Pestiviral infections in sheep and pigs in Northern Ireland

Serological surveys were carried out to determine the prevalence of pestiviral infections in sheep and pigs in Northern Ireland. Sera from 918 ewes in 92 flocks from 10 regions were tested by ELISA for antibodies to border disease virus and positive results were obtained from 49 ewes (5.3 per cent) in 28 flocks (30.4 per cent). There were highly significant geographical variations in its flock prevalence ranging from 0 per cent in the Enniskillen region to 70 per cent in the Coleraine region. There was no significant association between the proportion of seropositive flocks and the presence of cattle on the farm (P = 0.583). In the positive flocks, the average rate of seroprevalence was 17.5 per cent, and the highest was 40 per cent. Comparative neutralisation studies on 14 positive sera with bovine viral diarrhoea virus type I (BVDV I) and border disease virus revealed higher titres (> or = four-fold) to BVDV I in all cases. Only one positive result was obtained when fluids from 186 aborted ovine fetuses were tested for border disease virus by ELISA. Serum samples from 680 pigs in 46 herds were tested for virus neutralising antibodies to border disease virus. Twenty sera (2.9 per cent) were cytotoxic, and only one of the remaining 660 sera gave a positive result. This sample tested negative for classical swine fever by ELISA, and comparative neutralisation studies showed that it had a four-fold higher titre to BVDV I than to border disease virus.     

A survey of antibodies to pestivirus in sheep in the Republic of Ireland

: Sera from 1,448 adult ewes in 91 flocks, representing all 26 counties in the Republic of Ireland, were examined for pestivirus antibodies using a commercially available ELISA which detected IgG1 antibody to border disease virus. Eighty-one sheep (5.6%) in 42 flocks (46.0%) were antibody-positive. Within infected flocks, the mean seroprevalence level was 11.4% with a range of 6.3% to 30.0%. The highest antibody prevalence was detected in sheep from central lowland counties of Ireland. Comparative neutralisation testing of 42 ELISA-positive sera detected geometric mean antibody titres of 136 to the NADL strain of bovine viral diarrhoea virus (BVDV), 92 to the Moredun strain of border disease virus and 21 to the 137/4 strain of border disease virus. These results suggest that BVDV may be the major ruminant pestivirus infecting sheep in Ireland. Although there are high numbers of infected flocks, many sheep within such flocks remain antibody-negative and are at risk of giving birth to lambs with congenital border disease.     

Serum antibodies directed against classical swine fever virus and other pestiviruses in wild boar (Sus scrofa) in the Republic of Croatia

The presence of serum antibodies directed against classical swine fever (CSF) virus and other pestiviruses among the wild boar (Sus scrofa) population in Croatia was investigated. During 2003, serum samples from 214 wild boars were collected in 10 hunting areas in the continental part of the country.The sera were examined by enzyme immunoassay (ELISA) and in the virus neutralization test (VNT). Out of 214 sera tested 111 (51.87 %) were positive by ELISA and regarding neutralising antibodies, against CSFV 75 (35.05 %) samples were positive. In the VNT with the C-strain (conventional live vaccine strain China) and the strain Uelzen were used. Samples were also tested for neutralizing antibodies against border disease virus (BDV) using the strain 137/4 and against bovine viral diarrhoea virus (BVDV) using the NADL strain. Neutralizing antibodies against the C-strain were detected in 36 sera (16.82 %), against strain Uelzen in 17 sera (7.94 %) and in 22 sera (10.28 %) against both strains. In five sera (2.33 %) neutralizing antibodies against BVDV and BDV were found.     

