Abstract
Since its introduction into northern Europe in 2006, bluetongue has become a major threat to animal health. While the efficacy of commercial vaccines has been clearly demonstrated in livestock, little is known regarding the effect of maternal immunity on vaccinal efficacy. Here, we have investigated the duration and amplitude of colostral antibody-induced immunity in calves born to dams vaccinated against bluetongue virus serotype 8 (BTV-8) and the extent of colostral antibody-induced interference of vaccination in these calves. Twenty-two calf-cow pairs were included in this survey. The median age at which calves became seronegative for BTV was 84 and 112 days as assayed by seroneutralisation test (SNT) and VP7 BTV competitive ELISA (cELISA), respectively. At the mean age of 118 days, 13/22 calves were immunized with inactivated BTV-8 vaccine. In most calves vaccination elicited a weak immune response, with seroconversion in only 3/13 calves. The amplitude of the humoral response to vaccination was inversely proportional to the maternal antibody level prior to vaccination. Thus, the lack of response was attributed to the persistence of virus-specific colostral antibodies that interfered with the induction of the immune response. These data suggest that the recommended age for vaccination of calves born to vaccinated dams needs to be adjusted in order to optimize vaccinal efficacy.
Highlights
Bluetongue (BT) is a non-contagious, arthropod-borne viral disease affecting sheep, some species of wild ruminants such as deer, and to a lesser extent, cattle and goats
Following the 2006 outbreak of bluetongue virus serotype 8 (BTV-8) in livestock in northern Europe, BT has become a major concern in animal health and trade
Extensive studies have not been performed to evaluate the effects of passive immunity in calves born to immunized dams on the humoral response to Bluetongue virus (BTV)-8 immunization
Summary
Bluetongue (BT) is a non-contagious, arthropod-borne viral disease affecting sheep, some species of wild ruminants such as deer, and to a lesser extent, cattle and goats. Bluetongue virus (BTV), the etiologic agent of the disease, is the type species of the genus Orbivirus within the family Reoviridae. In August 2006, a sixth serotype, BTV-8, was first identified in northern Europe, from where it Newborn calves acquire passive immunity from their dams by ingestion and absorption of antibodies present in colostrum. Very few data are available as regards the duration and effect of maternally acquired immunity against BTV in calves that were born to vaccinated cows. This prompted us to investigate: (1) the time required for nursing beef calves to become seronegative; (2) the effect of colostral antibodies on the humoral response in calves after vaccination with an inactivated BTV-8 vaccine
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