Viral gut pathogens (norovirus, rotavirus, adenovirus, astrovirus, sapovirus)

Noroviruses (genogroups GI and GII), rotaviruses, enteric adenoviruses, astroviruses and sapoviruses are the most common viruses that cause acute vomiting and diarrhoea (gastroenteritis). Their genetic material is detected in stool by PCR, a method that picks up even very small amounts of virus. Bacterial causes of diarrhoea such as salmonella or campylobacter and single-celled parasites are described on their own pages. Detection of noro- and rotaviruses is notifiable in Germany; the laboratory reports it to the public health office.

How viral gut pathogens attack the small-intestinal lining

The viruses are transmitted via smear infection, contaminated food or – in the case of noroviruses – also via tiny droplets released during vomiting. They survive stomach acid and infect the cells at the tips of the small-intestinal villi. There they multiply, the cells die and the villi become shorter. This reduces the surface through which water, salts and nutrients are absorbed, and enzymes such as lactase on the cell surface are temporarily missing. Rotaviruses also produce the protein NSP4, which acts like a toxin, stimulating the release of chloride and water into the gut and activating the nervous system of the gut wall. Noroviruses also delay gastric emptying, which explains the sudden vomiting.

What happens with a norovirus or rotavirus infection?

Noroviruses are highly contagious: just a few virus particles are enough for infection, and they remain infectious on surfaces for a long time. After about one to two days, vomiting, watery diarrhoea, nausea and abdominal cramps begin abruptly, often with mild fever; symptoms usually subside after one to three days. Rotaviruses mainly affect babies and toddlers and often cause longer-lasting diarrhoea. Through the loss of water and salts the body can become dehydrated, which strains the circulation in small children and older people. The viruses are often still shed in stool for days to weeks after symptoms have subsided.

What do adenoviruses, astroviruses and sapoviruses do in the gut?

The gut adenoviruses of types 40 and 41 mainly affect children in the first years of life. They multiply more slowly than noroviruses and cause watery diarrhoea that often lasts more than a week. Astroviruses and sapoviruses cause a similar, usually milder picture than noroviruses, with diarrhoea, nausea and occasional vomiting; mainly children are affected, but also older people and people with weakened immunity. In the latter, all of these viruses can remain in the gut for longer. Until the villi have renewed themselves, milk sugar is often less well tolerated. Studies have occasionally observed persistent irritable bowel symptoms after viral gut infections.

No viral gut pathogens detected – what does it mean?

Without detection, the viruses tested for are an unlikely cause of the current diarrhoea. Diarrhoea can equally be caused by bacteria, single-celled parasites, Clostridioides difficile or non-infectious causes such as intolerances. Because the viruses are shed only for a limited time, a stool test taken later often no longer shows a past infection. Conversely, the sensitive PCR can pick up viral remnants even after symptoms have subsided; detection in people without symptoms therefore occurs, especially in children.

The interpretation is given in your report.