Introduction Directory UMM :Data Elmu:jurnal:A:Animal Reproduction Science:Vol60-61.Issue1-4.Jul2000:

Ž . Animal Reproduction Science 60–61 2000 643–651 www.elsevier.comrlocateranireprosci Bluetongue and equine viral arteritis viruses as models of virus-induced fetal injury and abortion N.J. MacLachlan a, , A.J. Conley b , P.C. Kennedy a a Departments of Pathology, Microbiology and Immunology, School of Veterinary Medicine, UniÕersity of California, 1126 Haring Hall, DaÕis, CA 95616, USA b Population Health and Reproduction, School of Veterinary Medicine, UniÕersity of California, DaÕis, CA 95616, USA Abstract A number of viruses have the capacity to cross the placenta and infect the fetus to cause, Ž . among other potential outcomes, developmental defects teratogenesis , fetal death and abortion. Ž . Bluetongue virus BTV infection of fetal ruminants provides an excellent model for the study of virus-induced teratogenesis. This model has shown that only viruses modified by passage in cell culture, such as modified live virus vaccine strains, readily cross the ruminant placenta, and that the timing of fetal infection determines the outcome. Thus, cerebral malformations only occur after fetal infection at critical stages during development and the precise timing of fetal BTV infection determines the severity of the malformation present at birth. Fetal BTV infection also can result in fetal death, followed by abortion or resorption, growth retardation, or no obvious Ž . abnormalities, depending on age of the conceptus at infection. Equine arteritis virus EAV infection of the equine fetus causes fetal death and abortion but not teratogenesis. These two fetal viral infections are useful not only for the study of teratogenesis and fetal disease, but also to further characterize and compare the complex process that is responsible for normal induction of parturition in ruminants and horses. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Bluetongue; Equine viral arteritis; Abortion; Teratogenesis

1. Introduction

The extended duration of pregnancy in domestic ruminants and horses facilitates fetal development in a highly insulated environment. Suboptimal reproductive performance is Corresponding author. Tel.: q1-530-752-1385; fax: q1-530-754-8124. Ž . E-mail address: njmaclachlanucdavis.edu N.J. MacLachlan . 0378-4320r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 3 7 8 - 4 3 2 0 0 0 0 0 1 0 5 - 6 common in these species. There are many causes of this reduced fertility; it can result from anything from lack of cyclic activity of the female to perinatal mortality. Insults that occur during the period of the fetus that result in fetal death and abortion, or teratogenesis, are best understood from the perspective of the normal embryology, gestational physiology, and the mechanism responsible for induction of parturition in each animal species. A wide variety of agents, both infectious and non-infectious, are capable of crossing the placenta to cause fetal injury. Most maternal virus infections are not transmitted to the fetus, however, several viruses that infect domestic animals have the capacity to cross the placenta and to subsequently induce disease andror developmental defects Ž . teratogenesis . Teratogenesis is the production of physical defects in offspring in utero. The outcome of virus infection of the fetus depends on the susceptibility of the fetus to the infecting virus which, in turn, is a reflection of the gestational age of the fetus at exposure as well as the virulence characteristics of the infecting virus. The potential consequences of fetal viral infections include teratogenesis, fetal disease with or without abortion, growth retardation, persistent postnatal infection, or no obvious abnormality Ž . Catalano and Sever, 1971 . This review will describe and compare aspects of blue- Ž . Ž . tongue virus BTV infection of the ruminant fetus and equine arteritis virus EAV infection of the equine fetus.

2. Maintenance of pregnancy and induction of parturition