Persistently Infected Calves Research Articles

Determining the Prevalence of Bovine Viral Diarrhea Virus Persistently Infected Calves Originating from a Number of Modem Western Well-vaccinated Dairy Herds

All arriving heifer calves and some additional bull calves were tested for bovine viral diarrhea virus (BVDV) persistently infected (PI) status when received by the calf ranch to determine incidence of occurrence across individual dairies contributing calves to this calf ranch. After confirmation of positive status, these animals were removed to eliminate potential for infection in subsequent breeding populations. In addition, 40 random positive PI samples were submitted for typing and genetic characterization to create a dendogram for comparison among PI calves and existing vaccination programs.

Excreção e transmissão do vírus da diarréia viral bovina por bezerros persistentemente infectados

Bezerros persistentemente infectados (PI) nascidos de vacas infectadas com amostras não-citopáticas do vírus da diarréia viral bovina (BVDV) se constituem nos principais reservatórios do vírus na natureza. Este trabalho relata uma investigação do padrão de excreção e transmissão viral por cinco bezerros PI produzidos experimentalmente pela inoculação de vacas prenhes com isolados brasileiros do BVDV. Cinco bezerros que sobreviveram a infecção intrauterina nasceram saudáveis, soronegativos e com a presença de vírus no sangue. Após o desmame - e desaparecimento dos anticorpos colostrais - os bezerros PI foram monitorados semanalmente durante 150 dias para a presença de vírus e títulos virais no soro e em secreções (ocular, oral, nasal e genital). Os títulos virais no soro de cada animal apresentaram pequenas variações durante o período (com exceção de um animal que apresentou um aumento de título tardiamente), mas os títulos variaram amplamente entre os animais (entre 10² e 10(6)TCID50/ml). O vírus também foi excretado continuamente nas secreções de todos os animais, com pequenas variações de título entre as coletas. Os maiores títulos virais foram geralmente detectados nas secreções nasais e oculares (títulos de 10(4) a 10(6)TCID50/mL), enquanto as secreções orais e genitais usualmente continham títulos virais baixos (10² a 10³TCID50/mL). Com o objetivo de avaliar a dinâmica de transmissão viral, um bezerro PI foi introduzido em um grupo de 10 bezerros soronegativos, mantido com uma alta densidade animal e submetido a manejo diário para simular as condições de manejo semi-intensivo. Após 30 dias de convívio com o bezerro PI, todos os demais animais haviam soroconvertido ao BVDV. Para investigar a transmissão viral sob condições extensivas, outro bezerro PI foi incorporado a um rebanho de 48 animais mantido a campo, com baixa densidade animal e submetido a manejo extensivo. Dentre estes animais, 8/48 (16,6%) foram soropositivos para anticorpos no dia 10, 26/48 (54,1%) no dia 40 e 37/48 (77%) haviam soroconvertido no dia 100, quando encerrou-se o monitoramento. Estes resultados demonstram que a viremia e excreção viral contínua em altos títulos por animais PI assegura a transmissão rápida do BVDV a animais mantidos em contato, sendo a transmissão notadamente mais rápida em condições intensivas e de alta densidade animal.

Genetic characterization of bovine viral diarrhea viruses isolated from persistently infected calves born to dams vaccinated against bovine viral diarrhea virus before breeding

To collect and partially characterize strains of bovine viral diarrhea viruses(BVDVs) isolated from persistently infected (PI) calves born to vaccinated dams, determine genetic diversity of the isolated viruses, and identify regional distribution of genetically similar virus subpopulations. 17 noncytopathic (NCP) BVDVs from PI calves from 11 herds of beef or dairy cattle. Viral RNA was extracted from infected cell cultures, and BVDV-specific PCR primers were used to amplify > 1,000 bases of the viral genome. Derived sequences were used for molecular phylogenetic analyses to determine the viral genotype and viral genogroup and to assess genetic similarity among BVDVs. Analysis of the 17 NCP strains of BVDV failed to detect a viral genotype or viral genogroup not already reported to exist in the United States. One virus was classified as genotype 1, genogroup 1b, and 16 viruses were classified as genotype 2, genogroup 2a. Genotype 2 strains were genetically diverse, and genetic similarities were not obvious among viruses from geographic regions larger than a small locale. Viruses isolated from herds where a genotype 1, genogroup 1a BVDV vaccine was administered prior to breeding were primarily genetically diverse genotype 2, genogroup 2a BVDVs. Vaccination with multiple BVDV genotypes may be needed to improve protection. Methods used in this study to obtain and analyze field strains are applicable to assessing efficacy of current BVDV vaccines. Candidates for future vaccines are viruses that appear able to elude the immune response of cattle vaccinated against BVDV with existing vaccines.

