The death of a person from bird flu in Mexico has sparked international concern, with scientists scrambling to identify the source of infection.
The 59-year-old, whose gender was not given, had been hospitalised in Mexico City and died on April 24 after developing a fever, shortness of breath, diarrhoea, nausea and general discomfort, the World Health Organisation (WHO) said.
It was the first laboratory-confirmed human case of infection with an H5N2 virus globally and the first avian H5 virus reported in a person in Mexico, according to the WHO.
A separate strain, named H5N1, has infected humans in several countries.
The WHO said that the infected person had multiple health conditions that made them more susceptible to severe illness.
But how worried should we be about bird flu spreading?
What is bird flu?
Bird flu, which is also known as avian influenza, is a highly contagious viral disease affecting the respiratory and digestive system of many species of birds. In rare cases, it can affect humans.
According to the WHO, there have been 889 H5N1 infections in humans from 2003 to 2024. Of those, 463 or 52 per cent resulted in death.
So far there is evidence of wild bird-to-cow, cow-to-cow, cow-to-poultry, and one case of cow-to-human transmission.
However, there is no evidence of human-to-human transmission.
Humans who have been infected with bird flu in the past have usually worked in poultry farms or been in contact with infected birds.
What are the symptoms of bird flu?
Bird flu infections generally happen when the virus makes direct contact with the eyes, nose or mouth.
The virus can also be inhaled through droplets, small aerosol particles or dust.
Some strains of bird flu can cause symptoms similar to severe human flu, such as a fever, cough, tiredness and muscle aches.
Severe infections can cause pneumonia and acute respiratory distress syndrome.
Has bird flu been found in the UK?
The first human case of bird flu was confirmed in England in January 2022.
The person, from the South West of England, acquired the infection from very close, regular contact with a large number of infected birds, which they kept in and around their home over a prolonged period of time.
Earlier this year, the UK Health Security Agency created a group of 26 experts to model a potential outbreak of H5N1 if the virus were to evolve to spread between humans.
Policies being examined by the group include the introduction of lateral flow tests for the disease.
Should we be worried?
Scientists are confident that bird flu does not currently represent a significant global health threat.
This is because the virus has not yet adapted to spread between humans. So far, it has only jumped from animals to humans.
There has only been one “likely” case of human-to-human transmission in 2006 in Indonesia.
If the virus were to evolve to be able to spread between humans, then it could potentially lead to another pandemic – but this remains a remote possibility.
Ian Jones, Professor of Virology at the University of Reading, said: “It is impossible to generalise from a single case. However, as H5N2 is present in Mexico and the infected individual had underlying medical conditions, which may have contributed to the outcome, it would be reasonable to suppose this is a one-off case of zoonotic transfer with no potential to spread.
“This would be consistent with previous examples of occasional avian influenza infections in people. Unless or until there is evidence of strain adaptation or sustained transmission, the risk to the population is very low. The case should act to reinforce the importance of monitoring and eradicating outbreaks in poultry as soon as they occur."
But Professor Sir Peter Horby, Director of the Pandemic Sciences Institute at the University of Oxford, said the case was “one more in a series of developments that collectively could be considered a red flag”.
“In the last few years H5N1 has infected multiple mammalian species, including an ongoing and evolving outbreak in dairy cattle in the USA, and sporadic human infections with H5N1 have been detected in multiple countries including Cambodia, Chile, China, Vietnam, Australia, USA and the UK,” he said.
Does bird flu pose a threat to other animals?
Bird flu does represent a significant threat to wildlife. Up to 90 per cent of chickens who contract the disease die and the virus has killed half a million birds in Chile and Peru since 2022.
In February, a deadly type of bird flu was confirmed on the mainland of Antarctica for the first time. Scientists said it created a potential risk for the southern region’s huge penguin colonies.
Only 131 cases of avian flu have been recorded in mammals since October 2021.
