Avian flu (H5n1 virus) has been around since the 1990s, detected in wild birds in China such as swans; and then spreading poultry around the world; before appearing in mammals such as cows in recent months.
Avian flu is caused by several influenza viruses, just like the seasonal flu that spreads every winter.
However, with the odd exception, the disease is only spread between animals; or from animal to human.
Human-to-human transmission is thought to be limited and unsustainable.
Since the 1990s, there have been 900 known cases in humans — nearly half of whom have died.
Israeli workers of Agriculture Ministry dispose chicken eggs at a quarantined farm in the northern village of Margaliot, Israel on 3 January 2022. Photo courtesy of AAP - Charlie Neibergall and EPA/ATEF SAFADI Credit: ATEF SAFADI/EPA
The disease was detected in a 59-year-old man, with a chronic health condition, who died in a Mexico City hospital on April 24, a week after being treated for fever, shortness of breath, and diarrhea.
It's unclear how he could have contracted bird flu, and Mexican health officials said he had no history of exposure to poultry or other animals.