Seroepidemiological survey of sheep in Carinthia for the dissemination of ruminant pestiviruses

In this study serological investigations were performed to determine the prevalence of pestiviral infections in sheep in one Federal State of Austria, namely Carinthia. 1527 blood samples from sheep in 147 flocks were collected and tested by Enzyme-linked immunosorbent assay and virus-neutralisation tests for antibodies to ruminant pestiviruses. The estimated flock prevalence was 47.6%, the individual prevalence 16.3%. Significant geographical variations in the flock as well in the individual prevalence were found. The highest prevalence in sheep and in sheep flocks was established in the region Spittal/Drau with 25.9% and 69.7%.The individual and the flock prevalence was significantly higher on farms where cattle or sheep from other farms were present than on farms with no cattle (p < 0.017). All Enzyme-linked immunosorbent assay positive sera were tested for Bovine viral diarrhea virus-1 (strain NADL), Bovine viral diarrhea virus-2 (strain 125) and for Border disease virus (strain MOREDUN) by virus neutralisation tests. Seventy out of 249 positive samples revealed the highest titres (> or = two-fold) to Bovine viral diarrhea virus-1 and 25 to Border disease virus. The remaining positive samples did not show clear results because of cross reactions.     

Toxoplasmosis and border disease in 54 Swedish sheep flocks. Seroprevalence and incidence during one gestation period.

Serum samples from 704 animals from 54 Swedish sheep flocks were analysed by ELISA twice during 1 breeding season for antibodies to Toxoplasma gondii and border disease virus (BDV). An ELISA, originally developed for the detection of antibodies to bovine viral diarrhoea virus (BVDV) in cattle, was assessed on sheep sera and the results were compared with those obtained in a virus neutralization test. The correlation between the 2 assays proved good. Before breeding, 132 (19%) sheep in 42 flocks had antibodies to T. gondii and 7 (1%) sheep in 5 flocks were seropositive to BDV. During the observation period 4 sheep seroconverted to T. gondii and 13 to BDV, giving an incidence rate of 0.7% and 1.9% respectively. No clinical signs due to the infections were observed. In 5 flocks the frequency of barrenness, abortion or stillbirths exceeded 5%, 5% and 8%, respectively, but there was no evidence that this was attributable to the agents studied. The proportion of BDV-positive flocks was significantly higher among flocks that had been in contact with cattle than among those that had not.     

Studies concerning etiology of sheep-associated malignant catarrhal fever in Europe.

The etiological agent of sheep-associated malignant catarrhal fever (MCF) in Europe has not been isolated directly from sheep. The occurrence of antibodies against the African bovine herpesvirus (BHV-3, WC 11) in cattle and sheep was examined using recently modified indirect immunofluorescence test (IIFT) and neutralization test (NT) methods. Studies revealed that sheep and cattle sera in Europe were free from neutralizing antibodies of BHV-3. The IIFT could not establish the presence of antibodies to African BHV-3 in cattle but revealed that about 22.4% of sheep sera reacted to it. Apart from the well known ovine herpesvirus (BHV-5), occurrence of another herpesvirus in Europe had been expected. This virus is not identical with the WC 11 strain, but it is in antigenic relationship to it. We had for the first time substantial serological evidence to the effect that sheep-associated MCF in Europe is a herpesvirus related to the African strain.     

Serological Diagnosis of Classical Swine Fever: A Comparison of a Modified Direct Complement Fixation Test with an Immunofluorescence Plaque Neutralization Test in the Diagnosis of Experimental Subclinical Infection

Antibody levels in post-infection sera from a pig inoculated with a low virulent strain of classical swine fever virus (Hannover 62) and in sera from two pigs inoculated with another low virulent strain (Spielbach 66) and from an in-contact pig were assayed by complement fixation and immunofluorescence using classical swine fever virus (ALD strain) and bovine virus diarrhoea virus (UG 59 strain) as antigens. The complement fixation test used was modified by addition of a preparation of porcine Glq to the complement and by mercaptoethanol treatment of the immune serum before use. The mercaptoethanol treatment of the immune serum resulted in complete elimination of a haemolytic prozone often seen with porcine immune sera.In the sera from the inoculated animals complement-fixing antibodies appeared earlier than neutralizing antibodies. A few weeks after inoculation there was a correlation between the presence of complement-fixing and neutralizing antibodies.During the entire observation period of 13 weeks it was not possible to demonstrate complement-fixing or neutralizing antibodies in serum from a pig exposed to infection by contact with the two pigs inoculated with the Spièlbach 66 strain of classical swine fever virus.     

