Birds and cattle have a tendency to spread bird flu
Does H5N1 spread through the air between ferrets and pigs? “It’s not normal,” says MacIntyre
They also found evidence the virus had spread through the air between ferrets in different cages, but they didn’t see severe illness in the animals who were infected in this way. It’s possible there wasn’t enough virus being transmitted to “overcome the immune barriers that would prevent infection,” he says.
The results are “very preliminary” and what happens under controlled lab conditions isn’t necessarily indicative of what can happen in the wild, he says. “We certainly don’t see any changes that would suggest that there’s any way to support efficient airborne transmission.”
Scientists from the Centers for Disease Control and Prevention analyzed how a human case in Chile spread from ferret to ferret after taking an isolate of the virus.
They found that variant had a “high capacity to cause fatal disease” among the animals and that it showed enhanced ability to replicate in human cells cultured in the lab, but “did not exhibit productive transmission in respiratory droplets” or via contaminated surfaces when tested in animals.
MacIntyre describes the infections in animals as not normal, and says that urgent investigation is necessary to make sure that H5N1 doesn’t spread between pigs or ferrets.
This kind of reasoning may not explain some mammal die-offs, such as the deaths of seals and sea lions in South America, or the outbreak of mink in Spain.
There are still big questions about exactly how bird flu plays out in cattle, since it’s only now being followed closely. “There certainly are many mutations that occurred with this jump from wild birds into cattle and we don’t necessarily understand what they mean,” says Hill.
The outbreak of the H5N1 bird flu in a dairy worker in Texas, which is potentially the next pandemic or bird flu?
These two changes – plus mutations in the PB2 gene to support replication – would all need to come together to support efficient spread in mammals, she says. She says that there’s possibly other factors that we don’t know about.
Lowen says that recent research shows that the virus needs to recognize human airway receptors in order to stay healthy, and that it doesn’t fall apart during air-to-air transmission.
Over the last several years, there’s been a lack of evolution of this function when the virus spilled into mammals, says Anice Lowen.
“That’s considered basically a main barrier that prevents this from becoming a virus that could spread efficiently between people,” says Darwyn Kobasa, head of high containment respiratory viruses at Canada’s National Microbiology Laboratory.
“It takes a very, very high dose,” he says, “It’s probably not just exposure to infected poultry – it’s exposure to processes that aerosolized the virus.”
Last Friday, a health alert from the Centers for Disease Control and Prevention pinged its way across the inboxes of clinicians and state health departments all over the US. The message described how a dairy farm worker in Texas had contracted H5N1, the highly infectious strain of avian influenza, or bird flu, that’s currently circling worldwide. The dairy worker was caught with the virus by cattle.
“It needs a handful [of markers] coordinated across multiple different gene segments for it to really be this breakthrough and the next pandemic,” she says.
Genetic sequencing of the virus in the Texas dairy worker showed it had undergone a mutation in a gene, PB2, that commonly gets affected when the virus infects mammals.
“We need to be on top of it, because we are at a sort of precipice where something interesting or unfortunate could happen,” says the senior research fellow at the Center for Pathogen Genomics at theUniversity of Melbourne.
On the Kuiken paradox in cattle influenza: How strange is it to be able to get into the herd of a cow?
“I want to emphasize how unusual it is,” says Thijs Kuiken, the professor of comparative pathology. “In other mammalian species with influenza viruses, it’s primarily a respiratory disease, which doesn’t seem to be the case in these cattle.”
Instead, federal health officials investigating the outbreak suspect some form of “mechanical transmission” is responsible for spreading the virus within the herd. This may be happening during the process of milking the cows, a theory supported by the fact that high concentrations of virus are being found in the milk.
The CDC’s alert urged doctors to be vigilant and consider H5N1 a possibility in any patients presenting with acute respiratory symptoms or sore eyes who had recently been in contact with animals.
A study of a human case in Chile’s Chile has found that the coronavirus had spread through the air between ferrets in different cages. However, scientists said it was possible that there wasn’t enough virus being transmitted to “overcome the immune barriers that would prevent infection”. The virus had mutated in a gene called PB2 that gets affected when it infects mammals.