| Popis: |
A single feeding of milk containing 2×07 TCID50 of infectious caprine arthritis-encephalitis virus (CAEV) infected 50% of newborn kids. Lesser amounts were not infectious when given as a single ingestion, indicating that 2 × 107 TCID50 was near the minimal infective oral dose. Seroconversion following intravenous innoculation of infectious CAEV was observed to occur more rapidly (4 weeks post-innoculation), at a lower level of exposure (2 × 106 TCID50), and more efficiently (100%) when compared to other routes of exposure. The occurrence of maternal-fetal transmission was supported by experiments in which kids were removed from their mothers immediately at birth and reared in isolation on virus-free milk or milk replacers. Five percent of a group of 40 kids born to naturally CAEV-infected does and handled in this manner seroconverted within 8 weeks. This indicated that at least two kids in the group were infected prior to birth or during the birth process. When seronegative kids were housed in intimate contact with CAEV-infected animals, an additional 10% became seropositive within 20 weeks, suggesting that contact transmission of CAEV also occurs later in life between infected and susceptible goats. Intramammary infusion of 2 × 107 TCID50 infectiious CAEV resulted in seroconversion in three of three lactating seronegative does within 4–8 weeks post-infusion. Thus, goats may be infected by a single oral exposure to infectious CAEV, by contact with infected individuals as occurs in normal husbandry practices, by intramammary route as might occur during routing machine milking of lactating does, and from doe to fetus either prior to or during the birth process. Control of CAEV on commercial goat dairies will be enhanced by incorporation of the findings of these studies in a preventive program. |
