Failure of embryos from bluetongue infected cattle to transmit virus to susceptible recipients or their offspring

Abstract

Sixty heifers were infected with bluetongue virus (BTV) by the bites of the vector and by inoculation with insect origin virus. During the acute and convalescent stages of the infection, embryos were collected nonsurgically from these animals and washed according to the recommendations of the International Embryo Transfer Society (1). No BTV was isolated from 77 of these embryos when they were inoculated onto cell culture and into embryonating chicken eggs. There was no evidence of lateral BTV transmission when 231 of these embryos were transferred into susceptible recipients, nor was there evidence of vertical BTV transmission to the 88 calves resulting from these transfers. Another six donors that were assumed to have recovered from a natural infection of BTV, were added to the study to increase the probability of obtaining embryos from a persistently infected BTV carrier. However, it was determined later that these animals had not been infected with BTV but with the closely-related epizootic hemorrhagic disease virus (EHDV). Embryos were collected from these donors and washed as above. Neither BTV nor EHDV was isolated from 26 of these embryos by the inoculation of cell culture and embryonating chicken eggs. There was no evidence of lateral BTV or EHDV transmission to recipients of 15 of these embryos or of vertical BTV or EHDV transmission to the resulting 7 calves. However, two recipients of embryos from one of these donors developed antibodies to BTV 6 to 9 months after transfer. Passive antibodies to BTV were also detected in their calves. There is good evidence that these two recipients acquired BTV from natural exposure to infected insect vectors and not from the transferred embryos.