The transmission of 2009 H1N1 flu might occur before symptoms appear

The transmission of 2009 H1N1 flu might occur before symptoms appear

During the 2009 H1N1 flu pandemic, actions were taken to stop the spread of the virus. A recent study on ferrets, published in PLOS One by a group of researchers at Imperial College London, suggests that some infection may occur well before the first symptoms of illness occur. If true, future policies to control flu epidemics should take this into account.

During the 2009 H1N1 flu pandemic, actions were taken to stop the spread of the virus. A recent study on ferrets, published in PLOS One by a group of researchers at Imperial College London, suggests that some infection may occur well before the first symptoms of illness occur. If true, future policies to control flu epidemics should take this into account.

 

The H1N1 flu pandemic in 2009 was due to the emergence of a new influenza virus to which most people had no immunity yet. It caused a very high rate of disease outbreaks with particularly severe symptoms for younger people. The spread of the swine flu was dramatically fast, even though strong attempts were made to contain the spread of the virus.

In 2010 the handling of this pandemic was criticized because governments had ordered huge stocks of vaccines, too many of them, that now lay unused. It was the World Organization of Health (WHO) who declared on 11 June 2009 that the swine flu outbreak had reached global pandemic proportions. One year later, the British Medical Journal (BMJ) and the Bureau of Investigative Journalism in London jointly published an investigative report pointing out that “many of the top advisers to the WHO had ties to pharmaceutical companies manufacturing the highly-demanded vaccines”.

 

Influenza (flu) are spread by cough, sneezing, or unclean hands. source: mcfarlandmo / Flickr
Flu sneezing

On the scientific front, there have also been troubling results on the efficiency of measures to control the spread of the virus. A study called “Transmission of a 2009 H1N1 Pandemic Influenza Virus Occurs before Fever Is Detected, in the Ferret Model” was published on Wednesday, 29 August, in PLOS One, the peer-reviewed open access journal. The researchers at Imperial College London have been studying influenza virus transmission between ferrets, the best animal model for the flu. The results suggest that the virus can be passed between individuals before the appearance of the first symptoms: a high fever, coughing, muscular pain and great fatigue.  This pre-symptomatic infection occurs both via contact and respiratory droplet exposure.

If confirmed for larger numbers of animals and for humans, these results could be important for strategies in case of pandemics. It also raises the question of when we are contagious. Can we really say: “Don’t worry, now that I’m sick I’m no longer contagious.” In the case of this study, the results showed that the ferrets could pass the virus 24h after they themselves were infected. They had fever 45h after infection and they started sneezing 3 hours later. The rate of infection seemed to decrease 5 or 6 days after infection.

According to the WHO, a flu pandemic arises every 27 years on average. So we might still have some time left to figure out a way to control the spread of the virus before the second epidemics of the 21st century. The new measures could focus on early actions taking place very early in the process of disease spread, beyond isolating infection individuals and with better knowledge of the virus spreading means.

 

To find out more:

 

Flu Is Transmitted Before Symptoms Appear, Study in Ferrets Suggests http://www.sciencedaily.com/releases/2012/08/120829171820.htm