Role of Anopheles Mosquitoes in Cache Valley Virus Lineage Displacement, New York, USA

Abstract

Cache Valley virus (CVV) is a mosquitoborne virus that infects livestock and humans. We report results of surveillance for CVV in New York, USA, during 2000-2016; full-genome analysis of selected CVV isolates from sheep, horse, humans, and mosquitoes from New York and Canada; and phenotypic characterization of selected strains. We calculated infection rates by using the maximum-likelihood estimation method by year, region, month, and mosquito species. The highest maximum-likelihood estimations were for Anopheles spp. mosquitoes. Our phylogenetic analysis identified 2 lineages and found evidence of segment reassortment. Furthermore, our data suggest displacement of CVV lineage 1 by lineage 2 in New York and Canada. Finally, we showed increased vector competence of An. quadrimaculatus mosquitoes for lineage 2 strains of CVV compared with lineage 1 strains.

Keywords: Anopheles punctipennis; Anopheles quadrimaculatus; Cache Valley virus; New York; United States; lineage displacement; mosquitoes; surveillance; vector competence; vector-borne infections; viruses; zoonoses.

Figure 1

Counties in New York, USA, in which Cache Valley virus was studied during 2000‒2016 (https://www.health.ny.gov/statistics/cancer/registry/images/nycounty). Asterisks (*) indicate counties in which samples positive for Cache Valley virus were collected. NA, counties not included in data; NT, counties not tested for Cache Valley virus.

Figure 2

Cache Valley virus infection rate, New York, USA, during 2000‒2016, calculated by using MLE, by year (A), mosquito species (B), New York regions (C), and combined mosquito species and years (D). Error bars indicate upper and lower limits of infection rate based on 95% confidence levels. Numbers next to bars indicate number of pools tested. MLEs were calculated by using a Centers for Disease Control and Prevention resource (https://www.cdc.gov/westnile/resourcepages/mosqsurvsoft.html). *p<0.05 by χ² test. CIN, Ae. cinereus; MLE, maximum-likelihood estimation; PUN, An. punctipennis; QUA, An. quadrimaculatus; SOL, Ae. sollictans; TVT, Ae. trivittatus.

Figure 3

Phylogenetic analysis of Cache Valley virus, New York, USA, 2000‒2016. Maximum-likelihood phylogenetic trees show complete nucleotide sequences of small (A), medium (B), and large (C) genome segments. Numbers at nodes indicate boostrap support estimated by using 500 neighbor-joining replicates. Trees were rooted to Fort Sherman virus small, medium, and large genome segments (GenBank accessions nos. KX100130, KX100131, and KX100132). Scale bars indicate nucleotide substitutions per site.