Epidemiological survey of Border disease virus among sheep from northern districts of Japan

The first epidemiological survey of Border disease virus (BDV) was undertaken in small ruminants in Japan. Ovine sera, collected from the northern prefectures of Hokkaido, Aomori and Iwate, were examined for the presence of antibodies against BDV using the neutralization peroxidase-linked antibody test. Twenty-nine (17.6%) of one hundred and sixty-five samples were seropositive for BDV. Results were specific, excluding cross-reactions with bovine viral diarrhea virus (BVDV). Only one sample (0.6%) was positive for BVDV, and was negative for BDV. Despite serological evidence of virus circulation, there have been no clinical cases of border disease in sheep in Japan. Although no diagnostic measures were performed, the infection did not appear to be associated with a reduction in ewe fertility nor with lamb mortality.     

Mucosal disease-like lesions in sheep infected with Border disease virus

An enteric disease characterised by diarrhoea and ill thrift affected 12 of a flock of 700 six- to 12-month-old ewe lambs in Cornwall between December 1996 and September 1997. The affected lambs were undersized, became thin and suffered an unremitting diarrhoea until they died. The illness lasted for three to 14 days, although, with hindsight, the owner considered that the lambs had been below average size before the enteric signs developed. The outbreak ceased only as a result of the dispersal sale of the flock as breeding ewes. The flock had been purchased from different sources, but 11 of the cases occurred in a group of 40 purchased from one source. Postmortem, the alimentary changes resembled mucosal disease in cattle, and immunostaining of histological sections of the affected tissues revealed pestiviral antigen. Non-cytopathic pestiviruses were isolated from the lesions of two of the affected lambs and from the blood of several clinically normal ewe lambs from the same group. All the pestivirus isolates were typed as Border disease virus.     

Border disease in sheep caused by transmission of virus from cattle persistently infected with bovine virus diarrhoea virus.

Two outbreaks of border disease occurred on farms with sheep flocks and breeding cattle. The infection of the pregnant sheep was probably caused by transmission of virus from calves persistently infected with non-cytopathic bovine virus diarrhoea virus (BVDV) which were kept in close confinement with the ewes during mid-pregnancy. Border disease was also induced experimentally in eight lambs by exposing their dams at 38 to 78 days of gestation to a heifer persistently infected with BVDV. Both the natural and the experimental infections were characterised by typical signs such as 'hairy-shaker' lambs and high lamb mortality. The diagnosis was confirmed by virus isolations from live-born lambs, seroconversion and pathology. The study supports the assertion that cattle persistently infected with BVDV and in close contact with pregnant sheep, are an important source of strains of virus capable of causing border disease.     

Presence of antibodies to bovine viral diarrhea-mucosal disease virus (border disease) in sheep and goat flocks in Quebec.

A seroepidemiological study of border disease was conducted in sheep and goats in various areas of Quebec. Sera of 10% of animals of selected flocks were collected and specific antibodies against bovine viral diarrhea- mucosal disease were tested by seroneutralization. Results show that 10.9% and 16% of sheep and goats respectively gave a positive reaction. The lower serological prevalence was found in sheep flocks of the Sherbrooke area (5.4%) while the highest percentage of positive sera was observed in the Quebec area (24.7%). The prevalence in goats varied according to areas (2.6 to 45.5%). No relation was observed in seropositive animals between age, sex, breed and the presence of abortions in the flocks. Our serological results indicate that border disease is probably present in Quebec sheep and goat flocks but that the clinical diagnosis of this disease is not well established.     

Border disease in Norway. Serological examination of affected sheep flocks

Serological examination of 4 Border disease affected flocks of sheep using the neutralization test showed antibody prevalences between 14 and 96 %. Prevalence in yearlings in 3 of the 4 flocks was 37 %, it increased with age to 72 % in 5-year-old sheep. Possible reason for low prevalence (2 %) in yearlings in one of the flocks is discussed.     

Enzyme-linked immunosorbent assay for the detection of antibodies to bovine virus diarrhea virus in sera from border disease virus-infected sheep.

