EMBRYO-TRANSFER AND ITS POTENTIAL ROLE IN CONTROL OF SCRAPIE AND BOVINE SPONGIFORM ENCEPHALOPATHY (BSE)

BSE is a new transmissible spongiform encephalopathy (SE) of cattle resulting from consumption of a scrapie-like agent in meat and bone meal of concentrate rations. There is evidence of a decline in the epidemic following the introduction of a feed ban in July 1988. Cow to cow transmission is not proven and may not occur. Scrapie is an endemic disease of sheep known for over 250 years where maternal and horizontal transmission are responsible for the difficulty in controlling the disease. Embryo transfer (ET) is a valued method of moving genetic material around the world with negligible risk of transmitting infectious diseases provided the International Embryo Transfer Society protocols are used. Data on ET and the control of SE in sheep and cattle is being investigated in the USA and the UK. In regard to sheep there are conflicting results. Washed embryos from experimentally infected sheep in the USA have not transmitted scrapie to recipients though no account was taken of the genetic susceptibility of the embryo or recipient. In contrast in the UK, using Sip and PrP genotyped experimentally-infected sheep and unwashed embryos, scrapie resulted in the homozygous susceptible (sAsA) offspring within 979 days. The question as to whether ET can be used to control natural scrapie in sheep is thus unresolved. Further studies to investigate the effect of washing embryos are in progress. In the UK 1000 embryos have been collected from confirmed BSE cows and some have been transferred into 347 heifers imported from New Zealand as calves and subsequently held under quarantine conditions. Some embryos and uterine flushings have been inoculated into susceptible mice. No disease has resulted but the experiment will not be completed until 2001.