Associations between health and productivity in cow-calf beef herds and persistent infection with bovine viral diarrhea virus, antibodies against bovine viral diarrhea virus, or antibodies against infectious bovine rhinotracheitis virus in calves

To measure associations between health and productivity in cow-calf beef herds and persistent infection with bovine viral diarrhea virus (BVDV), antibodies against BVDV, or antibodies against infectious bovine rhinotracheitis (IBR) virus in calves. 1,782 calves from 61 beef herds. Calf serum samples were analyzed at weaning for antibodies against type 1 and type 2 BVDV and IBR virus. Skin biopsy specimens from 5,704 weaned calves were tested immunohistochemically to identify persistently infected (PI) calves. Herd production records and individual calf treatment and weaning weight records were collected. There was no association between the proportion of calves with antibodies against BVDV or IBR virus and herd prevalence of abortion, stillbirth, calf death, or nonpregnancy. Calf death risk was higher in herds in which a PI calf was detected, and PI calves were more likely to be treated and typically weighed substantially less than herdmates at weaning. Calves with high antibody titers suggesting exposure to BVDV typically weighed less than calves that had no evidence of exposure. BVDV infection, as indicated by the presence of PI calves and serologic evidence of infection in weaned calves, appeared to have the most substantial effect on productivity because of higher calf death risk and treatment risk and lower calf weaning weight.

Doença das mucosas associada à dermatite generalizada em bovinos, Mato Grosso do Sul

São descritos os aspectos epidemiológicos, clínicos, patológicos e diagnósticos de uma forma de dermatite associada à doença das mucosas (DM) em bovinos. Também são abordadas metodologias para a identificação de animais persistentemente infectados (PI) e o impacto nos índices zootécnicos no rebanho afetado. Os casos de dermatite associados com DM ocorreram em dois bovinos Nelore, de 12 e 24 meses de idade, pertencentes a uma fazenda de ciclo completo de bovinos de corte no estado de Mato Grosso do Sul. Os sinais clínicos nesses animais consistiam de emagrecimento lento e progressivo, formação de crostas difusas na pele de todo o corpo, pele ressecada, múltiplas ulcerações nas gengivas e face dorsal da língua, que evoluíram para fendas longitudinais, formação de projeções cornificadas e desprendimento dos cascos. Em um caso, também ocorreu diarréia no estágio final da doença. Na necropsia observaram-se ainda erosões longitudinais no esôfago. O exame histológico revelou focos de necrose de coagulação na mucosa do esôfago e língua, com infiltrado de neutrófilos e linfócitos. As lesões da pele consistiam de necrose de coagulação da epiderme associada com infiltrado de neutrófilos e hiperqueratose. Nos dois casos, a suspeita clínica foi confirmada pelo isolamento viral e identificação dos biótipos citopático e não-citopático do vírus da diarréia viral bovina (BVDV), além da detecção de antígenos virais em tecidos por imunoistoquímica. De um lote de 300 bovinos que tiveram contato com animais afetados, 38 foram testados e apresentaram altos títulos de anticorpos para o BVDV. Amostras de sangue coletadas de 1.025 animais jovens e 40 touros da propriedade foram submetidas a pesquisa de vírus para se identificarem possíveis animais persistentemente infectados (PI). O vírus foi isolado do sangue de três bezerros no teste inicial e, 12 meses depois, em dois deles que permaneceram na propriedade. Imunoistoquímica realizada em biópsia de orelhas identificou apenas um destes animais como positivo. O rebanho apresentou redução no índice de fertilidade e taxa de desmame no ano seguinte ao nascimento dos bezerros PI, mas estes indicadores retornaram posteriormente aos valores anteriores. Os resultados apresentados demonstram a presença da infecção por BVDV em rebanhos de corte no estado de Mato Grosso do Sul, e evidenciam a necessidade da inclusão dessa enfermidade no diagnóstico diferencial de causas de dermatites generalizadas.

