In the last few months, schools all over America have closed because of the norovirus outbreak. Norovirus infections, also known as the stomach flu, cause a low-grade fever, watery diarrhea and most alarming of all, projectile vomiting, which is a very effective way of spreading the virus.
Norovirus is known to be infectious and it spreads fast through a confined population, like at a school or on a cruise ship. Even though most sufferers recover in just 24 to 48 hours, the norovirus is the leading cause of childhood illness and, in most developing countries, it results in about 50,000 child deaths every year. But not everyone is vulnerable to the virus, and whether you get sick or not may depend on your blood type.
Norovirus is hard to get rid of
As debilitating as the illness it causes can be, the norovirus particles are visually beautiful under the microscope. It is a kind of virus known as non-enveloped or naked, which means that it does not have a membrane coating typical of other viruses, like the flu virus. The norovirus surface is a protein coat, also called the capsid. The capsid protects the norovirus's genetic material.
The capsid coat is one factor that can make norovirus difficult to control. Viruses with membrane coating are susceptible to detergents and alcohol, but not so norovirus. Norovirus can survive at freezing temperatures to temperatures as high as 145 degrees Fahrenheit, mild solutions of bleach and soap. It can also persist on human hands for hours and even solid surfaces and food for days and it can be resistant to alcohol-based hand sanitizers.
To make matters worse, only a bit of dose of the virus, like a few as 10 viral particles, is needed to cause the disease. Given that an infected person can excrete a lot of viral particles, billions even, it is very difficult to prevent the virus from spreading.
Susceptibility to norovirus depends on blood type
When norovirus is ingested, it usually infects the cells that line in the small intestine. Researchers do not know exactly how the infection can cause the symptoms of the disease. A fascinating aspect of the norovirus is that after exposure, the blood type determines in a massive part, whether a person gets sicks or not.
Your blood type: A, B, AB or O is dictated by genes that determine which kinds of molecules are found on the surface of your red blood cells. Those molecules are called oligosaccharides. The oligosaccharides are made from different kinds of sugars that are linked together in complex ways.
The same oligosaccharides on the red blood cells also show on the surface of the cells that line the small intestine. Norovirus and some other viruses use the oligosaccharides to get onto and infect the intestinal cells. It is the specific structure of these oligosaccharides that determines whether a strain of the virus can attach and invade in a person.
The H1-antigen, also known as the presence of one oligosaccharide, is needed for attachment by a lot of norovirus strains. People who do not make H1-antigen in their intestinal cells can make up 20% of the European-derived population and they are resistant to a lot of strains of norovirus. More sugars can be attached to the H1-antigen to give the A, B, and AB blood types. People who can't make the A and B modifications have the O blood type.
Immunity to norovirus is short-lived
Norovirus infection can provoke a robust immune response that removes the virus in a few days. But the response appears to be short-lived. Most studies have found that immunity that is guarding us against reinfection with the same norovirus strain lasts less than 6 months. Also, the infection with one strain of norovirus offers just a little protection against infection from another norovirus strain. This means that you have repeated bouts with norovirus.
The diversity of norovirus strains and the impermanence of the immune response complicates the development of an effective vaccine. Right now there are clinical trials that are testing the effects of vaccines that are made from the capsid proteins of the two most prevalent norovirus strains.
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