Vaccination of calves against bovine herpesvirus-1: assessment of the protective value of eight vaccines

Eight separate, but related experiments, were carried out in which groups of six calves were vaccinated with one of eight commercial vaccines. In each experiment the vaccinated calves were subsequently exposed to three calves infected with virulent bovine herpesvirus-1 (BHV-1). In each experiment, all infected donor calves developed a typical severe infectious bovine rhinotracheitis (IBR) infection and excreted virus in their nasal secretions of up to 10(8.00) TCID50/0.1 ml. One live BHV-1 gE-negative vaccine (A) and three modified live vaccines (B, C, D), administered intranasally, all protected against clinical disease. The calves vaccinated with one vaccine (C) also did not excrete virus in the nasal secretions, whereas the calves protected by vaccines A, B and D excreted virus in their nasal secretions but at low titres (10(0.66)-10(1.24) TCID50/0.1 ml). A fourth modified live vaccine (E), given intramuscularly, failed to prevent mild clinical disease in the calves which also excreted virus in the nasal secretions at titre of 10(1.00) TCID50/0.1 ml. An analogous result was given by the calves vaccinated with either of the two inactivated vaccines (F and G) or with a BHV-1 subunit vaccine (H). All calves developed mild clinical signs and excreted virus at titres of 10(2.20)-10(3.12) TCID50/0.1 ml. Calves vaccinated with C vaccine were subsequently given dexamethasone, following which virus was recovered from their nasal secretions. The virus isolates did not cause disease when calves were infected and appeared to be closely related to the vaccine strain.     

Evaluation of safety and efficacy of DNA vaccines against bovine herpesvirus-1 (BoHV-1) in calves

Four DNA vaccines against BoHV-1 were evaluated for their efficacy in calves. Twelve animals were divided into four groups which were injected with four different DNA vaccines: pVAX-tgD (Vaccine A); pVAX-tgD co-immunised with pVAX-48CpG (Vaccine B); pVAX-UbiLacI-tgD-L (Vaccine C); pVAX-UbiLacI-tgD-L co-immunised with pVAX-48CpG (Vaccine D). Three additional calves were given the plasmid vector and served as controls. Ninety days after the first vaccination all calves were challenge infected with BoHV-1.All animals developed a severe form of infections bovine rhinotracheitis. Only the calves given the pVAX-tgD co-immunised with pVAX-48CpG (Vaccine B) developed humoral antibodies against BoHV-1 between 56 and 90 days after the first vaccination, whereas in calves of other groups and in the controls, antibodies appeared only after the infection. In the calves vaccinated with either pVAX-tgD (Vaccine A) or pVAX-tgD combined with pVAX-48CpG (Vaccine B), BoHV-1-specific IFN-γ secreting cells were detected in PBMCs 90 days after the first vaccination and their number increased after challenge exposure. In the other groups the IFN-γ secreting cells were detected after virus infection and at low values.     

Immunization against bovine herpesvirus-1 infection. Preliminary tests in calves with a DNA vaccine

A bovine herpesvirus-1 (BHV-1) vaccine expressing glycoprotein D, the form with the transmembrane anchor removed, was evaluated for inducing immunity in calves. The plasmid encoding gD of BHV-1 was injected three times to nine calves, using three animals for each of the following routes: intramuscularly (i.m.), intradermally (i.d.), or intranasally (i.n.). Three additional calves were given the plasmid vector only and served as unvaccinated controls. When calves were subjected to challenge infection with BHV-1, all vaccinated calves as well as the controls developed a typical severe form of infectious bovine rhinotracheitis. However, compared to the controls, the vaccinated calves showed earlier clearance of challenge virus. Moreover, the calves given the vaccine i.m. developed neutralizing antibody to BHV-1 between 21 and 42 days following the first injection of vaccine, whereas in calves vaccinated either i.d. or i.n., as well as the controls, antibody first appeared in their sera 14 days post-challenge infection.     