Evidence of Schmallenberg virus circulation in ruminants in Greece

During March 2013, we investigated the presence and the levels of Schmallenberg virus (SBV) circulation in three dairy cow herds and three sheep flocks in Central Macedonia, Greece. In two cow herds, a high number of abortions had been observed during the winter. Six bulk-tank milk samples and 147 individual sera were screened for SBV-specific antibodies by ELISA. Positive reactions were obtained from 5 out of 6 bulk-tank milk samples, 58 out of 90 sera from the 3 cow herds, and 2 sera from 2 of the 3 sheep flocks. Twenty-two ELISA-positive sera were tested by serum neutralization test (SNT). SNT confirmed the presence of neutralizing antibodies against SBV in all samples tested, with titers ranging between 1:32 and ≥1:256. No neutralizing antibodies against Akabane virus (AKAV) or Shamonda virus (SHAV) were detected, indicating that neutralizing antibodies against SBV do not cross react with AKAV or SHAV in SNT. ELISA testing of bulk-tank milk samples proved to be convenient and reliable. None of the tested sera was found positive for SBV by real-time RT-PCR, indicating that the sampling was conducted past the viremia stage. This is the first report of SBV circulation in Greece.     

Serum antibodies to bovine coronavirus in Swedish sheep.

Altogether 218 sheep sera from 40 flocks in different parts of Sweden were screened for antibodies to bovine coronavirus (BCV). Nineteen per cent of the sera were positive and there was a significantly higher frequency (p < 0.05) of at least one positive sample in flocks with more than 100 adult sheep than in smaller flocks. There was also a significantly higher frequency (p < 0.001) of positive samples from sheep older than 4 years than from younger ones. Only a weak relationship between BCV positivity (2 or more positive samples, p < 0.05) and cattle contact was demonstrated in this study. Possible transmission routes and other factors that could have affected the result are discussed. In light of our finding that all 5 sheep experimentally exposed to BCV through contact with infectious cow faeces seroconverted, we conclude that the antibodies found in Swedish sheep are probably the result of BCV infections directly or indirectly transmitted from cattle.     

Serological evidence for exposure to bovine viral diarrhoea virus in sheep co-grazed with beef cattle in New Zealand

ABSTRACT

Aims: To determine whether sheep that co-grazed with cattle that were suspected to be positive for bovine viral diarrhoea (BVD) virus had serological evidence of exposure to the virus.

Methods: Eighteen commercial farms that routinely co-grazed cattle and sheep in the same paddocks were recruited through purposive sampling. The recruiting veterinarians identified nine farms with cattle herds that were known or highly suspected to be positive for BVD and nine farms that were considered to be free of BVD. Blood samples were taken from 15 ewes aged 1 year on each farm and samples were submitted to a commercial diagnostic laboratory to test for antibodies against pestiviruses using an ELISA. All samples that were positive were then tested using a virus neutralisation test (VNT)for antibodies against BVD virus.

Results: Of the 270 blood samples, 17 were positive for pestivirus antibodies by ELISA and these originated from two farms that were known or suspected to have BVD virus-positive cattle. None of the samples from the nine flocks co-grazed with cattle herds that were known or suspected to be BVD virus-negative were positive for pestivirus antibodies. Within the two positive farms, 2/15 samples from the first farm and 15/15 samples from the second farm were antibody-positive. When the 17 positive blood samples were submitted for VNT, all 15 samples from the second farm tested positive for BVD virus antibodies with the highest titre being 1:512.

