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

Abstract

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. Graphical abstract

Biting midges (Diptera: Ceratopogonidae) as putative vectors of zoonotic Onchocerca lupi (Nematoda: Onchocercidae) in northern Arizona and New Mexico, southwestern United States

“…Blast results showed the closest match to this unknown sample was Onchocerca lienalis with 94.56% identity. Little is known regarding unknown Onchocerca species in wildlife and arthropods ( 23 ), however, a more comprehensive examination of unknown Onchocerca species within North America is needed to catalog the diversity of both Onchocerca and the arthropods vectoring them.…”

“…Blast results showed the closest match to this unknown sample was Onchocerca lienalis with 94.56% identity. Little is known regarding unknown Onchocerca species in wildlife and arthropods (23), however, a more comprehensive examination of unknown Onchocerca species within North America is needed to catalog the diversity of both Onchocerca and the arthropods vectoring them. Current O. lupi surveillance tools targeting the COI mitochondrial gene are limited to detection and cannot provide insight into population structure, at least within the United States.…”

“…An additional study has identified O. lupi DNA sequences acquired from head and bodies of Simulium griseum , but has not yet been published in peer-reviewed literature. Subsequent black fly sampling in areas of California failed to detect O. lupi DNA but identified DNA of other Onchocerca genetic lineages likely associated with wild ungulates ( 23 , 24 ).…”

What lies behind the curtain: Cryptic diversity in helminth parasites of human and veterinary importance

“…Cryptic diversity has been described in Onchocerca spp. associated with wild animals, especially hosts of the family Cervidae in the Nearctic ( McFrederick et al., 2013 ; Verocai et al., 2018 ; Kulpa et al., 2021 ). Adult worms and microfilariae collected from the moose Alces alces have been molecularly identified as O. cervipedis , which was for decades assumed to represent the only species infecting North American cervids ( Verocai et al., 2012 ; McFrederick et al., 2013 ).…”