BackgroundDeer tick virus, DTV, is a genetically and ecologically distinct lineage of Powassan virus (POWV) also known as lineage II POWV. Human incidence of POW encephalitis has increased in the last 15 years potentially due to the emergence of DTV, particularly in the Hudson Valley of New York State. We initiated an extensive sampling campaign to determine whether POWV was extant throughout the Hudson Valley in tick vectors and/or vertebrate hosts.MethodsMore than 13,000 ticks were collected from hosts or vegetation and tested for the presence of DTV using molecular and virus isolation techniques. Vertebrate hosts of Ixodes scapularis (black-legged tick) were trapped (mammals) or netted (birds) and blood samples analyzed for the presence of neutralizing antibodies to POWV. Maximum likelihood estimates (MLE) were calculated to determine infection rates in ticks at each study site.ResultsEvidence of DTV was identified each year from 2007 to 2012, in nymphal and adult I. scapularis collected from the Hudson Valley. 58 tick pools were positive for virus and/or RNA. Infection rates were higher in adult ticks collected from areas east of the Hudson River. MLE limits ranged from 0.2-6.0 infected adults per 100 at sites where DTV was detected. Virginia opossums, striped skunks and raccoons were the source of infected nymphal ticks collected as replete larvae. Serologic evidence of POWV infection was detected in woodchucks (4/6), an opossum (1/6), and birds (4/727). Lineage I, prototype POWV, was not detected.ConclusionsThese data demonstrate widespread enzootic transmission of DTV throughout the Hudson Valley, in particular areas east of the river. High infection rates were detected in counties where recent POW encephalitis cases have been identified, supporting the hypothesis that lineage II POWV, DTV, is responsible for these human infections.

TOC Summary: The epidemiologic pattern and limited laboratory testing indicate that this virus lineage might account for most of these illnesses.

Blacklegged ticks, Ixodes scapularis Say, were collected from 27 sites in eight New York State counties from 2003 to 2006 to determine the prevalence and distribution of tick-borne pathogens in public-use areas over a 4-yr period. In total, 11,204 I. scapularis (3,300 nymphs and 7,904 adults) were individually analyzed using polymerase chain reaction to detect the presence of Borrelia burgdorferi (causative agent of Lyme disease), Anaplasma phagocytophilum (formerly Ehrlichia phagocytophila, causative agent of human granulocytic anaplasmosis), and Babesia microti (causative agent of human babesiosis). Overall prevalence of B. burgdorferi, A. phagocytophilum, and B. microti was 14.4, 6.5, and 2.7% in nymphs and 45.7, 12.3, and 2.5% in adult ticks, respectively. Rates varied geographically and temporally during the time period examined, and were related to measurements of tick density. Average rate ofpolymicrobial infection for nymphs and adults, respectively, was 1.5 and 8.5% overall, with 0.5 and 6.3% coinfection of B. burgdorferi and A. phagocytophilum, 1.0 and 1.5% B. burgdorferi and B. microti, and 0.05 and 0.6% A. phagocytophilum and B. microti. Thirty-three individual adult ticks from seven study sites in Westchester, Putnam, Dutchess, and Rockland counties tested positive for simultaneous infection with all three agents by multiplex polymerase chain reaction assay.

The population densities of many organisms have changed dramatically in recent history. Increases in the population density of medically relevant organisms are of particular importance to public health as they are often correlated with the emergence of infectious diseases in human populations. Our aim is to delineate increases in density of a common disease vector in North America, the blacklegged tick, and to identify the environmental factors correlated with these population dynamics. Empirical data that capture the growth of a population are often necessary to identify environmental factors associated with these dynamics. We analyzed temporally- and spatially-structured field collected data in a geographical information systems framework to describe the population growth of blacklegged ticks (Ixodes scapularis) and to identify environmental and climatic factors correlated with these dynamics. The density of the ticks increased throughout the study’s temporal and spatial ranges. Tick density increases were positively correlated with mild temperatures, low precipitation, low forest cover, and high urbanization. Importantly, models that accounted for these environmental factors accurately forecast future tick densities across the region. Tick density increased annually along the south-to-north gradient. These trends parallel the increases in human incidences of diseases commonly vectored by I. scapularis. For example, I. scapularis densities are correlated with human Lyme disease incidence, albeit in a non-linear manner that disappears at low tick densities, potentially indicating that a threshold tick density is needed to support epidemiologically-relevant levels of the Lyme disease bacterium. Our results demonstrate a connection between the biogeography of this species and public health.

