Friday, 21 April 2017

Reoviruses and Celiac Disease: A Possible Connection

Reoviruses infect the respiratory tract and intestine of humans. Researchers have recently made a potentially important discovery about the viruses in relation to celiac disease. The scientists have found a link between a reovirus infection and the development of celiac disease in mice that are genetically susceptible to getting the disease. The scientists have also discovered that at least in the people that they tested, people with celiac disease have an elevated level of antibodies against reoviruses compared to people without the disease.


Wheat bread contains gluten, which is harmful for people with celiac disease.
Public domain photo by Couleur

What Is Celiac Disease?


Celiac disease involves an immunological reaction to a protein complex in certain grains known as gluten. As a result of this reaction, the inner lining of the small intestine becomes inflamed and the villi (tiny folds on the lining) flatten. Villi increase the surface area for nutrient absorption. When they're flattened, the quantity of nutrients that can be absorbed is greatly reduced. The intestinal effects can lead to a host of unpleasant and sometimes dangerous symptoms that appear in the digestive system and sometimes far beyond this location. Even a small amount of gluten can trigger inflammation. The immediate effects of this inflammation are not the only problem. Untreated celiac disease produces an increased risk of intestinal cancer.

Gluten is found in wheat and all its varieties, including spelt and kamut, as well as in rye and barley. It's not completely understood why the gluten provokes an immune response and triggers inflammation, although researchers have found some possible or partial explanations.

What Are Reoviruses?


Reoviruses get their name from the term "respiratory enteric orphan viruses". They were originally referred to as orphan viruses because they were thought to have no effect on the human body. The words respiratory and enteric in the name refer to the parts of the body where the viruses are most often found. ("Enteric" refers to the intestine.)

Viruses contain DNA or RNA surrounded by a protein coat called a capsid. Many viruses have a lipid envelope outside their capsid. The DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) contain the genome or genetic instructions of the virus. Reoviruses have double-stranded RNA, a double-shelled capsid, and no lipid envelope.


People with celiac disease must avoid these products, but fortunately
gluten-free breads are available.
Public domain photo by Couleur

Avoiding Gluten 


If scientists knew that reoviruses can cause celiac disease in genetically susceptible people, it would be useful to develop a vaccine or other method to prevent an infection. The current cure for celiac disease is to stop eating gluten so that the villi grow back. This may seem like an easy step to take. There are problems with the treatment, however. 

One problem is that it's hard to avoid gluten. Though there are gluten-free grains, they may be contaminated with gluten in the field, in the storage area, in the processing area where products are made, or in the home when meals containing gluten are made. Flour containing gluten can drift through the air and land on gluten-free food. A person with celiac disease may pick up gluten from crumbs left in a toaster or particles left on countertops and cutting boards. In addition, non-food items such as toothpaste may contain gluten. Eating outside the home, such as in restaurants or at school events, is always a time for vigilance.

Despite the potential difficulties, someone with celiac disease who tries hard to avoid all sources of gluten can generally reduce their exposure to such a low level that the intestinal inflammation disappears and their villi recover. Some people find that even after avoiding gluten for as long as a year, however, their intestine doesn't heal. This condition is rare, but it's very unfortunate for the people who experience it.



Mice are often used in lab experiments that may apply to humans.
Public domain photo by auenleben


The Mouse Experiments


The scientists involved in the recent research found that one type of reovirus triggered celiac disease in genetically susceptible mice if the animals were eating gluten when they developed the viral infection. While it's true that results of mouse experiments don't always apply to humans, they often do. An interesting aspect of the research was the fact that the scientists also found that antibodies against reovirus were two to five times higher in people with celiac disease compared to the situation in people without the disease. This doesn't mean that all patients respond abnormally to the virus, but some may. 

It could be very helpful if reoviruses are proven to cause celiac disease because the discovery could lead to prevention of the disease. Biologically, though, one mystery will have been replaced by another. We don't know all the details involved in gluten's action in the body and we don't know how reoviruses trigger celiac disease in humans (if in fact they do). Many discoveries in science build on previous ones, so we may eventually have answers to the puzzles.

References


A common virus might trigger celiac disease (from NPR, or National Public Radio)

Celiac disease information (from the Mayo Clinic)