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ARS Home » Southeast Area » Booneville, Arkansas » Dale Bumpers Small Farms Research Center » Research » Publications at this Location » Publication #409324
Research Project: Sustainable Small Farm and Organic Grass and Forage Production Systems for Livestock and Agroforestry

Location: Dale Bumpers Small Farms Research Center

Title: Impact of Cache Valley Virus in Arkansas sheep flock

Author
item Burke, Joan
item Wood, Erin
item Lee, Charles - Chad

Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/30/2023
Publication Date: 8/1/2024
Citation: Burke, J.M., Wood, E.L., Lee, C.T. 2024. Impact of Cache Valley Virus in Arkansas sheep flock. American Society of Animal Science Southern Section Meeting. https://doi.org/10.1093/jas/skae019.102.
DOI: https://doi.org/10.1093/jas/skae019.102

Interpretive Summary:

Technical Abstract: Cache Valley Virus (CVV) is an arbovirus transmitted between mosquitos and several vertebrate species. Infections in sheep and goats during pregnancy is a growing animal welfare issue as it can result in embryo or pregnancy loss, fetal malformation, and dystocia. There are no outward signs of infection in dams. Diagnosis in fetus or offspring is made using serologic or molecular testing. Serologic diagnosis in the dam can indicate past infection but does not confirm CVV infection in the fetus. ARS first noted clinical signs of possible CVV during the Nov/Dec 2015 lambing; first seropositive dam identified in Jan 2021. To estimate incidence of CVV infections among ewes bred from 2019-2023 and lambing in Jan/Feb (n=185), adverse pregnancy outcome such as embryo loss, birth of dead or deformed, and weak lambs, were used as surrogate markers. The relationship of animal BW (ewes at breeding and post-breeding; lambs at birth and ~60 d of age), age, lamb outcome, and breeding year were compared by likely CVV infection status. To estimate seroprevalence in ewes and correlate serology results with pregnancy outcomes, serum was collected from ewes (n=46) exposed to rams in Aug 2022 at 0 (first day of ram exposure) and ~60 d later. Tissue from aborted or dead lambs and serum from live lambs exhibiting signs of CVV (swollen joints, parrot mouth, deformities) were collected. Serum was screened for neutralizing antibodies using a CVV-specific plaque reduction neutralization test using a 50% cut-off (PRNT50). For this preliminary analysis, specimens with PRNT50 antibody titers = 10 were considered positive. Tissue specimens were tested using Bunyavirus and CVV reverse transcriptase-PCR. Animal data were analyzed by GLM. Using surrogate markers, an estimate of incidence of CVV during pregnancy was 26.5 ± 2.9% without year differences (P = 0.16) or age (yearling vs older ewes, P = 0.44). There was no association between CVV and dam BW (P > 0.10), number of live+dead lambs born, but CVV possibly reduced number of live lambs by 18% (P = 0.02) and those weaned by 27% (P = 0.002). Live litter birth (CVV, P < 0.001) and weaning BW (CVV × year, P = 0.04) were reduced by CVV. Of 42 ewes bred in Aug 2022, 13 (31%) had a positive titer in Aug (pre-pregnancy) indicating possible past infection. An additional 13 (31%) ewes were newly positive in Oct, indicating possible infection during pregnancy. Of the 13 newly positive ewes, 4 (9.5%) had adverse pregnancy outcomes, including one stillbirth with deformities that had a positive PCR on kidney tissue. Further studies are needed to determine whether CVV is becoming more widely prevalent in small ruminants, and technology for early detection and prevention.