New swine flu virus unstable, more changes seen: Expert

[Watchman]

New swine flu virus unstable, more changes seen: Expert
A leading virologist has described the new swine flu virus as "very unstable", meaning it could mix and swap genetic material when exposed to other viruses.
Tuesday, 12 May 2009 16:37

A leading virologist has described the new swine flu (H1N1 influenza) virus as "very unstable", meaning it could mix and swap genetic material when exposed to other viruses.

The new virus, which has infected 5,251 people in 30 countries and killed 61, has displayed great efficiency in spreading among people, said Guan Yi, a microbiologist with the University of Hong Kong.

"This virus has been around only a few months, it is very unstable ... and we know that its presence is dramatically increasing in human population, so the chance of it meeting with H5N1 is actually increased," Guan said in an interview on Tuesday.

"Both H1N1 and H5N1 are unstable so the chances of them exchanging genetic material are higher, whereas a stable (seasonal flu) virus is less likely to take on genetic material."

While H1N1 appears to be mild so far with many infected people recovering even without treatment, the H5N1 has a mortality rate of between 60 to 70 percent.

Experts are fearful about the emergence of a hybrid which combines the killing power of the H5N1 with the efficient transmissibility of H1N1. H5N1 is believed to be endemic in countries like China, Indonesia, Vietnam and Egypt.

Guan, an expert on both the H5N1 and SARS, has analysed the genetic sequences of the new virus, which is a triple reassortant containing genetic material from swine, human and bird.

He said there was a huge information gap due to a lack of regular surveillance on animal disease.

Each one of the eight gene segments in the new virus has been seen in pigs in the past 10 years, but experts have no clue when this new H1N1 virus strain first appeared and in which animal species it had been incubating, Guan said.

"We know when each gene segment appeared, but we don't know when this strain first appeared, there is an information gap of about five to 10 years, from 1999 to 2009. If there was regular surveillance, we would know when this virus came about," he said.

"We don't know if this reassortment happened in pigs or human ... It's likely to have come from pigs because all the segments have been found in pigs, but we can't be 100 percent sure."

Guan backed stringent moves taken by some governments to keep the virus at bay, such as quarantining.

"They are useful because we are now fighting for time to develop vaccines and antivirals, which will then minimise its impact on people (over the longer term)," he said.

"Already it appears to more virulent than seasonal flu because it is killing younger people and it appears to have higher mortality than seasonal flu, so it doesn't make sense to treat this like seasonal flu."

Seasonal flu kills about 250,000 to 500,000 people annually with a fatality rate of less than 0.1 percent.

A study published in Science on Monday estimated that the new H1N1 flu virus has a case fatality ratio of 0.4 percent based on confirmed and suspected deaths.

Reuters

 

[Watchman]

Swine Flu Data 'Very Consistent' With Early Stages Of A Pandemic

ScienceDaily (May 12, 2009) — Early findings about the emerging pandemic of a new strain of influenza A (H1N1) in Mexico are published in the journal Science.

Researchers from the MRC Centre for Outbreak Analysis and Modelling at Imperial College London, working in collaboration with the World Health Organisation and public health agencies in Mexico, have assessed the epidemic using data to the end of April. Their key findings are as follows:
The data so far is very consistent with what researchers would expect to find in the early stages of a pandemic.
The researchers' best estimate is that in Mexico, influenza A (H1N1) is fatal in around 4 in 1,000 cases, which would make this strain of influenza as lethal as the one found in the 1957 pandemic. The researchers stress that healthcare has greatly improved in most countries since 1957 and the world is now better prepared.
The epidemic of influenza A (H1N1) is thought to have started in Mexico on 15 February 2009. The data suggests that by the end of April, around 23,000 people were infected with the virus in Mexico and 91 of these died as a result of infection. However, the figures are uncertain – for example, some mild cases may have gone unreported. The numbers infected could be as low as 6,000 people or as high as 32,000 people.
The uncertainty around the numbers of people who have been infected with influenza A (H1N1) in Mexico means that the case fatality ratio (CFR) of 0.4% (4 deaths per 1000) cannot be definitely established. The CFR is in the range of 0.3% to 1.5%, but at this stage the researchers believe that 0.4% is the most likely.
For every person infected, it is likely that there will be between 1.2 and 1.6 secondary cases. This is high compared to normal seasonal influenza, where around 10-15 percent of the population are likely to become infected. However, it is lower than would be expected for pandemic influenza, where 20-30 percent of the population are likely to become infected.
In an outbreak in an isolated village called La Gloria, Mexico, children were twice as likely to become infected as adults, with 61% of those aged under 15 becoming infected, compared with 29% of those over 15. This may suggest that adults have some degree of immunity against infection, because of having been previously infected with a related strain of influenza, or it may mean that children are more susceptible to infection because they interact much more closely together, for example in school, than adults.

Professor Neil Ferguson, the corresponding author of the new research from the MRC Centre for Outbreak Analysis and Modelling at Imperial College London, said: "Our study shows that this virus is spreading just as we would expect for the early stages of a flu pandemic. So far, it has been following a very similar pattern to the flu pandemic in 1957, in terms of the proportion of people who are becoming infected and the percentage of potentially fatal cases that we are seeing.

"What we're seeing is not the same as seasonal flu and there is still cause for concern – we would expect this pandemic to at least double the burden on our healthcare systems. However, this initial modelling suggests that the H1N1 virus is not as easily transmitted or as lethal as that found in the flu pandemic in 1918," added Professor Ferguson.