Tuesday, 28 April 2009


“From the bitterness of disease man learns the sweetness of health.” - Catalan Proverb

The outbreak of swine influenza in Mexico was no surprise to epidemiologists. A pandemic (a worldwide epidemic) of influenza was long overdue. The last one was in 1968 and it began in Southeast Asia, becoming known as the “Hong Kong ‘flu”. That one in the late 60s killed about a million people worldwide. Virologists advise that a major pandemic of influenza occurs once every couple of decades or so. The present strain of influenza virus that is causing us problems has killed about 160 people in Mexico and more than 50 confirmed cases in the US, two in Scotland, one in Spain, and possible cases in New Zealand, France, Norway Germany, Sweden and Israel. One of the ominous signs is that most people who died were between the ages of 20 and 50 years. A hallmark of past influenza pandemics is deaths in previously healthy young adults.

Influenza comes from the Italian, meaning literally ‘influence’ (from medieval Latin influentia). The Italian word also has the sense ‘an outbreak of an epidemic,’ hence ‘epidemic.’ It was applied specifically to an influenza epidemic that began in Italy in 1743, later adopted in English as the name of the disease. In the past, people thought these epidemic diseases arose out of the evil influence of malaligned planets. In the late 19th and early 20th century, people thought influenza could be due to bacteria, as the then newly-discovered micro-organisms were proven to be the cause of many diseases: Diphtheria, cholera, plague, tuberculosis, typhoid fever, tetanus, whooping cough, etc. Microbiologists looked for bacteria in the lungs of people who had died of influenza and found them in the billions. An almost ubiquitous bacterium that was found in these cases was one that was subsequently called Haemophilus influenzae (literally: The blood-loving bacterium of influenza). However, this was a false lead. It was only a secondary infection that colonised the diseased lungs of influenza sufferers (the name stuck!).

That influenza was caused by viruses was demonstrated by Richard Shope in 1931 in swine. Patrick Laidlaw and his group at the Medical research Council of UK in 1933 isolated the virus. Since then, we have learnt much about the biology of the disease. There are three main types of the virus: Influenza A (birds are the natural hosts with humans being affected and suffering the most severe disease. Horses and pigs can also be infected by this type); Influenza B (almost exclusively human hosts); and Influenza C (the natural hosts of which are swine and humans).

All of these influenza viruses share certain characteristics, for example they all have genetic material made of RNA, which exists in eight segments inside the virus. Also, all of these viruses have a coating of proteins, which are known as haemaglutinin (H) and neuraminidase (N). Numbers after the H and N proteins indicate the specific form that these proteins take. For example, the Spanish ‘flu of 1918 that killed 40 million people worldwide was the H1N1 subtype of the infuenza A virus; the Asian ‘flu of 1957/8 that killed 1.5 million people worldwide was the H2N2 subtype of the influenza A virus. The Hong Kong ‘flu of 1968 was the H3N2 subtype of the influenza A virus.

The current strain of swine ‘flu was first detected in Mexico in March 2009. It is a recombinant influenza virus derived in part from H1N1. By recombinant we mean that the virus has had a rearrangement of its genetic material. This happens naturally in cells, typically in animals that are infected by more than one strain of virus. As the viruses multiply in infected cells, the genetic material from two strains of virus gets mixed up and a new “recombinant” virus is created spontaneously. These double infections and such recombinations of viral genetic material are more likely to occur where there are overcrowded conditions and people live close to animals.

Furthermore, the influenza virus is notorious for its spontaneous mutations. It is these spontaneous mutations (slight changes in its genetic material occurring naturally) that cause the influenza epidemics every few years or so. The more genetically different a new influenza virus is to its predecessors the more “foreign” it looks to our immune system (even if we have been immunised against influenza in the past). Essentially, each new subtype of virus is regarded by our immune system as a completely different virus and this is the reason why we have to get immunised every now and then with the latest “version” of influenza that is around a the time. The recombinant virus causing the current swine ‘flu is very different to past strains and people all over the world have no immunity against it. This means the virus spreads easily between individuals and causes severe disease before the immune system “kicks in” with an effective response. In many cases of course, this immune response is much too late and the infected patient dies as the virus multiplies out of control in their body.

How do we fight such pandemics of influenza? Firstly by trying to check the spread of infection: Isolating patients, preventing close contact between large numbers of people in confined spaces (hence the closing of schools) and destroying infected animals. Also by good hygiene, washing of hands, not touching the face and the wearing of face masks (however, these face masks rapidly become ineffective barriers as they become moistened ). Patients who present with the infection may be given antiviral drugs. These are not antibiotics (antibiotics will not kill viruses, they are only effective against bacteria), although antibiotics may be prescribed to deal with secondary bacterial infections (remember the Haemophilus influenzae?). On April 27, the Centre for Disease Control (CDC) recommended the use of oseltamivir (Tamiflu) and zanamivir (Relenza) for both treatment and prevention of the new strain of swine influenza virus, but it warned that it was resistant to amantadine and remantadine.

A new vaccine can be manufactured as soon as new virus samples are isolated and purified, but such a process can take as long as six months. Given the gravity of the present situation, this development time may be shortened somewhat. The WHO has already warned that to try to contain the new influenza virus outbreak is impossible. All we can do is try to mitigate its effects. This is in the wake of the WHO upgrading the pandemic status to phase 4 (phase 4, implies sustained human to human transmission with community-wide outbreaks). Phase 5 is widespread human infection, with human-to-human transmission in at least two countries in one WHO region. Phase 6 is a global pandemic proper.

So how do you know if you have swine ‘flu? The symptoms are fever, chills, sore throat, cough, body aches and pains, muscle aches, headache and fatigue. Some patients have also reported diarrhoea and vomiting. All of these symptoms are not specific to swine ‘flu, so a great deal of suspicion must also accompany the diagnostic process and there needs to have been some contact with a suspected case of the disease.

Should we be afraid? Being apprehensive makes us cautious, and discretion is the better part of valour. Being sensible and avoiding travel if we can, taking good care of our health, having a good diet, good hygiene and avoiding crowded places are all good strategies. And of course see a doctor at the first sign of a ‘flu-like illness!

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