The New Scientist has an interesting article on swine flu, the current strain that’s jumped from pigs to humans–Swine flu: The predictable pandemic? For more, visit the New Scientist website. – Ilene
Summary:
- the virus is very different from those we have immunity to and there are no existing vaccines
- the virus is spreading readily among people, but how readily is unknown – it could go pandemic or fizzle out
- this virus emerged in 1998 and has been endemic and evolving on hog farms throughout North America
- this virus is a member of the H1N1 family (with H and N being the virus’s surface proteins haemagglutinin and neuraminidase). It is endemic in pigs, causing mild pig illness, but in 1998 hybrids formed in the pig "mixing vessels" combining the pig virus with viral material found in humans and birds.
- there are various hybrids, triple reassortants. They were rapidly evolving by 1999. The one we’re now seeing has H1 and N1 surface proteins of swine origin and a "cassette" of internal genes" of human and bird origin. These hybrids switch surface proteins to evade the pigs’ immune system, outcompeting the endemic swine flu virus.
- the rapid evolution in pigs created the potential for a human pandemic, it’s been brewing for about 10 years.
- last year, the CDC warned that swine H1N1 would "represent a pandemic threat" if it started circulating in humans.
- the avian polymerase genes are worrisome, similar genes made H5N1 bird flu lethal in mammals and made the 1918 human pandemic virus so lethal.
- this new strain appears to have originated in pigs owned by a subsidiary of Smithfield Foods.
- our lack of previous exposure to the swine H1 and N1 surface proteins means we have no immunity, however, it is not clear how transmissible (contagious) and how virulent these new viruses are in humans.
– Ilene
Swine flu: The predictable pandemic?
THE swine flu virus has been a serious pandemic threat for years, New Scientist can reveal – but research into its potential has been neglected compared with other kinds of flu.
As New Scientist went to press, cases were being reported far from the original outbreak in Mexico. The clusters of milder infections in the US suggest the virus is spreading readily among people. The US Centers for Disease Control and Prevention (CDC) says this strain is so different from existing human flu viruses that most people have no immunity to it. There are no existing vaccines.
All this means the virus could go pandemic. Or it might not: if the virus spreads less readily than is feared, it might not be able to maintain itself in the human population and could fizzle out (see "What makes flu go global?").
We could have seen this coming, though. This type of virus emerged in the US in 1998 and has since become endemic on hog farms across North America. Equipped with a suite of pig, bird and human genes, it was also evolving rapidly…
By 1999, these viruses comprised the dominant flu strain in North American pigs and, unlike the swine virus they replaced, they were actively evolving. There are many versions with different pig or human surface proteins, including one, like the Mexican flu spreading now, with H1 and N1 from the original swine virus.
All these viruses still contained the same "cassette" of internal genes, including the avian and human polymerase genes, reports Amy Vincent of the US Department of Agriculture (USDA) in Ames, Iowa (Advances in Virus Research, vol 72, p 127). "They are why the swine versions of this virus easily outcompete those that don’t have them," says Webby…
Our immune response to flu, which makes the difference between mild and potentially lethal disease, is mainly due to the H surface protein. The Mexican virus carries the swine version, so the antibodies we carry to human H1N1 viruses will not recognise it….
The avian polymerase genes are especially worrying, as similar genes are what make H5N1 bird flu lethal in mammals and what made the 1918 human pandemic virus so lethal in people. "We can’t yet tell what impact they will have on pathogenicity in humans," says Webby…
All the evidence suggests that swine flu was a disaster waiting to happen…
What makes flu go global?
A "pandemic" is an epidemic that goes global, so technically there is a flu pandemic every year. But the term is usually reserved for bad outbreaks that follow large changes in the virus.
The influenza virus constantly evolves, and pandemics happen every few decades when the flu virus gets new surface proteins that people have little immunity to, generally because they come from an animal strain. The lack of immunity means the virus affects more people more severely…
It must also transmit efficiently in people. Every victim must infect more than one other person for the virus to spread. The new strain could do this, as it is packing an altogether faster engine than previous H1N1 strains. It has an avian gene that has powered it to dominance in pigs, though no one knows for certain if this will make it dangerous in people.
