Good Thinking

For faster mosquito virus detection, their waste may be the way to go

West Nile virus, Murray Valley encephalitis virus, and Ross River virus have all been detected in mosquito waste
West Nile virus, Murray Valley encephalitis virus, and Ross River virus have all been detected in mosquito waste
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A diagram shows how passive box traps were modified: (a) feeding substance fixed with a magnet, (b) specimen jar holding a sponge, (c) a rope covered with plastic tubing to transfer water to the sponge, (d) bottle filled with water, (e) mesh preventing dead mosquitoes falling into the waste collection insert, and (f) an insert with nucleic acid preservation cards, which can preserve viral RNA at room temperature for later testing
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A diagram shows how passive box traps were modified: (a) feeding substance fixed with a magnet, (b) specimen jar holding a sponge, (c) a rope covered with plastic tubing to transfer water to the sponge, (d) bottle filled with water, (e) mesh preventing dead mosquitoes falling into the waste collection insert, and (f) an insert with nucleic acid preservation cards, which can preserve viral RNA at room temperature for later testing
West Nile virus, Murray Valley encephalitis virus, and Ross River virus have all been detected in mosquito waste
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West Nile virus, Murray Valley encephalitis virus, and Ross River virus have all been detected in mosquito waste

If the mosquitos in a given area are carrying a potentially lethal virus, then the sooner that local health authorities know about it, the better. According to new research, traps that collect the insects' liquid waste may allow that to happen – and cheaply, too.

Typically, in order to test for mosquito-borne viruses, large numbers of the actual insects are collected and analyzed. Additionally, blood samples from frequently-bitten animals such as pigs are sometimes tested. In both cases, though, a considerable amount of work is involved, plus the samples need to be kept in cold storage throughout the process – the latter can be challenging in developing nations or remote locations.

It's also possible to detect viral RNA in mosquito saliva, which is collected from room-temperature "nucleic acid preservation cards" left in baited traps. That said, a virus must incubate within a mosquito's body for up to 15 days before it can be detected in the saliva.

By contrast, that same virus can be detected in the insect's liquid waste – known as excreta – in just three days. Additionally, mosquitos expel much more excreta than saliva, giving health officials more material to work with.

A diagram shows how passive box traps were modified: (a) feeding substance fixed with a magnet, (b) specimen jar holding a sponge, (c) a rope covered with plastic tubing to transfer water to the sponge, (d) bottle filled with water, (e) mesh preventing dead mosquitoes falling into the waste collection insert, and (f) an insert with nucleic acid preservation cards, which can preserve viral RNA at room temperature for later testing
A diagram shows how passive box traps were modified: (a) feeding substance fixed with a magnet, (b) specimen jar holding a sponge, (c) a rope covered with plastic tubing to transfer water to the sponge, (d) bottle filled with water, (e) mesh preventing dead mosquitoes falling into the waste collection insert, and (f) an insert with nucleic acid preservation cards, which can preserve viral RNA at room temperature for later testing

Given those facts, scientists from Australia's James Cook University, Queensland Department of Health, and Northern Territory Department of Health converted existing inexpensive mosquito traps to collect excreta. Depending on the type of trap, this conversion involved either adding a polycarbonate collection sheet that got manually wiped with one of the nucleic acid preservation cards, or simply placing one of those cards where the insects relieved themselves onto it directly.

In either case, when the collected liquid waste was subsequently analyzed, the presence of West Nile virus, Murray Valley encephalitis virus, and Ross River virus was detected. It is now hoped that such traps could be used for faster, easier and more cost-effective detection of such microbes.

"Our study, to our knowledge, is the first to have detected arboviruses from field-collected mosquito excreta," says James Cook's Dr. Dagmar Meyer, lead author of a paper on the study. That paper was published this week in the Journal of Medical Entomology.

Source: Entomological Society of America

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