It’s hard to believe, but almost exactly ten years ago surgical masks were worn by non-physicians as the World Health Organization (WHO) reacted to the outbreak of what we now know as Severe Acute Respiratory Syndrome, or SARS. And four years ago this month, we were working hard to track and stop the spread of the 2009 H1N1 pandemic swine flu.
Today, the public health and medical worlds are faced with not one, but two emerging diseases: the novel coronavirus, and avian influenza H7N9—a virus previously only seen in animals.
We’re rapidly learning a lot about both of these viruses. Yet there’s one essential fact that remains unknown, particularly about the H7N9 virus: What’s transmitting this virus to humans?
As we previously reported at Disease Daily/HealthMap, on March 31, three cases, including two deaths, of H7N9 were confirmed in Shanghai and Anhui Province, China. These marked the first documented cases of human H7N9.
Since then, the case count has steadily increased; it now stands at 16 cases, including six deaths. The latest cases, a 61-year-old woman and a 79-year-old man from Nanjing, were reported today, April 5. Sixty-five people are now under surveillance; officials are looking for abnormal symptoms and evidence of human-to-human transmission.
As Canadian reporter Helen Branswell explains, through genetic sequencing of the virus, scientists know that all the genes are avian (bird), but it’s a bird flu virus that knows how to adapt to mammals—specifically, to humans. The WHO suggests not only that this virus can bind to human cells, but it can also grow at temperatures close to human body temperature.
Yesterday, the Chinese Ministry of Agriculture revealed that strains of H7N9 that bore significant resemblance to the H7N9 now infecting humans were found in pigeons in Shanghai. In an encouraging sign of transparency, the Chinese government promptly reported this finding to the OIE, the world health organization for animals. As a result, Shanghai officials are ordering the slaughter of poultry. Influenza infects and spreads in different animals. Birds, pigs, dogs, horses, and aquatic mammals (seals and whales) can all be infected and sick with the flu.
Different subtypes of the influenza virus can infect and cause disease in different species. Birds, according to the WHO, provide a vast reservoir for influenza A viruses. One of the most concerning is H5N1. In the past, H5N1 only infected birds, but in 1997, there was an outbreak among humans in Hong Kong. The virus then re-emerged in people in 2003 and 2004. Since 2003, about 387 people have been infected with H5N1 and 245 have died. The good news is that this virus is not well-adapted to humans, so human-to-human transmission is rare, at least for the moment.
If there is no sustained human-to-human spread of H7N9, this virus could prove similar to H5N1. In the rare case when human-to-human transmission of H5N1 was suspected, it was typically in a small cluster. Clearly, we will have to continue careful monitoring of the spread of H7N9.
The bottom line is that we should take the flu far more seriously than we do. It is an immensely tricky virus that’s prone to change and therefore a constant challenge to producers of vaccines. We have seen influenza viruses change in the past and cause outbreaks both mild and quite serious (for example, the 2009 H1N1 pandemic).
H7N9 is typically what’s called a “low-pathogenic” virus in birds, meaning that if it infects birds, it causes a mild illness that’s not very obvious. This makes it hard to know how common it is in Chinese birds that appear healthy.
So far, H7N9 seems to be more pathogenic in humans, but we can’t say for certain. As Branswell points out, flu illness follows a specific pattern in people: There are a few severe and fatal cases, and loads of sick people with mild illness that may not even know they have the flu. For the most part, people stick out the illness in bed, without giving it a second thought. So we should remember that the cases we are counting now don’t necessarily represent the whole spread of this virus; there could be very mild cases that are not being diagnosed. If that is the case, maybe the virus is not as severe as it seems. Also, it could suggest that something different about how it spreads.
People infected with H7N9 are presenting with severe pneumonia. The WHO recommends that people wash their hands—as often as possible, and then wash them again. So far, no travel or trade restrictions have been issued for China, and there’s currently no vaccine for H7N9, but experts are debating developing one. Reuters reports that creating an H7N9 vaccine would be at the expense of developing vaccines for seasonal flu shots—i.e., the vaccine we’ll need next flu season. There’s no specific treatment for H7N9, either, but the WHO states that it’s vulnerable to some drugs, including oseltamivir and zanamivir.
One of my professors famously stated that public health is “the art and science of deciding who dies, when, and with what degree of misery.” Public health policy decisions are based on maximizing overall public health, but there is no way to protect everyone from everything. The seasonal flu may not be serious for most of those infected, but every year between 3,000 and 49,000 Americans die from the flu, according to the Centers for Disease Control. Experts are working to learn more about the biology of the virus, and H7N9’s potential to cause a pandemic, so that they can make fully informed decisions on vaccine manufacturing.
Are you afraid of the new strain of flu virus? What do you think about prioritizing development of a vaccine for H7N9 over vaccines for next year's flu season?
A version of this story first appeared on HealthMap.
--By Anna Tomasulo