Influence of herd structure and type of virus introduction on the spread of bovine viral diarrhoea virus (BVDV) on the spread of bovine viral diarrhoea virus (BVDV) within a dairy herd

A herd is a population structured into groups not all equally in contact, which may influence within-herd spread of pathogens. Herd structure varies among cattle herds. However, published models of the spread of bovine viral diarrhoea virus (BVDV) assume no herd structure or a unique structure chosen as a representative. Our objective was to identify--for different index cases introduced into an initially BVDV--free dairy herd - risky (favourable) herd structures, which increased (decreased) BVDV spread and persistence compared to a reference structure. Classically, dairy herds are divided into calves, young heifers, bred heifers, lactating cows and dry cows. In the reference scenario, groups are all equally in contact. We evaluated the effect of isolating or merging groups. Three index cases were tested: an open persistently-infected (PI) heifer, an open transiently-infected heifer, an immune heifer carrying a PI foetus. Merging all groups and merging calves and lactating cows were risky scenarios. Isolating each group, isolating lactating cows from other groups, and merging calves and young heifers were favourable scenarios. In most structures, the most risky index cases were the following: first, the entry of a PI heifer; second, the birth of a PI calf; last, the entry of a transiently-infected heifer. Recommendations for dairy herds are to raise young animals together before breeding and to isolate lactating cows from others as much as possible. These recommendations will be less efficient if a PI adult enters into the herd.

Prevalence of calves persistently infected with bovine viral diarrhea virus in beef cow-calf herds enrolled in a voluntary screening project

To report the prevalence of bovine viral diarrhea virus (BVDV) in calves and calf groups (ie, calves from the same farm) in beef breeding herds and evaluate the ability of biosecurity risk assessment questionnaires to identify calf groups with positive results for BVDV. Nonrandom survey. 12,030 calves born in spring from 102 operations. Cow-calf producers that voluntarily enrolled in a screening project submitted ear notch specimens from calves and answered a 29-question survey instrument. Ear notch specimens were tested for BVDV with an antigen-capture ELISA (ACE), and ear notch specimens with positive ACE results for BVDV were immediately retested by performing immunohistochemistry (IHC). Follow-up testing, 3 to 4 weeks after initial positive ACE results, was done by use of a second IHC test and virus isolation on a subsequently submitted ear notch specimen from the same calves to identify those that were persistently infected (PI). 102 producers submitted ear notch specimens for BVDV screening. Initially, 24 of 12,030 calves had positive ACE results for BVDV. A second ear notch specimen was submitted for 20 of these 24 calves. Of 20 retested calves, 12 had positive ICH results for BVDV, confirming PI status. The 12 PI calves came from 4 calf groups (3 singletons and 1 calf group with 9 PI calves). Prevalence of BVDV in calf groups was low, and questions designed to identify high-risk biosecurity behaviors had little value in identifying calf groups with positive results for BVDV.

Effects of short-term exposure of feeder cattle to calves persistently infected with bovine viral diarrhea virus

Research using 2,954 auction-derived feeder steers and heifers was conducted at a single commercial feedlot in Kansas to determine the effects of testing for cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) at 10-14 days-on-feed (DOF), and removing them at 13-18 DOF. After removal of test-positive animals, the effect of the short-term exposure (STE) to PI cattle on health, performance and carcass characteristics was determined. The percentage of calves exhibiting signs of illness was increased (P<0.01) in cattle with STE to PI-BVDV. Cattle with no exposure (NE) to PI-BVDV calves had a morbidity rate of 18.8%, while a 29.6% morbidity rate was observed in pens of calves with STE to a PI-BVDV calf. Characterization of the temporal pen morbidity rate of STE and NE calves revealed that 31.7% of all STE and 15.3% of NE illness occurred in the first seven DOF. Additionally, the incidence of cattle treated for bovine respiratory disease in STE calves was 2.17 (95% CI 1.73 to 2.72) initial treatments per 1,000 head-days at risk, whereas the incidence of treatment of calves in NE pens was 1.28 (95% CI 0.98 to 1.68) initial treatments per 1,000 head-days at risk. Short-term exposure to PI-BVDV calves had no effect on retreatment rate, death loss, or performance. There was no evidence of a BVD-PI exposure X sex interaction (P=0.62) for carcasses that graded USDA Choice or better, but there was a main effect of sex (P<0.01). There was evidence of a BVD-PI exposure X sex interaction for Yield Grade 2 or greater carcasses (P=0.03). In this study, testing at 10-14 DOF was too late in the feeding period to eliminate the initial morbidity spike that occurred during 0-7 DOF, and the subsequent morbidity differences between calves with STE or NE to PI calves.

