HOW SWINE FLU OUTBREAK EMERGED

HOW SWINE FLU OUTBREAK EMERGED

BY-- BBC

 

Flu viruses mutate over time causing small changes to proteins on their surface called antigens. If the immune system has met a particular strain of the virus before, it is likely to have some immunity; but if the antigens are new to the immune system, it will be weakened.

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Cases of swine flu, which has killed people in Mexico, have been confirmed around the world. With experts scrambling to develop a vaccine, there is concern at the potential for a pandemic affecting millions of people.

What is swine flu?

Swine flu is a respiratory disease, caused by influenza type A which infects pigs.

There are many types, and the infection is constantly changing.

Until now it has not normally infected humans, but the latest form clearly does, and can be spread from person to person - probably through coughing and sneezing.

What is new about this type of swine flu?

The World Health Organization has confirmed that at least some of the human cases are a never-before-seen version of the H1N1 strain of influenza type A.

SWINE FLU - THE BASICS

Symptoms usually similar to seasonal flu - but deaths recorded in Mexico

It is a new version of the H1N1 strain which caused the 1918 flu pandemic

Too early to say whether it will lead to a pandemic

Current treatments do work, but there is no vaccine

Good personal hygiene, such as washing hands, covering nose when sneezing advised

H1N1 is the same strain which causes seasonal outbreaks of flu in humans on a regular basis.

But this latest version of H1N1 is different: it contains genetic material that is typically found in strains of the virus that affect humans, birds and swine.

Flu viruses have the ability to swap genetic components with each other, and it seems likely that the new version of H1N1 resulted from a mixing of different versions of the virus, which may usually affect different species, in the same animal host.

Pigs provide an excellent 'melting pot' for these viruses to mix and match with each other.

How dangerous is it?

Symptoms of swine flu in humans appear to be similar to those produced by standard, seasonal flu.

These include fever, cough, sore throat, body aches, chills and fatigue.

It is worth remembering that seasonal flu often poses a serious threat to public health: each year it kills 250,000 - 500,000 around the world.

So far, most cases of swine flu around the world appear to be mild, albeit with diarrhoea more common than it is with seasonal flu.

But lives have been lost in Mexico, and a single death - of a Mexican child - has been confirmed in the US.

How worried should people be?

When any new strain of flu emerges that acquires the ability to pass from person to person, it is monitored very closely in case it has the potential to spark a global epidemic, or pandemic.

FLU PANDEMICS

1918: The Spanish flu pandemic remains the most devastating outbreak of modern times. Caused by a form of the H1N1 strain of flu, it is estimated that up to 40% of the world's population were infected, and more than 50 million people died, with young adults particularly badly affected

1957: Asian flu killed two million people. Caused by a human form of the virus, H2N2, combining with a mutated strain found in wild ducks. The impact of the pandemic was minimised by rapid action by health authorities, who identified the virus, and made vaccine available speedily. The elderly were particularly vulnerable

1968: An outbreak first detected in Hong Kong, and caused by a strain known as H3N2, killed up to one million people globally, with those over 65 most likely to die

The World Health Organization has warned that swine flu could potentially trigger a global pandemic, and stress that the situation is serious.

However, experts say it is still too early to accurately assess the situation fully.

Currently, they say the world is closer to a flu pandemic than at any point since 1968 - upgrading the threat from four to five on a six-point scale following a meeting on Wednesday.

This means all governments have to mobilise their pandemic flu plans.

Nobody knows the full potential impact of a pandemic, but experts have warned that it could cost millions of lives worldwide. The Spanish flu pandemic, which began in 1918, and was also caused by an H1N1 strain, killed millions of people.

There is hope that, as humans are often exposed to forms of H1N1 through seasonal flu, our immune systems may have something of a head start in fighting infection.

However, the fact that many of the victims are young does point to something unusual. Normal, seasonal flu tends to affect the elderly disproportionately

Is Mexico different?

The death toll in Mexico - where the virus at present seems to producing much more severe symptoms - suggests there may be unusual factors coming into play there.

Some experts have suggested the possibility that other, unrelated viruses may also be circulating in Mexico, making symptoms worse.

This would be unlikely to come into play in the rest of the world.

WHO PANDEMIC ALERT PHASES

Phase 1: No infections in humans are being caused by viruses circulating in animals.

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Alternatively, people infected in Mexico may have sought treatment at a much later stage than those in other countries.

It may also be the case that the form of the virus circulating in Mexico is subtly different to that elsewhere - although that will only be confirmed by laboratory analysis.

The Mexican authorities have downgraded the official death toll from the virus, ordering a new round of more stringent tests.

Can the virus be contained?

The virus appears already to have started to spread around the world, and most experts believe that, in the era of readily available air travel, containment will be extremely difficult.

