A New Strain of Bird Flu Jumps From Animals to Humans

China reports the first cases—and deaths—in people from a new strain of influenza called H7N9.

HealthMap tracks outbreaks around the world, including the new report of the H7N9 strain of influenza in three people in Asia. (Image courtesy of HealthMap/Disease Daily)
The Disease Daily is a publication from HealthMap at Boston Children's Hospital.

Until this weekend, H7N9 was a type of influenza A virus that was known to only infect birds. On Sunday, March 31, HealthMap picked up a story from China that told of three human infections of H7N9. These are the first recorded human cases of H7N9.

How a Virus Changes the World

According to Chinese news, the first cases were found in Shanghai and Anhui. The first reports collected by HealthMap indicate that a father and two sons arrived at a Shanghai hospital in late February with severe pneumonia. According to Malaysia’s The Star, the father died on March 4. The sons were diagnosed with an unexplained pneumonia. A fourth Shanghai resident became ill and died on March 10. A fifth person, from the Anhui province, became ill on March 9 and remains in critical condition.  

The Chinese version of the U.S. Centers for Disease Control reportedly confirmed three cases of H7N9 by lab samples on March 30. These three cases include the two deaths from Shanghai and the case in Anhui. Health officials are monitoring close contacts of those who have been infected and have not yet detected anything abnormal. The cases reported symptoms of high fever, cough, and respiratory tract infection in the early stages of the disease. According to the Chinese agency, five to seven days after disease onset the patients developed severe pneumonia and respiratory difficulties, which led to death.

Bird Flu Transmission: How Many Mutations Away?

Here's a quick brush-up on the ever-confusing influenza virus: There are three types of influenza viruses—A, B, and C. Influenza A and B typically cause seasonal flu. Easy enough. Let’s take it to the next level, then: Influenza A can be broken down into different subtypes. These subtypes change over the years, through what's called antigenic shift and antigenic drift, creating different strains. Antigenic shift refers to the changing of the hemagglutinin and neuraminidase (the H and N in the names of different strains of the flu) proteins on the influenza virus. These proteins allow the virus to attach to host (human) cells and infect them. Different combinations of these proteins (H1N1, H7N9, H3N2, etc.) essentially create a new virus.

Also changing the virus is the process of antigenic drift, which refers to little changes that slowly occur over a long period of time. The H1N1 subtype of influenza has different variants due to these small evolutions.

Is This Scary New Virus the Next SARS?

Birds are the natural host for influenza A viruses, though these viruses can infect several different animals, including humans, horses, pigs, and dogs. The influenza virus currently in the news is H7N9, which is an influenza A and avian (bird) influenza virus. Avian influenza viruses are separated into two groups: highly pathogenic avian influenzas and low pathogenic avian influenzas. In birds, low pathogenic influenza may cause a mild illness (decreased egg production among the birds, for example), but is sometimes never even detected. Highly pathogenic avian influenzas, such as H5N1, can result in severe pneumonia and a high mortality rate.

According to the CDC, most influenza A H7 viruses are low pathogenic. Of the H7 subtypes, H7N2, H7N3, and H7N7 have caused illness in humans. The Chinese agency reports that not only are these the first cases of H7N9 in humans, but they are the first cases of any H7 virus in humans in China. Previously, H7N9 had only been detected in birds in the Netherlands, Japan, and the U.S.

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The Hong Kong Centre for Health Protection and the Department of Health published a press release on March 31 stating that there was no link between the three cases. Because there are only three confirmed cases, officials know very little about how it is transmitted. Two of the cases had exposure to poultry before getting sick. Influenza A H7 is notifiable in China and the Department of Health explained that it will be heightening its surveillance. The press release also recommended that the public avoid contact with poultry, to thoroughly cook all poultry products before consumption, to avoided crowded places, to seek care in the event of symptoms of influenza-like illness, and, as always, to wash your hands carefully and frequently.

There is no vaccine to prevent H7N9 transmission, nor is there a specific treatment. However, the Chinese disease-tracking agency reported that certain anti-influenza drugs have shown to be effective in the early stage of infection.  In an interview with the Shanghai Daily (also reported by the Associated Press), Jiang Qingwu, head of Fudan University School of Public Health, stated that this was not yet a human influenza virus; it remains an “animal virus.”

This story first appeared on the Disease Daily website.

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