Flu is transmitted before symptoms appear, study suggests

August 29, 2012

Research at Imperial College London examining influenza transmission in ferrets suggests that the virus can be passed on before the appearance of symptoms. If the finding applies to humans, it means that people pass on flu to others before they know they're infected, making it very difficult to contain epidemics.

The research was supported by the National Institute for Health Research (NIHR) Imperial Biomedical Research Centre.

Knowing if people are infectious before they have symptoms is important to help authorities plan for an epidemic, but is has been difficult to establish this from data collected during outbreaks. Previous research using mathematical models estimated that most transmission occurs after the onset of symptoms, but some happens earlier.

The new study, published in the open access journal , is the first to investigate this question experimentally in an . Ferrets are commonly used in flu research because they are susceptible to the same and show similar symptoms to humans.

Ferrets with flu were put in contact with uninfected ferrets for short periods at different stages after infection. Transmission occurred before the first symptom, fever, appeared, both when the ferrets were in the same cage and when they were in adjacent cages.

Professor Wendy Barclay, the study's lead author from the Department of Medicine at Imperial College London, said: "This result has important implications for pandemic planning strategies. It means that the spread of flu is very difficult to control, even with self-diagnosis and measures such as temperature screens at airports. It also means that doctors and nurses who don't get the flu jab are putting their patients at risk because they might pass on an infection when they don't know they're infected."

The flu strain used in the study was from the 2009 , which killed almost 300,000 people worldwide.

The researchers found that ferrets were able to pass on flu to others just 24 hours after becoming infected themselves. The animals did not suffer from fever until 45 hours after infection and began sneezing after 48 hours. The results are consistent with earlier studies which found that sneezing is not necessary to transmit flu – droplets of virus are expelled into the air during normal breathing.

In the late stages of infection, after five or six days, flu was transmitted much less frequently, suggesting that people can return to work or school soon after symptoms subside with little risk of passing flu on to others.

The first author, Dr Kim Roberts, who is now based at Trinity College Dublin, said: " are the best model available for studying flu transmission, but we have to be cautious about interpreting the results in humans. We only used a small number of animals in the study, so we can't say what proportion of transmission happens before symptoms occur. It probably varies depending on the ."

Explore further: Flu cases from county fair traced to pigs

More information: KL Roberts et al. Transmission of a 2009 H1N1 pandemic influenza virus occurs before fever is detected, in the ferret model. PLOS ONE, 29 August 2012. dx.plos.org/10.1371/journal.pone.0043303

Related Stories

Flu cases from county fair traced to pigs

July 26, 2012
(HealthDay) -- Four people attending an Indiana county fair this month came down with flu traced to pigs, U.S. health officials report.

Mutant bird flu 'less lethal', says paper's author

April 3, 2012
The author of a paper on a mutant bird flu strain said Monday that experts agreed to publish it only after he explained that the virus was "much less lethal" than previously feared.

When well-known flu strains 'hook up' dangerous progeny can result

July 13, 2011
A new University of Maryland-led study finds that 'sex' between the virus responsible for the 2009 flu pandemic (H1N1) and a common type of avian flu virus (H9N2) can produce offspring -- new combined flu viruses -- with ...

Recommended for you

Google searches can be used to track dengue in underdeveloped countries

July 20, 2017
An analytical tool that combines Google search data with government-provided clinical data can quickly and accurately track dengue fever in less-developed countries, according to new research published in PLOS Computational ...

MRSA emerged years before methicillin was even discovered

July 19, 2017
Methicillin resistant Staphylococcus aureus (MRSA) emerged long before the introduction of the antibiotic methicillin into clinical practice, according to a study published in the open access journal Genome Biology. It was ...

New test distinguishes Zika from similar viral infections

July 18, 2017
A new test is the best-to-date in differentiating Zika virus infections from infections caused by similar viruses. The antibody-based assay, developed by researchers at UC Berkeley and Humabs BioMed, a private biotechnology ...

'Superbugs' study reveals complex picture of E. coli bloodstream infections

July 18, 2017
The first large-scale genetic study of Escherichia coli (E. coli) cultured from patients with bloodstream infections in England showed that drug resistant 'superbugs' are not always out-competing other strains. Research by ...

Ebola virus can persist in monkeys that survived disease, even after symptoms disappear

July 17, 2017
Ebola virus infection can be detected in rhesus monkeys that survive the disease and no longer show symptoms, according to research published by Army scientists in today's online edition of the journal Nature Microbiology. ...

Mountain gorillas have herpes virus similar to that found in humans

July 13, 2017
Scientists from the University of California, Davis, have detected a herpes virus in wild mountain gorillas that is very similar to the Epstein-Barr virus in humans, according to a study published today in the journal Scientific ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.