New mutant viruses responsible for gastroenteritis outbreaks in New South Wales in recent times have been identified by research published in Emerging Infectious Diseases, a journal of the US Centers for Disease Control.
Known as recombinant noroviruses, they are thought to be one of the reasons for a five-fold increase in infectious gastroenteritis cases in the period 2000 - 2003 (see Table 1, p2). Noroviruses cause up to 90 per cent of infectious gastroenteritis cases globally each year.
Last year - 2004 - there were well over 10,000 NSW cases of infectious gastroenteritis. Outbreaks in recent years were reported at a Sydney children’s hospital (February 2002), a Sydney aged care facility (September, 2002), a Picton aged care facility (July 2003) and in Wagga Wagga (October 2003).
Viral gastroenteritis is a common infection of the stomach and intestines that results in vomiting and diarrhoea. Other symptoms can include nausea, fever, abdominal pain, headache and muscle aches. Non-viral causes of gastroenteritis include bacteria, toxins, parasites and some non-infectious diseases.
Spread by air, water and personal contact, noroviruses are highly contagious and can survive in food, water and the environment for long periods, according to University of New South Wales virologist, Dr Peter White, one of the research authors.
“An inoculum of as few as 10 viral particles is enough to infect an individual,” says Dr White. “The virus can be spread by person-to-person contact, for example shaking hands with someone who has been sick and has the virus on their hands. It can also be picked up from contaminated surfaces, food or drink, and it’s possible that infection can spread through aerosol particles when people vomit,” he says.
The research team made four new findings:
- they “genetically fingerprinted” ten main types of mutant (or recombinant) norovirus from among hundreds of known varieties of noroviruses from around the world.
- they isolated four of these main types in the greater Sydney region.
- two of the main types found in Sydney are new forms of the virus never identified before.
- they located the “break-point” within the viruses’ genetic code where the viruses mutated by swapping part of their genome.
“Viral recombination refers to a virus’s ability to swap parts of it genetic material with another related virus,” says the study’s lead author and UNSW PhD candidate, Ms Rowena Bull.
“This can happen when a person is infected with two forms of the norovirus at once. It’s how viruses create diversity in their genome and gives them a better chance of spreading and surviving in different host environments,” Ms Bull says.
The genetic diversity of noroviruses is now known to be much greater than was thought when the first strain was discovered some 30 years ago.