A new antiviral treatment has been found to reduce the risk of ferrets with influenza spreading the virus to healthy animals.

The findings, published in the journal PLOS Pathogens, show how the drug, called baloxavir, can reduce the risk of animals transmitting the influenza virus. 

The researchers from Imperial College London, Roche, and colleagues in Australia, Switzerland and Japan, suggest the treatment could potentially help to control flu outbreaks by limiting community-based viral spread. 

If further trials prove successful, baloxavir could dramatically change how we manage seasonal influenza outbreaks and pandemic influenza in the future Professor Wendy Barclay Department of Infectious Disease

Influenza viruses cause seasonal outbreaks and pose a continuous pandemic threat, such as the H1N1 swine flu outbreak in 2009.

Although vaccines are available to help keep seasonal influenza under control, their effectiveness varies each season and a vaccine for a new pandemic virus – made using current technology – will not be available fast enough to mitigate the effect of the first pandemic wave.

Antiviral drugs can be effective against many different influenza viruses but have not been used extensively for outbreak control. 

However, a recently licensed drug called baloxavir has been shown to reduce the amount of virus particles produced by infected people more effectively than the widely-used drug oseltamivir, known as Tamiflu.

Researchers tested whether baloxavir might also interrupt onward virus transmission in animal models – from infected to healthy ferrets.

Ferrets are used to study influenza as they contract the same respiratory viruses as humans. Their lungs and airways are physiologically similar to humans, and they are a closer biological match to us than rats or mice.

Reducing viral shedding

In the latest study, researchers found that baloxavir treatment reduced infectious viral shedding in the upper respiratory tract of ferrets infected with H1N1 influenza viruses compared to placebo, and reduced the frequency of transmission, even when treatment was delayed until two days after infection.

By contrast, the research found that treatment with oseltamivir did not substantially affect viral shedding or transmission compared to placebo.

The researchers did not detect the emergence of baloxavir-resistant variants in the animals.

The results support the idea that antivirals which decrease viral shedding could also reduce influenza transmission in the community.

According to the authors, such an effect has the potential to dramatically change how we manage influenza outbreaks, including pandemic influenza.

Professor Wendy Barclay, Head of the Department of Infectious Disease at Imperial and senior author, said: “We know that influenza can have serious and devastating outcomes for people with compromised immune systems, such as those in care facilities and hospitals, where finding more ways to reduce transmission is essential.

A first-of-its-kind clinical trial is currently underway to test the effectiveness of baloxavir on reducing the spread of influenza virus in human household settings, by treating infected individuals and monitoring for the transmission of influenza in household contacts.  

“If further trials prove successful, baloxavir could dramatically change how we manage seasonal influenza outbreaks and pandemic influenza in the future,” added Professor Barclay.

First author Leo Yi Yang Lee, from the Peter Doherty Institute for Infection and Immunity in Melbourne, said: “Our research provides evidence that baloxavir can have a dramatic dual effect: a single dose reduces the length of influenza illness in infected patients, while reducing the chance of passing it on to others as well.

“This is very important, because current antiviral drugs only treat the infected patient. If you want to reduce the spread of influenza to others, those people in close contact need to take antiviral drugs themselves to stave off infection.”

The authors explain that the antivirals in the current study are specifically designed to combat influenza and that it is highly unlikely they would be effective in reducing the spread of other respiratory viruses, such as coronaviruses.

However, they add the study demonstrates the potential for using antivirals to limit transmission of respiratory viruses, an approach that could be relevant in the current outbreak.

This article is based on materials provided by PLOS and the Peter Doherty Institute for Infection and Immunity.

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‘Baloxavir treatment of ferrets infected with influenza A(H1N1)pdm09 virus reduces onward transmission’ is published in PLOS Pathology.

Article image: Flickr / NIH NIAID - Colourised transmission electron micrograph showing H1N1 influenza virus particles.