Influenza viruses circulating in animals pose threats to human health in that they can develop the ability to infect humans and cause illness. In rare cases, these viruses become capable of spreading between humans, causing what is known a “pandemic”. It is important to be prepared for pandemics from viruses jumping from animals to people. Flu researcher Ron Fouchier from the Erasmus Medical Centre in the Netherlands explains how this can happen and what can be done to mitigate risks for public health.
Flu researcher from the Erasmus Medical Centre in the Netherlands
Can influenza strains jump from animals to humans?
R.F.: Yes. Several strains circulating in poultry or pigs have infected humans (e.g. from subtypes H1N1, H3N2, H5N1, H6N1 H7N7, H7N9, H10N7). Luckily, this generally results in single human cases of infection, with no sustained transmission between humans.
Why is this a concern?
R.F.: Of course every human infection is one too many, especially if they lead to severe diseases or fatalities. The biggest concern, however, is that animal viruses adapt to their new host and become capable of sustained transmission between humans. In such cases, we speak of a "pandemic threat"- the threat of a globally spreading disease.
Does this happen often? And how?
R.F.: Over the last decade, there have been less than a 1,000 documented human cases of infections with avian influenza virus, and approximately 100 documented human cases of infections with pig influenza virus. These cases generally occurred after direct contact of humans with infected animals. Sustained human-to-human transmission of such viruses is, however, a rather rare event. Four influenza pandemics occurred in the 20th century: in 1918, 1957, 1968, and 2009. Pandemics start when animal viruses acquire the ability to transmit between humans via aerosols or respiratory droplets, through coughing, sneezing, or talking.
Is it possible to predict this?
R.F.: At present, we can not predict which viruses will jump from animals to humans, and which viruses will acquire the ability to adapt to humans and spread between them. Major research projects are ongoing all over the world to identify what factors are responsible for this.
What are the public health risks for the future?
R.F.: Wild birds are the natural hosts for influenza viruses.Therefore influenza viruses will always be in our environment, in the wild bird reservoir. There is nothing we can do about that. Public health risks arise when these viruses are introduced in domestic animals and humans are exposed to them.
What can be done?
R.F.: It is important to limit the introduction of wild bird viruses in domestic animals, their continued circulation in domestic animals, and human exposure to animal influenza viruses.
Currently, there are a number of viruses of considerable concern to public health that we are aware of. H5N1 birdflu in Egypt and Asia, H7N9 birdflu in China, H9N2 birdflu in large parts of the eastern hemisphere, and H3N2 swineflu in the USA. Public health authorities are monitoring these viruses carefully and are investigating options to control them.
At the same time, the WHO and FAO networks are also working to generate "pre-pandemic vaccine candidates", which are intended for use before a pandemic to protect against a strain of flu that could cause a future pandemic. A full prevention of future influenza pandemics originating from animal influenza is unlikely, but we should try to reduce the likelihood of pandemics and limit their public health impact. In this light, EFSA’s FLURISK initiative is another valuable step towards the global efforts to understand and control the transmission of influenza viruses from animals to humans.