Bloody parasites!

For the princely sum of $20 a year, I belong to the New Zealand Society for Parasitology. It’s kind of them to let me join, since I’m not a parasitologist or even a scientist. But I am interested in their work because it crops up often in the magazines I produce (one for vets and the other for farmers), and my hosts are happy to accommodate this media parasite.

Earlier in October I attended the NZSP’s annual meeting and was rewarded with some excellent papers and, I’m happy to admit, some gruesomely fascinating stories.

Hookworm larva - you really don't want to catch this one.
Hookworm larva – you really don’t want to catch this one.

Keynote presenter was Professor Graham Le Gros from the Malaghan Institute. He pointed out that the relationship between human hosts and their parasites might be more mutually beneficial and complex than we thought. While the thought of hookworm, tapeworm, pinworms, head lice and countless other parasites that enjoy our hospitality is pretty distasteful, it turns out that parasites appear to modulate our immune systems in ways that can be helpful. For example, the occurrence of inflammatory bowel disease appears to be inversely related to the presence of internal parasites. Beyond that, parasites seem to be protective against a whole range of inflammatory diseases. Hmm. Hookworm anyone? It turns out people have been trying controlled doses of that very parasite as a last resort to try and control chronic coeliac disease. No-one seemed sure this was a very good idea – it’s a very nasty parasite that causes internal bleeding and intense itching as it emerges.

One treatment that definitely works well is “faecal microbiota transplantation” for treating recurrent infections with the bacterium Clostridium difficile,  responsible for diarrhoea, colitis and even death. We all carry the bug, but if the balance in our gut flora is knocked out of whack, they can overgrow and cause considerable grief. Antibiotics usually work with a first-time infection but if it becomes recurrent, they lose their efficacy. Enter the seemingly miraculous and low-cost treatment which, not to put too fine a point on it, involves taking on board a 50ml slurry of someone else’s poo. According to the fresh-faced Dr Brendan Arnold from Wellington Hospital, the best method involves an enema – taking the treatment down the other end can result in some unpleasant sulfurous belching. He’s treated seven patients this way over five years and the success rate has been 100 percent. Often the chronic symptoms resolved within 24 hours as the introduced bacteria quickly helped restore a healthy balance. Arnold said patients were unfazed by the treatment – it was the attending doctors and nurses who were more distressed by the “yuck factor”.

On the other side of the ledger are people who self-diagnose with internal parasites, blaming a whole range of maladies on unseen passengers. Dr Ian Wilson said “parasite cleansing” is big business, but unless you’ve been travelling overseas recently or are a newly arrived migrant, your chances of carrying a pathogenic gut parasite are pretty small. That’s not to say we don’t carry them – it’s just that they don’t normally cause any problems unless we become immunocompromised. These scientists don’t lack for humour or the same morbid fascination shared by me and other civilians. Wilson’s favourite tale involved a tapeworm discovered in a patient during a colonoscopy. The worm, spotting an opportunity, disappeared up the colonoscope, wrapping its tail around the handle – much to the horror of the operator and amusement of just about everyone else.

External parasites also got their moment in the sun at the NZSP meeting and there were two presentations about the use of fly larvae – OK, maggots – for cleaning wounds. This is done in both human and animal medicine, but is probably easier in humans who are a bit more cooperative when it comes to protecting the delicate grubs as they diligently clean up wounds under the bandage. It’s not a new therapy but has recently come back into fashion to help with cleaning up dead tissue and infective bacteria from chronic wounds. It turns out the maggots need special care. They can drown if the wound is too weepy and they need a bit of air and light through the gauze covering – and of course they can be easily squashed if you’re not careful. Also they aren’t suitable for all kinds of wound. As with the faecal transplantation, it is squeamish doctors and nurses who have a problem with the treatment, rather than the patients.

Returning to the theme of people’s obsession with parasites, Dr Mark Jones, Wellington Hospital, gave a tongue-in-cheek presentation on “delusional parasitosis”. He recalled the frustration he felt when in just one month, his lab had to process 760 tests for “ova and parasites” in faeces samples. Of these, just 11 revealed giardia cysts, which could have been detected using other means (the ELISA test). The rest were clear of pathogenic parasites. Jones said the testing tied up three full-time scientists and were largely a waste of time. Removing the “ova and parasites” tick box from the standard lab form helped cure the over-testing problem, he said.

Jones said a small group of people were convinced they were crawling with parasites and were never satisfied with negative tests. Often they would submit samples under false names and could damage themselves gouging out skin and flesh to offer as samples, helpfully packaged up in a matchbox. Delusional parasitosis emerged into the mainstream about 10 years ago with the arrival of “Morgellons disease” in which sufferers were convinced they had parasites in their skin, often emerging as fibres. A Centres for Disease Control study concluded the fibres were actually just from people’s clothing. It was a lot of fluff.

I found from another speaker that it’s not a good idea to flush your cat’s poo down the toilet because the nasty Toxoplasma gondii protozoan parasites they carry will end up in the sea and infect dolphins.

So many parasites, so little time!

I’ll be back next year.