Highlights
- Influenza A viruses were first identified in birds in 1963.
- After initially showing up in North American waterfowl in 2002, H3N8 has been known to be circulating since then.
- It is known to affect horses, dogs, donkeys, pigs and seals.
- WHO reported the world's first human death from H3N8 bird flu.
H3N8 “avian flu”, or "bird flu" is also known as equine influenza A virus. The virus is known to have the ability to infect other specifies, including dogs and humans.
It is not typically transmitted to humans, though there have been a few reported cases of human infections.
Recent studies, and an April 2023 World Health Organisation (WHO) report, provide important insights into the avian flu viral infections, the genetic changes that may be contributing to its virulence, and the effectiveness of vaccines in protecting against the virus.
What you need to know about H3N8:
What is it?
H3N8 is a subtype of the Influenza A virus, which belongs to the Orthomyxoviridae family, first identified in birds in 1963. It is closely related to the modern horse Influenza A virus subtype H3N8.
This subtype is a highly contagious respiratory illness that affects a variety of animals, and is commonly found in wild birds. Usually, it causes only mild or no disease in infected birds.
However, they have crossed the species barrier and have been associated with outbreaks in horses, dogs, donkeys, pigs and seals.
When and how did it cross the species barrier?
H3N8 avian flu virus is believed to have crossed the species barrier from horses to dogs in the 2000s. In 2002, researchers found that an outbreak of severe respiratory disease in a pack of English foxhounds in the UK was caused by what was then known as an “equine influenza A virus” (H3N8). They discovered that canine lung tissue possesses the receptors for infection with influenza virus found in horses.
Researchers found that more than 96 per cent of the “nucleotides” (organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate) in these viruses are identical.
In 2004, canine influenza virus subtype H3N8 emerged in greyhound dogs in the US, from horses. Moreover, evidence indicated virus circulation in dog breeds other than greyhounds.
In 2005, a team of researchers at the US Centres for Disease Control and Prevention (CDC), based on Atlanta, conducted virologic investigation of 7 non-greyhound dogs that died from respiratory disease in Florida and isolated influenza subtype H3N8 virus.
This indicates that the complete virus was directly transferred from horses to dogs without “reassortment” with other strains, according to a 2005 research that studied the transmission of equine influenza virus to dogs, published in the journal Science.
In 2011, more than 160 harbour seals died along the New England coast in the US, during which the avian H3N8 virus was isolated by investigators.
What illness does the virus cause?
The virus can cause mild to severe respiratory symptoms, including:
- Coughing
- Fever
- Nasal discharge
- Pneumonia
In some cases, it can lead to death.
What mutations had been seen in the H3N8 virus?
In September 2014, a study led by St. Jude Children’s Research Hospital scientists found the avian Influenza A H3N8 virus that killed the harbour seals can spread through respiratory droplets and posed a threat to humans.
The researchers, whose work was published in the journal Nature Communications, discovered the virus had “naturally-acquired mutations” in a key protein that previous laboratory research had shown allowed the highly pathogenic avian H5N1 virus to spread though respiratory droplets.
Recent studies on H3N8 avian flu:
(2018) “Infectivity and pathogenicity of H3N8 equine influenza virus in dogs”. This study investigated the potential for H3N8 avian flu to infect dogs. The researchers found that while the virus could infect dogs, it did not cause severe disease and was not easily transmitted from dog to dog.
(2020) “Evaluation of a single-dose H3N8 influenza vaccine in dogs”. This study evaluated the efficacy of a single-dose H3N8 avian flu vaccine in dogs. The researchers found that the vaccine was highly effective in protecting dogs against the virus and that a single dose was sufficient to provide immunity for at least six months.
(2021) “Molecular characterisation of H3N8 equine influenza virus responsible for an outbreak in 2018 in Indian horses”. This study analysed the genetic makeup of an H3N8 avian flu virus responsible for an outbreak in Indian horses in 2018. The researchers found that the virus had undergone genetic changes that may have contributed to its increased virulence.
(2022) “A child with acute respiratory distress syndrome caused by avian influenza H3N8 virus”. This study was published in the Journal of Infection (Issue 2, 2022). It was the first case of human infection with H3N8 virus. Researchers found that the clearance time of H3N8 virus in human lungs is "prolonged". They found that after the H3N8 virus infects the human body, it can cause severe “interstitial lung lesions”, and patients can develop severe acute respiratory distress syndrome (SARDS).
What does the WHO say about H3N8 infections in humans?
In August 2022, a four-year-old boy tested positive for the H3N8 strain after being admitted to the hospital with a fever and other symptoms, according to a Reuters report.
The boy's family kept chickens at home and resided in a region where wild ducks were common, the report added. The boy was infected directly by birds. However, the strain was not found to have the “ability to effectively infect humans”.
On April 12, 2023, the World Health Organisation (WHO) reported that a 56-year-old woman was the first human death on record from H3N8 “bird flu”.
The patient had multiple underlying conditions, said the WHO, and a history of exposure to live poultry.
Are there vaccines available top help prevent H3N8 infection?
There are vaccines available for H3N8 in horses and dogs, as several outbreaks in horses and dogs were recorded over the years. The vaccines, typically given as a series of two doses, are designed to prevent horses from becoming ill or spreading the virus to other horses. For dogs, the vaccine is recommended if they are at high risk of exposure to the virus, such as those that go to dog parks or boarding facilities. A vaccine for use in dogs to protect against the canine influenza virus (CIV), which includes the H3N8 subtype, has also been approved.
However, there are no vaccines specifically designed for H3N8 in humans as the virus strain does not typically cause infections in humans.
What precautions are advised?
As for H3N8 avian flu in humans, confirmed cases are rare and typically involve people who have had close contact with infected animals. In general, the risk of human infection with H3N8 avian flu is considered to be low.
The WHO, however, advises the following: “To minimise the risk of infection, countries should increase public awareness of the importance of avoiding contact with high-risk environments such as live animal markets/farms, live poultry, or surfaces that may be contaminated by poultry or bird faeces.”
“It is recommended to maintain good hand hygiene by frequently washing hands or using alcohol-based hand sanitiser and wearing respiratory protection when in a risky environment.”
“Travellers to countries with known outbreaks of animal influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or contact with any surfaces that appear to be contaminated with animal faeces or other body fluids. Travellers should also wash their hands often with soap and water and follow good food safety and good food hygiene practices,” the WHO stated.
