Science Centres: Aquatic Biodiversity and Biosecurity

Hypothetical foot-and-mouth viral plumes over Waiheke Island for actual weather conditions on 12 & 13 May 2005, assuming four properties with pigs were possible sources of infection. The concentrations of virus are expressed in units of TCID50/m3, where TCID50 means Tissue Culture Infectious Dose in 50% of exposed animals.

NIWA can conduct similar modelling for other airborne and aquatic diseases, and invasive pests.

Last month’s foot-and-mouth hoax on Waiheke Island provided a test of NIWA’s rapid-response modelling of transport of airborne pests and diseases.

NIWA is on call around the clock in case of a biosecurity alert from the Ministry of Agriculture and Forestry (MAF). We use a computer system called Plume Dispersion Emergency Management System (PDEMS) to predict where potential plumes of foot-and-mouth virus could disperse in the air, and can deliver an answer to MAF within 4 hours. ‘We’ve put a lot of effort into automating the system for rapid response,’ says NIWA meteorologist, Dr Richard Turner.

Richard is intensely aware of the need for the best possible information. ‘We take it really seriously. If you’re a farmer and our model says your farm’s in the path of the plume, it’s potentially your livelihood at stake,’ he says.

Throughout the alert, NIWA worked closely with EpiCentre, part of Massey University’s Institute of Veterinary, Animal and Biomedical Sciences, with results from their model of production of the virus being fed into PDEMS. We also received valuable assistance with weather data from MetService and the Auckland Regional Council, and lo cal weather observations from Waiheke farmers.

Pigs pose the greatest risk for airborne dispersal of the virus.Given the weather conditions at the time, and the few on the island, our modelling showed the risk of long-range spread of the disease was slight.

A perfect day?

Think of a typical winter’s day in Christchurch and you’ve got good conditions for spreading foot-and-mouth: a dull day with a slight breeze (not blustery) can maintain high concentrations of virus within a plume. A typical Wellington day, by contrast, produces poor conditions for spreading foot-and-mouth: sunny, with strong and gusty winds that ‘dilute’ plumes.

To gauge the risk of aerial spread of foot-and-mouth, we look at the ‘boundary layer’ – the often turbulent layer of air close to the earth’s surface. PDEMS incorporates information on factors such as the terrain, the wind strength, the cloud cover, land use, and other weather features to predict the wind direction and turbulent state of the boundary layer with as much accuracy as possible.