The effect of maternal antibodies on the detection of bovine virus diarrhoea virus in peripheral blood samples.

Persistently infected animals (PI animals), that is those animals born after an intrauterine infection of the dam during the first 120 days of gestation, are the main source of bovine virus diarrhoea virus (BVD virus) in a cattle population. The success of any BVD virus eradication programme depends on the ability to detect all PI animals at a young age. The purpose of this study was to evaluate the use of the antigen ELISA test and the reverse transcriptase-polymerase chain reaction (RT-PCR) test for the diagnosis of PI animals in the presence of maternal antibodies, and to compare them with the classical virus isolation test. In this experiment, 25 calves born after an experimental infection with a mixture of BVD virus field strains were used. All calves were found to be positive for BVD virus using the virus isolation test, both before the ingestion of colostrum and again at 10 weeks of age. Both the virus isolation test and the antigen ELISA test were shown to be unreliable indicators for the diagnosis of persistent infections with BVD virus, when used in the presence of high levels of maternal antibodies. However, the RT-PCR test gave positive results even in the presence of high maternal antibody titres, indicating the suitability of the RT-PCR test for use in eradication programmes.

Failure of foetal protection after vaccination against an experimental infection with bovine virus diarrhea virus.

A protocol is described to measure the protection of the bovine fetus against an experimental bovine virus diarrhea virus (BVDV) infection after vaccination. Two inactivated experimental vaccines were applied twice with a 3 week interval. A mixture of three different Dutch field strains was used as challenge on mainly the 82nd day of gestation to vaccinated and unvaccinated control animals. The challenge was applied 5 months after completion of the two-fold vaccinations. All calves born from unvaccinated control animals were persistently infected. The calves born from dams vaccinated with the two different inactivated BVDV vaccines were persistently infected in 78 and 60%, respectively.

[Outbreak of bovine virus diarrhea on Dutch dairy farms induced by a bovine herpesvirus 1 marker vaccine contaminated with bovine virus diarrhea virus type 2]. / Uitbraak van bovine virus diarree op Nederlandse rundveebedrijven na vaccinatie met een met BVDV type 2 gecontamineerd BHV1 markervaccin.

On 23 February 1999, the Dutch Animal Health Service advised all Dutch veterinary practices to postpone vaccination against bovine herpesvirus 1 (BHV1) immediately. The day before severe disease problems were diagnosed on four dairy farms after vaccination with the same batch of BHV1 marker vaccine. Using monoclonal antibodies, bovine virus diarrhoea virus (BVDV) type 2 was found in the vaccine batch. This paper describes an outbreak of BVDV type 2 infection caused by the use of a batch of modified live BHV1 marker vaccine contaminated with BDVD. Sources of information used were reports of farm visits, minutes of meetings, laboratory results, and oral communications from the people involved. The first symptoms of disease were observed on average six days after vaccination. Morbidity was high on 11 of the 12 farms. On five farms more than 70% of the animals became ill, while on one farm no symptoms could be detected. During the first week after vaccination, feed intake and milk production decreased. During the second week, some animals became clinically diseased having nasal discharge, fever, and diarrhoea. At the end of the second week and at the start of the third week, the number of diseased animals increased rapidly, the symptoms became more severe, and some animals died. Mortality varied among herds. Necropsy most often revealed erosions and ulcers of the mucosa of the digestive tract. In addition, degeneration of the liver, hyperaemia of the abomasum, and swollen mesenterial lymph nodes and swollen spleen were found. On 11 of the 12 farms all animals were culled between 32 and 68 days after vaccination after an agreement was reached with the manufacturer of the vaccine. This was the third outbreak of BVD in cattle after administration of a contaminated vaccine in the Netherlands. The possibilities to prevent contamination of a vaccine as a consequence of infection of fetal calf serum with BVDV are discussed. Improvement of controls to prevent contamination before and during vaccine production, and improvement of the monitoring of side-effects is necessary.

An inactivated gE-negative marker vaccine and an experimental gD-subunit vaccine reduce the incidence of bovine herpesvirus 1 infections in the field.