Conclusions and clinical relevance: In this small sample of New Zealand sheep and beef farms with suspected BVD infection in cattle, there was evidence of pestivirus exposure in co-grazed sheep. Although we were unable to confirm the origin of the exposure in these sheep, these findings highlight that farmers who are trying to eradicate BVD from their cattle should be mindful that the infection may also be circulating in sheep, and both populations should be considered a possible risk to each other for generating transient and persistent infections. Further work is needed to estimate the true prevalence of New Zealand sheep flocks that are affected by BVD and the associated economic impacts.     

Application of modelling to determine the absence of foot-and-mouth disease in the face of a suspected incursion

AIM: To use disease modelling to inform a response team about the number of animals per herd/flock to be examined, and the start date and duration of clinical surveillance required to be confident that foot-and-mouth disease (FMD) was not present on an island in New Zealand with a population of approximately 1,600 cattle, 10,000 sheep and a small number of pigs, goats and alpacas. METHODS: Because the probability of detecting clinical disease in (the) primary case(s) in larger herds and flocks was extremely low, deterministic and stochastic mathematical SLIR (susceptible, latent, infectious, recovered) models for the transmission of infection were constructed to estimate the date when clinical lesions in herds and flocks would be detected with 95% confidence. Surveillance targeted the first wave of infections following a suspect index case. RESULTS: If 70 cattle in herds of about 400 cattle were examined it was estimated it would take approximately 13 (90% stochastic range 9-19) days from first exposure before it would be possible to achieve 95% confidence for detecting clinical signs for a low-virulence virus, and 9 (7-14) days for a high-virulence virus. The duration of sufficiently accurate clinical detection was 17 (15-19) days and 13 (12-14) days for low- and high-virulence viruses, respectively. A sample of 70 sheep from flocks of >1,000 would be required to achieve clinical detection at about the same time but with a shorter period of detection than for cattle. The duration of effective detection could be increased by examining a larger sample in most sheep flocks, however the small size of many cattle herds in the study population limited the confidence of detecting group-level disease in cattle, therefore necessitating repeated herd inspections. The model suggested that group-level detection was not feasible if it was based on elevated body temperature alone because of short durations of fever in infected animals. CONCLUSION AND CLINICAL RELEVANCE: Simulation modelling is a useful and powerful tool for informing ongoing surveillance activities in the face of an exotic disease incursion. Results of modelling suggested to start clinical inspection activities at 4 days and to continue regular inspection twice a week for about 35 days after the date of first exposure, to satisfy the required 95% confidence threshold of clinical detection of FMD in cattle herds and sheep flocks.     

Epizootiologic study of bluetongue: virologic and serologic results

Heparinized blood and serum samples were obtained from 1,295 ruminants in herds or flocks with bluetongue virus (BTV) infection in 4 western states. Submissions were from herds or flocks with clinical bluetongue (BT), as well as from animals on premises with no history of BT disease. Insects, including Culicoides variipennis, were collected in areas enzootic for BT disease. Viral isolations were in 10-day-old embryonating chicken eggs that were then adapted to Vero cells for serotyping. Sera were tested from group-specific antibody to BTV by the micro agar gel precipitin (AGP) test. Viral isolations were from cattle (81), sheep (122), goats (9), antelope (2), and C varipennis (5). There were 7 isolates of serotype 120, 114 of serotype 11, 42 of serotype 13, and 56 of serotype 17. In herds or flocks from which BTV was isolated, 51% of cattle, 56% of sheep, 21% of goats, and 52% of antelope had AGP antibodies. Virus was isolated from 43% of the cattle and 23% of the sheep that had no demonstrable evidence of AGP antibodies. Viral isolations were seasonal, occurring from August until December. Approximately 30% of the herds or flocks from which virus was isolated had more than one serotype of virus causing infection.     

