A flock level analysis of an outbreak of natural border disease in Sakiz ewes and their progeny

ABSTRACT

Background: Pestiviruses cause economically important diseases in domestic ruminants worldwide. Border Disease is a congenital viral infection of sheep, caused by a pestivirus, and is first reported in the Border region of Wales and England. The BDV has worldwide distribution in sheep with different prevalences among countries. Vertical transmission is an important route in the epidemiology of this virus. Infection of fetuses may cause birth of persistently infected lambs, that are viremic, antibody negative, and are excreting virus. The disease is characterized by abortion, barren ewes, stillbirth and persistently infected weak lambs showing neurological and dermatological signs. The economic importance of the disease is related to reproductive failure, abortions and significantly low survival rate of affected lambs. In the present study the aim was to describe clinical, hematological and serological aspects of natural Border disease virus (BDV) infection in a sheep flock in Cine, Aydin. Besides we sought to elucidate the relationship between natural (active infection) and persistent BDV disease and the serum concentration of haptoglobin (Hp) and serum amyloid A (SAA) in infected sheep Materials, Methods & Results: Field observations were carried out in a sheep flock comprising 327 sheep with a history of an outbreak abortion in Cine town in Aydin, Turkey. Twenty-five out of 327 sheep in the flock was monitorized by blood sampling. The animals were selected among aborted ones, at least once, into two weeks preceeding period or with a history of weak lambing. BDV antigen (persistent infection) was detected in 8 out of 25 sheep (32%) while antiviral antibodies (active infection) were detected in 18 animals tested (68%). The disease was mainly characterized by abortions, stillbirth/weak lamb and abnormal brown/black fleece pigmentation, which occurred in an epidemic form. Twenty five sheep were related to disease condition as detected serologically, and the ratio of the number affected to number at risk being was 178. The culling rate was 50% of the affected animals. Most of the affected animals were second lambing sheep (5/25, 20%). Hematological variables did not reveal statistical difference whereas serum concentrations of Hp (P < 0.05) and SAA (P < 0.01) were significantly higher in naturally infected sheep in contrast to persistently infected sheep with BDV. Discussion: Clinical signs and detailed laboratory analysis related to natural Border disease outbreak have never been reported in Turkey, although previous epidemiological studies had shown that Border disease virus infection is relatively common in some parts of Turkey in sheep flocks and persistent Border disease virus infection had been described in apparently healthy sheep in Turkey. In the present study the disease was mainly characterized by abortions, stillbirth/weak lamb and abnormal brown/black fleece pigmentation, which occurred in an epidemic form. Besides bronchopneumonia, enteritis and conjunctivitis were detected in a limited population. Neurological signs were only observed in 2 animals. Besides persistent infection was detected in 32% of sheep enrolled. An acute phase reaction involving Hp and SAA has been identified in the present study. These results indicate that the monitoring of selected acute phase proteins may increase the diagnostic information available as a result of their analyses in naturally infected sheep and persistently infected sheep with BDV.