Swine flu virus spreads

[General Duke]

 

Swine flu virus may become less deadly as it spreads around the globeThe virus is likely to become less virulent the faster it is transmitted, writes Ian Sample, but in the short term the more people it infects the more people will die

 

 

Health officials fully expect swine flu to reach Britain and today's confirmation of the first case in Europe suggests we may not have long to wait.

 

The Spanish health ministry has identified the virus in one patient and is investigating a further 17 people who have fallen sick.

 

 

On Saturday night, Britain's chief medical officer Liam Donaldson sent an alert to hospitals with details of how to spot potential cases, and what quarantine precautions to take.

 

 

The £500m government stockpile of the antiviral drug tamiflu is largely earmarked for frontline health workers, who may be given the drug early on if a pandemic is thought to be looming. If the disease does spread through Britain, the foremost concern is to keep the health system running smoothly.

 

 

This is arguably the most frustrating time for those charged with tracking and responding to the disease. There is as yet too little information to know how it will pan out.

 

 

Swine flu is nothing new. The first virus was isolated in the US in 1930, and since then there has been roughly one human case a year there. Occasionally the disease has spread more widely among humans, though only two people have died from the infection since 1976.

 

 

The latest swine flu virus is different from those that have caused these more minor outbreaks in the past. It appears to be far more infectious, and could be more lethal. But major questions remain. For example, it is not yet clear that the strain that has killed in Mexico – and so far only in Mexico – is the same strain causing more mild illness in the US, Canada and elsewhere.

 

 

There is good reason to suspect the virus will become less lethal as it spreads. The virus is constantly mutating, and the strains that will spread fastest are the ones that do not stop people going about their daily lives and coming into contact with others. The most lethal viruses tend to be short-lived because they kill their host before the virus has had a chance to be passed on.

 

 

The complexity of the issue does not stop there. Although the virus is likely to lose potency as it spreads, it will reach more people, so the odds of further fatalities could still rise.

 

 

Work at World Health Organisation laboratories is ongoing to figure out what features of the virus make it infectious and virulent.

 

 

Another task for WHO researchers is to model the future spread of the disease. This week, epidemiologists will try to find out how many people each infected person spreads the disease to, and how this figure changes with time and place.

 

 

Another issue of concern is apparent from looking at a map of confirmed cases to date. In many ways, having the US on Mexico's doorstep ensured that as soon as the infection crossed the border, it was picked up quickly and that crucial information was shared immediately with the WHO. But it is no surprise that most confirmed cases outside Mexico are in developed countries with good surveillance for such diseases. The surveillance in countries south of Mexico – such as Guatemala, Honduras and Nicaragua – and on to South America, is generally much less effective. The disease could have been there for weeks, but the true nature of the spread in those countries may take some time to emerge.

 

 

In the coming weeks, the WHO will decide whether it is necessary to make fresh vaccine to combat the spread of this particular swine flu strain. It is a delicate decision, because overreacting will have serious consequences. It will take between four and six months to develop a vaccine tailored to the virus in Britain, but pharmaceutical companies do not have the resources to make this as well as the seasonal flu virus, which needs to be ready for the winter.