Cache Valley virus abortions in goat kids
Amanda Mansz, Emily zur Linden, Heather Murray, Heindrich N. Snyman
Animal Health Laboratory, University of Guelph, Guelph & Kemptville, ON (Mansz, Snyman), Metzger Veterinary Services, Linwood, ON (Linden), Dundas Veterinary Services, Winchester, ON (Murray)
AHL Newsletter 2022;26(1):9
In early December 2021, two separate and distinct dairy goat herds (one in Eastern Ontario and one in Southwestern Ontario) were entering their kidding season when they suddenly started to experience significant reproductive losses. In both cases, aborted fetuses exhibited various combinations of fetal malformations, including, limb contracture/arthrogryposis, scoliosis/kyphosis/lordosis, cerebellar hypoplasia, and hydrocephalus (Fig. 1) .
The first herd (n = 25 with 7 pregnant does) consisted of 2nd and 3rd lactation does with approximately half of the animals kidding affected fetuses. The second herd (n = 225 with 85 pregnant does) contained does of various lactation stages with 16/120 kids (13%) being affected, and four does lost as a result of associated birthing complications. The first herd had no previously reported reproductive losses, while the second herd had reported similar fetal malformations 5 years previously.
Following postmortem and microscopic evaluation, samples of placenta, fetal tissues and fetal thoracic fluid from both cases were independently sent to Texas Veterinary Medical Diagnostic Laboratory (TVMDL) for detection of Cache Valley virus (CVV). PCR testing for CVV on placental and/or fetal tissues was negative, while the virus neutralization (VN) assay on fetal thoracic cavity fluid was positive in both cases. Tissues from both cases also tested negative for both Coxiella burnetti and Chlamydia abortus by PCR testing. Toxoplasma gondii PCR on samples from the first herd was also negative, and no bacterial pathogens were isolated in that case.
In sheep and goats, CVV infection can cause infertility, abortion, stillbirths and congenital anomalies with the latter occurring specifically when infection occurs between 28 - 48 days of gestation. CVV is a mosquito-borne bunyavirus that is considered endemic across much of North America, including Ontario. Transmission occurs predominately through mosquitoes (various Aedes spp.), but biting culicoid midges are also implicated. In Ontario, the population of infected mosquitos reaches its peak in late summer/early fall, resulting in abortions/stillbirths during December and January. Does are typically asymptomatic with rapid clearance of the virus following infection, and therefore, virus is often not present within tissues at the time of abortion.
The rapid clearance of the virus is the reason for a high likelihood of a negative PCR test result. Although fetal fluid is not the specifically validated sample type for serological antibody testing, it is often the only sample available for testing in aborted fetuses. The positive antibody titre on fetal thoracic fluid in this case is indicative of historic infection with CVV and supports CVV infection as the cause of these abortions. Performing titres on the ewes/does may also be helpful to confirm exposure in a flock.
Similar congenital malformations can also be associated with other infections (e.g., border disease, bluetongue virus, bovine viral diarrhea virus), inherited genetic defects (e.g., ovine hereditary chondrodysplasia/spider lamb syndrome), and ingestion of teratogenic plants (e.g., Lupinus spp.). Therefore, submission of the whole fetus and placenta for diagnostic evaluation forms an important component in any investigation of fetal losses in a flock.
Given the endemicity of the virus in Ontario, CVV-associated abortions are sporadically diagnosed in sheep at the AHL. However, to date, these are the only two cases where CVV has been confirmed as the cause of abortion in any goat population tested at the AHL. AHL
Figure 1. Aborted goat fetuses following CVV infection. A. The fetus has prominent thoracic kyphosis with a shortened vertebral column and variable arthrogryposis of all four limbs (photo courtesy of Dr. Heather Murray; Dundas Veterinary Services). B. The entire length of the vertebral column of this fetus is markedly twisted (scoliosis) and all four limbs contain flexural contracture (photo courtesy of Dr. Emily zur Linden; Metzger Veterinary Services).
References
1. LWaddell L, et al. Cache Valley virus: A scoping review of the global evidence. Zoonoses Public Health. 2019;66:739–758.
2. Rodrigues Hoffmann A, et al. Ovine fetal immune response to Cache Valley virus infection. Journal of Virology, 2013; 87:5586-5592.
3. Menzies PI. Abortion in Sheep: Diagnosis and Control. In: Youngquist RA, Threlfall WR, eds. Current Therapy in Large Animal Theriogenology. 2nd ed. St Louis, MO: Saunders Elsevier Inc, 2007:667-680.