Transmission of Bluetongue Virus Serotype 8 by Artificial Insemination with Frozen–Thawed Semen from Naturally Infected Bulls

Abstract

Transmission of bluetongue (BT) virus serotype 8 (BTV-8) via artificial insemination of contaminated frozen semen from naturally infected bulls was investigated in two independent experiments. Healthy, BT negative heifers were hormonally synchronized and artificially inseminated at oestrus. In total, six groups of three heifers received semen from four batches derived from three bulls naturally infected with BTV-8. Each experiment included one control heifer that was not inseminated and that remained BT negative throughout. BTV viraemia and seroconversion were determined in 8 out of 18 inseminated heifers, and BTV was isolated from five of these animals. These eight heifers only displayed mild clinical signs of BT, if any at all, but six of them experienced pregnancy loss between weeks four and eight of gestation, and five of them became BT PCR and antibody positive. The other two infected heifers gave birth at term to two healthy and BT negative calves. The BT viral load varied among the semen batches used and this had a significant impact on the infection rate, the time of onset of viraemia post artificial insemination, and the gestational stage at which pregnancy loss occurred. These results, which confirm unusual features of BTV-8 infection, should not be extrapolated to infection with other BTV strains without thorough evaluation. This study also adds weight to the hypothesis that the re-emergence of BTV-8 in France in 2015 may be attributable to the use of contaminated bovine semen.

Bluetongue and Epizootic Hemorrhagic Disease in the United States of America at the Wildlife–Livestock Interface

“…These factors include ruminant species/breeds, age, and immune status of the animals as well as the presence of competent Culicoides vectors in the area, virus serotypes co-circulating, and co-infecting mammal and vector hosts ( Figure 2 ) [ 48 , 49 ]. However, there is observed variation in susceptibility to infection and clinical signs between ruminant species and individual animals, and associated with different virus serogroups [ 50 ]. Thus, to better understand the transmission cycle of BTV and EHDV, there is a need to evaluate the susceptible host species’ physiology, immunology, and genetics and understand the ecology of insect vectors [ 18 , 49 ].…”

“…Oral infection of neonate calves and kids after uptake of colostrum from BTV-8 infected cattle and BTV-25 infected goats, respectively, have been reported [ 71 , 75 , 76 ]. Contact transmission has been reported in experimental BTV-3 infection in white-tailed deer [ 77 ] and via artificial insemination of BTV-8 contaminated frozen semen from naturally infected bulls [ 50 ]. In addition, the spread between animals of BTV-25, 26, and 27 via direct contact with ocular or nasal secretions have also been reported [ 5 , 33 ].…”

Vaccination as a Strategy to Prevent Bluetongue Virus Vertical Transmission

“…BTV is also known to target ram and bull semen quality and can be isolated from this fluid in infected animals [55,56]. Recently, BTV transmission to heifers through insemination with semen from naturally infected bulls has been demonstrated [57]. Previous reports had already established that BTV could be transmitted through this route using semen from experimentally infected ruminants [58,59].…”

“…Vertical transmission from the pregnant female to the fetus is the alternative BTV transmission route with the most epidemiological significance. Indeed, venereal BTV transmission can also result in vertical transmission of the virus to the fetus, which often leads to abortions [57]. Vertical BTV transmission was first suspected in the 1950s as a result of vaccination with a live attenuated virus that increased stillbirth and weak lambs in vaccinated flocks [61].…”

Failure to detect Schmallenberg virus RNA in ram semen in the UK (2016–2018)

“…23 While the presence of SBV RNA in semen does not automatically indicate venereal transmission 24 or any effect on the embryo or successful conception, this is thought to be the mechanism by which the re‐emergence of bluetongue virus (BTV) in Europe occurred (BTV is a ruminant arbovirus that can cause cross‐placental infections) via the use of frozen reproductive materials. 25 , 26 …”