Killer slugs

Killer slugs

The speaker at my Rotary club meeting last week had a remarkable story to tell, one in which I had an intense personal interest. Paul McNabb of the Cawthron Institute spoke about the discovery of New Zealand’s most poisonous animal, an inconspicuous little sea slug.

sea slug

The story began about one year ago when a whole series of unexplained dog deaths occurred along East Coast beaches in Auckland. The deaths were highly alarming, especially to a population that love their beaches. Fingers were pointed in all directions: farmers causing toxic algae blooms, pest control activities on Rangitoto Island carried out by the Department of Conservation, fishermen illegally dumping unwanted catch – you get the idea.

Here were some of the headlines at the time:

  • Fear keeps popular beaches almost bare.
  • Beaches off-limits to kids after mystery dog deaths.
  • Dog deaths and vomiting after beach walks.
  • Are dead fish to blame for Shore’s sick dogs?

Researchers at our local Cawthron Institute were very quick to respond. At their own expense, they sent Andy Selwood up to collect samples of just about everything he could lay his hands on. Concentrated extracts from these samples were sent to Hamilton to a long-time associate, toxicologist Rex Munday. He rapidly found that one of these was extremely toxic indeed. Then the chemists got to work and within just two days had found the toxin. It was tetrodotoxin (TTX), the compound found in pufferfish which even today regularly accounts for a few deaths each year amongst Japanese foodies who love their “fugu”.  TTX was present in large quantities in sea slugs, small creatures with a large name: Pleurobranchaea maculata.  It was also found in some of the dead dogs.

As usual after something has first been discovered, these toxic slugs have now been found in quite a few other areas. No one knows for sure exactly where the TTX comes from. It’s very unlikely to have been produced by the slugs themselves.  Why should the problem suddenly appear? Paul had an interesting theory, yet to be proven. Some areas of the seabed have colonised by a marine invader, the Asian date mussel. These appear to provide a good habitat for the sea slugs and some large populations have been observed. Under suitable conditions (for example a large storm occurring when the slugs are in a weak condition after spawning) many of the slugs may be washed up on the shore. There are a lot of unanswered questions and, at least at the moment, no funding for the research required to answer them.

Paul’s talk was received very well. One of his props was a live sea slug in a beaker of sea water which was passed around the room. It was interesting to observe how people reacted, being close to something which contained enough poison to kill half the people in the room.

The problem has not gone away and indeed only last month authorities were again issuing warnings as more of these creatures washed ashore. So far, no TTX seems to have been found in fish (much to the relief of the seafood industry and recreational fishers).

There’s a little more to this story however. Over the past 10 years, Paul McNabb has become an international expert on the detection of these marine biotoxins. Along with colleague Pat Holland, his advice has been sought in Ireland, Spain, Canada and the USA. The underlying reason for this prominence can actually be traced to a few key people.

In the mid-90s, the shellfish industry was struggling to cope with the impacts of New Zealand’s first large-scale toxic algae bloom. This event, in the summer of 91/92, led to testing on an amazing scale in the name of public health. Helicopters were being used to collect samples from some inaccessible beaches, and I suspect some shellfish populations were becoming depleted from all the sampling. The only test available at that time was a bioassay using mice (thousands of them, the country ran out at one stage). The annual cost exceeded $3 million, a completely unsustainable figure given the actual risk to public health.

A few well-informed, farsighted people in the shellfish industry were acutely aware of the potential impact on the brand of New Zealand export shellfish. A new approach to the testing was required. Cawthron scientists were pushing for the information available in sea water samples to be properly utilised. Analysis of phytoplankton for “nasties” was much quicker, cheaper and more reliable than mouse tests. Analytical chemists at Tohoku University in Japan (Prof Takeshi Yasumoto) and the Institute of Marine Biosciences in Halifax, Nova Scotia (Dr Mike Quilliam) had begun to use mass spectrometers to identify the toxic compounds themselves.

With their help, an investment of well over $1 million and a commitment from industry to support this new approach, Cawthron purchased its first LC-MS instrument and started to develop analytical procedures for routine testing. Paul McNabb was hired to work on the project and a specialist in mass spectrometer techniques, Pat Holland, joined him. It was a formidable task. Not only must routine test protocols be rapid and cost-effective, but they require extensive validation before they can be accepted by authorities as an alternative to established test methods. In this case, it wasn’t just the New Zealand authorities but regulators throughout Europe and North America. Cawthron had to persuade the US FDA to change its approach.

They did it. It took a few years longer than the early estimates, but now New Zealand is acknowledged to have the best surveillance system in the world for monitoring marine biotoxins. Oh, and by the way, Cawthron won an award from a government animal welfare committee for the elimination of the use of mice for routine shellfish testing.

One of the reasons for this success was New Zealand’s small size. It’s relatively easy to get people to meet face-to-face and, with good leadership, it was possible to have everyone – central government regulators, industry players, local health authorities, researchers and testing laboratories – all working together.   I was heavily involved in all of that and I well remember the champions that drove the project. Here are some of them: Teresa Borrell from Sanford Ltd, Paul Lupi from the Mussel Industry Council, and Helen Smale from the Marlborough Shellfish Quality Program. Within Cawthron, key players were Lesley Rhodes, Kirsten Todd and Lincoln McKenzie (phytoplankton specialists), as well as Paul McNabb and Pat Holland.

So the TTX incident shows the benefit of having this capacity within the country. It had raised such public interest that who knows what crazy decisions would have been made if the mystery had dragged on?

Here are some links for anyone who wishes to follow the story a little further:

(acknowledgment:  the sea slug image was lifted from Cawthron’s website)

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