Februry 2019-This year’s tick season is in full swing. With the heavy rains over the past few months, the adult ticks have been hiding out and staying dry, waiting for the sun to shine and their hosts to walk by!

The District lab staff take every opportunity to conduct tick surveillance on public trails during the dry days, and it is clear that the rain has not washed the ticks away. Adult Ixodes pacificus are abundant in both Marin and Sonoma counties, and on February 22 District staff found the first Ixodes pacificus nymphs of the season. Each year, the timing of the tick stages varies slightly, depending on several factors including temperature and precipitation.

The District staff conduct tick surveillance as often as possible during the winter months so they can provide the public with the most up to date information about the risk of tick bites. The ticks that the District collects will be tested for two bacteria: Borrelia burgdorferi (the causative agent of Lyme disease), and Borrelia miyamotoi (which can cause a tick-borne relapsing fever-type disease).

Over the past 10 years, the average minimum infection rate of B. burgdorferi in adult ticks in Marin and Sonoma counties was 2.0%, while the minimum infection rate in nymphs was 4.3%. For B. miyamotoi, it was 2.5% in adults and 0.7% in nymphs.