Variation in E rns viral glycoprotein associated with failure of immunohistochemistry and commercial antigen capture ELISA to detect a field strain of bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) affects cattle populations causing clinical signs that range from subclinical immunosuppression to severe reproductive and respiratory problems. Detection and removal of persistently infected (PI) calves is the single most important factor for control and eradication of BVDV. Current testing strategies to detect PI calves rely heavily on immunohistochemistry (IHC) and a commercially available antigen capture ELISA (ACE) assay. These viral assays depend on 1 or 2 monoclonal antibodies which target the E rns glycoprotein of BVDV. The sensitivity and specificity of these two tests have been reported previously. The purpose of this research was to characterize a strain of BVDV (AU501) that was undetectable using IHC and ACE based on a single monoclonal antibody, but was consistently detected in samples from a Holstein steer using virus isolation and PCR testing. Sequencing of this AU501 viral isolate revealed a unique mutation in the portion of the genome coding for the E rns glycoprotein. This unique field strain of BVDV demonstrates the risk of relying on a single monoclonal antibody for detection of BVDV. Multiple testing strategies, including polyclonal or pooled monoclonal antibodies that detect more than one viral glycoprotein may be necessary to detect all PI calves and facilitate eradication of BVDV.

Mature open cows are rarely persistently infected with bovine viral diarrhea virus (2007)

Bovine viral diarrhea virus (BVDv) is an immunosuppressive virus affecting cattle in a multitude of ways. The varied presentation makes this disease difficult to identify in cow herds and the signs of a BVD infection may be very subtle. The syndrome causes economic problems by reducing herd fertility and increasing disease rates. The persistently infected (PI) animal is a unique reservoir for BVDv. These cattle are the result of in utero exposure to the noncytopathic biotype of BVDv prior to the development of a competent fetal immune system at about 125 days of gestation. Persistently infected animals are the primary method for the disease to propagate over time. PI cattle consistently shed BVD virus in relatively high levels and this exposure to the breeding herd can result in new PI calves. PI animals propagate BVDv in the herd and decrease pregnancy percentages compared to herds without PI animals. Farms must assess risk and manage for biosecurity when purchasing adult animals with an unknown history of disease exposure. Breeding herds that introduce new animals to the herd face the risk of importing a BVD PI animal. To mitigate this risk, PI animals must be accurately identified prior to herd introduction, but visual appraisal is not an accurate method of discovering these animals. Multiple diagnostic tests are available to determine the BVD status of incoming animals and all have an associated cost. Economic feasibility of determining the BVD PI status of animals depends to a large degree on the frequency with which PI animals occur in a population. Previous research has illustrated that PI calves entering the feedyard phase of production are fairly rare (about three per 1,000 calves); however, very little work has been done in mature animals. This project provides an estimate of BVD PI frequency for a specific population. This assessment should allow the formulation of a BVD-specific risk management plan which addresses the economic efficiency of testing mature females upon arrival. The primary objective of this research is to determine the prevalence of BVD PI animals in a population of young (3- to 6-year-old) cows purchased as non-pregnant mature animals. The results can guide biosecurity decisions for producers when purchasing and introducing this class of animal to the herd.

Association between the existence of calves persistently infected with bovine viral diarrhea virus and commingling on pen morbidity in feedlot cattle

