A 3D-printed funnel produced a complete West Nile genome from mosquito droppings

The reason to look at excreta at all is host DNA. Mosquito waste contains far less mosquito tissue, and therefore less mosquito DNA, than a crushed insect, and the researchers reasoned that viral material would be easier to find in it ^[7]. "What we did, colloquially, was build a mosquito toilet," said Dana Price, an associate professor at the Rutgers Center for Vector Biology and a lead author of the paper in Microbiology Spectrum ^[1][2].

Shotgun metagenomic sequencing reads all the genetic material in a mixed sample; software then assembled the millions of fragments and compared them with known sequences in scientific databases ^[9]. Standard mosquito tests target specific pathogens, so a program has to decide in advance what it is testing for ^[6]. "If you don't look for it, you won't find it," Price said. "But what if you don't know what to look for?" ^[18]

The same run also identified parasites and confirmed which mosquito species had left the droplets ^[5]. In the conventional workflow, that species identification is done by hand, before the insects are combined into pools and ground up ^[6].

Hedwig virus was first identified in Europe in snowy owl tissue and named for Harry Potter's white owl, and some of the infected birds also carried West Nile ^[13]. Whether Hedwig-like viruses make birds sick, facilitate West Nile infection or simply coexist with other viruses is not known ^[14]. Price said the Rutgers detection does not establish that the virus is a threat, only that it has been circulating where nobody knew to search ^[15]. "We didn't even look for it specifically," Price said. "We just looked for everything, and we found Hedwig in there." ^[16]

Then the denominator. Two groups of 50 comes to 100 mosquitoes in total, and the complete genome came out of the 2022 sample, one of the two ^[19][20]. Two samples cannot show how often the method returns a genome, and the authors did not run the same mosquitoes through pooling and grinding for comparison ^[21].

The insects were not sampled where they were caught. Each group went into a screened container set over the funnel and was fed a sugar solution until it produced drops of waste ^[8]. Catching wild mosquitoes is still the first step, and the paper does not give a cost for the printed funnel ^[24]. Price is working with officials at the New Jersey Department of Environmental Protection's Division of Fish and Wildlife to screen organ and tissue samples taken from birds found dead during postmortem examination ^[17].