Understand what H3N8 avian flu is and the risks – 04/13/2023 – Health

A third case of avian flu caused by the H3N8 strain was confirmed this Tuesday (11) by the WHO (World Health Organization). The infection occurred in China, the same country where there were two other infections with the lineage in 2022. In the new case, the patient died.

WHO says the risks of the infection rising to levels of concern for global health are low. According to existing evidence, the virus does not have a high capacity for human-to-human transmission. An example of this is that, in the three cases already registered, there was no transmission to other people.

But the organization recommends that epidemiological surveillance measures be taken to monitor possible changes in pathogens. Influenza viruses, the same as the common flu, have a history of undergoing mutations that lead to changes in their ability to infect organisms, both human and other animals.

Avian flu mainly affects birds, both domestic and wild. But there are already cases of spread to other species of living beings: the H3N8 strain, for example, has already been reported in horses and dogs.

In humans, the first record of this subtype was in April 2022 and, a month later, the second confirmation came, both in China. Current information shows that the two patients were infected after direct contact with infected birds.

Now, the third case has been confirmed by the Chinese government. Symptoms in the 56-year-old patient began on February 22. In early March, she developed pneumonia. On the 16th of that month, she died.

Helena Lage, president of SBV (Brazilian Society of Virology) and professor at USP (University of São Paulo), says that the H3N8 found in humans from 2022 onwards has undergone changes compared to the same virus that was previously recorded in birds.

From these changes, the pathogen began to invade human cells – before, the ability was restricted to birds. “That is what causes concern”, says Lage.

Although it resulted in one death in the most recent record, avian flu is not necessarily fatal.

Typical symptoms of a flu are the most common among infected people. In some cases, the infection is even asymptomatic.

Depending on the patient’s history, he may be more susceptible to more severe conditions. This was the case of the last record in Chinese territory: the WHO reported that the patient already had a series of pre-existing health conditions, but did not specify what they were.

One factor that is open to question is how the virus jumped from the bird to the patient. The suspect is a live bird market that the lady attended before the symptoms started, but the definitive origin is still unclear.

“To better understand the current risk to public health, more information from human and animal research is needed,” the WHO said.

The residence of this last patient is also a hypothesis to explain the infection. The WHO cites that there was a large circulation of birds near her house. That is, the environment was conducive to possible contact with an animal infected by the virus.

Considering the suspicions, samples were collected at the patient’s home and at the poultry market. It was in the latter location that positive results for the H3 influenza virus occurred.

In the cases of the other two patients with records of infection in 2022, the main hypothesis is that transmission occurred through direct contact with infected birds.

In all three patients, there was no record of direct transmission from them to other humans. That is, the chance of becoming infected with the virus remains restricted to contact with infected animals.

For Lage, this demonstrates that, although the H3N8 has undergone mutations that allow the infection of human cells, the virus still does not have other alterations that make possible the ability to spread between people.

“Infection occurs by high exposure to the pathogen [em contato direto com um animal infectado]. The virus manages to multiply in the person, causes the disease, but does not have the necessary mutations to infect another person”, summarizes Lage.

another strain

In addition to H3N8, another strain of avian flu of concern is H5N1. Records for the latter are much higher when compared to H3N8.

According to PAHO (Pan American Health Organization), there were 868 humans infected with H5N1 between 2003 and 2023 worldwide. Of these, 53% died.

The organization even issued an alert at the end of March due to the outbreak caused by the virus in animals in different countries of the American continent – ​​Brazil is not included.

The increase in cases among animals can lead to the transmission of the virus to humans. For example, in January of this year, the second case of the infection in humans in America was identified. Before that, another record had taken place in April 2022.