Bovine herpesvirus-1 (BHV-1), bovine leukemia virus (BLV) and bovine viral diarrhea virus (BVDV) infections in Algerian dromedary camels (<Emphasis Type="Italic">Camelus dromaderius</Emphasis>)

This study was performed to investigate the presence of bovine herpesvirus-1 (BHV-1), bovine leukemia virus (BLV) and bovine viral diarrhea virus (BVDV) infections in dromedary camels (Camelus dromaderius) kept in mixed herds with sheep and goats in Algeria, since the prevalence of BHV-1, BVDV, and BLV infections among dromedary camels in Algeria is unknown. Totally, 111 camel sera were collected from two provinces (Laghouat and Ghardaia) in Algeria. The sera were analyzed for BHV-1 specific antibodies, BVDV specific antibodies and BVDV antigen using the ELISA, and BLV nucleic acid using PCR. The seropositivity rate was 9.0% for BVDV-specific antibody, although 41.4% of camels tested were positive for BVDV antigen. Moreover, there was no evidence of BHV-1 and BLV infections. The results indicated that camels might represent an important source for BVDV infection in all ruminants, including cattle, sheep, and goats bred in mixed herds in Algeria, since they had a higher BVDV prevalence rates. Therefore, the prevention and control measures for BVDV infection should put in place in camel populations to limit the spread of BVDV infection to ruminant populations in Algeria.     

Field observations during the Bluetongue serotype 8 epidemic in 2006. II. Morbidity and mortality rate, case fatality and clinical recovery in sheep and cattle in the Netherlands

Data collected in the Netherlands during the Bluetongue serotype 8 (BTV-8) epidemic indicated that in outbreak cattle herds, predominantly dairy and nursing cows were clinically affected and not young stock, beef cattle, beef calves, or breeding animals. In outbreak sheep flocks, mainly ewes and - if present - rams, were clinically affected and not the lambs. Median morbidity rate in outbreak herds was 1.85 per 100 sheep-month at risk and 0.32 per 100 cattle-month at risk for sheep and cattle, respectively. The mean proportion of BT-affected animals in outbreak herds that recovered from clinical disease was approximately eight times higher for cattle compared to sheep in the Netherlands. Median mortality rate in outbreak herds was 0.5 per 100 sheep-month at risk of dying and 0 per 100 cattle-month at risk of dying for sheep and cattle, respectively. Median recovery time of both sheep and cattle that recovered from clinical disease in outbreak herds was 14 days. Median case fatality was 50% in sheep outbreak flocks and 0% in outbreak cattle herds. It is concluded that morbidity and mortality in outbreak cattle herds was very limited during the BTV-8 epidemic in the Netherlands in 2006. In outbreak sheep flocks, morbidity was limited, with exceptions for a few flocks. However, almost 50% of the clinically sick sheep died in outbreak sheep herds.     

Differential diagnosis of classical swine fever and border disease: seroepidemiological investigation of a pestivirus infection on a mixed sheep and swine farm.]

During recent years neutralizing antibodies against Border Disease Virus (BDV) were found repeatedly in German pig herds. Consequently there was a demand for a differential diagnostic system. A permanent sheep cell line and BDV reference strain Moredun were chosen and were applied in a could be used case study. A pestivirus could be isolated from piglets on a mixed farm and was characterised as 'non-Classical Swine Fever' (CSF) by using monoclonal antibodies. Due to a CSF suspicion the pig herd was destroyed immediately. Serum samples of sheep from the same farm were used for further characterisation of the new virus isolate. A neutralization test of the sheep sera was performed against different pestiviruses and the new isolate. Neutralizing antibody titres against the new virus pig isolate were significantly higher than against all other pestiviruses. BDV strain Moredun recognised the antibodies clearly, whereas CSF viral strain Alfort 187 and several isolates of bovine viral diarrhoea virus (BVDV) strains scored the lowest cross reaction.     

A congenital persistent swine fever infection. II. Immune response to swine fever virus and unrelated antigens

After the disappearance of maternal antibodies, no antibodies were detected in five pigs that were congenitally infected with the Bergen strain of swine fever virus. The pigs lived for 2–11 months. One pig showed low levels of precipitating antibody during the last month of its life. The pigs had a normal immune response to sheep red blood cells and to pig parvovirus. These observations suggest the presence of immunological tolerance to swine fever virus in these pigs.Cell mediated immunity, measured by phytohaemagglutinin lymphocyte stimulation, appeared to be normal.     

