Jamestown Canyon Virus in Collected Mosquitoes, Maine, United States, 2017-2019.

Jamestown Canyon virus (JCV) is a mosquito-borne arbovirus that circulates in North America. We detected JCV in 4 pools of mosquitoes collected from midcoastal Maine, USA, during 2017-2019. Phylogenetic analysis of a JCV sequence obtained from Aedes cantator mosquitoes clustered within clade A, which also circulates in Connecticut, USA.

Prevalence and Genetic Diversity of Deer Tick Virus (Powassan Virus, Lineage II) in Ixodes scapularis Ticks in Five Habitats at a Nature Reserve in Southern Maine, United States.

Deer tick virus (DTV), also known as Powassan virus lineage II, is a rising health concern due to increased recognition as a cause of human encephalitis. Since European tick-borne encephalitis virus persists in nature in enzootic foci (i.e., higher prevalence rates in small pockets in nature), we sought to determine whether DTV is also focally maintained in relation to habitat type, to better understand factors leading to human risk of exposure. From 2018 to 2021, questing Ixodes scapularis ticks were collected from five habitats at the Wells National Estuarine Research Reserve (WNERR) in Wells, ME: forest with invasive vegetation in the understory, edge, shrub, forest with native vegetation in the understory, and open field. Deer tick virus prevalence was greater in adult ticks (2.0%) than in nymphs (0.5%). Deer tick virus prevalence in adult ticks collected from forest with invasive vegetation was 3.2% compared to 0 to 1.7% in other habitat types. A hot spot analysis revealed a higher number of infected adults collected per hour on one of the transects located in forest with invasive vegetation. Phylogenetic analysis of 37 full-length DTV genomes sequenced in this study revealed four major clades from the WNERR, and there was high genetic diversity within each transect, suggesting frequent, short-range dispersal between habitats. Analysis of DTV sequences from other New England counties and states also indicated long-distance dispersal to and/or from the WNERR. This study provides preliminary evidence that DTV is focal and that the risk of encountering DTV-infected ticks in forest with invasive vegetation may be greater than in other habitat types.

Emergence of Ixodes scapularis (Acari: Ixodidae) in a Small Mammal Population in a Coastal Oak-Pine Forest, Maine, USA.

In the United States, surveillance has been key to tracking spatiotemporal emergence of blacklegged ticks [Ixodes scapularis Say (Ixodida:Ixodidae)] and their pathogens such as Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner (Spirochaetales: Spirochaetaceae), the agent of Lyme disease. On the Holt Research Forest in midcoastal Maine, collection of feeding ticks from live-trapped small mammal hosts allowed us to track the emergence and establishment of I. scapularis, 1989-2019. From 1989-1995, we collected only I. angustus Neumann (Ixodida: Ixodidae)(vole tick), Dermacentor variabilis Say (Ixodida: Ixodidae) (American dog tick), and I. marxi Banks (Ixodida: Ixodidae) (squirrel tick) from seven species of small mammals. The most abundant tick host was the white-footed mouse [Peromyscus leucopus Rafinesque (Rodentia:Cricetidae)] followed by the red-backed vole (Myodes gapperi Vigors (Rodentia: Cricetidae)). Emergence of I. scapularis was signaled via the appearance of subadult I. scapularis in 1996. Emergence of B. burgdorferi was signaled through its appearance in I. scapularis feeding on mice in 2005. There was a substantial increase in I. scapularis prevalence (proportion of hosts parasitized) and burdens (ticks/host) on white-footed mice and red-backed voles in 2007. The ~11-yr time-to-establishment for I. scapularis was consistent with that seen in other studies. White-footed mice comprised 65.9% of all captures and hosted 94.1% of the total I. scapularis burden. The white-footed mouse population fluctuated interannually, but did not trend up as did I. scapularis prevalence and burdens. There were concurrent declines in I. angustus and D. variabilis. We discuss these results in the broader context of regional I. scapularis range expansion.