A third farm worker in the United States has been found to have bird flu, raising concerns about an outbreak among dairy cows that was first identified in March.
Federal officials announced Thursday that the worker was the first case in the outbreak to show respiratory symptoms such as coughing, sore throat and watery eyes – symptoms that typically increase the chance of spreading the virus to others.
The remaining two suffered only severe eye infections that were likely caused by exposure to the contaminated milk.
All three people had direct contact with dairy cows and so far none of them have transmitted the virus to anyone else, Dr. Nirav Shah, principal deputy director at the Centers for Disease Control and Prevention, said at a press conference.
This suggests that the virus, called H5N1, has not acquired the ability to spread between humans and the threat to the general public remains low, Dr Shah said.
“This latest case does not change CDC's assessment of the risk level of H5N1 influenza to the general public,” he added. “We need to remain vigilant and not alarmed.”
But the case highlights the ongoing risk to agricultural workers, Dr Shah said: “Our number one priority in this response is protecting the health of agricultural workers.”
This is the second case in Michigan, but the person worked on a different farm than the farmworker identified last week as infected. All three people infected so far have been treated with the antiviral drug oseltamivir, sometimes sold as Tamiflu, according to officials.
There were few other details. available, to the dismay of some experts.
“There is no excuse for a lack of testing, transparency and trust,” said Rick Bright, CEO of Bright Global Health, a consulting firm focused on improving responses to public health emergencies.
He noted that federal officials have been “months delayed in sharing viral sequence data.”
“This is how pandemics start,” he said.
Experts say it's not surprising to see a third case among farm workers, as they work closely with dairy cows. The new flu virus often causes respiratory symptoms without spreading to others, Dr Shah said.
Angela Rasmussen, a research scientist at the Vaccine and Infectious Diseases Institute at the University of Saskatchewan in Canada, said the different symptoms in this latest patient could be due to different radiation doses, route of exposure, genetic or medical predispositions or a combination of these.
Still, she said it's important to have more information about how infected people are infected and whether the virus has evolved to spread more easily between people.
Because the amount of virus recovered from the patients was so small, genetic analysis of the virus that infected the workers may be difficult.
“But every time a virus is able to replicate in the human body, it opens the door for it to adapt to humans, acquire the molecular characteristics that allow it to replicate in the respiratory system and then spread from person to person,” said Seema Lakdawala, a virologist at Emory University in Atlanta.
Officials are monitoring about 350 people for possible infection, about 220 of them in Michigan, and so far a relatively small number of farmworkers — about 40 — have agreed to be tested.
The USDA announced Thursday it was setting aside $824 million in new funding to quickly detect infections in poultry and livestock. The department is also launching a voluntary program for producers to mass-test milk and allow virus-free herds to be transported across state lines without testing each individual cow.
Federal researchers have completed analysis of 109 beef samples and found the virus in only one, reported last week, officials said at a briefing.
Experts said federal authorities could do more to protect farmworkers and the public.
“The vaccines in the national stockpile should be distributed to veterinarians and dairy workers who want to be vaccinated,” Dr Lakdawala said. “We have an opportunity to reduce human infections and we need to do it now.”
