35-year Hudson Valley record links Lyme-vector nymph surges to mice and acorns, not deer

A paper in Proceedings of the National Academy of Sciences, led by Richard Ostfeld of the Cary Institute of Ecosystem Studies, reports that more than 35 years of Hudson Valley monitoring tie Lyme-vector risk more tightly to mice and oak mast than to deer. Blacklegged nymphs transmit Borrelia burgdorferi. Federal estimates put U.S. diagnoses near 500,000 a year. The methodological point is the length of the record: short slices once suggested a deer effect that the full series does not sustain.

The design is observational, not experimental: acorn counts, small-mammal traps, deer indices, and tick drags on one roughly 2,000-acre Dutchess County forest, analyzed across decades rather than a single season. Years with large white-footed mouse populations were followed by about 40 percent more nymphal ticks. That matches a lagged pathway published earlier by the same group: mast feeds mice the next summer; larvae pick up Borrelia from those mice; infected nymphs quest the summer after that. Deer feed adult ticks but are poor reservoirs, so more deer need not mean more infected nymphs.

Coverage that treats acorns as a cause of Lyme disease skips the inference limit. These are within-site associations; weather can move oaks, mice, and ticks together, and the press account does not show a pre-registered forecast beating a null model out of sample. The policy miss is larger. Many towns still treat deer reduction as the main ecological control, yet human cases track nymphs, whose infection prevalence is set by rodent reservoirs. Acorn counts might flag risk one to two years ahead in similar oak forests, but not where host communities differ.

What would strengthen the evidence is independent replication, an experimental manipulation of mice or mast, and a public forecast scored against future nymph density and human case reports. Until that test, deer policy should not be sold as a proven Lyme control on the strength of this correlation, and acorn watching should be framed as surveillance, not prevention. Personal protection in late spring and early summer remains the intervention with the clearest near-term effect. Ostfeld and co-lead Shannon LaDeau show why short studies mislead; they have not yet handed counties a calibrated lever.