Movement of Ixodes pacificus and Dermacentor occidentalis (Acari: Ixodidae) adult ticks in chaparral under natural conditions in Northern California, U.S.A.

The movement of Ixodes pacificus and Dermacentor occidentalis adult ticks down a hill slope under natural conditions was investigated using the mark-release-recapture (MRR) method. We evaluated the movement of host-seeking adult ticks down a hill slope to determine if ticks travel downhill from an uphill area to trail margins below. During the tick seasons in 2016-2018, the ticks were collected by flagging, marked with paint, released at a predetermined location, and recaptured by weekly flagging. Of the 188 female and 114 male I. pacificus marked and released 30 m above the trail in 2016, 11 (5.8%) females and one (0.9%) male were recaptured at the trail. In 2017, of the 71 female and 52 male I. pacificus, none were recaptured. In 2018, nine (3.6%) female and one (0.4%) male I. pacificus were recaptured of the 247 female and 287 males marked and released. Fifteen (18.5%) female and six (7.3%) male D. occidentalis were recaptured of the 81 females and 82 males marked and released in 2017. The trail deterred further movement with only 0.6% of I. pacificus and 8.3% of D. occidentalis recaptured on the opposite side of the trail. This study demonstrated that some I. pacificus and D. occidentalis adults found along the uphill side of trails may have originated from an area 30 m from the trail margin, some travelling at a rate of 1.6-1.9 m/day under natural conditions in chaparral.

Borrelia maritima sp. nov., a novel species of the Borrelia burgdorferi sensu lato complex, occupying a basal position to North American species.

Borrelia species are vector-borne parasitic bacteria with unusual, highly fragmented genomes that include a linear chromosome and linear as well as circular plasmids that differ numerically between and within various species. Strain CA690T, which was cultivated from a questing Ixodes spinipalpis nymph in the San Francisco Bay area, CA, was determined to be genetically distinct from all other described species belonging to the Borrelia burgdorferi sensu lato complex. The genome, including plasmids, was assembled using a hybrid assembly of short Illumina reads and long reads obtained via Oxford Nanopore Technology. We found that strain CA690T has a main linear chromosome containing 902176 bp with a blast identity ≤91 % compared with other Borrelia species chromosomes and five linear and two circular plasmids. A phylogeny based on 37 single-copy genes of the main linear chromosome and rooted with the relapsing fever species Borrelia duttonii strain Ly revealed that strain CA690T had a sister-group relationship with, and occupied a basal position to, species occurring in North America. We propose to name this species Borrelia maritima sp. nov. The type strain, CA690T, has been deposited in two national culture collections, DSMZ (=107169) and ATCC (=TSD-160).

Large scale spatial risk and comparative prevalence of Borrelia miyamotoi and Borrelia burgdorferi sensu lato in Ixodes pacificus.

Borrelia miyamotoi is a newly described emerging pathogen transmitted to people by Ixodes species ticks and found in temperate regions of North America, Europe, and Asia. There is limited understanding of large scale entomological risk patterns of B. miyamotoi and of Borreila burgdorferi sensu stricto (ss), the agent of Lyme disease, in western North America. In this study, B. miyamotoi, a relapsing fever spirochete, was detected in adult (n=70) and nymphal (n=36) Ixodes pacificus ticks collected from 24 of 48 California counties that were surveyed over a 13 year period. Statewide prevalence of B. burgdorferi sensu lato (sl), which includes B. burgdorferi ss, and B. miyamotoi were similar in adult I. pacificus (0.6% and 0.8%, respectively). In contrast, the prevalence of B. burgdorferi sl was almost 2.5 times higher than B. miyamotoi in nymphal I. pacificus (3.2% versus 1.4%). These results suggest similar risk of exposure to B. burgdorferi sl and B. miyamotoi from adult I. pacificus tick bites in California, but a higher risk of contracting B. burgdorferi sl than B. miyamotoi from nymphal tick bites. While regional risk of exposure to these two spirochetes varies, the highest risk for both species is found in north and central coastal California and the Sierra Nevada foothill region, and the lowest risk is in southern California; nevertheless, tick-bite avoidance measures should be implemented in all regions of California. This is the first study to comprehensively evaluate entomologic risk for B. miyamotoi and B. burgdorferi for both adult and nymphal I. pacificus, an important human biting tick in western North America.

Remarkable diversity of tick or mammalian-associated Borreliae in the metropolitan San Francisco Bay Area, California.

The diversity of Lyme disease (LD) and relapsing fever (RF)-group spirochetes in the metropolitan San Francisco Bay area in northern California is poorly understood. We tested Ixodes pacificus, I. spinipalpis, and small mammals for presence of borreliae in Alameda County in the eastern portion of San Francisco Bay between 2009 and 2012. Analyses of 218 Borrelia burgdorferi sensu lato (Bb sl) culture or DNA isolates recovered from host-seeking I. pacificus ticks revealed that the human pathogen Bb sensu stricto (hereinafter, B. burgdorferi) had the broadest habitat distribution followed by B. bissettii. Three other North American Bb sl spirochetes, B. americana, B. californiensis and B. genomospecies 2, also were detected at lower prevalence. OspC genotyping of the resultant 167 B. burgdorferi isolates revealed six ospC alleles (A, D, E3, F, H and K) in I. pacificus. A novel spirochete belonging to the Eurasian Bb sl complex, designated CA690, was found in a questing I. spinipalpis nymph. Borrelia miyamotoi, a relapsing-fever (RF) group spirochete recently implicated as a human pathogen, was detected in 24 I. pacificus. Three rodent species were infected with Bb sl: the fox squirrel (Sciurus niger) with B. burgdorferi, and the dusky-footed wood rat (Neotoma fuscipes) and roof rat (Rattus rattus) with B. bissettii. Another spirochete that clustered phylogenetically with the Spanish R57 Borrelia sp. in a clade distinct from both the LD and RF groups infected some of the roof rats. Together, eight borrelial genospecies were detected in ticks or small mammals from a single Californian county, two of which were related phylogenetically to European spirochetes.

Cercarial dermatitis transmitted by exotic marine snail.

Cercarial dermatitis (swimmer's itch) is caused by the penetration of human skin by cercariae of schistosome parasites that develop in and are released from snail hosts. Cercarial dermatitis is frequently acquired in freshwater habitats, and less commonly in marine or estuarine waters. To investigate reports of a dermatitis outbreak in San Francisco Bay, California, we surveyed local snails for schistosome infections during 2005-2008. We found schistosomes only in Haminoea japonica, an Asian snail first reported in San Francisco Bay in 1999. Genetic markers place this schistosome within a large clade of avian schistosomes, but do not match any species for which there are genetic data. It is the second known schistosome species to cause dermatitis in western North American coastal waters; these species are transmitted by exotic snails. Introduction of exotic hosts can support unexpected emergence of an unknown parasite with serious medical or veterinary implications.