To determine the association between the existence of a calf persistently infected (PI) with bovine viral diarrhea virus (BVDV) and pen morbidity. 5,041 calves in 50 pens at a feedlot in Iowa. In a longitudinal study, ear notches were collected from cattle and tested for BVDV antigen. Characteristics of each pen (owner, sex, disease rate, number of groups, and source) were recorded. The association between the existence of a BVDV-PI calf and morbidity in each pen was examined. Commingling was associated with an increase in respiratory tract disease (odds ratio [OR], 3; 95% confidence interval [CI], 2.5 to 3.6). Ten BVDV-PI calves (10/5,041 [0.2%]) were identified in 8 of 50 pens. A BVDV-PI calf was associated with reduced pen-level respiratory tract disease (OR, 0.7; 95% CI, 0.5 to 0.9). Disease prevalence (mean +/- SD morbidity, 7.9 +/- 3.1%) was lowest in pens containing single-source cattle and a BVDV-PI calf (4 pens containing 302 cattle), compared with single-source cattle with no BVDV-PI calf (mean morbidity, 11.89 +/- 9.7%; 31 pens containing 3,093 cattle), commingled cattle with no BVDV-PI calf (mean morbidity, 29.3 +/- 16.22%; 11 pens containing 1,127 cattle), and commingled cattle with a BVDV-PI calf (mean morbidity, 28.6 +/- 10.1%; 4 pens containing 519 cattle). Commingling was the greatest risk factor associated with morbidity in each pen. A BVDV-PI calf in a pen was not associated with increased disease prevalence in commingled groups.

Viral Antigen Distribution in the Respiratory Tract of Cattle Persistently Infected with Bovine Viral Diarrhea Virus Subtype 2a

Tissues were obtained at necropsy from the nasal vestibule, turbinates, nasopharynx, trachea, tracheobronchial bifurcation, and lung from each of 10 clinically healthy calves persistently infected (PI) with bovine viral diarrhea virus (BVDV) serotype 2a. Tissues from the nasal vestibule were obtained by biopsy from five additional PI calves. Formalin-fixed tissues were processed for immunohistochemistry to localize the distribution of BVDV throughout the respiratory tract. Antigen distribution and intensity were subjectively evaluated. Throughout the respiratory tract, mononuclear leukocytes, vascular smooth muscle, and endoneural and perineural cells had BVDV immunoreactivity (BVDV-IR). Multifocally, squamous and ciliated columnar epithelium throughout the respiratory tract contained weak to moderate BVDV antigen. Viral antigen was not seen in goblet cells. BVDV-IR in mixed tubuloalveolar glands of the nasal cavity was weak to strong in serous secretory cells and ductular epithelium. Chondrocytes of the concha often contained BVDV antigen diffusely. Nasal mucus-secreting and tracheobronchial glands multifocally contained weak viral signal. In all cases, alveolar macrophages had moderate to strong BVDV-IR, whereas BVDV-IR in alveolar epithelial cells was weak to moderate. BVDV was present in interalveolar leukocytes and mesenchymal cells. Results indicate that serous secretions of the nasal cavity, productive viral infection of epithelium, and infected leukocytes in respiratory secretions are likely major sources of infectious BVDV from PI calves. The presence of BVDV antigen in respiratory epithelium is, at least, indirect support for the notion that this virus predisposes PI cattle to secondary microbial infections.

Relationship of bovine viral diarrhea virus persistent infection to incidence of diseases on dairy farms based on bulk tank milk test by RT-PCR

The prevalence of bovine viral diarrhea virus (BVDV) in dairy herds in Hokkaido, Japan, was estimated by reverse transcription polymerase chain reaction (RT-PCR) using bulk tank milk samples. Sixteen out of 265 dairy herds were identified as BVDV positive, and at least one persistently infected (PI) cattle was recognized in each of the positive herds except for two herds of which, owners did not agree to examine individual cows. The proportion of positive herds with a history of BVDV PI was significantly higher than that with no history of BVDV PI (odds ratio (OR) 4.25, 95% confidence interval (CI) 1.471–12.278, p = 0.004). The herds examined for BVDV were divided into two groups, high and low disease incidence groups based on the occurrence of diseases such as diarrhea, pneumonia or abortion in the past 1 year. The BVDV positive herds in the high disease incidence group were significantly more than that in the low disease incidence group (OR 2.92, CI 1.110–7.683, p = 0.024). It was observed that there were significantly ( p = 0.008) more PI calves or heifers in farms of high disease incidence group than in farms of low disease incidence group. These results suggested that bulk tank milk test was available method for the detection of PI animals in dairy herds, and the existence of PI non-lactating cows in herd correlated with the incidence of diseases of the diarrhea or respiratory disorders.

