Crime-scene technology adapted for mosquitoes to predict Ross River Virus outbreak

The suspects are bloodthirsty and remorseless, but no more so than the general population.

The challenge for investigators is distinguishing from about 300 species of mosquito the dozen or so that present a present danger to humans.

Cutting-edge technology developed for investigating crime scenes is now being adapted for mosquitoes, in a bid to contain the health risks posed by those carrying viruses.

Last summer was the worst on record for Ross River virus outbreaks, mostly in northern NSW and Queensland, and it took health authorities by surprise.
NSW Health Pathology mosquito researcher Cameron Webb is collaborating with interstate colleagues on a process of barcoding the DNA of mosquitoes. Their goal is to identify which species are most likely to cause disease.
“We’re trying to learn from what happened last summer, so in the years to come we’re better able to predict when these outbreaks might occur,” Dr Webb said.
Thirty councils around the state are sending weekly mosquito samples to NSW Health under the arbovirus surveillance program.
They are caught in carbon dioxide traps, which trick mosquitoes into believing a warm-blooded animal is nearby.
After identifying the species under a microscope, scientists mash some with a mortar and pestle and culture any viruses they might be carrying.
But some of the trapped mosquitoes are playing a role in an experiment scientists hope will allow them to identify viruses and issue public health alerts more quickly.
Inside the traps, pathologists have planted a cardboard type substance developed by forensic scientists to trap bodily fluids at crime scenes.
The cardboard is smeared with honey and when the mosquito sinks her proboscis into the material and spits out – which is how she gets the blood flowing in an animal – she leaves behind a coat of saliva that is analysed for viruses.
Only female mosquitoes bite.
“Mosquitoes aren’t like a dirty syringe that passes blood from person to person,” Dr Webb said.
“The virus infects a mosquito itself and it passes on the virus when it injects spit.
“So if we can collect saliva we don’t need to mash up the mosquito to see what they’re carrying.”
Ross River Virus is not deadly, but it causes flu-like symptoms, such as headache, fever, muscle pain and chills, and can last from a few weeks to a few years.
People catch it from mosquitoes that have bitten wallabies or kangaroos with the virus, and about 5000 cases are usually reported annually – although there have already been 8000 cases this year.
Last summer presented ideal conditions for the mosquitoes, with a warm spring followed by a wet summer and a cyclonic depression in Queensland.
But it is notoriously difficult to predict outbreaks, which depend on a complex interplay of climate conditions, local wildlife, the wetlands where the virus is found and the species of mosquito.
Fewer people are expected to be infected this summer because a lot of the animals have been exposed to the virus already and will not catch it again.



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