A new study shows how the contraction of chickenpox is associated with a reduced chance of brain cancer. It is believed a biological mechanism may be discovered which may explain the correlation, the findings may contribute to actually preventing gliomas.
Many studies in the past have shown how numerous pathogens are associated with an increased possibility of developing brain cancer. It is estimated 15% of all human tumours are caused by viral infections, the reason for this is complex and likely involves the immune system and viral replication; the impact of the viral infection upon the cells of the body or the neurons of the brain may be the cause of the development of cancer later on in life. Many proviruses imbed a viral genome into the DNA of a host cell which then may replicate and be inherited, if latent the provirus may evade further replication and may become reactivated by a later internal or external factor including other pathogens or even sunlight.
Some viral infections however have the potential to reduce cancer cell proliferation. One of these; chickenpox (Varicella) is caused by a pathogen named Varicella zoster (VZV) it is capable of entering the nervous system and has an affinity for nerve cells. It may then exist in a latent state in the cranial nerve being reactivated later in life, depending on the direction the pathogen travels it may culminate in different conditions. If towards the skin then shingles (Zoster) may eventuate, if from the cranial nerve (where the pathogen is dormant) it travels out into the brain, central nervous system related conditions may result. Nonetheless, this latent relationship exists between VZV infection, immunity and glioma development.
The new study carried out by an international consortium looked at the association between VZV and brain cancer. Recruiting 4533 participants (4171 controls) all with a confirmed type of brain glioma, the team via questionnaires determined the medical history of each individual and importantly; if the individual had contracted chickenpox or shingles (or any other pathogen) and at what age. Approximately 79% and 83% of controls reported having a history of chickenpox, which was associated with a 21% reduced glioma development probability. The strongest association between chickenpox and high grade glioma was demonstrated for the youngest age group although the age of contraction of VZV was shown to be irrelevant. A productive history of shingles was insignificantly associated with glioma development.
A protective effect may be demonstrated for high grade glioma’s, these are tumours which grow at a faster rate especially for those under 40 years of age. The average age for the initiation of a glioma is 55 years of age suggesting it may be favourable to develop the condition before this age and different glioma types present at different times. For children with the condition(s) tumours are more sensitive to radiation therapy and chemotherapy in comparison to adults and furthermore the rate of the types of tumours differs. Vitally for adults a prognostic factor is whether the MGMT gene is silenced (methylated) which appears to offer further protection and extend survival chances.
In many countries children are given a vaccine for VZV although the antibodies differ in comparison to the wild contracted type which causes a more diverse immune response to VZV than the vaccine. This may suggest it might differ in the protection it bestows on an individual and until today it is unknown why; the consortium is optimistic an answer may be found into why this occurs.
For individuals who have contracted chickenpox a relief may rest in a conceivably reduced chance of developing brain cancer. Although the biological mechanism has yet to be found, this data may point scientists in the correct direction providing ample clues, the full explanation may be unnecessary if observations suggest VZV is an adequate remedy. The potential exists to create a virotherapy using VZV to break down malignant cells, compromising its integrity and preventing the development of cancer.
How does a pathogen immunity lead to protection from other conditions?