Presence of a cryptic Onchocerca species in black flies of northern California, USA.

BACKGROUND: Black flies (Diptera: Simuliidae) serve as arthropod vectors for various species of Onchocerca (Nematoda: Onchocercidae) that may be associated with disease in humans, domestic animals, and wildlife. The emergence of zoonotic Onchocerca lupi in North America and reports of cervid-associated zoonotic onchocerciasis by Onchocerca jakutensis highlight the need for increased entomological surveillance. In addition, there is mounting evidence that Onchocerca diversity in North America is far greater than previously thought, currently regarded as Onchocerca cervipedis species complex. This study reports new geographic records and black fly vector associations of an uncharacterized Onchocerca species. METHODS: To better understand the biodiversity and geographic distribution of Onchocerca, 485 female black flies (2015: 150, 2016: 335) were collected using CO2-baited traps from February to October 2015-2016 in Lake County, northern California, USA. Individual flies were morphologically identified and pooled (≤ 10 individuals) by species, collection date, and trap location. Black fly pools were processed for DNA extraction, and subsequent PCR and sequencing targeting of the NADH dehydrogenase subunit 5 gene of filarioids. RESULTS: Among the pools of black flies, there were 158 individuals of Simulium tescorum (2015: 57, 2016: 101), 302 individuals of Simulium vittatum (sensu lato [s.l.]) (2015: 82, 2016: 220), 16 individuals of Simulium clarum "black" phenotype (2015: 5, 2016: 11), and 13 individuals of S. clarum "orange" phenotype (2015: 6, 2016: 7). PCR analysis revealed the percentage of filarioid-positive pools were 7.50% (n = 3) for S. tescorum, 3.75% (n = 3) for S. vittatum (s.l., likely S. tribulatum), 7.69% (n = 1) for S. clarum "black" phenotype, and no positives for S. clarum "orange" phenotype. Genetic distance and phylogenetic analyses suggest that the northern California Onchocerca isolates belong to the same species reported in black flies from southern California (average pairwise comparison: 0.32%), and seem closely related to Onchocerca isolates of white-tailed deer from upstate New York (average pairwise comparison: 2.31%). CONCLUSION: A cryptic Onchocerca species was found in Lake County, California, and may be a part of a larger, continentally distributed species complex rather than a single described species of North America. In addition, there are at least three putative vectors of black flies (S. clarum, S. tescorum, S. vittatum) associated with this cryptic Onchocerca species. A comprehensive reassessment of North American Onchocerca biodiversity, host, and geographic range is necessary.

Rickettsia Species Isolated from Dermacentor occidentalis (Acari: Ixodidae) from California.

The Pacific Coast tick (Dermacentor occidentalis Marx, 1892) is one of the most widely distributed and frequently encountered tick species in California. This tick is the primary vector of an unclassified spotted fever group rickettsial pathogen, designated currently as Rickettsia 364D, the etiologic agent of a recently recognized tick-borne rickettsiosis known as Pacific Coast tick fever. Despite intensified interest in this pathogen, important questions remain regarding its taxonomic status and possible variations in genotype among different strains that could influence its pathogenicity. Only the extensively passaged prototypical isolate (strain 364-D) is widely available to rickettsiologists and public health scientists worldwide. To achieve a larger, more geographically diverse, and contemporary collection of strains, 1,060 questing adult D. occidentalis ticks were collected from 18 sites across six counties in northern and southern California in 2016 and 2017. Fourteen ticks (1.3%) yielded DNA of Rickettsia 364D and from these, 10 unique isolates from Lake and Orange counties were obtained. Additionally, Rickettsia rhipicephali was detected in 108 (10.2%) ticks, from which eight isolates were obtained, and Rickettsia bellii in six (0.6%), from which three isolates were obtained. The panel of recently acquired, low-passage strains of Rickettsia 364D derived from this study could enhance opportunities for investigators to accurately determine the taxonomic standing of this agent and to develop specific diagnostic assays for detecting infections with Rickettsia 364D in ticks and humans.

Picky eaters are rare: DNA-based blood meal analysis of Culicoides (Diptera: Ceratopogonidae) species from the United States.

