Able to leap tall buildings bound to their victims. Able to travel up to 100 miles per hour in your sneeze. Too small to be seen by the light microscope. And capable of causing grief for you and me.
What I'm referring to here is the common virus. While 5,000 viruses have been described, there are millions. They're ubiquitous. One common one is the influenza virus, yet many are known to cause the common cold.
Any infection caused by a virus can cause major complications for an asthmatic. In fact, many asthma experts, including those at the Mayo Clinic, believe viruses "are the most common cause of asthma flare-ups, especially in children.
Another common virus is the Respiratory Syncytial Virus (RSV). This little pest is known to cause a common head cold in adults, yet in children it can cause bronchiolitis, and RSV pneumonia, which can lead to asthma trouble and even respiratory failure.
Do Viruses Cause Asthma?
As noted by the Food and Drug Administratino (FDA) in this post, new research shows that not only do viruses trigger asthma, they may also cause some children to develop asthma. Since RSV is a common virus, and most infants are exposed to it early in life, it's believed to be the most common virus to cause asthma.
Likewise, studies show that children who develop RSV pneumonia are at an even greater risk for developing asthma.
To understand how viruses cause asthma, we must first revisit the Hygiene hypothesis, which is basically an "educated guess" that postulates that one develops asthma during the first three months of life when the immune system is maturing.
The basis of this hypothesis is that in our modern society children are not being exposed to enough bacteria, and therefore aren't being exposed to enough bacterial lipopolysaccharide (LPS). In other words, we are too clean.
LPS is a molecule on bacteria that, according to the FDA, "stimulates and educates the immune system by triggering signals through a molecular 'switch' called TLR4, which is found on certain immune system cells."
Thus, when the level of LPS is low in the environment around the child (not enough bacteria), the immune system does not develop properly.
The immune system therefore becomes bored and creates a defense against things that normally don't pose a threat to their bodies, such as dust mites, cockroach urine, pollen, grass, molds, fungus and other allergens.
How does it all work?
So what do viruses have to do with all this. Well, as the FDA explains, RSV is believed to carry "a molecule on its surface called the F protein, which flips the same immune system 'switch' (TLR4) as do bacterial endotoxins."
One would think the F protein would turn the immune system on, or cause it to mature, as bacteria LPS protein would, although this does not seem to be the case.