We are currently attending worst bird flu outbreak in history, which is causing massive deaths of birds and is beginning to affect many mammals. The scenario is ominous as there are concerns that another major global outbreak could be triggered.
Raul Rivas Gonzalez
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Professor of Microbiology, University of Salamanca
But what do we know about the H5N1 bird flu virus?
What is the highly pathogenic H5N1 avian influenza virus?
There are four types of seasonal flu viruses, called virus influenza A, virus influenza B, virus influenza C y virus influenza D. All known flu pandemics have been caused by influenza A viruses, which are solely responsible for bird flu, as well as causing common human flu and swine and equine flu.
The ancestral reservoir of all type A are waterfowl, particularly those included in the order Anseriformesto which geese or ducks belong, and in the order Charadriiformes, where gulls are found.
Type A influenza viruses They can be divided into different subtypes depending on the genes that constitute the surface proteins: hemagglutinin (H) and neuraminidase (N). Both proteins are the antigens that are recognized by the host’s immune system.
There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes, H1 to H18 and N1 to N11, respectively. This implies that there are potentially dozens of combinations of the influenza A subtype, H5N1 being one of them. Within each subtype there is considerable variability, which affects the pathogenicity of the strain.
What is the scope of the current outbreak?
During the year 2020, from previously circulating viruses, H5N1 viruses from clade 2.3.4.4b emerged highly pathogenic avian influenza (HPAI). This clade spread predominantly through migratory birds to many parts of Africa, Asia, and Europe. And they became a threat to animal and human health across the planet.
At the epizootic – the equivalent of an epidemic but in animals – caused unprecedented numbers of outbreaks in domestic poultry and deaths in wild birds. Between October 2021 and December 2022, Europe suffered a total of 2,918 outbreaks in poultry and 378 outbreaks in captive birds, it recorded. 4,480 infections in wild birds and slaughtered 50 million birds in the affected establishments.
These viruses crossed into North America in late 2021, and subsequently into South America in the fall of 2022.
Can it infect mammals?
In recent weeks, more than 600 sea lions have been found dead or dying on Peruvian beaches in what has been the first event of Mass mortality of wild mammals due to H5N1 avian influenza in South America.
And it is not exceptional. Some of the recent genotypes have caused severe infections with neurological signs in mammals such as badgers, bobcats, coyotes, dolphins, ferrets, foxes, bobcats, opossums, otters, pigs, porpoises, raccoons, dogs, and mink.
Specifically, the H5N1 viruses of the 2.3.4.4b clade detected at the end of 2022 in mink from a Spanish farm have a rare mutation (T271A) in the PB2 gene that may have implications for public health. In fact, the same mutation is present in the avian-type PB2 gene of the 2009 pandemic swine-origin influenza A(H1N1) virus (H1N1pdm).
In vitro studies suggest that viruses with the T271A mutation could more readily infect mammals, including humans.
Is it dangerous for humans?
The H5N1 Highly Pathogenic Avian Influenza (HPAI) Virus of Asian origin was first detected in 1996 in geese in China, and for the first time in humans in 1997 amid an outbreak originating in poultry in Hong Kong.
Worldwide, from January 2003 to January 2023, 868 cases of human infection with the avian influenza A(H5N1) virus have been reported in 21 countries. Of these, 457 were fatal, representing a mortality of 53%.
Between 2020 and 2022, the total number has been 7 cases and 2 deaths.
Virus sequences from these human cases, where available, did not show markers for mammalian adaptation or resistance to antiviral drugs used against H5N1 such as oseltamivir and baloxavir.
Fortunately, at the moment this virus does not have the ability to easily bind to receptors in the respiratory tract superiors of human beings, which implies that contagion is difficult.
Another piece of good news is that, to date, no person-to-person transmission has been detected. Based on available information, human population immunity against clade 2.3.4.4b is expected to be minimal.
Who is more at risk?
The people most vulnerable to infection are those who directly or indirectly maintain a close and regular contact with birds (domestic, wild or captive). For example, poultry farmers, veterinarians, slaughterers, infected farm staff, etc.
For this reason, the use of adequate personal protective equipment (PPE) and other protection measures is recommended to avoid zoonotic transmission in these operators.
What symptoms does bird flu present in humans?
The main clinical symptoms of avian influenza in humans are fever over 38 degrees, muscle pain, shortness of breath, cough and general malaise. In addition, most patients have a significant decrease in lymphocytes and abnormalities in liver enzymes.
The first symptoms appear 2 to 8 days after infection.
Are there treatments available?
It is recommended that infected people receive treatment as soon as possible with antiviral drugs. Some of the recommended treatments in the first instance are oseltamivir, zanamivir, peramivir y baloxavir.
Are there vaccines?
Candidate vaccine viruses against different H5 clades are currently under development and are updated regularly, twice a year, during WHO Vaccine Composition Meetings.
At the moment, there are candidate vaccine viruses that have passed relevant safety tests, such as A(H5N8) clade 2.3.4.4b made from A/Astrakhan/3212/2020 and an A(H5N1)-like virus, A/ chicken/Ghana/AVL-76321VIR7050-39/2021.
The Centers for Disease Control and Prevention The US has produced an experimental vaccine virus nearly identical to the hemagglutinin (HA) protein of the H5N1 clade 2.3.4.4b viruses detected in recent months in birds and mammals. If necessary, it could be used to produce a vaccine for people.
Furthermore, in November 2022, a paper published in Science showed that an mRNA vaccine in development protected mice and ferrets against 20 known subtypes of influenza A and B viruses.
What preventive measures are useful?
Some simple measures are the following:
Avoid direct and close contact with sick or dead wild birds, poultry and wild animals.
Do not eat poultry or poultry products that are raw or undercooked, including raw eggs. Consumption of properly cooked poultry, poultry products, and eggs is safe.
Wash hands with soap and water and extreme hygiene after touching birds.
Don’t touch your mouthnose, or eyes after contact with birds or surfaces that may be contaminated with droppings or fluids from domestic or wild birds.
In addition, it is advisable that people who may be exposed to sick birds get a seasonal flu shot.
Does it have the potential to cause a pandemic?
It’s hard to predict when the next flu pandemic will occur and what virus will cause it. To date, there is no evidence of sustained person-to-person transmission of highly pathogenic H5N1 virus and no evidence of genetic rearrangement with human influenza A viruses.
However, highly pathogenic H5N1 viruses are constantly changingand the numerous current outbreaks increase the possibility of human exposure to infected birds or adaptation of the virus to other mammalian species that may act as an intermediate species.
Therefore, it is essential to maintain prevention, surveillance, detection and control work on the present and future episodes that the H5N1 virus will lead, because the current ones will not be the last ones we will see.
This article has been published in The Conversation.