Experience with simple ELISA test systems for Brucella serology in cattle, sheep and goats

The objective of this work was to use the ELISA technique for the serological surveillance for freedom of brucellosis of cattle, sheep and goats. By comparing 28 cattle sera taken after a brucellosis outbreak, 15 bovine sera supplied by the Federal Institute for Health Protection of Consumers and Veterinary Medicine (BgVV) and 497 serum slow agglutination test (SSAT) and complement fixation test (CFT) negative bovine sera from herds officially declared free of brucellosis, the ELISA technique not only shows higher sensitivity as compared to SSAT and CFT but also distinguishes clearly between positive and negative reactions. The serological comparison by SSAT, CFT and ELISA of 615 cattle, 624 sheep and 630 goat sera from herds acknowledged as brucellosis free showed equivalent specificities for both CFT and ELISA. The specificity of the SSAT was much lower, 81.1% in cattle and 96.2% in goat sera. The examination of 5796 cattle, 1337 calf, 5031 sheep and 1796 goat sera demonstrates the advantage of the ELISA technique as routine method. The possible application of the ELISA technique as a screening method for serological brucellosis tests in sheep, goats and possibly also in pigs is discussed.     

Carcass quality in certified organic production compared with conventional livestock production

By studying carcass quality, expressed as affection, pathological findings, slaughter-weight and evaluation, a picture of an animal's health and potential as high quality food is achieved. This study compares the carcass quality in Swedish certified organic meat production with that of conventional meat production slaughtered during 1997. The study involves 3.9 million pigs, about 570,000 cattle and 190,000 sheep, all reared conventionally and 3483 pigs 4949 cattle and 4997 sheep reared according to organic standards. Pathological and additional findings are registered by meat inspectors from the Swedish National Food Administration at the post-mortem inspection. There was a significant difference at the post-mortem inspection of growing-fattening pigs; 28% of conventionally and 17% of the organically reared pigs had one or more registered lesion. The carcass evaluation of swine shows a higher meat percentage in conventional swine production. The total rate of registered abnormalities in cattle was systems around 28% from organic and 27% from conventionally reared herds. Carcass evaluation of cattle from organic herds gave higher classification in the EUROP system, whereas the fat content was lower than that of conventionally reared cattle. Sheep, reared both organically and conventionally, showed a lower rate of registered abnormalities than swine and cattle.     

Enzyme-linked immunosorbent assay for detection of antibodies to Rift Valley fever virus in ovine and bovine sera

An enzyme-linked immunosorbent assay (ELISA) was developed for the rapid detection of antibodies to Rift Valley fever virus (RVFV) in ovine and bovine sera. Conditions to reduce nonspecific reactions were optimized. The ELISA results correlated with those of a plaque-reduction neutralization test, revealing 100% specificity and 90.7% sensitivity. In sera from sheep and cattle inoculated against RVFV, the hemagglutination-inhibition test in combination with the ELISA provided a better indication of response to killed RVFV vaccine than did either test alone.     

Bovine viral diarrhoea virus infections in piglets born to sows vaccinated against swine fever with contaminated vaccine

On eight farms a congenital pestivirus infection in piglets was detected which could be traced to vaccination of the dams against swine fever (SF). Viruses isolated from the piglets were not recognised by monoclonal antibodies (MCAs) against swine fever virus (SFV) and were shown to be bovine viral diarrhoea virus (BVDV) or Border disease virus. The expected 'Chinese' strain of SFV could not be demonstrated in the batch of vaccine that had been used on these farms. Instead, a contaminating pestivirus was recovered which was not recognised by the MCAs against SFV. The contaminant had an unexpectedly high virulence for lambs and induced antibodies against BVDV in lambs and pigs. It could, therefore, be characterised as BVDV or Border disease virus.