The more I hear about norovirus, the more it puzzles me.
Apparently as few as a dozen individual virus particles are enough to infect a single person, and infected people shed millions of them, even long after they feel fit and well. The virus can live on hard surfaces for days or even weeks, and is resistant to many disinfectants and sanitisers. It makes people ill, but hardly ever kills them, and they are up and about to spread infection within a few days.
It sounds like the almost perfect virus, and when you look at the info above it seems almost impossible to avoid it — so my question is, why haven’t we all got it? Even in the UK where it has been more prevalent than ever, there have been an estimated 1.1 million or so cases, or roughly 2% of the population. What stops it spreading much more widely?
Approximately 20% of Caucasians have a genetic mutation that makes them resistant to infection by noroviruses. The virus binds to molecules on the cell membranes of gut cells as a point of entry - mutations in some folks (called ‘non-secretors’) reduce or eliminate those particular cell surface molecules and therefore protect against infection. The surface molecules in question are blood group (ABO) carbohydrates, and evidence suggests that even if you are a secretor, individuals with type B or AB blood are less likely to have symptomatic infections than those with O or A blood types.
I happen to be a nonsecretor with blood type B, and I’ve been in the middle of some pretty remarkable norovirus outbreaks and never been symptomatic. I was once on a dogsledding trip in which fourteen out of sixteen people got sick over a five-day stretch; I can’t claim that my hygiene was better than everyone else’s but I felt fine the whole time. I think it was natural immunity that saved my bacon. I never really had any diarrheal illnesses as a child or adolescent, either.
People have immune systems. They work amazing well, most of the time.
It’s not that a dozen viruses will always cause an infection. Better to say “Even a single virus could cause an infection, under the right circumstances”. Generally, the more individual viruses, the bigger the chance of infection, but it also depends on how healthy the person is, whether their immune system has experienced that strain of virus before, and characteristics of the strain. Plus, as **brossa **points out, characteristics of the person.
How does one tell if they are a secretor/nonsecretor? This is fascinating. While I do occasionally get stomach bugs, I have never gotten a norovirus - though I also haven’t really been in a big outbreak yet. I am known in family as having a cast iron stomach [one SCA feast event something around a quarter of the people attending, including the entire table of people I was with got ‘food poisoning’ while I didn’t and as far as I know we all ate the same things.]
I’m the same. In fact two or three months ago I suspect I might have caught a very mild dose of this or a similar virus - in the space of about 10 minutes I went from feeling absolutely fine to feeling very feverish and slightly nauseous. I had a slight attack of the runs but that was it and decided to go home from work, but by the time I got home I felt pretty much fine. Next day I had no symptoms whatsoever.
Well, you can have a relative who is a norovirus researcher and who will do the test for you.
It’s a saliva test based on antibody reactions; you can probably request it from a physician, or you can order a test kit online from any number of quackery sites that purport to give you a personalized diet plan based on your blood type and secretor status, if you trust them. Amazon has them, for that matter.
I should point out that being a nonsecretor is not an absolute protection against norovirus; there have been outbreaks of particular strains that infected secretors and nonsecretors equally. Even in those strains, though, some rare minor blood types (Lewis a-,b-) may still be protective, but that’s present in only ~5% of the population. So if you wanted to be thorough, you would check your secretor status as well as your blood type including Lewis. Lewis a-b+ are secretors, Lewis a+b- are nonsecretors, but Lewis a-b- can be either secretors or nonsecretors.
Tempting I am AB neg, not certain of the specific phenotype though at one point in time I had a copy of a pre-op blood workup that did actually have the info on it [I used to get my body worked on at Strong Memorial up in Rochester and was a guinea pig for a couple things there]. If I get the spare cash laying around I might just check into seeing about splurging on a test kit
We have pretty effective immune systems. Your ancestors who succumb every time they were exposed to enough of a pathogen to theoretically make them ill, didn’t live long enough to be your ancestors.
I am AB neg, not certain of the specific phenotype though at one point in time I had a copy of a pre-op blood workup that did actually have the info on it [I used to get my body worked on at Strong Memorial up in Rochester and was a guinea pig for a couple things there]. If I get the spare cash laying around I might just check into seeing about splurging on a test kit