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Migration is a primary force of biological evolution that alters allele frequencies and introduces novel genetic variants into populations. Recent migration has been proposed as the cause of the emergence of many infectious diseases, including those carried by blacklegged ticks in North America. Populations of blacklegged ticks have established and flourished in areas of North America previously thought to be devoid of this species. The recent discovery of these populations of blacklegged ticks may have resulted from either in situ growth of long-established populations that were maintained at very low densities or by migration and colonization from established populations. These alternative evolutionary hypotheses were investigated using Bayesian phylogeographic approaches to infer the origin and migratory history of recently detected blacklegged tick populations in the Northeastern United States. The data and results indicate that newly detected tick populations are not the product of in situ population growth from a previously established population but from recent colonization resulting in a geographic range expansion. This expansion in the geographic range proceeded primarily through progressive and local migration events from southern populations to proximate northern locations although long-distance migration events were also detected.

The increasing incidence of TTB correlated with increases in community-acquired babesiosis and infection of ticks with B. microti. Surveillance of ticks and community-acquired cases may aid identification of emerging areas at risk for Babesia transfusion transmission.

B ourbon virus (BRBV; genus Thogotovirus, family Orthomyxoviridae) is a suspected tickborne human pathogen isolated in 2014 from a patient residing in Bourbon County, Kansas, USA (1). BRBV is closely related to Oz virus, which was isolated from Amblyomma testudinarium ticks in Japan (2,3). Since the initial discovery of BRBV, human cases have been identified in Kansas, Missouri, and Oklahoma (4). The Amblyomma americanum lone star tick has been identified as the likely vector of BRBV transmission and maintenance (5,6). Small and medium-sized mammals and ground-dwelling birds such as wild turkeys (Meleagris gallopavo) are hosts for the immature ticks. Adults feed on large mammals, such as coyotes (Canis latrans) and white-tailed deer (Odocoileus virginianus). All 3 active developmental stages of the tick will bite humans (7). Virus detection in ticks and serologic evidence in mammalian hosts, including white-tailed deer, have been demonstrated in Missouri, Kansas, and North Carolina (6,8-10). The StudyIn July 2019, New York State Department of Health (NYSDOH) epidemiologists were notified that BRBV RNA was detected in an individual, partially engorged female A. americanum tick removed from a Long Island, New York, resident. Comprehensive testing performed through the University of Massachusetts TickReport service (https://www.tickreport.com) revealed the tick was also positive for Ehrlichia ewingii bacteria. Notes on the tick submission form indicated the person was experiencing fever, chills, and fatigue; officials with NYSDOH and Suffolk County Department of Health Services (SCDHS) attempted to contact the resident for a follow-up investigation. No additional information was provided, and no blood samples were available to assess potential infection with BRBV.In 2016, NYSDOH and SCDHS initiated active tick surveillance targeting A. americanum ticks for BRBV and Heartland virus (HRTV). HRTV-infected ticks and seropositive deer were detected on Long Island in 2018 and reported in 2021 (11). We used standardized flag sampling for the collection of hostseeking A. americanum ticks on public lands in Suffolk County. During 2016-2020, a total of 1,265 pools, representing 4,189 adults, 7,227 nymphs, and 97 larvae, tested negative for BRBV RNA by real-time reverse transcription PCR using an in-house multiplex assay to detect HRTV and BRBV (11). The BRBV primers for this assay were designed based on the St. Louis strain (GenBank accession no. MK453528) (12). During 2021, we expanded sampling for A. americanum ticks on Long Island to collect a greater number of ticks from more locations, and we modified molecular detection protocols to use BRBV-specific primers developed at TickReport (Table 1). We designed BRBV-specific primers based on the original virus strain deposited in GenBank (accession no. KU708254) (13). We collected a total of 1,058 pools, consisting of 4,406 adults