It’s only been a couple of years since face masks and home isolation, and once again we have to fear a new pandemic. A new type of bird flu virus is killing birds in an unprecedented manner and it has also been found in numerous mammals.
Only isolated infections have been found in humans, and the virus is not transmitted from one person to another. However, viruses change – that’s what the bird flu virus has done from decade to decade.
The disease caused by the bird flu virus has been known in poultry for at least more than 150 years, even though viruses were not known then. The virus is found every year in wild birds and poultry around the world, sometimes more, sometimes less.
The virus occurs naturally in wild ducks. They are often asymptomatic or have a very mild disease. Poultry is more susceptible to symptomatic and even fatal disease.
In this story, we tell about significant events in the known history of bird flu.
First known mention in 1878
The earliest mention of an avian respiratory disease affecting poultry with high mortality is from Italy in 1878.
At that time, the cause of the disease was not yet known – influenza viruses could only be isolated in the 1930s – and the disease was called avian plague.
In 1894 and 1901, new infections were reported in Italy. The disease spread with poultry traders to Austria, Germany, Belgium and France.
In 1901, a virus was found to be the cause of the disease.
The bird virus turned into a human pandemic virus
As World War I drew to a close, the bird virus mutated into a virus that caused a deadly influenza pandemic in humans.
The first case of influenza, erroneously called the Spanish flu, was found in Kansas, USA in March 1918. Soon the disease spread to France, Germany and Britain.
In two years, the disease spread to almost all inhabited areas. About a third of the world’s population, an estimated 500 million people, were infected. Estimates of the number of dead vary from 50 to 100 million.
In Finland, about 210,000 people fell ill and about 20,000 people died.
Later, as medicine developed, it was discovered that the disease was caused by the H1N1 virus, similar to the bird virus.
The origin of fowl disease began to be clarified
By the 1950s, bird flu had been found in poultry in most of Europe, North America, the Middle East, Africa and Asia.
In 1955, it was discovered that the disease is caused by the type A influenza virus. In the 1960s, it became clear that poultry influenza is connected to wild birds and that there is a connection between human and bird influenza viruses.
Information was brought by two new human influenza pandemics linked to bird viruses. In 1957, the so-called Asian pandemic broke out. It was caused by the H2N2 virus, which had received genes from the bird flu virus. The virus was first detected in China.
1.1 million people died from the disease. In Finland, about a third of the population fell ill and 1,300 people died.
In 1968, the so-called Hong Kong pandemic killed between 700,000 and 1,000,000 people. The disease was caused by the H3N2 virus, which has genes from the bird flu virus. About a thousand people died of the disease in Finland.
1.3 million chickens were slaughtered in Hong Kong
In 1996, a highly pathogenic, i.e. easier-to-kill, H5N1 virus was found in poultry in southern China and Hong Kong.
The disease spread in China and Hong Kong. The H5N1 virus was also transmitted from birds to humans. 18 people got sick and 6 of them died.
The virus was eradicated from poultry by slaughtering 1.3 million chickens in Hong Kong. However, it remained alive in wild birds.
The bird epidemics of the 21st century raised the fear of a pandemic
In the early years of the 21st century, numerous cases of bird flu raised fears that that the virus becomes contagious from one person to another and the world is threatened by a new pandemic.
In 2003, an H7N7 bird flu epidemic broke out on Dutch farms. It affected about 28 percent of the country’s poultry. 89 people got sick and one of them died.
Around the same time, the H5N1 virus began to spread again in Asia, first in wild birds and then in poultry. In 2005, wild birds spread the virus to Africa, the Middle East and Europe. The virus was found in 63 countries by 2010.
55.2 million poultry died or were slaughtered. In humans, 516 infections were found and 306 died.
Pig, bird and human viruses brought the pandemic
In the spring of 2009, a pandemic called swine flu broke out, caused by a new type of influenza virus A (pdmH1N1). The virus contained genes from swine, bird and human influenza viruses.
The virus was first detected in the United States, but it probably originated in Mexico.
It is estimated that 150,000–575,000 people died from the disease. There were around 50 deaths in Finland.
In the 2010s, there was fear again
At the turn of the decade, bird flu started to spread more strongly than usual.
Several subtypes of the H5 virus emerged in Asia, Europe, Africa and North America. 139.9 million poultry died or were slaughtered.
In 2013, the H7N9 virus, which is low pathogenic in poultry, was detected in humans in China. The virus was traced to the poultry market. The virus in question usually does not cause noticeable symptoms in birds, but exceptionally the disease in humans could be serious and lead to death.
In 2017, the virus spread among people the most in years. By 2019, 1,568 infections had been confirmed. Of the sick, 614 died.
This time the focus is on Europe
The current bird-killing epidemic season began at the end of October 2020 and has developed into Europe’s worst bird flu epidemic to date.
The first highly pathogenic H5N8 viruses were detected in wild birds in the Netherlands. By the end of the year, large numbers of dead and sick birds with one of the H5 virus subtypes, H5N8, H5N5, H5N1 or H5N3, had been found in EU countries and Britain.
The sick birds were most often migratory birds, but the virus was also found in poultry in Croatia, Denmark, France, Ireland, Norway, Poland, Sweden and Great Britain.
A new H5N1 type virus, subtype 2.3.4.4b, emerged and became the dominant virus type by the end of 2021 in Asia, Africa, Europe and the Middle East. At the end of the year, the virus was detected in the United States and Canada. In 2022, the virus also spread to Central and South America.
The virus has led to an unprecedented number of wild bird and poultry deaths in Africa, Asia and Europe. More than 131 million poultry individuals have died or been slaughtered. A virus has caused significant destruction in local populations of some bird species.
There are also an exceptionally large number of infected mammals. The virus has been found in at least 26 species, including mink, seals, sea lions, cats and dogs.
A large number of fur animals have died or been euthanized due to bird flu, among other things. In Finland alone, a total of around 70,000 mink and foxes had been ordered to be killed by the beginning of August.
However, there are still no signs that the virus will become contagious from person to person. There were 17 infections in humans from 2020 to July 2023. Three people have died.
In total, H5N1 has infected 878 people between 2003 and 2023. 458 of them have died. There have been 1,568 cases of H7N9 infection in humans and 614 deaths. After 2019 no new H7N9 infections had been reported by the end of July this year.
At least 422 million heads of poultry have been lost since 2005.
The first cases of infection were found in Finnish birds in 2016
Highly pathogenic H5 subtype avian influenza virus was found in Finland for the first time in autumn 2016 with wild birds.
The current epidemic spread to Finland in early 2021, when the H5N8 type was found in wild birds and in a pheasant farm. The virus has also been found in fox, otter and lynx.
About fur animals virus was found in July 2023.
The story uses the following sources:
CDC, Researchgate, Food Agency, Duodecim, WHO and WHO, Eph, Taylor & Francis Online, THL, European Union, British Food Standards Agency, NIHTHL special researcher Erika Lindh