Analysis of variation of bovine viral diarrhoea virus E2 sequence following transplacental infection of cattle

The genetic and antigenic diversity observed in field isolates of bovine viral diarrhoea virus (BVDV) is thought to occur during acute infection because of the genetic stability observed in BVDV throughout the lifetime of persistently infected (PI) cattle. In this study, 15 cows in early pregnancy were inoculated with identical challenge doses obtained from a single infectious inoculum of the virologically cloned isolate Pe515nc. In order to examine the diversity that may develop in utero in the PI foetus, the variable E2 sequence of the virus isolated directly from the serum of each PI calf was compared. A high degree of sequence similarity was demonstrated, with 0–4 nucleotide differences out of 608 bases compared. Thus, the virus showed relatively few genomic changes in any of the PI calves, although we observed that the in utero environment did provide some opportunity for genetic variation to become established.

Case Study

This study was conducted to determine the effect of removing cattle persistently infected (PI) with bovine viral diarrhoea virus (BVDV) on seroprevalence and prevalence of PI calves in an endemically infected beef herd in Colorado, USA. The prevalence of PI animals and the serum neutralizing (SN) titres of heifers, bulls and calves were determined for three cow-calf herds in a beef cattle ranch over a period of 2 years [date not given]. In the first year, identified PI animals were removed from the herd within 3 weeks of identification. Five PI animals of 2921 (0.171%) cattle tested were identified in the first year. One PI animal was a yearling heifer and the remaining 4 were calves. Three of the 4 PI calves identified were removed prior to the breeding season, when the calves averaged 2 months of age. One PI animal was not identified until weaning at 6 months of age, and was present in the herd during the breeding season. The percentage of animals with high SN titres (?1:512) were 20.6% (367/1784) to type I BVDV and 44.8% (799/1784) to type II BVDV. In year 2, PI calves were not identified and the percentage of calves with high SN titres to BVDV type I and type II decreased to 5.91 (58/981) and 18.04% (177/981), respectively. Removal of PI animals in the first year reduced transmission of BVDV as evidenced by a significant decrease in the prevalence of high BVDV SN titres and the absence of PI animals the following year. These findings support the use of PI animal identification and removal as an effective BVDV control strategy in beef herds.

Bovine viral diarrhea (BVD)

Characteristics of bovine viral diarrhoea virus (BVDV), such as its genetic diversity and ability to induce a persistently infected (PI) carrier state, make its control a challenge. A systematic control programme that utilizes diagnostic testing strategies to identify PI cattle, vaccination to increase fetal protection from infection, and biosecurity to reduce the risk of exposure to infected animals is necessary for control of BVD. The primary reservoir for BVDV is PI cattle. If a herd has had recently confirmed PI calves, or if the history strongly suggests the presence of PI calves, then all calves, replacement heifers, bulls, and nonpregnant dams without calves should be tested for PI status. Positive cattle should be removed prior to the start of breeding. Because of the low prevalence of herds with PI animals, whole-herd screening protocols for herds at low risk for PI cattle may not be justified. Several strategies short of whole-herd screening can be employed to monitor herds for the presence of PI cattle. Biosecurity to reduce the risk of exposure to BVDV should also be implemented. Replacement heifers and bulls should be tested and confirmed PI-negative prior to the start of breeding. If a pregnant animal is purchased, she should be segregated until both dam and calf are confirmed PI-negative. Fence line contact with neighbouring herds should be avoided during early gestation unless they also have a strict biosecurity programme in place. Vaccination to reduce the risk of fetal infection in the event of exposure to a BVDV-shedding animal is an integral part of a biosecurity programme.

Association Between Persistently Bovine Viral Diarrhea Virus-Infected Calves and Pen Levels of Morbidity and Mortality in an Iowa Feedlot

As persistently infected (PI) cattle are the primary reservoirs of bovine viral diarrhea virus (BVDV) in cattle populations, there is general agreement that effective control of BVDV-induced losses requires the detection and elimination of these carriers from dairy and cowcalf herds. However, the significance of the presence of PI calves in pens of feedlot cattle is unknown. Our long-range goal is to determine whether identification and removal of PI calves prior to shipment to feedlots would be economically advantageous to feeders, and if such testing should be incorporated into preconditioning programs. As the first step toward answering this question, the objective of this study is to determine whether differences exist in morbidity and mortality in groups of calves that include PI calves and groups that do not include PI calves. If PI calves negatively impact morbidity and mortality, then future studies can be designed to examine the feasibility and economic impact of including BVDV PI testing in preconditioning programs.

