The recent confirmation of a death from bird flu in the United States and the outbreak detected on a farm in Sintra revive questions about the H5N1 virus. Experts interviewed by SIC Notícias clarify myths, they explain the risks, the spread and how we can prevent new infections. They are in agreement regarding the weak transmissibility of the virus to humans but warn that “the main risk is that the virus could undergo mutations that make it more transmissible between humans, which could trigger a pandemic”.
A ensures that there is no record of infected people in Portugal and clarifies that the virus is not transmitted through the consumption of meat.
What is bird flu and where did it originate?
The H5N1 virus, identified in 1996, is the main cause of avian influenza, a disease that mainly affects birds, but can also infect mammals, including humans.
Miguel Castanho, scientist at the Institute of Molecular Medicine, explains that “avian flu is a viral disease that mainly affects birds, but presents a risk” for humans.
“The main risk is that the virus could undergo mutations that make it more transmissible between humans, which could trigger a pandemic.”
This primarily animal disease – a zoonosis – sporadically infects humans.“Since 1997, H5N1 has shown the ability to overcome the species barrier, increasing the risks of adaptation to the human organism”, second Lúcio Meneses de Almeida, Public Health doctor.
How did bird flu spread around the world?
Since its identification in 1996, o virus H5N1 circulates globallyhaving been detected in wild birds, poultry farms and even mammals, such as seals and sea lions.
As of 2021, H5N1 has expanded from Europe to the Americas, causing outbreaks in dairy cows and poultry. In 2022, the virus spread across South America, where it killed countless birds and marine mammals.
In March 2024, the virus was detected in US dairy cows and subsequently reached herds in 16 states. The virus was detected in dairy herds in three states in the last 30 days, according to the US agency
As for cases of human infection, in 2024, in the USA, 66 were confirmed and seven were identified as probable and all associated with variants of the virus present in poultry and livestock.
“Cows can act as vectors for the virus, carrying it without becoming seriously ill. On dairy farms, transmission can occur through direct contact, such as rubbing the eyes after handling the animals”, explains Miguel Castanho.
How is bird flu transmitted to humans?
- By direct contact with secretions and excretions of infected birds, namely respiratory secretions and feces
- Due to consumption of infected water and food
- By indirect contact through contaminated materials and products with the avian influenza virus (bird transport vehicles, equipment, clothing and footwear, animal products, insects, etc.)
- Aerogenously – spread of the virus in a certain geographic area through the wind.
Transmission of influenza from birds to humans occurs mainly through direct contact with sick birds or their droppings. Although person-to-person transmission is rare, The great fear is that the virus will undergo mutations that make it more easily transmissible between humans.
“If the bird virus mixes with the human flu virus in a person, it can cause recombination, creating a new strain adapted to humans. This scenario could trigger a pandemic.”
It is a virus that transmits mainly through the respiratory tract, but contagion is also possible through the eyes, where can enter the body, according to Miguel Castanho.
“Transmission is possible through close contact, if the virus has characteristics that allow infectivity. Flu, regardless of whether it is avian or human, is transmitted by contact, that is, over relatively short distances, less than one meter, explains Lúcio Meneses de Almeida.
“The infection of a human being will only have significance in public health if the virus acquires characteristics that allow it to be transmitted to more people. What has happened with H5N1 is that the virus is transmitted sporadically to humans and there have been no large chains of transmission. In 2003, there were cases, but they did not spread,” highlights Lúcio Meneses de Almeida.
Is it safe to consume meat and eggs?
Yes. Cooking food eliminates the virus and the acidic environment of the human stomach neutralizes it.
Miguel Castanho explains that “Viruses are fragile and destroyed by heat during cooking. Furthermore, our digestive system effectively neutralizes any viral traces.”
“Consuming meat or eggs from infected animals does not pose a risk, as the temperature during cooking destroys the viruses. Furthermore, the human digestive system is a hostile environment for viruses.”
