Disease ecology and host range of Cyprinid herpesvirus 3 (CyHV‐3) in CyHV‐3 endemic lakes of North America

Abstract

Cyprinid herpesvirus‐3 (CyHV‐3) is an important pathogen of common carp (Cyprinus carpio, carp) causing significant economic and ecological impacts worldwide. The recent emergence of CyHV‐3 in the Upper Midwest region of the United States has raised questions related to the disease ecology and host specificity of CyHV‐3 in wild carp populations. To determine the prevalence of CyHV‐3 in wild populations of fishes in Minnesota, we surveyed five lakes in 2019 in which the virus was known to have caused mass mortality events in carp from 2017 to 2018. A total of 28 species (n = 756 total fish) of native fishes and 730 carp were screened for the presence of CyHV‐3 DNA using specific qPCR. None of the native fish tissues tested positive for CyHV‐3 although the prevalence of CyHV‐3 in carp was 10%–50% in the five lakes. A single lake (Lake Elysian) with a 50% DNA detection rate and evidence of ongoing transmission and CyHV‐3‐associated mortality was surveyed again in 2020 from April to September. During this period, none of the tissues from 24 species (n = 607 total fish) tested positive for CyHV‐3 though CyHV‐3 DNA and mRNA (indicating viral replication) was detected in carp tissues during the sampling period. CyHV‐3 DNA was detected most often in brain samples without evidence of replication, potentially indicating that brain tissue is a site for CyHV‐3 latency. Paired qPCR and ELISA testing for Lake Elysian in 2019–2020 identified young carp (especially males) to be the primary group impacted by CyHV‐3‐associated mortality and acute infections, but with no positive detections in juvenile carp. Seroprevalence of carp from Lake Elysian was 57% in 2019, 92% in April of 2020 and 97% in September 2020. These results further corroborate the host specificity of CyHV‐3 to carp in mixed wild populations of fishes in Minnesota and provide additional insights into the ecological niche of CyHV‐3 in shallow lake populations of carp in North America.