Testing mosquito pee could help track disease spread

There are no teensy cups. But a new urine test for wild mosquitoes has proved for the first time that it can offer an early warning that local pests may be spreading disease.

The new test added a pee-collecting card to a mosquito trap. That card picked up telltale genetic traces of West Nile and two other worrisome viruses. Researchers in Australia described the new technique April 4 in the Journal of Medical Entomology.

The idea grew out of testing insect saliva. Scientists unveiled such tests in 2010. These lured mosquitoes into tasting cards coated with honey. The skeeters left some saliva behind. Scientists then checked for genetic traces of viruses in that saliva.

Saliva checking had its charms. The cards do not have to stay cold the way samples of whole insects do.  And the saliva method did not take as much work as checking chickens or pigs for signs of a virus.

But the tiny traces of saliva left on these cards were almost too small to test.  A mosquito drools fewer than five nanoliters of saliva when it tastes a card. In contrast, mosquitoes excrete about 1.5 microliters of liquid per pee. That’s a flood compared with saliva.

That flood prompted Dagmar Meyer of James Cook University in Cairns, Australia and her colleagues to create a urine collector. They used standard overnight traps that lure mosquitoes with light. They also used longer-standing traps that exhale carbon dioxide, which lures a mosquito.

The team set out 29 urine traps in two insect-rich spots in Queensland, Australia. Researchers also set out saliva traps. When mosquitoes entered a urine trap, their pee dripped through a mesh floor onto a collecting card. Adding a moist wick of water kept trapped mosquitoes alive and peeing longer. That improved the sample.

Pee traps picked up three viruses — West Nile, Ross River and Murray Valley encephalitis (En-seff-uh-LY-tis). The saliva ones only detected two, the researchers report.