SWINE FLU H1N1 VS AVIAN FLU H5N1(sars)

Infection control experts are scrambling to respond to outbreaks of swine flu in Mexico and the US, and suspected cases elsewhere.

What is swine flu?

Swine flu is a respiratory disease which infects pigs.

Caused by influenza type A, there are regular outbreaks among herds of pigs, where the disease causes high levels of illness but is rarely fatal.

It tends to spread in autumn and winter but can circulate all year round.

There are many different types of swine flu and like human flu, the infection is constantly changing.

Can humans catch swine flu?

Swine flu does not normally infect humans, although sporadic cases do occur - usually in people who have had close contact with pigs.

There have also been rare documented cases of humans passing the infection to other humans.

Human-to-human transmission of swine flu is thought to spread in the same way as seasonal flu - through coughing and sneezing.

In the latest outbreak it is clear that the disease is being passed from person to person.

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

Is this a new type of swine flu?

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

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.

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.

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 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 taken together the Mexican and US cases could potentially trigger a global pandemic, and stress that the situation is serious.

However, it is stressed that 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 - rating the threat at three on a six-point scale.

Nobody knows the full potential impact of the 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.

The fact that all the cases in the US have so far produced mild symptoms is encouraging. It suggests that the severity of the Mexican outbreak may be due to an unusual geographically-specific factor - possibly a second unrelated virus circulating in the community - which would be unlikely to come into play in the rest of the world.

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

What about treatments and vaccines?

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.

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.

US scientists are already developing a bespoke new vaccine, but it may take some time to perfect it, and manufacture enough supplies to meet what could be huge demand.

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 hold the potential to trigger a pandemic because of its ability to mutate rapidly. However, up until now it has 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.

UK monitoring swine flu outbreak

Dr John Watson, Health Protection Agency: 'The UK must be prepared'

Health officials in the UK say they are monitoring closely a deadly outbreak of swine flu in Mexico, amid fears of a potential pandemic.

The Health Protection Agency (HPA) said it was working with the government to assess any threat posed to the public.

It described the outbreak as "unusual" and warranting "further investigation and vigilance" by other countries.

Northwick Park Hospital said a BA worker who arrived from Mexico City and fell ill does not have swine flu.

At least 81 people in Mexico are now thought to have died after contracting a new strain of flu being linked to an outbreak of swine flu in the US.

There have been no confirmed cases so far in Europe.

1. Is this a flu pandemic?

The influenza virus is constantly mutating. That's why we can't get full immunity to the flu, the way we can to diseases like chicken pox, because there are multiple strains of the flu virus and they change from year to year. However, even though the virus makes us sick, our immune systems can usually muster enough of a response so that the flu is rarely fatal for healthy people.

But every once in awhile, the virus shifts its genetic structure so much that our immune systems offer no protection whatsoever. (This usually happens when a flu virus found in animals — like the avian flu still circulating in Asia — swaps genes with other viruses in a process called reassortment, and jumps to human beings.) A flu pandemic occurs when a new flu virus emerges for which humans have little or no immunity and then spreads easily from person to person around the world. In the 20th century we had two mild flu pandemics, in 1968 and 1957, and the severe "Spanish flu" pandemic of 1918, which killed an estimated 40 to 50 million people worldwide.

The WHO has the responsibility of declaring when a new flu pandemic is underway, and to simplify the process, the U.N. body has established six pandemic phases. Thanks to H5N1 avian flu, which has killed 257 people since 2003 but doesn't spread very well from one human to another, we're currently at phase 3. If the WHO upgraded that status to phase 4, which is marked by a new virus that begins to pass easily enough from person to person that we can detect community-sized outbreaks, such a move would effectively mean that we've got a pandemic on our hands.

The H1N1 swine flu virus has already been identified as a new virus, with genes from human and avian flus as well as the swine variety. And since it is apparently causing large-scale outbreaks in Mexico, along with separate confirmed cases in the U.S. and Canada and suspected cases in other countries, it would seem that we've already met the criteria for phase 4. But though an emergency committee met on April 25 to evaluate the situation, the WHO hasn't made the pandemic declaration yet. Keiji Fukuda, the WHO's interim assistant director-general for health, security and environment, said on Sunday that its experts "would like a little bit more information and a little bit more time to consider this." The committee is set to meet again by April 28 at the latest.

As health officials have repeatedly emphasized, with good reason, the swine flu situation is evolving rapidly, and more lab tests are needed to ascertain exactly what is going on in Mexico and elsewhere. "We want to make sure we're on solid ground," said Fukuda, a highly respected former CDC official and flu expert.



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