IT’S THAT TIME of year again, when everybody is ill in some way or another, and people throw the word ‘flu’ around like it’s nothing. Everything from a cold to a cough to a hangover gets lumped under the ‘flu’ umbrella. Rates of influenza-like illnesses peak in the winter months, with 35 cases per 100 000 people aged 15-44 reported to the NHS in the winter of 2015-16. Although cases appear to be more common in young adults, it is old people and young children that have the most to fear from the virus, with mortality rates peaking at 7.9 per cent in the UK this time last year.
What elicits the scepticism and eye-rolling, though, is the phrase ‘man flu’ – the idea that the influenza virus might somehow have a greater impact on one sex than another. It is often dismissed with words along the lines of “oh stop being over-dramatic, you’ve just got a cold like the rest of us”.
However, recent research has suggested that there may be some truth to these supposedly spurious claims of ‘man flu’. In a paper published last month from the Royal Holloway, University of London, mathematical modelling was used to look at the effects of viral infection on both men and women. The results showed that natural selection would theoretically favour viruses that are less harmful towards women. The one caveat of this was that for this to happen, the woman must be pregnant or have had a child. This is because it is advantageous for the virus to pass from mother to child, perhaps while the child is in the womb or during breastfeeding due to specialised immunological mechanisms. This is not the first time a disease has been seen to affect one gender more than another.
Tuberculosis kills men at a rate which is 1.5 times greater than it does women, and in chickens retroviruses cause more tumours in male chicks than female. Contrary to what you might think, it’s actually to the disadvantage of a virus to k i l l its host. A virus’ ability to spread underpins its life cycle – if it can’t spread, it can’t replicate, and if it kills its host, it can’t spread. Therefore, it makes sense that a virus should prefer a host it can use for its spread – in this case, a mother and child. While there are still many unknowns regarding how this works, it has interesting implications for our understanding of how various viral diseases function, including HTLV-1. Infection with HTLV-1 can lead to leukaemia, but it occurs much more quickly in the Japanese rather than in individuals from the Caribbean.
This new research suggests this might be because the Japanese breastfeed their children much more commonly, so the virus can spread to another host more quickly. So does this mean that man-flu is real and us sceptics have been disproved by science? Probably not, say researchers. For a virus to affect a man more harshly, transmission from mother to child needs to be an advantageous route for that virus. For influenza, it’s not an important route, giving little support to the claims of man-flu’s existence. So for now, we’re just going to have to assume that it’s probably just someone with a cold.