The World Health Organization says that restricting flights will have little effect. It argues that screening of passengers is also unlikely to have much impact, as symptoms may not be apparent in many infected people.

Can it be treated?

The US authorities say that two drugs commonly used to treat flu, Tamiflu and Relenza, seem to be effective at treating cases that have occurred there so far. However, the drugs must be administered at an early stage to be effective.

Use of these drugs may also make it less likely that infected people will pass the virus on to others.

The UK Government already has a stockpile of Tamiflu, ordered as a precaution against a pandemic.

However, there is concern that if too many people start taking anti-virals as a precaution, it could raise the risk of the virus developing resistance, reducing the drugs' effectiveness.

What about a vaccine?

It is unclear how effective currently available flu vaccines would be at offering protection against the new strain, as it is genetically distinct from other flu strains.

A new bespoke vaccine is being worked on by scientists in the UKand the US, but it may take months to perfect it, and manufacture enough supplies to meet what could be huge demand.

A vaccine was used to protect humans from a version of swine flu in the US in 1976.

However, it caused serious side effects, including an estimated 500 cases of Guillain-Barré syndrome. There were more deaths from the vaccine than the outbreak.

What should I do to stay safe?

Anyone with flu-like symptoms who might have been in contact with the swine virus - such as those living or travelling in the areas of Mexico that have been affected - should seek medical advice.

But patients are being asked not to go into GP surgeries in order to minimise the risk of spreading the disease to others. Instead, they should stay at home and call their healthcare provider for advice.

Countries around the world have taken varying measures but are mostly stepping up monitoring and issuing advice about travel to Mexico.

In the UK, the Foreign Office is advising against all but essential travel to Mexico.

What measures can I take to prevent infection?

Avoid close contact with people who appear unwell and who have fever and cough.

General infection control practices and good hygiene can help to reduce transmission of all viruses, including the human swine influenza. This includes covering your nose and mouth when coughing or sneezing, using a tissue when possible and disposing of it promptly.

It is also important to wash your hands frequently with soap and water to reduce the spread of the virus from your hands to face or to other people and cleaning hard surfaces like door handles frequently using a normal cleaning product.

If caring for someone with a flu-like illness, a mask may be worn to cover the nose and mouth to reduce the risk of transmission. The UK is looking at increasing its stockpile of masks for healthcare workers for this reason.

In Mexico masks have been handed out to the general public, butexperts are sceptical about how useful this is.

May it take some time for a pandemic to strike?

Possibly. The flu virus tends to thrive in cooler conditions, and to struggle in warmer weather.

The initial cases have developed right at the tail end of the winter flu season in the northern hemisphere, so it is possible that the number of infections may only begin to accelerate once the weather turns colder in the autumn.

However, the southern hemisphere is about to enter its winter season and it is possible that the virus will take hold there first.

Is it safe to eat pig meat?

Yes. There is no evidence that swine flu can be transmitted through eating meat from infected animals.

However, it is essential to cook meat properly. A temperature of 70C (158F) would be sure to kill the virus.

Experts are also stressing that this is now a disease which is being passed between people.

The World Organisation for Animal Health said culling pigs, as Egypt has proposed, was therefore "inappropriate" as a measure to stop swine flu spreading.

It added there was no evidence of infection in pigs, nor of humans acquiring infection directly from pigs.

What about bird flu?

The strain of bird flu which has caused scores of human deaths in South East Asia in recent years is a different strain to that responsible for the current outbreak of swine flu.

The latest form of swine flu is a new type of the H1N1 strain, while bird, or avian flu, is H5N1.

Experts fear H5N1 holds the potential to trigger a pandemic because of its ability to mutate rapidly.

However, it has so far remained very much a disease of birds.

Those humans who have been infected have, without exception, worked closely with birds, and cases of human-to-human transmission are extremely rare. There is no suggestion that H5N1 has gained the ability to pass easily from person to person.

Where can I get further advice?

Further information and advice on swine flu can be found at websites of leading health and research organisations around the world. TheWorld Health Organisation gives background information on the virus.

The UK's government services website is carrying regularly updated health and travel information. The Health Protection Agency advises the public about what to do if returning from an affected area. NHS Choices outlines how swine flu is different from other flu.

The US government's Centre for Disease Control is counting the number of cases in the US.

You can also track the spread of swine flu reports using unofficial sources. Google is mapping search term data as an indicator of flu activity both across the US down to state level and in Mexico.Healthmaps maps viruses using news reports. Social media guideMashable lists a range of ways to track the virus .

Information and links to useful websites are being shared on Twitter,the micro-blogging service, while social networking website Facebook is tracking swine flu discussion amongst users.

Further questions from our readers have been answered by a UK-based expert.