Passive collection of ticks in New Hampshire reveals species-specific patterns of distribution and activity

Abstract

Ticks and tick-borne diseases are increasing in the United States, including New Hampshire (NH). We report on the findings of an ongoing free crowdsourcing program spanning four years within NH. The date of tick's submission was recorded along with species, sex, stage, location they were collected (translated into latitude and longitude), the activity the individual was doing when the tick was found, and host species. A total of 14,252 ticks belonging to subclass Acari, family Ixodidae and genera Ixodes, Dermacentor, Amblyomma, and Haemaphysalis was recorded from the period 2018-2021 throughout NH. A total of 2,787 Ixodes scapularis and 1,041 Dermacentor variabilis, were tested for the presence of Borrelia sp. (Spirochaetales: Spirochaetaceae), B. burgdorferi sensu lato, B. miyamotoi, B. mayonii, Babesia microti (Piroplasmida: Babesiidae), Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), Francisella tularensis (Thiotrichales: Francisellaceae), and Rickettsia rickettsii (Rickettsiales: Rickettsiaceae) by PCR. For the I. scapularis ticks tested, the pathogen prevalence was 37% B. burgdorferi s.l. 1% B. miyamotoi, 6% A. phagocytophilum, and 5% Ba. microti. Only one D. variabilis resulted positive to F. tularensis. We created state-wide maps informing the differences of ticks as detailed by administrative divisions. Dermacentor variabilis peaked in June and I. scapularis peaked in May and October. The most reported activity by people with tick encounters was while walking/hiking, and the least was biking. Using the reported distribution of both species of ticks, we modeled their climate suitability in the target territory. In NH, I. scapularis and D. variabilis have distinct patterns of emergence, abundance, and distribution. Tick prevention is important especially during April-August when both tick species are abundant and active.

Keywords: Dermacentor variabilis; Ixodes scapularis; climate modeling; community science; tick borne pathogens.

Fig. 1.

The spatial distribution of the sites in New Hampshire from which ticks were submitted for this study, according to the coordinates provided by the participants. The dots only indicate occurrence but not abundance. In some cases, specimens were submitted without coordinates but with the name of a town. In these cases, coordinates of the town were obtained and plotted. The map shows where participants have concentrated as well as the sites in the northern parts of the State from where no ticks were submitted.

Fig. 2.

The distribution of ticks mapped in New Hampshire according to the number of submitted specimens in the period 2018–2021 at the level of ‘city boundaries’. The distribution of I. scapularis (Fig. 2A), with a total number of 3,642. The distribution of D. variabilis (Fig. 2B), with a total number of 6,494. The legend reflect the total number of specimens received from each administrative division.

Fig. 3.

The seasonal pattern of abundance of I. scapularis (Fig. 3A) and D. variabilis (Fig. 3B) in New Hampshire at a time resolution of one week, with indications of the month of the year, based on the number of each specimen submitted by the participants. Different lines indicate the different years 2018–2021.

Fig. 4.

Totaled ticks found per human activity over years 2018–2021. Figure 4A depicts the percent of I. scapularis (black) and D. variabilis (white) found for each associated category of human activity. Figure 4B and C depicts heat maps for the number of I. scapularis (Fig. 4B) and D. variabilis (Fig. 4C) shown according to the week of the year and the associated category of human activity. Scale is from 0 to 200 darker shades representing more numbers of ticks.

Fig. 5.

Predicted distribution of ticks within New Hampshire based on a weather-dependent model. I. scapularis (Fig. 5A), and D. variabilis (Fig. 5B), mapped as probabilities from 0 to 100 as indicated by the legends.