An inactivated glycoprotein E-negative vaccine and an experimental glycoprotein D-subunit vaccine against bovine herpesvirus 1 (V1) were examined for their effectiveness in a randomized, double-bline, placebo-controlled field trial comprising 130 dairy farms. The use of these marker vaccines enabled us to monitor the incidence of infections in vaccinated populations. The aims of this trial were to evaluate whether these vaccines: (1) reduce the proportion of outbreaks in dairy herds; and (2) reduced virus transmission within dairy herds and to what extent. Vaccination with either of the two vaccines significantly reduced the proportion of herds wherein an outbreak occurred as well as the virus transmission within herds, as compared to placebo-treated herds. The estimated number of secondary cases caused by one infectious animal, expressed as the reproduction ratio R, was for both vaccines significantly > 1. This indicates that when BHV1 is introduced into vaccinated herds, major outbreaks may still occur.

Increased prevalence of Mycoplasma bovis in the Netherlands.

The epidemiology, therapy, and prevention of M. bovis infections are briefly reviewed. In a survey begun in 1982, M. bovis was found frequently in the respiratory tract [corrected] of veal calves and beef cattle with respiratory problems. In replacement calves infected with respiratory disease in dairy herds, however, the organism has only been detected since 1986. Respiratory tract specimens collected from calves with respiratory disease were submitted for examination for M. bovis from 1986 to 1991 and originated from 83 herds. Mycoplasma bovis was detected in specimens from 59 of the herds, 20% of which were dairy herds and 80% fattening herds. Arthritis caused by M. bovis was observed in 12 herds until July 1991. Since 1976 when the first mastitis outbreak caused by M. bovis was diagnosed, M. bovis has caused 14 more outbreaks. The number of diseased cattle varied from 1 tot 16 per farm, and clinical signs of mastitis varied from mild to severe. In all instances the infection has been eradicated from the herds. Because M. bovis can cause great losses in intensively reared cattle herds, it is advisable to separate purchased veal calves and beef cattle from dairy cattle to prevent further spread of M. bovis.

[Bovine virus diarrhea/mucosal disease virus: diagnosis and approach in clinical practice]. / Bovine virus diarree/mucosal disease-virus: diagnostiek en benadering in de praktijk.

Recent studies on bovine virus diarrhoea (BVD virus) afforded a deeper understanding of the epizootiology of this virus. It is of vital importance to determine whether BVD virus infection occurs within the uterus prior to the 120th day of gestation, during a later stage of pregnancy or after birth. When infection occurs before the 120th day of gestation, normal or abnormal calves which persistently carry the BVD virus, will be delivered. When infection occurs during a later stage of gestation, the calves which are born, will be immune to BVD virus. Symptoms of the disease (directly or indirectly associated with BVD virus) may appear in infections at an age under six months. As a rule, effects of BVD virus infection are slight in older animals. The very severe clinical picture of Mucosal Disease is confined to persistently infected carriers of BVD virus. The most important source of BVD virus infection consists in persistently infected carriers of BVD virus, which continue to excrete large quantities of BVD virus. The diagnosis of BVD virus infection is usually established at a late stage during the course of the disease so that vaccination is no longer relevant. Moreover, it is not clear to which extent immunity of gestating animals, induced by BVD virus vaccines, will be able subsequently to protect a foetus from infection due to BVD virus.

Pathogenesis of naturally acquired bovine respiratory syncytial virus infection in calves: morphologic and serologic findings.

Lesions in 32 calves that died or were euthanatized during the course of severe natural infection with bovine respiratory syncytial virus (BRSV) are described. All calves had been dyspneic for 1 to 2 days. At necropsy, lesions that could be related to dyspnea included congested and cyanotic mucosae and widespread petechiae. The lungs had various lesions in the cranioventral (CV) and caudodorsal (CD) portions. The CV portion of the lungs was consolidated, firm, and edematous. Histologically, the main characteristic was degenerative, necrotic bronchiolitis, with few syncytial cells. Signs of repair, such as epithelial hyperplasia, fibrosis, and bronchiolitis obliterans, often were observed. The CD portion of the lungs was markedly distended, owing to severe edema and emphysema. Bronchiolar lesions were lacking in the CD portion. In 14 calves, hyaline membranes were seen in the CV and CD portions. Results of immunofluorescence for BRSV were positive in 24 calves, but only in the CV portion of the lungs. The calves had variable concentrations of BRSV-specific IgG1 and IgM in serum, lung lavage fluid, or both. The BRSV-specific IgA, on the contrary, was seldom detected. Thus, 2 discrepancies existed. Although the clinical picture appeared to be acute, bronchiolar lesions and serotest results suggested infection of longer duration. Also, although virus and viral cytopathologic features were detected only in the CV portion of the lungs, the CD portion had extensive lesions that consisted of emphysema and edema.

