Monday, January 18, 2010

The weekly vector-borne WTF?

How could the "international peer-reviewed journal" called Global Health Action have escaped my notice for so long? (I like that they use the word ACTION, but they had me at "Global", anyway). Their home page is decorated with pictures of mosquitoes and polar bears, so I instantly knew I was on the right track.

Just recently they published an Australian article: Climate change could threaten blood supply by altering the distribution of vector-borne disease: an Australian case-study, (available here) which is basically concerned with the fact that during a recent dengue outbreak in far north Queensland, regional blood supplies ran low due to transfusion service bans on collecting from people who were in, or had been to, the dengue prone area.

I've discussed before this the many reasons why climate change is not linked to an increase in vector-borne diseases so much as public health is. You can find stuff on the topic here, here and here. No need to rehash. So on to a discussion of dengue in Australia.

The main dengue vector, Aedes aegypti is apparently an introduced species to Australia, but has been here long enough that it's probably not useful drawing the distinction, except to point out that its highly likely they haven't reached the limit of their possible distribution across the country. There are other mozzies that can be dengue vectors in Australia, but the thing about Ae. aegypti, is that its an urban mozzie. According to the UNSW mosquito nerds:

It is assumed that Ae. aegypti is the vector of greatest concern because of its distribution and close association with humans. Ae. aegypti is predominantly a day-biting mosquito whose larvae may be found almost exclusively in clean water in man-made containers such as water-barrels, rainwater tanks, wells, vases, tyres, bottles, tins, and most other water-holding containers found in the domestic environment. Although the species is currently restricted to Queensland, there are past records of Ae. aegypti being found in NSW, the NT and WA.

Interestingly, the UNSW crew also note that:
Ae. albopictus, poses a threat to Australia. It is an important vector that has been introduced from Asia to many countries, as eggs or larvae transported in artificial container habitats such as used motor vehicle tyres, and water barrels on ships. If it was introduced to Australia it is likely it could readily establish and present a threat for dengue transmission.

This cute little stripey bugger was made famous (if you hang out in the right cirlces and don't get out much) by turning up unannounced many years ago in Houston in the USA, after hitchiking from Asia in used car tyres or such. A past-time that is distinctly unrelated to climate change. (If we wind up with ae. albopictus immigrating from Asia, we can console ourselves with the fact that we have already shipped red-back spiders to Japan).

The fact that Ae. albopictus made its way all the way from Asia to the US would make it seem likely it could handle the little tootle across from New Guinea (where it is already) to the Torres Strait. Especially considering our northernmost island of Saibai is something like, 4 or 5 km away from the New Guinea mainland. Oh, wait, too late. Given that it is native to territory as far north as Beijing, there is no reason why it needs the help of global warming to colonise our southern states.

I'm thinking that when it comes to the spread of dengue vectors in this country, climate change is the least worrying possibility. We've got more immediate problems when it comes to vector borne disease knocking on our doors.

A part of the premise of this article is vaguely sound. Yes, I agree, more dengue outbreaks would put a strain on regional blood supplies. They could have written the whole article on this topic, and just omitted all the bits about extrapolating poorly considered "climate change scenarios". Although admittedly that would have buggered up their conclusion a bit, which was:
Unless there is strong intergovernmental action on greenhouse gas reduction, there could be an eight-fold increase in the number of people living in dengue prone regions in Australia by the end of the century.

I think a far better conclusion would be to go away and remember exactly how we went about eradicating dengue from mainland Australia by the 1950's, and which holes in the public health system lined up to allow it to come back in the 1980's.

1 comment:

  1. Thanks for reading! Ha ha, yes, we appreciate any opportunity to stick it to Rachael Carson here at the Daily Suppository. I think the last time was here:


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