Germs of an idea

The 19th-century French microbiologist and chemist Louis Pasteur was the first scientist to confirm that microbes cause diseases. He also made two essential observations while studying ailing silkworms. The first was that their infection was contagious, and the second was that the worms actually transmitted the infection to their offsprings. Although the first observation has served us well in the development of antibiotics, the second has long been forgotten. Nearly 150 years later, the idea that susceptibility to infectious diseases can be inherited has finally resurfaced once again.

It is thought that some individuals are unable to produce certain molecules that are essential to the immune system because they have a mutation of one or more genes. This is the reason scientists believe such individuals could be more susceptible to infections.

Let us use the example of the Herpes simplex virus. Infecting 80% of all adults, its worse symptom is usually the infamous cold sore. However, for a few unlucky children, the virus can cause serious inflammation of the brain (H. simplex encephalitis or HSE), which can lead to lesions resulting in epilepsy, mental retardation and even death. A French physician has identified two genetic mutations resulting in the same deficiency in children who had survived HSE. In both cases, the children’s systems were unable to produce enough type 1 interferon, a molecule that plays a role in innate immunity. Innate immunity is the defence mechanism we are born with. This discovery appears to show that HSE is not a purely infectious disease, as was originally thought. In fact, in certain people, genetic mutations may increase their susceptibility to the disease. Half a dozen other diseases, where genetic mutations are thought to play a role, have already been identified.

Individuals who carry these mutations seem more vulnerable to infections than those who do not. Scientists will now be able to use this information to develop treatments that are better adapted to the actual cause of the problem. Therefore, we could give people suffering from an infection and who present one ore more genetic mutations, the molecules their immune systems are unable to produce. The next generation of antibiotics could very well target the human immune system, as opposed to the microbes themselves.

Finally, Louis Pasteur’s second observation, the heredity of susceptibility to infections, could also lead to revolutionary treatments. We will keep you posted!