Epidemiological study of bovine respiratory syncytial virus infections in calves: influence of maternal antibodies on the outcome of disease.

A prospective epidemiological survey on bovine respiratory syncytial virus (BRSV) infections in calves was carried out on 21 dairy farms during one BRSV epidemic season. Special attention was paid to the role of maternal antibodies. On 15 farms the spread of the virus was demonstrated during the investigation period and on eight farms this was accompanied by an outbreak of acute respiratory disease. Disease seldom occurred in calves younger than two weeks old and the most severe disease was observed in calves from one to three months old. Although maternal antibodies did not effectively prevent the disease, both the incidence and severity of disease were inversely related to the level of specific maternal antibodies. Two serodiagnostic techniques were compared. In calves older than three months from herds with disease outbreaks associated with bovine respiratory syncytial virus the diagnosis was established in 80 per cent of the animals by an increase in IgG titre against BRSV and in 77 per cent by the detection of BRSV specific IgM. In comparison, only 10 per cent of the calves younger than three months were positive by IgG serodiagnosis, and 51 per cent by IgM serodiagnosis. On farms where the spread of the virus was accompanied by an outbreak of clinical disease more calves were present, a higher proportion of the calves was younger than three months, and calves of all ages were more often housed together.

Diagnosis of bovine respiratory syncytial virus infections improved by virus detection in lung lavage samples.

The potential of lung lavage to diagnose and study infections with bovine respiratory syncytial virus (BRSV) was investigated. The technique was simple to perform under field conditions, and even in calves with respiratory tract disease, serious drawbacks were not observed. In 9 epizootics of respiratory tract disease, BRSV infection was diagnosed in 1 or more calves. The BRSV was detected from a total of 21 of 32 calves by immunofluorescence in cells recovered from lavage fluids, and the virus was recovered by cell culture from 17 of these. In the 4 remaining calves, infectious bovine rhinotracheitis virus or parainfluenza type 3 virus was isolated. In calves with high levels of maternally derived antibodies, direct demonstration of the virus was found to be essential for making a diagnosis of BRSV. In 3 of the 9 epizootics, the majority of 4- to 8-month-old calves had a significant increase in antibody concentration against BRSV, whereas only a few 1- to 2-month-old calves present during the other 6 epizootics did so. However, at least in 4 of the 6 herds with younger calves, direct detection of the virus in 2 or more calves indicated that BRSV was involved in the epizootic. Cytologic examination of wash fluids from BRSV-infected animals identified an increased neutrophil/large mononuclear cell ratio. Occasionally, bronchiolar casts and syncytial giant cells with inclusion bodies were seen. In lung lavage fluids of 4 experimentally infected specific-pathogen-free calves, BRSV-containing cells were detected by immunofluorescence for 12 to 18 days after inoculation.

[The prophylactic effect of a morantel sustained release bolus (Paratect) on lungworm infections in vaccinated and non-vaccinated calves]. / Het profylactisch effect van een morantel bevattende bolus (Paratect) op longworminfecties bij gevaccineerde en niet gevaccineerde kalveren.

Groups of four calves received a vaccination, a vaccination combined with a morantel sustained release bolus (Paratect) together with the second vaccination dose, a vaccination combined with a Paratect bolus 14 days after the second dose, a Paratect bolus alone or remained untreated. From the faecal, serological and clinical observations it was concluded that the larval output, the course of the antibody titers against lungworm and the clinical picture of the calves which had received a bolus after or together with the vaccination did not differ from the observations in the only vaccinated calves. Calves provided with a Paratect bolus were excreting lungworm larvae in the faeces and showed mild symptoms of parasitic bronchitis. It was not necessary to treat these calves in contrast with the untreated controls.