Love affair with parasites

From scabies to flesh-eating fire fish (okay we made that one up), Dr Deborah Holt knows, and loves, parasites. We find out why.

Healthy Tomorrow (HT): What are the most ‘garden variety’ parasites around and how do they affect you?

Deborah Holt (DH): For starters, more than 50 per cent of all animal species are parasites. Parasites that most people in Australia would be familiar with include head lice and intestinal worms. They get nutrition from feeding on humans and even a mild infection can make us extremely uncomfortable.

In the Top End, scabies is very prevalent. This is caused by mites that burrow into your skin and lay their eggs there. This can cause nasty skin lesions and secondary bacterial infections and is extremely itchy.

HT: And which are the weirdest parasites?

DH: I’m not sure about the weirdest but a couple of my favourites for presentations are the amoeba that can swim up your nose while you are swimming and then can cause infection in the brain.

And then there are worms, such as hookworm, that can be in the soil and then burrow through your feet, travel through your body to your lungs, then to your intestines. The way that they can move around your body to get where they want to be is quite amazing.

HT: What's the coolest thing about parasites?

DH: I find parasites so clever and complicated. Despite the fact that many of them are small and some are just single cells, they have the ability to live in a variety of environments and can manipulate those environments to suit their own purposes.

HT: Do you have a favourite?

DH: My favourite is probably the malaria parasite Plasmodium as it’s the first parasite I ever worked on. It’s a microscopic single celled parasite that you might expect to be quite straight forward, but they have sophisticated life cycles involving a mosquito as well as a very different host species, such as humans. They need different sets of genes and proteins to survive in either environment.

They have also developed some extremely clever techniques to avoid being detected by their host’s immune system. Despite some of the world’s greatest minds studying malaria and a whole lot of money being invested in malaria research, there is still so much that is not understood.

HT: What's been the most exciting project you've worked on, or breakthrough you've made?

DH: My most exciting moment would have been receiving an email from Annette Dougall. She was doing her PhD and had already spent over two years trying to identify the insect responsible for transmitting a new Australian species of the parasite Leishmania, without any luck. This parasite had only recently, and very unexpectedly, been discovered in Australia, so we were pretty excited about the whole thing.

I checked my email and there was one from Annette titled something understated like “Check this out”. The email had no other words; just a picture she had taken of thousands of Leishmania parasites streaming out of the stomach of a biting midge that she had dissected.

It was absolutely amazing; I couldn’t get into the lab quick enough. It was the first evidence from anywhere in the world that an insect other than a sand fly could transmit this parasite. It was a bit like finding evidence that an insect other than mosquitoes could transmit malaria.

The next challenge was to convince the rest of the world that it was true…. and I’m happy to report that we seem to have done that.

HT: What's next for you?

DH: We are hoping to complete a full genome sequence of the scabies mite with collaborators at the Queensland Institute of Medical Research and the Walter and Eliza Hall Institute in Melbourne. We want to also complete the genome sequence of the house dust mite at the same time.

Allergy to house dust mites is one of the major causes of asthma so we are hoping the comparison between these mites, one which is parasitic and one which is not, will provide us with lots of useful information about how they affect humans. It’s something I’ve wanted to do for quite a few years so fingers crossed we can get some funding to do it.

HT: What gets you out of bed and into the lab each day?

DH: The great thing about laboratory research is that every day is different. You might be using similar techniques often, but the results will be different, something new or unexplained will come up and we have to find creative ways to answer questions. It’s never boring, you’re always learning something.

I’m a molecular biologist, so most of my work focuses on DNA. We extract it from organisms that we are interested in and then analyse it.

For instance I’ve been working on scabies mites for many years. One of the things we have done is to sequence a lot of scabies mite genes, and from there tried to work out how what happens when they burrow into human skin. To be able to try and stop them successfully living and breeding in human skin, we need to understand how they survive in human skin.

In other work we’ve also discovered a new type of bacteria that is commonly found on people’s skin and can cause skin infections. It’s like Golden Staph but has some unique and interesting differences. We are currently sequencing the genomes of a whole lot of them and it's going to be really interesting data from which we can learn a lot about both these bacteria and Golden Staph.

HT: Why did you choose to work at Menzies in Darwin?

I first came to work to Menzies to work on malaria with the previous Deputy Director Professor Dave Kemp. It was a spur-of-the-moment thing. I was working in Melbourne, had a chat to Dave one morning then moved to Darwin two weeks later.

I’ve had one stint interstate since then, but as I’ve become more involved in research on infectious diseases which are important in Indigenous communities, I can’t really imagine working anywhere else. I also really love living in Darwin – which helps!