Updated November 7, 2011
Researchers say a rare case of people being infected with both swine and seasonal flu in Cambodia could lead to a potent combination strain emerging in the future.
A study looking at historical data found a boy and his teacher were infected with both H1N1 and a seasonal flu in 2009 - the year the pandemic swine flu emerged.
In these cases, tests showed there was no "genetic recombination," or mingling of the two flu strains.
The study, published in the American Journal of Tropical Medicine and Hygiene, says that while the cases don't pose a current threat they are a reminder of the dangers that a strain such as avian flu could mix with human flu and affect millions.
Presenter: Sen Lam
Speaker: Dr Ian Barr, deputy director of WHO Collaborating Centre for Reference and Research on Influenza in Melbourne
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BARR: Swine flu has symptoms of any of the standard influenza viruses. It's not particularly different, so normally people will suffer from sudden onset, so something will come on them with a short period of time, 8 to 12 hours, usually involving respiratory symptoms, such as a cough, in many cases a fever greater than 38 degrees centigrade and they'll generally feel unwell and may have muscle soreness, and some of the classic symptoms of influenza-like illness.
LAM: And so what do we know about the rare cases of co-infection?
BARR: Co-infections are not unusual with influenza, they usually involve children. Sometimes they can occur with pandemic viruses with other seasonal viruses and we've seen this with a virus that we call the H1 virus, H1N1 virus and we've also seen it with a virus we call the H3 and 2 virus. But these are usually co-infections that are self-limiting and don't appear outwardly any different from an infection with a single type of influenza virus.
LAM: So what do you make of this study then that's published in the American Journal of Tropical Medicine and Hygiene that says that co-infection is a reminder of the dangers?
BARR: Well, I agree with that and I think that these viruses are very tricky and they've learned different ways of making themselves not obvious to our immune systems and so this is one of the tricks they have is that they get together and from two different viruses, they can make a third completely different virus again. So this is one of the tricks of the virus and one that doesn't happen that often, but when it does happen, can have consequences.
LAM: And Ian Barr, the study says that South East Asia is a hot spot for seasonal influenza viruses as well as virus transmission from animals to human beings. Why is South East Asia particularly susceptible do you think?
BARR: Well, it's to do with many factors and some of those factors are the density, the population density, so these infectious diseases obviously spread more widely when population densities are high and so many areas of South East Asia, the population densities are high, both for humans and for animals. So a number of animals are susceptible to influenza, pigs are susceptible to influenza and so are some birds and chickens, so there's all those ingredients there and South East Asia has an abundance of both populations of animals and humans and that's why it's usually regarded as a hot spot for influenza activity.
LAM: And Avian Influenza or Bird Flu is still a major threat as you say in South East Asia, with a high fatality rate in human beings there. Is the danger real do you think that Bird Flu may co-mingle with seasonal flu and thereby creating a potent combination strain, such as the study suggests. How real are the dangers?
BARR: Well, I think it's a numbers game and the numbers are quite low for that type of event to occur, that paper in fact didn't find any recombination and it's something we look for as well. So recombination events are relatively rare, but they can occur and we can get them to occur in the laboratories, so it's certainly possible to do that. So it's something which we need to be aware of and while there is H5 activity in South East Asia, and there is activity currently in Cambodia, it is something which we need to be aware of and to try and reduce the amount of H5 out there and to recognise any unusual cases of influenza in the human population.
LAM: Bird Flu and Swine Flu have both been around for some years now. Do you think this has helped in preparing Asian countries for another outbreak, do you think the health authorities in those countries might have learnt some lessons here?
BARR: Oh, undoubtedly. I think South East Asia has had incredible improvement in their diagnostic capacity and in health care capacity for influenza viruses, especially H5N1 in the last ten years. Unfortunately, it is quite a severe disease and the results of people surviving these infections hasn't improved that much, but I think that the ability to diagnose these cases has certainly improved and now we hope that we might be able to have some improvements in treatment in the next few years as well.
LAM: And so what do we know about the rare cases of co-infection?
BARR: Co-infections are not unusual with influenza, they usually involve children. Sometimes they can occur with pandemic viruses with other seasonal viruses and we've seen this with a virus that we call the H1 virus, H1N1 virus and we've also seen it with a virus we call the H3 and 2 virus. But these are usually co-infections that are self-limiting and don't appear outwardly any different from an infection with a single type of influenza virus.
LAM: So what do you make of this study then that's published in the American Journal of Tropical Medicine and Hygiene that says that co-infection is a reminder of the dangers?
BARR: Well, I agree with that and I think that these viruses are very tricky and they've learned different ways of making themselves not obvious to our immune systems and so this is one of the tricks they have is that they get together and from two different viruses, they can make a third completely different virus again. So this is one of the tricks of the virus and one that doesn't happen that often, but when it does happen, can have consequences.
LAM: And Ian Barr, the study says that South East Asia is a hot spot for seasonal influenza viruses as well as virus transmission from animals to human beings. Why is South East Asia particularly susceptible do you think?
BARR: Well, it's to do with many factors and some of those factors are the density, the population density, so these infectious diseases obviously spread more widely when population densities are high and so many areas of South East Asia, the population densities are high, both for humans and for animals. So a number of animals are susceptible to influenza, pigs are susceptible to influenza and so are some birds and chickens, so there's all those ingredients there and South East Asia has an abundance of both populations of animals and humans and that's why it's usually regarded as a hot spot for influenza activity.
LAM: And Avian Influenza or Bird Flu is still a major threat as you say in South East Asia, with a high fatality rate in human beings there. Is the danger real do you think that Bird Flu may co-mingle with seasonal flu and thereby creating a potent combination strain, such as the study suggests. How real are the dangers?
BARR: Well, I think it's a numbers game and the numbers are quite low for that type of event to occur, that paper in fact didn't find any recombination and it's something we look for as well. So recombination events are relatively rare, but they can occur and we can get them to occur in the laboratories, so it's certainly possible to do that. So it's something which we need to be aware of and while there is H5 activity in South East Asia, and there is activity currently in Cambodia, it is something which we need to be aware of and to try and reduce the amount of H5 out there and to recognise any unusual cases of influenza in the human population.
LAM: Bird Flu and Swine Flu have both been around for some years now. Do you think this has helped in preparing Asian countries for another outbreak, do you think the health authorities in those countries might have learnt some lessons here?
BARR: Oh, undoubtedly. I think South East Asia has had incredible improvement in their diagnostic capacity and in health care capacity for influenza viruses, especially H5N1 in the last ten years. Unfortunately, it is quite a severe disease and the results of people surviving these infections hasn't improved that much, but I think that the ability to diagnose these cases has certainly improved and now we hope that we might be able to have some improvements in treatment in the next few years as well.
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