A recent outbreak of avian flu at a mink farm has reignited concerns about further spread of the virus to humans.
Scientists have tracked this bird flu virus since the 1950s, although it was not considered a human threat until a 1997 outbreak in Hong Kong among visitors to live poultry markets.
As bird flu affects a wider range of different animals, such as those in mink farms, there is concern that the virus could evolve to spread more easily among humans and potentially start a pandemic.
Scientists say another strain of bird flu may have been behind the devastating influenza pandemic in 1918-1919, and avian viruses played a role in other influenza pandemics in 1957, 1968 and 2009.
Even so, the risk to the general public is now low, said Dr. Tim Uyeki of the US Centers for Disease Control and Prevention.
A glimpse of the bird flu virus and why it is getting new attention:
What is bird flu?
Some influenza viruses primarily affect humans, while others are primarily found in animals. For example, there have been cases of influenza occurring in dogs, along with a swine virus or swine flu. And then there are avian viruses that spread naturally in wild waterfowl like ducks and geese, and then in chickens and other domesticated birds.
The bird flu virus that is attracting attention today – type A H5N1 – was first identified in 1959 by researchers studying an outbreak of chicken flu in Scotland. Like any other virus, it evolves over time and creates newer versions of itself.
In 2007, this virus has been found in more than 60 countries. In the US, it was recently detected in wild birds in all states and in commercial poultry farms or backyard flocks in 47 states. Since early last year, tens of millions of chickens have either died from the virus or been killed to stop the outbreak from spreading, one of the reasons egg prices have soared.
How often do people get bird flu?
The 1997 outbreak in Hong Kong was the first time bird flu was blamed for a serious disease in humans. Six of the 18 infected died. To contain the outbreak, the Hong Kong government closed the live poultry market, killed all the birds in the market and stopped importing chicken from southern China. It works for a while.
Symptoms are similar to other cases of the flu, including cough, body aches and fever. Some people have no visible symptoms, but some develop severe symptoms. Life-threatening pneumonia.
Globally, nearly 870 human infections and 457 deaths in 20 countries have been reported to the World Health Organization. But the pace has slowed, and over the past seven years there have been some 170 infections and 50 deaths. In most cases, infected humans get it directly from infected birds.
The first and only case in the US occurred last April. An inmate in the labor program caught him while killing infected birds on a poultry farm in Montrose County, Colorado, in the western part of the state. His only symptom was exhaustion and he recovered.
Can it spread between people?
In some cases, researchers have concluded that the bird flu virus appears to have spread from one person to another. This has happened in Thailand, Vietnam, Indonesia, China and Pakistan, most recently in 2007.
In each cluster, it spreads to the families of the sick at home. Scientists don’t think it can be spread as easily as the seasonal flu through casual contact. But viruses mutate and change. Scientists are concerned about the increased opportunities for bird flu to mix and mutate with other flu viruses in infected humans or animals, facilitating transmission to humans.
It won’t be long before that happens, and then we’re going to get into a very difficult situation, says Dr. Louis Ostrosky, head of the Department of Infectious Diseases and Epidemiology at the University of Texas Health Science Center at Houston.
The CDC’s Wecki said he was most concerned about H5N1 during the previous cluster. Such person-to-person spread does not appear to be occurring at this time, he said.
What happened on the mink farm?
Recent concern among public health experts has been driven in part by the discovery of the infection in a variety of mammals. The growing list includes foxes, raccoons, skunks, bears and even marine mammals such as seals and dolphins. Officials in Peru say three sea lions found dead in November have tested positive and the recent deaths of hundreds of lions can be linked to bird flu.
Then, last month, a European medical journal reported an October outbreak of avian flu in a mink farm in Spain with nearly 52,000 animals, where the disease was spreading like wildfire.
Mink that are fed poultry and wild birds in the region have contracted bird flu. But researchers say that however it started, they believe the virus then spread from mink to mink a worrying scenario. None of the workers were infected despite wearing masks as part of the COVID-19 precautions.
Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health, said viral outbreaks were being monitored for mutations that could make them more easily transmissible to humans and possibly between humans.
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