An enzyme-linked immunosorbent assay (ELISA) was established for the rapid detection of specific antibodies against the causative agent of border disease in ovine sera. Polyethylene-glycol concentrated, equilibrium density gradient purified bovine virus diarrhea virus was used as test antigen. The optimal amount of antigen was 0.5 microgram/well, and the optimal concentration of conjugate was at 1/4,000 dilution. A total of 20 ovine serum samples, which had been collected from animals with or without border disease, were compared by ELISA and serum neutralization test for the detection of border disease-specific antibodies. ELISA was shown to be equally specific but less time-consuming and easier to perform than serum neutralization test. A positive correlation (r = 0.60) between the two tests was found.     

Age-specific seroprevalence of Border disease virus and presence of persistently infected sheep in Basque dairy-sheep flocks

Using p125/p80 antibody and antigen-ELISA tests, age-specific seroprevalence and presence of persistently infected (PI) sheep were investigated in six commercial latxa dairy-flocks, housed for variable periods. The flocks all had a recent history of Border disease (BD). Every flock included seropositive sheep and seven 0.5-3-year-old PI sheep were detected in two of four flocks tested. Age-specific antibody patterns differed according to the presence or absence of PI sheep in the flock. In flocks free of PI sheep, seroprevalence was 6-13% in 1-year-old sheep and 42-93% in older sheep. In contrast, seroprevalence was 67-99% in sheep raised with PI sheep for at least 1 year and 29-33% in replacement 0.5-0.6-year-old sheep (including a PI sheep) indicating that Border disease virus (BDV) transmission in Basque dairy-flocks can be relatively slow. Moderate seroprevalence in young replacement sheep should not discourage further testing to detect PI sheep, and our results highlight the risk of failing to achieve "natural vaccination" prior to pregnancy by mixing PI sheep with BDV-unexposed ewes.     

Prevalence, regional distribution and control of blowfly strike in England and Wales.

The prevalence and control of blowfly strike in England and Wales was investigated by a postal survey of 2451 sheep farmers, divided into five regions, who were asked about the blowfly seasons of 1988 and 1989. These were important years for the control of blowfly strike because the number of compulsory dips for the control of sheep scab was reduced from two to one in 1989. The response rate was 74.2 per cent. A larger proportion of farmers in the south west and south east reported strike (90 per cent), than in the north of England (60 per cent). The proportion of sheep with strike showed a similar regional variation (0.7 per cent in the north of England to 2.8 per cent in the south west). Dipping was the most common method of blowfly control, followed by tail amputation, dagging, spraying and cyromazine. Twenty per cent of farmers reported reducing the frequency of dipping in 1989, and of those 20 per cent increased the frequency of spraying and 20 per cent used cyromazine.     

Border disease of sheep: the disease in the newborn, adolescent and adult.

Border disease (BD) is a condition of newborn sheep that results from congenital infection by a non-cytopathic pestivirus occurring during the first half of gestation. The expression of the virus is largely determined by the age of the fetus at the time of infection, producing four distinct disease syndromes: (1) early embryonic death, (2) abortion and stillbirth, (3) birth of lambs with malformations, and (4) birth of small, weak lambs, lacking characteristic clinical signs, but bearing features of immunosuppression. The effects of the virus infection during the developmental stages of the fetus are most apparent as distinctive clinical signs at the time of birth but a state of specific immuno-tolerance with associated virus persistence remains for the lifetime of the sheep. Although the clinical signs disappear with time, some effects of virus persistence may continue into adolescence and often into adulthood. Characteristic lesions are found in the nervous, endocrine, skeletal and integumentary, and immune systems.     

Prevalence of antibodies to Coxiella burnetii (Q fever) in bulk tank milk in England and Wales.

In the United Kingdom, the infection of people with Coxiella burnetii, the causative agent of Q fever, is of significant public health importance and is associated with contact with dairy cattle. An ELISA was developed for the detection of IgG antibodies against C burnetii in bulk tank milk, and in a survey of randomly selected samples from dairy herds in England and Wales, 21 per cent showed serological evidence of C burnetii infection.