Inoculation of 53 ewes after 35, 45, 60, or 80 days of gestation with bluetongue virus serotypes 10, 11, 13, or 17, or with epizootic hemorrhagic disease virus serotypes 1 or 2, resulted in overt clinical disease in the 47 ewes inoculated with bluetongue virus but not in the 6 ewes inoculated with epizootic hemorrhagic disease virus. None of the lambs produced by these ewes had developmental defects or any evidence of persistence of viremia.

A regional prospective study of the epidemiology of bluetongue virus (BTV) serotypes covering 11 countries in Central America and the Caribbean took place between 1987 and 1992. Active surveillance revealed BTV infection to be endemic in the absence of confirmed indigenous cases of bluetongue. During the 6-year span of the study, over 300 BTV isolations were obtained from cattle and sheep. Results of the earlier years of the study were summarized, and surveillance activities in the concluding months of the study from November 1990 to February 1992 were evaluated. Forty-five BTV isolations were made during this time, 44 from sentinel cattle and 1 from a ram with clinical signs compatible with contagious ecthyma. Virus isolation from potential vectors also was attempted, yielding a further 9 BTV isolates from parous Culicoides insignis and C pusillus, 2 BTV isolates from blood-engorged C filarifer, and 1 epizootic hemorrhagic disease virus type-2 isolate from parous C pusillus. Our extensive network of sentinel herds in the region detected BTV-1 as the predominant serotype in Central America in 1991, after an apparent absence of 1 year in the sentinel animals. Other serotypes in Central America at that time included BTV-3 and BTV-6. In Puerto Rico and the Dominican Republic, BTV-4 became the predominant serotype, without detection of BTV-8 and BTV-17, which were common in recent years of the study. The serotypes found in the Caribbean Basin continued to have marked differences from those in North America. The importance of viewing bluetongue as an infection, the distribution of which is determined principally by ecologic factors, is emphasized.

The consequences of inoculation of bluetongue virus (BTV) serotype 11 into 16 susceptible cows either at the time of breeding or at specified stages of pregnancy were studied. The cows were free of BTV or epizootic hemorrhagic disease virus, and none had antibodies to BTV before virus inoculation. A group of 4 cows was mated naturally to a bull reported to shed BTV (CO75B300 strain) in the semen. The bull was suspected of infecting cows at mating with BTV-11, which subsequently transplacentally infected the developing fetuses and induced persistently infected and congenitally malformed progeny. Two groups of 4 pregnant cows were inoculated with an insect-derived strain of BTV-11 (CO75B300), one group by direct deposit into the uterus at estrus, the other, by intradermal and sc administrations. A 90-day fetus was inoculated in utero with virus from the same pool. Four pregnant cows were inoculated with sheep blood-passaged virus of the same BTV-11 strain (CO75B300) by intradermal and sc routes. Three cows were inoculated with BTV-free suspending fluids and ovine erythrocytes by the intrauterine and intradermal-sc routes and were used as in-contact controls.Infection with insect-derived BTV-11 was confirmed in 3 cows of 1 group by virus isolation and by detection of serum antibodies. The 4 cows inoculated with sheep blood suspension of BTV-11 developed viremia and produced antibodies to the virus. None of the cattle had clinical signs of bluetongue, other than 2 cows that had a slight rectal temperature increase on postinoculation day 4.All cows and fetuses that ranged in gestational age from 69 to 217 days appeared grossly normal at necropsy. Antibodies were not detected in fetal blood. Viral antigen was not detected in fetal tissues by inoculation into sheep or by immunofluoerscence, and viral RNA was not detected by use of the polymerase chain reaction. Developmental deformities were not seen in any fetus. The BTV-11 was not transmitted via the bull semen after natural mating. The BTV-11 strain CO75B300, isolated from this bull and passaged either as insect-derived or ovine erythrocyte suspensions, infected 8 cows. However, the virus was not transplacentally transmitted to their fetuses. It was concluded that there was no evidence for congenital BTV-11 infection in this study.

Results of testing of 19,731 samples from a serologic survey of cattle with bluetongue virus (BTV) infections in Australia were analyzed for association between age, species, or sex and test result. Bivariate analysis indicated that all 3 host factors were associated with test result. After adjusting for confounding caused by the location of each animal in the study (high, moderate, and low BTV prevalence regions), cattle greater than or equal to 4 years old had an odds ratio of 4.33 (95% confidence interval, 3.99, 4.71) for a positive test result, compared with that for cattle < 2 years old. Cattle 2 to 4 years had an odds ratio of 2.28 (2.14, 2.54), compared with cattle < 2 years old. Bos taurus cattle had an odds ratio of 1.76 (1.63, 2.05) of a positive test result, compared with crossbred cattle, and B indicus cattle had an odds ratio of 1.20 (1.09, 1.33), compared with crossbred cattle. Sexually intact (+) male cattle were found to have an odds ratio of 3.13 (2.66, 3.49) for a positive test result, compared with castrated male (-) cattle, and female cattle were found to have an odds ratio of 1.38 (1.29, 1.48), compared with male (-) cattle. Multivariate analysis of BTV testing results was performed, using stepwise logistic regression. The most parsimonious model selected included age, species, and sex factors, and first-order interaction terms between these factors. This model was only able to be fit to data from cattle restricted to the high (> 25%) BTV prevalence region. Odds ratios were found to increase with age for male (-) cattle of all species. Odds ratios were found to be greatest at 2 to 4 years of age for female cattle of all species and for B taurus and crossbred male (+) cattle.