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Citizen Science Project Helps Determine Distribution of Tick Pathogens in US

NEW YORK (GenomeWeb) – A new study has demonstrated the feasibility of identifying tick-borne pathogens through genetic analysis on samples submitted by citizen scientists across the country.

Using quantitative PCR, a team from Northern Arizona University and Colorado State University screened for four pathogens — Anaplasma phagocytophilum, Babesia microti, Borrelia burgdorferi, and Borrelia miyamotoi — in thousands of tick samples mailed in by citizen scientists from the mainland US and Puerto Rico. In addition to getting a look at the prevalence of these pathogens, the analysis offered a look at the distribution of tick species in the Amblyomma, Dermacentor, and Ixodes genera.

The study, published online yesterday in PLOS One, "offers a unique and very valuable perspective, as it looks at risk to humans that goes beyond the physician-reported infection rates and involved ticks that were found on or near people," first and corresponding author Nathan Nieto, a biological sciences researcher at Northern Arizona University, said in a statement.

In an effort funded by a non-profit organization called the Bay Area Lyme Foundation, the researchers focused on 16,080 tick samples submitted by mail from more than 12,000 individuals in 49 mainland states and Puerto Rico from early 2016 to August 2017, representing more than a dozen tick species. Most of the ticks were reportedly found on human hosts, they noted, though some came from dogs, cats, other domestic animals, livestock, or wildlife.

After removing 265 ticks from consideration due to decomposition, the team used qPCR to identify the Lyme disease-causing bacterium B. burgdorferi in ticks from dozens of sites in two dozen states. It turned up in between 6.5 percent and 23 percent of deer ticks (Ixodes scapularis) received from the northeastern US, for example, as well as western black-legged ticks (I. pacificus) on the West Coast and lone star ticks (Amblyomma americanum) — a species that is largely found in the eastern and southeastern US.

The deer tick was also most apt to carry A. phagocytophilum, a granulocytic anaplasmosis-causing bacterial species. That pathogen was found in adult and nymph representatives from several other tick species as well, the researchers reported, but turned up only rarely in Dermacentor tick species.

The team identified DNA from a spirochete pathogen called B. miyamotoi in several tick vectors where it was not previously documented, though it was particularly common in the western black-legged ticks. On the other hand, up to 2.5 percent of adult lone star ticks contained yet another pathogen, Babesia microti, a protozoan behind a human condition called babesiosis.

The researchers saw co-infection — the presence of two or more pathogens per tick — in just shy of 1 percent of the samples tested. Nearly 90 percent of those co-infections occurred in the I. scapularis deer ticks, they noted, and many involved the Lyme disease pathogen B. burgdorferi in combination with A. phagocytophilum.

Along with these and other insights into pathogen prevalence across the tick species and locations considered, the authors noted, the data is expected to provide a resource for predicting the spread of tick-borne diseases in the future.

"[C]itizen science data on tick ecology, combined with pathogen screening, offers insights into geographic patterns and distributions of these organisms at a scale that is difficult to compete with by laboratories or government agencies," the authors concluded. "These data can also be used at a more local scale to examine the phenology of human-tick encounters, geographical diversity of tick and pathogen genetics, and so on."