“British scientists have created a mouse that can catch colds,” reported the Guardian. The paper and other sources report on a “breakthrough” scientific experiment in which a mouse model of the common cold has been created.
The development of a mouse susceptible to rhinoviruses (the most common cold-causing virus and one that worsens asthma) challenges the long-held theory that the virus could only infect humans and chimpanzees. The development represents a significant scientific advance. The implication for the treatment of human cold remains to be seen.
Dr Nathan Bartlett and colleagues from the Imperial College London and other academic institutes in the UK, France and Italy carried out the research. Funding was provided by the Medical Research Council UK, GlaxoSmithKline, Sanofi Pasteur and Asthma UK. The study was published in the peer-reviewed medical journal: Nature Medicine.
Rhinoviruses are one of the most common cold-causing viruses. They are categorised into two groups: the major group and minor group viruses. The major-group viruses gain entry into cells by attaching to a cell receptor called ICAM-1. Although mice have a similar receptor, the virus does not bind to this and consequently cannot cause infection in mice. The minor group viruses - a smaller group - use a different type of receptor molecule to infect cells and so can infect mice.
In this laboratory study, the researchers attempted to develop a mouse model of the common cold, with both major and minor cold models (i.e. using both groups of rhinovirus).
To create the minor-group model, specially bred laboratory mice were infected with several types of rhinovirus. Over the next two weeks, the mice were assessed for any cold symptoms and had their lung fluid analysed for the presence of mucus proteins and proteins produced by the immune system in response to the infection (known as interferons, cytokines, chemokines).
For the major-group model, the researchers created a genetically modified mouse that had cells with the human ICAM-1 receptor. They then determined whether this type of mouse could be infected with the major-group rhinoviruses (which usually do not infect mice) and what their symptoms were like.
The researchers also attempted to create a model of the inflammation of the airway caused by an allergy (which sometimes occurs with a rhinovirus infection) by exposing mice to a protein irritant and a minor-group type of rhinovirus (1B). The symptoms in these mice were then compared to those in mice exposed to either the virus or irritant alone.
The researchers found that mice exposed to rhinovirus-1B (a minor-group type of the virus) developed cold like symptoms. They also found that mice that were genetically modified to carry human ICAM-1 cells, developed similar cold-like symptoms when infected with rhinovirus-16, one of the major group viruses to which mice usually have immunity.
Mice exposed to an allergen and also infected with rhinovirus-1B, showed symptoms similar to those seen in humans when asthma is worsened by a viral infection (i.e. further inflammation, mucus secretion and an immune system response).
The researchers concluded that their models of rhinovirus infection should be useful in investigating the origin, development and treatment of the common cold and acute asthma attacks.
They say that with further development similar models may be useful for research into other conditions including chronic obstructive pulmonary disease.
This experiment will be of particular interest to the scientific community. Mice are often used in models of disease to gain a better understanding of how diseases work and to test early treatments. The lack of such a model for the common cold has undoubtedly hindered research. Therefore, this study represents a significant scientific advancement.
However, animal-models of human disease are an early step. Creating and refining new therapies takes many years. Viruses have many different strains and so developing an antiviral treatment that will cure a particular strain that an individual has is difficult. Newspaper headlines such as "The miracle mouse that can cure our sniffles" are unrealistic, and an oversimplification.
It should also be remembered that overprescribing medications to treat infections such as the common cold which, in most cases, are typically mild and self limiting, may lead to the development of resistant strains. These mice will probably feature in further studies of rhinovirus infections.
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