Lecture 18-Helicobacter pylori gastritis, Rotavirus and Norovirus

**Who is affected by H. pylori infection?

o 80 % of the population is infected by the age of 75.

**How can infection and disease from these viruses be prevented?

o A live attenuated Rotavirus vaccine is available since 2006. o Frequent hand-washing and avoiding tap water and uncooked food when traveling in undeveloped countries. o Babies can be protected by maternal antibodies (breastfeeding).

**What are typical scenarios of infection with norovirus or rotavirus?

o Both viruses are very stable and persist for months in water or on surfaces. o Only very few virions are sufficient for infection. o Therefore the viruses are very efficient at causing an epidemic where people are living in crowded condition (retirement homes, daycare, cruise ships, hotels, etc..) o Often food is contaminated by infected "food workers" - outbreaks in restaurants, large kitchens, etc.. are very common.

**Why are Rotavirus and Norovirus very dangerous for small children?

o Both viruses cause severe dehydration, which can be fatal in small children.

**H. pylori is often associated with stomach cancer - why?

o H. pylori infections are often chronic, persisting for many years o H. pylori secretes proteins such as CagA and VacA that damage the epithelial cells on the stomach. Persistent damage to cells lining the stomach causes chronic inflammation and constant proliferation of the epithelial cells - this increases the likelihood that cells transform into cancer cells.

**Why is there no efficient vaccine (yet) for Norovirus?

o Norovirus evolves very efficiently by antigenic drift and many "genogroups" of norovirus exist. A vaccine is very difficult to make, because it would need to contain surface antigens of most or all genogroups. This is impossible as new genogroups are constantly evolving. o A vaccine is not very economical for the reasons above and also because norovirus us usually not fatal or persistent.

**How does Helicobacter pylori survive the acidic environment of the stomach

o Produces urease, which converts urea (from proteins) to ammonia, a strong base, which neutralizes stomach acid and produces a microenvironment in which Helicobacter pylori can live. o H. pylori has a flagella to burrow within mucus layer that coats stomach lining, follow pH gradient to epithelial cell

**Name two viruses that infect the epithelial cells that line the intestine and cause acute, severe diarrhea.

o Rotavirus and Norovirus

**How did Barry Marshall and Robin Warren prove that Helicobacter pylori causes stomach ulcers?

o They did a self-experiment: They drank a culture of helicobacter pylori and both developed peptic ulcers shortly afterwards. o Of course they also had a lot of additional evidence that back up their claim. o Prior to their work, the medical profession thought stress causes peptic ulcers and for a long time disregarded the evidence presented by Marshall and Warren.