Presence of a cryptic Onchocerca species in black flies of northern California, USA Academic Article uri icon


  • 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 20152016 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

published proceedings

  • Parasites & Vectors

altmetric score

  • 3.5

author list (cited authors)

  • Kulpa, M., Nelson, K. J., Morales, A. M., Ryan, B. M., Koschik, M. L., Scott, J. J., & Verocai, G. G.

citation count

  • 0

complete list of authors

  • Kulpa, Matthew||Nelson, Kimberly J||Morales, Alana M||Ryan, Bonnie M||Koschik, Michelle L||Scott, Jamesina J||Verocai, Guilherme G

publication date

  • December 2021