Prenatal viral infections can be teratogenic in cattle, sheep, goats, pigs, dogs, and cats; however, they have rarely been incriminated in cases of congenital defects in horses.
The stage of fetal or embryonic development at the time of exposure to a virus determines the type and extent of the anomalies observed. Viral infection in late gestation can result in fetal infection and seroconversion without observed clinical signs; exposure during earlier stages can induce pregnancy loss or congenital defects.
Production of neonates with congenital anomalies after in utero infection can follow observable clinical signs in the dam; however, anomalies also occur without a history of disease during pregnancy. On occasion, use of modified live virus vaccines in pregnant animals has produced congenital defects; such use is discouraged.
Pestivirus infections are teratogenic in many species. Bovine viral diarrhea virus (BVDV) is among the most economically important infectious agents affecting cattle worldwide. Prenatal BVDV infection can cause a variety of congenital defects in survivors, including cerebellar hypoplasia, brachygnathia, alopecia, ocular defects, internal hydrocephalus, and impaired immunocompetence. Immunotolerant, persistently infected animals can result from fetal infection with noncytopathic BVDV before gestational day 120. These animals are a major reservoir of infection.
Pestivirus infections in other species also result in congenital defects. Infection of pregnant ewes with border disease virus can manifest as embryonic and fetal death or congenital defects involving the integumentary, nervous, skeletal, endocrine, and immune systems. Defects include tremors, ataxia, abnormal coat, low birth weight, facial and ocular abnormalities, depressed immune response, and birth of small, weak lambs with poor growth and viability. Infection of pregnant ewes with BVDV from cattle has produced identical congenital anomalies in sheep.
Classical swine fever, a pestivirus infection of swine, was once known as hog cholera. The virus has been eradicated in the US; however, it remains a major cause of swine disease in some regions of the world. Prenatal infection can result in congenital defects similar to those in cattle infected with BVDV.
Cache Valley virus is a vector-borne orthobunyavirus. Infection of pregnant ewes by this virus can result in anomalies in their lambs, including arthrogryposis, torticollis, scoliosis, lordosis, hydranencephaly, microcephaly, porencephaly, and cerebellar and muscular hypoplasia. Cache Valley virus is transmitted by mosquitoes and is found in the US, Canada, and Mexico. Other ruminant species can be affected, and other bunyaviruses have been reported to cause similar congenital defects.
Bluetongue is an insect-transmitted viral disease of domestic and wild ruminants caused by an orbivirus. Bluetongue virus is endemic in many areas of North America, South America, Africa, and parts of Asia, and it has expanded its range in Europe. In utero exposure can induce hydranencephaly, porencephaly, and arthrogryposis in sheep, and it can result in abortion, stillbirth, arthrogryposis, campylognathia, prognathism, hydranencephaly, and “dummy calf” syndrome in cattle. Other orbiviruses, such as Chuzan virus and perhaps epizootic hemorrhagic disease (EHD) virus, can cause abortion, congenital defects, and neonatal losses similar to the effects of bluetongue virus.
Akabane virus, an orbivirus present in many tropical and subtropical areas, is transmitted by Culicoides spp (biting midges). Infection of naive animals can be followed by transplacental infection of the fetus and can produce deformities similar to those caused by viruses such as bluetongue virus and Cache Valley virus.
Congenital cerebellar hypoplasia in kittens has long been recognized as a result of infection of pregnant queens with feline panleukopenia virus. In ferrets, infection with feline panleukopenia virus during pregnancy also can result in congenital cerebellar hypoplasia.
Key Points
Viral infections during pregnancy can lead to embryonic loss, abortion, or the birth of congenitally infected offspring with severe defects.
Offspring affected in utero can exhibit low birth weight, poor viability, tremors, abnormal physical traits (eg, excessively hairy coats), and other developmental problems.
Viral infections are often transmitted by vectors (eg, biting midges) or by direct contact with persistently infected animals.
Congenitally infected surviving offspring often remain persistently infected and serve as reservoirs for viral infection of susceptible populations.
Where these viruses are endemic, animals exposed before reaching breeding age have lower susceptibility during reproduction.
For More Information