Response of calves persistently infected with noncytopathic bovine viral diarrhea virus (BVDV) subtype 1b after vaccination with heterologous BVDV strains in modified live virus vaccines and Mannheimia haemolytica bacterin-toxoid

Seronegative persistently infected (PI) calves with bovine viral diarrhea virus (BVDV) subtype 1b were vaccinated with each of four modified live virus (MLV) BVDV vaccines and a Mannheimia haemolytica bacterin-toxoid. Nasal swabs and peripheral blood leukocytes (PBL) were collected for virus isolation and serums were collected after vaccination and tested for BVDV1a, BVDV1b, BVDV2, bovine herpesvirus-1 (BHV-1), bovine parainfluenza-3 virus (PI-3V), and bovine respiratory syncytial virus (BRSV) antibodies. M. haemolytica and Pasteurella multocida antibodies were detected using ELISA procedures. None of the PI calves developed mucosal disease (MD) after MLV vaccination. None of the BVDV PI calves seroconverted to BVDV1b after MLV vaccination. Calves receiving MLV vaccines seroconverted to the respective type/subtype in the vaccine. Calves receiving a MLV vaccine with noncytopathic (NCP) BVDV1 (subtype not designated) did not seroconvert to BVDV1a, BVDV1b, or BVDV2. The PI calves were positive for BVDV subtype 1b, in the PBL and nasal swabs throughout the study. Calves receiving each of three vaccines with known BVDV1a strains had BVDV1a positive samples after vaccination, in some but not all calves, up to Day 28. The PI BVDV1b calves did not respond with increased M. haemolytica antibodies after vaccination compared to BVDV negative calves receiving the same M. haemolytica vaccine.

Transmission of Bovine Viral Diarrhoea Virus by Unhygienic Vaccination Procedures, Ambient Air, and from Contaminated Pens

Knowing how bovine viral diarrhoea virus (BVDV) infection spreads via indirect contacts is required in order to plan large-scale eradication schemes against BVDV. In this study, susceptible calves were exposed to BVDV by an unhygienic vaccination procedure, by ambient air and from contaminated pens. Primary BVDV infection was observed in two calves vaccinated with a vaccine against Trichophyton spp that had been contaminated by smearing nasal secretion from a persistently infected (PI) calf on the rubber membrane and penetrating it twice with a hypodermic needle. Four other calves, housed in pairs in two separate housing units near a PI calf for one week—at distances of 1.5 and 10 m, respectively—became infected without having direct contact with the PI calf. Furthermore, two of the three calves housed in a pen directly after removal of a PI calf, but without the pen being cleaned and disinfected, also contracted primary BVDV infection, whereas two calves that entered such a pen four days after removal of another PI calf, did not. In herds where most animals are seronegative to BVDV, indirect airborne transmission of BVDV or contact with a contaminated housing interior may be an important factor in spreading of the virus, once a PI animal is present. However, the spreading of BVDV within herds can be stopped by identifying and removing PI animals and also by ensuring that susceptible breeding animals do not become infected during this procedure. In contrast, injectables contaminated with BVDV may prove to be a significant vector for spreading the infection, not only within an infected herd but, most importantly, also between herds. In our opinion, it is questionable whether medicine bottles, once opened and used within an infected herd, should be used in other herds. In any case, prior knowledge of a herd’s BVDV status will help practising veterinarians and technicans to undertake appropriate hygienic measures.

Pestivirus in cattle: experimentally induced persistent infection in calves.

Twenty-two heifers were infected intranasally with non-cytopathic bovine viral diarrhoea virus (BVDV) between days 74 and 82 of pregnancy. All animals had developed serum antibodies against BVDV 5 weeks later. No clinical effects were seen in the heifers, and they all delivered a live calf. The newborn calves were generally small, appeared unthrifty as typical 'poor doers', and some developed secondary infections with diarrhoea and signs of respiratory disease. Eighteen of the 22 calves were born without antibodies against BVDV and were persistently infected (PI) with the virus. One was weak at birth and died the following day. Four calves were born with serum antibodies against BVDV and with no detectable virus. Three of these showed signs and/or pathological changes indicating disease in the central nervous system. Otherwise, there were no obvious clinical differences between these calves and the PI calves, nor were there any apparent significant differences in blood parameters between these groups. In general, the calves showed low gamma-globulin values and thrombocytopaenia, but moderately increased fibrinogen values and relatively normal lymphocyte numbers.