates that H9N2 viruses from mammals exhibit increased replication, raising concerns about treatment efficacy. Repeated human infections increase the likelihood of viral mutation and reassortment with seasonal flu, potentially resulting in highly transmissible variants. Furthermore, H9N2 may infect humans through intermediate hosts like pigs or dogs, heightening the pandemic threat. Although human-to-human transmission evidence is lacking, identifying unidentified H9N2 cases is vital. Limited immunity and severe symptoms in older adults emphasize the importance of early detection and control measures. Rapid diagnosis, stamp-out strategies in poultry, and stringent biosecurity are vital for pandemic readiness [7].

Although H9N2 strains cause mild respiratory symptoms in humans, these viruses have been infecting individuals sporadically since 1998 in various countries, predominantly in Asia. Due to their high prevalence in bird populations, particularly in Vietnam, their potential for zoonotic infections, constant evolution, and accumulation of mutations typical of adaptation to humans, it is imperative to take such threats seriously and initiate protective measures in advance. Timely detection, prompt vaccination, and response measures are vital to minimize the risk and protect local and world populations. Early action, learning from previous lessons, effective early detection, thoughtful vaccination, and strict biosecurity are paramount in avoiding the emergence of a pandemic strain. Collaboration with international partners and continuous monitoring plays a major role in reducing the threat associated with H9N2 and other influenza viruses capable of starting a pandemic.

Ethics approval and consent to participate. Not applicable.

Consent for publication. All authors have given their consent regarding the publishing of the manuscript.

Availability of data and materials. Not applicable.

Литература/References

1. World Health Organization. Avian Influenza A(H9N2) - Viet Nam. URL: https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON514 (date of accessed April 22, 2024).

2. Homme P., Easterday B. Avian influenza virus infections. I. Characteristics of influenza A - Turkey - Wisconsin - 1966 virus. Avian Dis. 1970; 14 (1): 66-74.

3. Seroprevalence of antibodies to avian influenza A (H5) and A (H9) viruses among market poultry workers, Hanoi, Vietnam. PLoS One. 2012; 7 (8): e43948.

4. Almayahi Z.K., Al Kindi H., Davies C.T., et al. First report of human infection with avian influenza A (H9N2) virus in Oman: the need for a One Health approach. Int J Infect Dis. 2020; 91: 169-73.

5. Zhang J., Huang L., Liao M., Qi W. H9N2 avian influenza viruses: challenges and the way forward. Lancet Microbe. 2023; 4 (2): e70-1.

6. Centers for Disease Control and Prevention. Vietnam Reports First Human Infection with Avian Influenza H9N2 Virus. Updated April 12, 2024. URL: https://www.cdc.gov/flu/avianflu/spotlights/2023-2024/vietnam-human-infection.htm (date of access April 22, 2024).

7. Song W., Qin K. Human-infecting influenza A (H9N2) virus: a forgotten potential pandemic strain? Zoonoses Public Health. 2020; 67 (3): 203-12.

8. Liu Y., Zhao D., Zhang J., et al. Development of an inactivated avian influenza virus vaccine against circulating H9N2 in chickens and ducks. Vaccines. 2023; 11 (3): 596.

9. Dong J., Zhou Y., Pu J., Liu L. Status and challenges for vaccination against avian H9N2 influenza virus in China. Life. 2022; 12 (9): 1326.

10. Sun Y., Yang C., Li J., et al. Construction of a recombinant duck enteritis virus vaccine expressing hemagglutinin of H9N2 avian influenza virus and evaluation of its efficacy in ducks. Arch Virol. 2017; 162: 171-9.

11. Centers for Disease Control and Prevention. Types of Influenza Viruses. Updated March 30. 2023. URL: https://www.cdc.gov/flu/about/viruses/types.htm#:~:text=Influenza%20A%20viruses%20are%20the,have%20little%20or%20no%20immunity (date of access April 22, 2024).

Материалы данного сайта распространяются на условиях лицензии Creative Commons Attribution 4.0 International License («Атрибуция - Всемирная»)