Astroviruses

These viruses infect vertebrates and appear to be specifically adapted to various groups: human, bovine, ovine etc. In humans, astroviruses are the most frequent viral cause of infectious intestinal disease, causing an enteritis of the small bowel resulting in a secretory diarrhoea. Infection is by contaminated food or water and occur mainly in childhood. Usually the symptoms last on average 12 hours with complete recovery in 48 hours. Associated symptoms may be nausea/vomiting, abdominal pain or fever. Clinically, these symptoms are similar to those of caliciviruses.

Astroviruses were first described in 1975 as a result of electron microscope studies of an outbreak of diarrhoea in a maternity unit and a survey into the aetiology of diarrhoea in childhood in a Scottish city.

Astroviruses have been isolated from birds, cats, dogs, pigs, sheep, cows and man.

In humans, exposure to astrovirus happens usually at an early age; 75% of children 5-10 years of age have astrovirus antibodies. Astrovirus infection occurs world-wide and accounts for 2-8% of cases of diarrhoea in infants. It is a significant cause of diarrhoea in developing countries. In Thailand, 8.6% of cases of diarrhoea were associated with astrovirus and a similar rate was found in Guatemala (7.3%).

Like rotaviruses, astrovirus infections occur through the year with peaks in the winter months.

Outbreaks of astrovirus infection involving children and elderly patients have been described and prolonged excretion documented in immunosuppressed, immunodeficient and AIDS patients.

There are at least 7 human astrovirus serotypes which are differently distributed around the world, for example astrovirus type 1 is the prevalent strain in the UK, accounting for 65% of the cases, whereas type 2 was the most prevalent in Mexico (31%) and type 1 relatively rare (6%); in Japan reported infection involving thousands of children and adults have been associated with astrovirus type 6.