Of worms, fish and people
13 September 2010
"Have you ever gone to a fish market in Melbourne and bought a couta fillet? You should. They're a tasty fish, and really cheap.
"Do you know why they're so cheap? Because they're full of worms."
So says University of Melbourne Professor of Veterinary Parasitology Ian Beveridge, who, on this CReefs trip, is examining fish, sharks and rays for trypanorynch cestodes, an order of tapeworms, and anisakid nematodes, a group of roundworms.
"When you think about tapeworms, you tend to be a bit anthropogenic, and think about human tapeworms and dog and cat tapeworms, but in fact the greatest diversity of tapeworms is in elasmobranchs, that is, sharks and rays," Professor Beveridge explains.
Trypanorynch cestodes and anisakid nematodes, found in fish and marine animals, are considered parasites, although Dr Beveridge says they do not seem to cause any harm to their hosts, and they only very rarely cause nuisance for humans.
People can eat fish with adult cestodes in the flesh, such as couta, worms and all, without consequence. In fact, cooking or freezing will kill any parasites. The only human problems ever associated with these groups of tapeworms and roundworms have been reported from people eating raw fish and squid.
"Some of the tapeworm larval stages occur in squid, and if a larva gets into a human mouth, it can put out its hooked tentacles and grab onto the tonsils. It's very painful, but it can be treated: the tapeworm can be pulled off the tonsils with a pair of forceps," Professor Beveridge explains.
"Some of the roundworm larval stages occur in fish. If larvae survive on a piece of raw fish and make it into a human stomach, they will do what they normally do in any other host: they come out and try to burrow into your stomach wall," he says.
Professor Beveridge is one of a team of scientists, drawn from the University of Melbourne, RMIT and Charles Sturt University, awarded an Australian Biological Resources Study grant to study anasakid nematodes. One of the team is concentrating on interactions between nematodes and people. Professor Beveridge is focusing on the biodiversity of species and their life cycles.