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Cold cure confusion?

Friday 13 February 2009

“A cure for the common cold could soon be a reality” the Daily Express claimed, reporting that scientists have “achieved a breakthrough” with new research into the virus. However, The Daily Telegraph reported that research shows the cold virus “may never be eradicated”, although it may one day lead to drugs to target different strains of the virus.

These reports are based on a study that has identified the complete genetic sequences that make up all 138 known strains of rhinovirus, the virus that causes the common cold. The reason why humans do not become immune to the common cold, and why vaccines and treatments generally prove ineffective, is that the genetic sequence of the rhinovirus can quickly mutate and create new viral strains. This study has also shown that the different strains of the virus can swap pieces of their genetic code, causing further variation.

Given the changing genetics of the cold virus, antibodies and treatments that target specific strains can quickly become less effective. Therefore, although the knowledge generated in this study is a key tool in helping scientists to understand the virus and, potentially, to develop new treatments, it does not mean that a cure is likely in the near future.

Where did the story come from?    

Dr Ann C Palmenberg and colleagues from the University of Wisconsin and other universities and institutes in the US carried out this research. The study was funded by the National Institutes of Health and the University of Maryland School of Medicine. It was published in the peer-reviewed journal Science.

What kind of scientific study was this?   

This was a genetic study where researchers aimed to identify the genetic sequences that make up all known strains of the human cold virus (human rhinovirus or HRV). This virus causes both upper and lower respiratory tract infections. It also causes almost half of all cases of intensification of asthma symptoms.

This virus’ genetic material is not made up of DNA, but a similar molecule called RNA. Like DNA, RNA is made up of four building blocks (nucleotides), and in RNA these are called A, C, G and U (DNA has T instead of U). These 'letters' are joined together in different sequences to make up chains (strands) of RNA. Each virus contains a strand of RNA that holds information for making the 11 to 12 proteins that make up the virus. The known strains of rhinovirus each contain different variations in the sequences of their RNA, but are thought to fall into three different species called HRV-A, HRV-B and HRV-C.

The researchers looked at all 99 known strains of the rhinovirus and 10 strains obtained from people with upper respiratory tract infections. They identified the sequence of the RNA of each of these different strains.

The researchers used computer programs to compare the RNA sequences from each strain as well as rhinovirus sequences already published by other researchers, looking for similarities and differences.

They used a number of different computer programs to help them work out a family tree for these viruses, exploring how they were likely to have developed from common ancestor viruses.

What were the results of the study? 

The researchers identified the complete RNA sequences of 99 known strains of the rhinovirus, as well as the 10 strains obtained from people with upper respiratory tract infections. Comparing their information with rhinovirus sequences already published by other researchers they found that, overall, they had the full genetic sequences for 138 different strains.

The strains all shared certain areas where their sequence was very similar (conserved regions), but there was also a lot of variation between the different strains. The genetic sequences of the strains were found to be made up of similar proportions of the four letters that make up RNA. Within each species, about two-fifths of the amino acids (building blocks of proteins) that these sequences encoded were the same.

The researchers found that a specific area near the start of each RNA sequence was very variable between the different strains, with each strain having a virtually unique sequence. The polio virus is known to have a similar region, and the variations in this region determine how infectious (virulent) the strain is. This suggests that genetic variations in this region may also contribute to levels of infectiousness in rhinovirus strains.

Building a family tree of the different strains based on their genetic sequences suggested that the HRV-A and HRV-C strains had a common ancestor, which was also related to the HRV-B group. They found that three of the strains within the HRV-A species had quite different RNA sequences to the others, which suggested that they might be a new species of rhinovirus called HRV-D.

The researchers also found evidence that different strains had been exchanging pieces of genetic material, which is thought to occur when a person is infected with two strains of the virus at the same time.

What interpretations did the researchers draw from these results?   

The researchers conclude that their results suggest that future studies of human disease caused by rhinovirus might benefit from identifying exactly which strain was involved by looking at its genetic sequence.

They say that, by using this approach, researchers might be able to obtain more information about the different levels of infectiousness of the various strains. They say it will help in studies of human disease, as well as in the development of new treatments and vaccines.

What does the NHS Knowledge Service make of this study?   

This thorough study provides a database of information that will be useful in future studies of the cold virus. It shows the high level of variability between different strains of rhinovirus, and highlights some of the reasons why this virus has proven so difficult for the human body and for medical treatments to defeat.

This information may help scientists to identify possible ways of tackling the cold virus. However, the fact that the virus’ genetic material changes quickly, and the ability of different strains to swap genetic material, mean that combating this virus is likely to remain a considerable challenge. Given the properties of this constantly changing virus, a cure is not likely to be just around the corner.

Analysis by Bazian
Edited by NHS Website

Links to the headlines

Scientists 'map DNA of common cold for the first time'.

The Daily Telegraph, 12 February 2009

Links to the science

Supporting online material

Palmenberg AC, Spiro D, Kuzmickas R et al.

Sequencing and Analyses of All Known Human Rhinovirus Genomes Reveals Structure and Evolution.

Science Februaury 12 2009 [Advanced online publication]