BACKGROUND: Biting midges in the genus Culicoides (Diptera; Ceratopogonidae) have been implicated in the transmission of a number of parasites and highly pathogenic viruses. In North America, the complete transmission cycles of many of these pathogens need further elucidation. One way to increase our knowledge about the evolution and ecology of Culicoides species and the pathogens they transmit is to document the diversity of vertebrate hosts that Culicoides feed upon. Our objective was to identify the diversity of Culicoides hosts in the United States. RESULTS: We sequenced two vertebrate mitochondrial genes (cytochrome c oxidase subunit 1 and cytochrome b) from blood-engorged Culicoides to identify Culicoides species and their blood meals. We detected the mitochondrial DNA of 12 host species from seven different Culicoides species from three states. The majority of the identified blood meals were from the C. variipennis species complex in California. The hosts included both mammals and birds. We documented new host records for some of the Culicoides species collected. The majority of the mammalian hosts were large ungulate species but we also detected a lagomorph and a carnivore. The bird species that were detected included house finch and emu; the latter is evidence that the species in the C. variipennis species complex are not strictly mammalophilic. CONCLUSIONS: These results demonstrate that Culicoides will feed on multiple classes of vertebrates and may be more opportunistic in regards to host choice than previously thought. This knowledge can help with identification of susceptible host species, pathogen reservoirs, and new vector species which, in turn, will improve disease outbreak risk assessments.

Abundance and Bloodfeeding Patterns of Mosquitoes (Diptera: Culicidae) in an Oak Woodland on the Eastern Slope of the Northern Coast Range of California.

The abundance and bloodfeeding patterns of mosquitoes was studied from 2008 to 2010 at an 18 ha. oak woodland in Lake County, CA. Host-seeking females were collected weekly from sunset to sunrise by paired dry-ice-baited CDC style traps, whereas resting females were aspirated from paired walk-in red boxes. Sequences of the COI gene amplified from bloodmeals from engorged resting females were used to identify the bloodmeal hosts. Aedes sierrensis (Ludlow) and Aedes increpitus Dyar complex mosquitoes were univoltine, although the timing of emergence and abundance varied temporally and seemed weather dependent. Abundance of both Anopheles franciscanus McCracken and Anopheles freeborni Aitken peaked in mid to late summer. Females of both genera bloodfed primarily on mule deer and black-tailed jackrabbits, and few fed on either dogs or humans that were consistently present within the woodland. In contrast, multivoltine Culex tarsalis Coquillett and Culex stigmatosoma Dyar were abundant throughout summer, especially from July to September. Both Culex species bloodfed on a wide variety of avian hosts, with most bloodmeals originating from California scrub-jay, wild turkey, oak titmouse, and house finch. Culex tarsalis fed on proportionately more mammals as summer progressed, peaking at 33% in September.

Bionomics and Vector Potential of Culex thriambus (Diptera: Culicidae) Mosquitoes in Lake County, California.

California statewide West Nile virus (WNV) minimum infection rates in Culex thriambus Dyar mosquitoes are high; however, few specimens are submitted and tested each year, as their distribution seems limited to larval habitats along riparian systems. To evaluate the role of Cx. thriambus in the amplification, maintenance, and overwintering of WNV in Lake County, CA, the bionomics and vector potential of the species was investigated during 2014 and 2015. Culex thriambus was the most abundant mosquito species, with 1,153 adults and 7,624 immatures collected by vacuum aspiration and dip sampling, respectively, at the primary study site. Detection of WNV in four mosquito pools during September through November coincided with peak seasonality. Females entered and maintained a reproductive diapause during winter under field and seminatural conditions. Diapause was initiated in the majority of Cx. thriambus females by October and was terminated by 30 March. Some parous females (7.1%) and those in host-seeking arrest (7.1%) were collected throughout the winter period. An accrual of 679.51 degree-days (°D) was necessary for diapause termination under seminatural conditions. Culex thriambus females fed on 16 different avian species during spring and summer, and no mammalian feeds were detected. West Nile viral RNA was detected in four of 42 Cx. thriambus pools tested during June through November and infection rates ranged from 3.53-28.15/1,000 tested. In summary, WNV transmission may be increased along riparian corridors throughout California where Cx. thriambus mosquitoes remain relatively abundant.