Bird Flu: Why We Should Care
Updated: May 5, 2022
“At least eight types of bird flu, all of which can kill humans, are circulating around the world’s poultry farms—and they could be worse than Covid-19.”
- John Vidal, The Guardian, journalist and environment editor
“I am beyond excited for the future of flu vaccination.”
- Jenna Bartley, immunologist, University of Connecticut
Each year bird flu exacts an enormous toll on poultry and wild birds without directly affecting humans. But in the past century, bird flu spilled over from birds to humans igniting three pandemics—the 1918 Spanish flu, 1957-58 Asian flu and 1968 Hong Kong flu. Many experts predict that another bird flu is just waiting in the wings to spawn the next pandemic. In this Germ Gems post, I discuss influenza viruses and explain why we should care about bird flu.
Brief overview of the discovery of influenza viruses. In the 5th century BCE, Hippocrates first reported that an influenza-like illness had spread from Northern Greece to the islands south and elsewhere. But it wasn’t until the 1918-1919 influenza pandemic killed up to 100 million people worldwide that researchers began taking influenza seriously and searched for its etiology (cause) and cure.
Initially, scientists thought that influenza was caused by the bacterium Haemophilus influenzae; they were mistaken. In the early 1930s, a young physician from Iowa, Richard Shope, turned his attention to swine influenza and established a viral etiology. Working at the Rockefeller Institute in New York City, Shope isolated influenza virus from infected hogs, injected it into healthy pigs that went on to develop influenza, and thus fulfilled Koch’s postulates—a set of criteria used to prove that a microbe is a pathogen. Shortly after Shope published his swine results, other scientists using his techniques isolated the human flu virus. The path was then opened to developing lifesaving flu vaccinations, the first of which appeared in the early 1940s.
Influenza viruses. The genome of influenza viruses is composed of RNA that has only eight genes—a paltry number. Nonetheless, influenza viruses are infamous for their incredible capacity to mutate.
There are four types of influenza viruses, namely, A, B, C and D. Types C and D are extremely rare. But types A and B cause annual or seasonal flu epidemics that typically sicken up to 20% of the population in any given year. It is the influenza A virus that is the cause of bird flu.
Influenza A viruses are also divided into multiple subtypes, based on two proteins on their surface: hemagglutinin (H) and neuraminidase (N). Influenza A viruses are found mainly in wild birds but also in humans, pigs, horses, and even whales.
Bird flu in birds. Avian influenza (bird flu) refers to disease in birds caused by infection with avian (bird) influenza type A viruses. Researchers have isolated avian influenza A viruses from more than 100 different species of wild birds around the world. These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Avian influenza A viruses are very contagious among birds, and some of these viruses can sicken and even kill certain domesticated bird species, including chickens, ducks and turkeys.
The viruses that pose the greatest risk—the ones that worry public health officials most—are called highly pathogenic avian influenza (HPAI). These viruses can wipe out an entire flock of chickens within 48 hours. One such HPAI strain, H5N8, hit the Midwestern U.S. in 2014-2015, and close to 50 million chickens and other commercially-raised birds were killed to control the epidemic; the economic loss was estimated to exceed $3 billion. Earlier this year, the U.S. Department of Agriculture reported H5N1 outbreaks in poultry and waterfowl in Maryland, Delaware, and South Dakota. All told, producers across the country slaughtered nearly 27 million commercial chickens and turkeys to help stop the spread of this virus.
In addition to the colossal losses of commercial poultry, in February of this year, the H5N1 HPAI strain was reported to be spreading to bald eagles. At least 36 bald eagles—in Florida, Nebraska, Ohio, Georgia, Kansas, South Carolina, and several other states—succumbed to this HPAI strain.
In recent years, H5N8 emerged as another HPAI that tore through thousands of chicken, duck, and turkey flocks across nearly 50 countries. Infected birds can shed avian influenza A viruses in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with the virus as it is shed by infected birds. They also can become infected through contact with surfaces that are contaminated with virus from infected birds.
Bird flu in humans. Fortunately, so far, the spillover of HPAI strains from birds to humans is rare, but in February 2021, the first human case of H5N8 was reported in Russia. And on April 28 of this year, the Center for Disease Control and Prevention (CDC) released a media statement that the H5N1 flu strain had sickened a Colorado man who was involved in the culling (depopulating) of poultry with presumptive H5N1 bird flu. At about the same time, China reported the first human infected with the H3N8 bird flu strain—a 4-year-old child who frequently came into contact with chickens on a farm in Henan Province where he lived.
In the 20th century, humans suffered the consequences of three flu pandemics, all caused by influenza A viruses that spilled over from birds: the 1918-19 pandemic, dubbed “The Mother of All Pandemics” because of its extraordinary death toll (up to 100 million people), caused by H1N1 influenza A virus; 1957-1958 (“Asian flu”), caused by the H2N2 bird flu virus; and 1968 (“Hong Kong flu”) from an H3N2 influenza virus strain.
Due to the recent spread of avian influenza H5N1 in various species, including a human, H5N1 is considered a prime candidate as a pandemic threat. An essential step in escalating a bird flu strain to the status of a pandemic strain is its acquisition of a gene that encodes transmissibility from human to human. If this happens, the set up for next bird flu pandemic is established.
Seasonal flu in humans. While we all should be aware of the bird flu and the potential havoc that would ensue if an avian flu strain triggers another pandemic, we shouldn’t forget that ordinary, seasonal flu remains a big health problem. Each year, 5% to 20% of all Americans get the flu, more than 200,000 are hospitalized because of seasonal flu-related complications, and on average 50,000 flu victims die.
As I discussed in my previous Germ Gem post on September 15, 2021, “This Year’s Flu Shot: With or Without a COVID-19 Booster?,” because of seasonal flu’s profound impact, the CDC recommends annual vaccination against seasonal flu for all persons aged 6 months or older. The effectiveness of seasonal influenza vaccine, however, varies by influenza season. At best, the vaccine is about 60% effective, and the data for the 2021-2022 flu season so far looks like the vaccine this year didn’t reduce the risk for outpatient respiratory illness caused by one of the culprit strains, influenza A(H3N2).
Flu vaccines. Since the emergence of COVID-19 in late 2019, the eyes (and brains) of many researchers have been on the coronavirus SARS-CoV-2. In my opinion, the development of highly effective and safe vaccines against this RNA virus is the single biggest scientific and public health achievement of the COVID-19 pandemic era.
Many researchers have been busy for the past two years characterizing the similarities and differences of respiratory tract infections caused by SARS-CoV-2 and influenza virus. For those who are focused on vaccine development, they share the same goal—development of a universal vaccine. A universal vaccine that protects against all coronaviruses or all influenza viruses remains the holy grail, and there is promising research that suggest such a goal is achievable.
As is discussed in a New York Times article last October by science writer Carl Zimmer, “First, Impressive Vaccines for Covid. Next Up: The Flu,” a great deal has been learned from the development of mRNA vaccines against SARS-CoV-2 that is now potentially applicable to influenza viruses. Time will tell what comes of the crosstalk between researchers working in this field.
The U.S. poultry industry provides 1,682,269 jobs, $96 billion in wages, $441.15 billion in economic activity, and $34 billion in government revenue per year. Also, the number of “birders” in the U.S. continues to rise every year. In 2018, approximately 12.34 million people were actively participating in this popular pastime. Therefore, although thedevelopment of a universal flu vaccine would be an extraordinary success story for those of us concerned about human health, it would also be a welcome accomplishment for researchers to come up with creative solutions to prevent bird flu in birds. I hope that veterinary biologists develop strategies to reduce avian flu in these marvelous animals.