“In relation to raw eggs, ingesting an infected egg has practically no chance of resulting in infection, as the human digestive system is effective in destroying the virus.”
How to prevent an H5N1 infection?
The best way to prevent transmission of H5N1 is limit contact with infected wild or domestic birds and reinforce hygiene measures on poultry farms. The most drastic measure is the slaughter of all birds on the identified farm.
Key prevention measures include:
“There are . When a case of bird flu appears on a farm, you isolate the farm, no birds come in, no birds go out and you track everyone who works there. This is the most immediate measure. It’s radical, but it’s what has to be done to try to contain the logo there and break any chain of contagion”, says Miguel Castanho.
Lúcio Meneses de Almeida states:“Pandemics are global phenomena. Only a coordinated response can reduce the impact of any public health crisis.”
Efficiency and lethality of the virus
H5N1 is, for now, not very efficient in transmitting between humans. However, the greatest danger lies in the possibility of genetic recombination. Miguel Castanho warns of the scenario in which a person with human flu is simultaneously exposed to H5N1.
“If recombination occurs, a hybrid virus may emerge, which is more efficient at transmitting between humans.”
This type of mutation could occur in regions with high population density, where humans, birds and other animals live in close proximity, such as live animal markets in Asia, as Lúcio Meneses de Almeida highlights.
“H5N1 is a virus very inefficient in terms of transmission (…) aIt still transmits very poorly to the human species, but this does not mean that the virus cannot acquire characteristics that make it more transmissible.”
Vepidemiological surveillance epreview of the evolution and lethality of the virus
It is essential to maintain epidemiological surveillance to identify changes in the behavior of the virus and prevent possible outbreaks. “The evolution of the virus is unpredictable, so it is necessary to be prepared for different scenarios”, underline Miguel Castanho.
“Epidemiological surveillance has two dimensions: clinical and laboratory. Clinical allows us to identify cases and the severity of the disease, while laboratory surveillance allows us to characterize the virus genetically and predict its evolution. There are molecular indicators that help predict evolution, but samples are collected with some delay in relation to the actual evolution of the virus, explains Lúcio Meneses de Almeida.
Contingency plans to prepare for the worst case scenario
Contingency plans must be drawn up in advance, based on possible threats, even without knowing what the exact disease will be. “Preparation is essential to prevent society from being caught by surprise”, highlights Lúcio Meneses de Almeida, because “There will surely be a new pandemic”.
Epidemiological situation in Portugal
At the moment, there are no cases of bird flu in humans in Portugal, but it is important to maintain vigilance so that, if they occur, they can be controlled quickly. Constant monitoring is crucial to prevent any outbreak from spreading.
Since 2005, there have been wild bird sentinel surveillancewhich are the natural reservoir of the virus. Nthe current epidemiological season, were confirmed in Portugal, tcattle cases of infection by the highly pathogenic avian influenza virus in wild birds: in a yellow-legged gull, in Quarteira, Loulé, in a dark-winged gull, in São Jacinto, Aveiro, and in a yellow-legged gull in Olhão, Faro.
“One thing that is difficult to control is wild birds, which are the reservoir for these viruses, and it is not exactly easy to control migratory birds. You can carry out sentinel surveillance, capture one bird or another, and see if it is infected or not.”
Will bird flu be the next pandemic?
The H5N1 virus currently has a high lethality rate that limits its transmission. However, the danger lies in the possibility of the virus evolving and undergoing mutations that increase its transmissibility between humans. This scenario, although still hypothetical, could trigger a pandemic with devastating consequences.
Epidemiological surveillance, effective contingency plans and international cooperation are therefore essential to prevent small outbreaks from turning into a global public health crisis.
“It is essential to put out all small fires before the entire forest burns down”alert Lúcio Meneses de Almeida, highlighting that, although there is no reason for immediate alarm, it is crucial to be prepared for the worst and hope for the best, in a global context of multiple threats, including pandemics, wars and nuclear instability.
