Environmental Drivers of Immature Ixodes scapularis in Minnesota's Metro Area.

Research on the public health significance of Ixodes scapularis ticks in the Midwest seldom focuses on extreme weather conditions that can modulate their population dynamics and ability to transmit pathogenic organisms. In this study, we assessed whether the distributional abundance of I. scapularis immatures is associated with current and time-lagged climatic determinants either directly or indirectly. We analyzed a 20-year longitudinal small mammal live-trapping dataset within a seven-county metropolitan area in Minnesota (1998-2016) using yearly tick counts at each site to assess whether inter- and intra-annual variation in immature I. scapularis counts is associated with climate and land-use conditions. We found that (1) immature I. scapularis ticks infesting mammals expanded southwesterly over the study period, (2) eastern chipmunks, Tamias striatus, supplied a substantial proportion of nymphal blood meals, (3) a suite of climatological variables are demonstrably associated with I. scapularis presence, and abundance across sites, most notably summer vapor pressure deficit, and (4) immature I. scapularis display an affinity for deciduous forests in metro areas. Our results suggest that climatic and land-type conditions may impact host-seeking I. scapularis ticks through numerous mechanistic avenues. These findings extend our understanding of the abiotic factors supporting I. scapularis populations in metro areas of the upper Midwest with strong implications for discerning future tick-borne pathogen risk.

Agents of human anaplasmosis and Lyme disease at Camp Ripley, Minnesota.

The transmission dynamics of Anaplasma phagocytophilum (Ap) and Borrelia burgdorferi (Bb) among Ixodes scapularis (Is) and mammalian hosts was investigated at Camp Ripley, an area representative of central Minnesota. Prevalence of white-footed mouse infection with Ap and Bb were 20% and 42%, respectively, with a coinfection level of 14%. Peak levels of infection with both agents occurred in May. The average levels of seropositivity to Ap and Bb were 29.3% and 48%, respectively. Of the mice infected with Ap, 47.5% were able to eliminate the pathogen as compared with 19.4% of mice infected with Bb. Ap was detected in 88.4% of 43 eastern chipmunks examined and isolated from 44.7% of the animals. Bb was present in 72.7% of 11 chipmunks examined, and 100% of the animals were also infected with Ap. The seasonality of tick activity differs from that reported for the New York area. Is infestation of mice began in May with peak nymphal infestation also occurring in May (7.4 per infested mouse) and overlapping with peak larval infestation in June (77.1 per infested mouse). Infestation ranged from 100% in May to 34.5% in October. Is comprised 98.4% of the ticks infesting the mice. The temporal pattern of the developmental stages of Is infesting chipmunks was the same as for mice, except that the tick burdens were greater. The nymphal stage peaked in May (81.3 per animal), and the larval stage peaked in June (164.7 per animal). Infestation was 100% in May-August, and >99% of the ticks were Is. Antibodies to Ap were present in >80% of the white-tailed deer examined, but they were infected with the Ap-1 variant rather than the Ap strain infecting mice and humans. Antibodies to Bb were detected in >80% of the deer, but Bb DNA was only detected in 1.5% of blood specimens.