As far as public health agencies know, avian influenza in dairy cows has so far infected only three farm workers in the United States. All had mild symptoms.
But that’s no guarantee that the virus known as H5N1 will remain benign if it begins to spread in humans. In fact, gathering evidence from the animal kingdom and data from other parts of the world suggests the opposite.
Some dairy cows never recover from H5N1, and died or were massacred because of. Infected terns appear disoriented and unable to fly. The baby elephant seal had difficulty breathing and trembled after being infected with the virus. Infected cats blindgo in circles; two-third their die.
“I certainly don’t think there’s any room for complacency here,” said Anice Lowen, a virologist at Emory University.
“H5N1 is a highly pathogenic influenza virus and we need to be very concerned about this if it jumps to humans,” she said.
According to one study, in minks experimentally inoculated with the virus through their eyes — the presumed route of infection in farmworkers in the United States — the virus rapidly spread to the respiratory tract, lungs, and intestines. their stomachs and brains. report announced on Wednesday.
Other studies have found similar patterns in the Rats eat contaminated milk. The findings suggest that entry through the eyes or digestive system may not ultimately make the virus less dangerous.
H5N1 has shown promiscuous behavior, Get a new server quickly — wild birds and fowl, rats and bears, cats and sea lions. Since its discovery in 1996 in Hong Kong, it has also infected nearly 900 people.
An older version of the virus circulating in Asia kills about half of those infected.
Of the 15 people known to have the virus currently spreading in livestock, one person in China has died and another has been hospitalized. Two patients in Chile and Ecuador had severe symptoms. Four Americans – one last year and three infected in the latest outbreak – fared better.
Importantly, no form of avian influenza virus appears to spread effectively from person to person. That’s no guarantee that H5N1 won’t acquire that ability, said Yoshihiro Kawaoka, a virologist and avian flu expert at the University of Wisconsin-Madison.
“I think this virus is clearly changing its characteristics, because we have never seen an outbreak in cows,” Dr. Kawaoka said. Conjunctivitis, also known as pink eye and the main symptom in two out of three farm workers, is not a typical symptom of H5N1 infection. The appearance of the virus in the mammary gland – in cattle and even in non-lactating mice – was also unexpected.
The concern now is that as H5N1 continues to infect mammals and evolve, it could create the mutations needed to spread effectively between humans, causing another pandemic.
Erin Sorrell, a virologist and senior scholar at the Johns Hopkins Center for Health Security, said the influenza’s incubation period is two to four days and the person-to-person version can spread far before when cases are detected.
“If it spreads to the public, it will be too late,” she said. “We missed the train.”
The flu is often most serious in older adults and children under 5 years old. (The 2009 swine flu outbreak was not as devastating as feared, however it was was killed nearly 1,300 children.) The severity of the disease also depends on how much virus the infected patient is exposed to and for how long, as well as the route of entry, their genetic background, and their general health.
Infected people often have fever and respiratory symptoms; Some cases progress rapidly to pneumonia or death. If avian flu viruses adapt to humans, the world will need billions of doses of vaccines and antiviral drugs to prevent these consequences.
The federal stockpile contains four flu antiviral drugs, but the drugs must be taken within 48 hours of symptoms appearing to be effective. One Recent reviews found too little evidence to rate the effectiveness of three of the four drugs, including the commonly used oseltamivir, sold under the name Tamiflu.
Some new versions of H5N1 have mutations that make the virus resistance to oseltamivir and come two other drugs, but fortunately, those changes have not been widely transmitted in animal populations. No mutations were observed for the fourth drug, baloxavir.
But according to David Boucher, infectious disease director for the federal Strategic Preparedness and Response Administration, there are only a few hundred thousand doses of that drug in the stockpile.
Vaccines are a better option for stopping the pandemic, but enough doses will be difficult to get for months at least. Even if global production of seasonal influenza vaccines were switched entirely to vaccines against H5N1, the number of doses produced would still be enough to under two billion people, let’s say two amount is necessary for every person.
In the United States, the national stockpile contains hundreds of thousands of doses of vaccine that could be given to at-risk people, including children. Dr. Boucher said the companies contracting with the government could produce more than 100 million doses in the first 130 days.
Officials recently announced that they had taken steps to have 4.8 million doses available that could be bottled without disrupting seasonal flu vaccine production.
But most of these plans will only be useful if the virus cooperates.
Since H5N1 first appeared, it has branched into many forms, and scientists have created a library of 40 viruses called vaccine candidates to match. Todd Davis, a virologist at the Centers for Disease Control and Prevention, said getting them ready to go saves crucial time because creating a new candidate can take three months.
So far, he said, the virus has changed only minimally, especially the part of the virus that binds to human cells, called hemagglutinin or HA.
Some experts note that if the virus is to spread between people, it must first change significantly. “If this virus jumps to humans, you can bet that the HA will change, because right now the HA of this virus doesn’t bind effectively to cells,” said Scott Hensley, an immunologist at the University of Pennsylvania. People”.
Traditional flu vaccines are made by growing the candidate virus in eggs or in mammalian cellsboth have many potential problems: The virus may not evolve fast enough or it may mutate too much as it evolves.
In 2009, this candidate virus grew well in eggs but evolved into a virus that was a poor match for the wild H5N1 virus, causing long delays in distribution to the public. “By the time the vaccine inventory was produced and distributed, the initial wave of the pandemic had subsided,” Dr. Hensley said.
CSL Sequiris, the leading manufacturer of seasonal flu vaccines, does Cell-based H5N1 vaccine approved by the Food and Drug Administration.
In the event of a pandemic, once CSL receives a vaccine candidate that matches the circulating virus, it can supply 150 million doses, said Marc Lacey, the company’s chief executive officer. to Americans within six months. (The company also has contracts with 19 other countries.)
But 150 million doses would only protect about 1 in 5 Americans. Federal officials also discover mRNA avian flu vaccines, as the Covid pandemic has illustrated, can be produced very quickly to protect both cows and humans. Dr. Hensley’s team is testing mRNA vaccines in cows.
Officials are still hesitant to deploy vaccine for cows Because of trade concerns, experts say: Some countries ban the import of products from vaccinated birds and animals.
But vaccinated cows Experts say it will limit the risk to farm workers and other cows, while also limiting opportunities for the virus to continue to spread and develop.
So far, federal officials have also been reluctant vaccinate farm workerssays the risk remains low.
Dr. Lowen of Emory said the real danger is if a farm worker becomes infected with both H5N1 and the seasonal flu virus. Influenza viruses are very good at swapping genes, so co-infection would give H5N1 the opportunity to acquire genes that would allow it to spread between people as efficiently as seasonal flu.
Dr. Lowen said this possibility underscores the importance of vaccinating farm workers: “Whatever we can do to limit seasonal transmission in people occupationally exposed to H5N1 can all actually reduce the risk.”
