The human-to-human transfer of the strain is a concern, writes Dr MUIRIS HOUSTON, Medical Correspondent
THE OUTBREAK of swine flu among humans in Mexico and the US is a cause for concern and vigilance, but there is no immediate threat of an influenza epidemic in Ireland.
Influenza viruses affect humans, pigs, birds and other animals. Most are species specific, but as we know from recent sporadic cases of avian flu in Asia, the virus can be transmitted from animals to humans.
Swine flu usually occurs in people who have contact with pigs. What is different in this latest outbreak is the ready human-to-human transfer of the H1N1 swine flu virus.
The World Health Organisation (WHO) has confirmed that some of the cases in Mexico and the US feature a version of the H1N1 strain of influenza A that has not been seen before.
This latest version of the virus contains genetic material from humans, birds and swine, which suggests it has arisen from a mixing of different versions of the virus. It is this type of genetic reassortment that scientists have warned could lead to a flu pandemic.
The symptoms of swine flu in humans are the same as the regular seasonal flu. They are: muscle aches, high temperature, cough, sore throat, runny nose, headache, and a general feeling of malaise. Diarrhoea and vomiting may also occur. Typically, the symptoms emerge within hours, rather than the slower development of symptoms seen with the common cold and other viruses.
There is no risk of contracting swine flu through eating meat from infected animals. However, it is essential to cook meat properly – a temperature of 70 degrees will kill the virus.
Currently available anti-viral drugs are effective against swine flu. Tamiflu, taken as a tablet, and Relenza, a spray, work if they are taken within 48 hours of the onset of flu symptoms.
Because this strain of swine flu is genetically distinct from previous strains, there is no vaccine to combat it. However, the US Centres for Disease Control and Prevention in Atlanta, Georgia, have begun growing the new strain with a view to making it available to pharmaceutical companies should the need arise. An appropriate vaccine would not be available for some months.
How worried should we be about the outbreak? The WHO has said there is a potential for a world pandemic, and has labelled the situation “serious”. The WHO has kept the pandemic threat level at three on a scale of one to six, where it has been since bird flu emerged as a potential threat. However, some experts are surprised it did not raise the level to four when it became obvious that human-to-human transmission had taken place in both Mexico and the US.
Phase four indicates a significant increase in the risk of a pandemic but does not mean it is a foregone conclusion.
A worrying feature of the outbreak is that, so far, none of the Mexican deaths have occurred in people older than 60 or younger than three. The old and the young represent the classic at-risk groups from regular flu outbreaks.
Deaths in otherwise healthy young adults are reminiscent of the 1918 Spanish flu pandemic.
We know that when a new virus emerges, death may occur in healthy adults, who mount the strongest immune response to infection. Such is the level of inflammation that fluid leaks from cells, causing serious illness. On a positive note, none of the US cases has died and just one has been hospitalised. None of the 10 schoolchildren in New Zealand who are likely to have swine flu following a trip to Mexico are seriously ill. This offers hope that, even if high levels of human-to-human transmission emerge, mortality will be low.