Characteristics of live bovine herpesvirus-1 vaccines

The common disease caused by bovine herpes virus 1 infection is febrile rhinotracheitis (FRT) and under certain conditions the virus is strongly implicated in pre-disposing cattle to pneumonic pasteurellosis. These illnesses account for a significant economic loss in the cattle industry worldwide and vaccination is widely applied. In naive cattle, and for a short period of time, old and new vaccines significantly reduce clinical signs of FRT and also virus shedding. A single intranasal vaccination affords significant protection in face of maternally derived antibodies, and the protection can be significantly prolonged by a booster intramuscular vaccination. Current data recommend vaccination in face of an outbreak and vaccines appear safe for pregnant cattle.     

Experimental latent and recrudescent bovine herpesvirus-1 infections in calves

Latent bovine herpesvirus-1 (BHV-1) infection was established in 6 calves and was demonstrated by reinduction of virus shedding after administration of corticosteroids. Latently infected calves failed to transmit BHV-1 during 4 weeks' contact with sentinel calves. Infected calves were killed and necropsied during latency or induced recrudescence. The BHV-1 DNA was demonstrated intranuclearly in trigeminal ganglion neurons by in situ hybridization. The BHV-1 antigen was demonstrated by immunofluorescence in trigeminal ganglion neurons during recrudescence. By electron microscopy, changes in the appearance of the Nissl bodies and a high frequency of nuclear bodies were observed in trigeminal ganglion neurons.     

Protective effect of inactivated bovine herpesvirus-1 in calves experimentally infected with bovine herpesvirus-1 and Pasteurella haemolytica.

The protective effect of an inactivated whole-virion bovine herpesvirus-1 (BHV-1) immunising inoculum, without adjuvant, against viral-bacterial respiratory disease was studied in three experimental treatment groups of five calves each. One group was boosted 14 days after the first vaccination and at this time the second group received their initial inoculation. Seven days later, calves were challenged with BHV-1 in aerosol and four days after this challenge all calves were exposed to Pasteurella haemolytica A1 in aerosol. Among the three groups, differences in rectal temperature responses four days after viral challenge (P less than 0.01) did not relate to protection. However the main response variable, viral-bacterial pneumonia, was reduced in boosted calves (P less than 0.05).     

Bovine herpesvirus-1 vaccination against experimental bovine herpesvirus-1 and Pasteurella haemolytica respiratory tract infection: onset of protection

The onset of protection offered by intranasal vaccination with attenuated bovine herpesvirus-1 (BHV-1) was studied in 18 calves given a virulent BHV-1 aerosol challenge inoculum and an aerosol challenge exposure to Pasteurella haemolytica. Calves challenge exposed with virus 3, 7, 11, 15, or 19 days after vaccination and challenge exposed 4 days later with Pasteurella haemolytica did not develop viral-bacterial pneumonia, whereas 2 of 3 control calves died of fibrinous bronchopneumonia 40 and 60 hours after the bacterial aerosol and the 3rd control calf had similar lesions. All vaccinated and control calves had detectable amounts of interferon at the time of viral challenge exposure. Protection was observed before detection of neutralizing antibodies to BHV-1 in nasal secretions or in serum. Protection was therefore present from day 3 through day 19 after vaccination, but the mechanism could not be explained completely by neutralizing antibody or interferon.     

Humoral immune response and assessment of vaccine virus shedding in calves receiving modified live virus vaccines containing bovine herpesvirus-1 and bovine viral diarrhoea virus 1a

Susceptible calves were administered modified live virus (MLV) vaccines containing bovine herpesvirus-1 (BHV1) and bovine viral diarrhoea type 1 (BVDV1a) strains intramuscularly, with one vaccine containing both MLV and inactivated BHV-1 and inactivated BVDV1a. There was no evidence of transmission of vaccine (BHV-1 and BVDV1a) strains to susceptible non-vaccinated controls commingled with vaccinates. No vaccinates had detectable BHV-1 in peripheral blood leucocytes (PBL) after vaccination. Each of three vaccines containing an MLV BVDV1a strain caused a transient BVDV vaccine induced viremia in PBL after vaccination, which was cleared as the calves developed serum BVDV1 antibodies. The vaccine containing both MLV and inactivated BHV-1 induced serum BHV-1 antibodies more rapid than MLV BHV-1 vaccine. Two doses of MLV BHV-1 (days 0 and 28) in some cases induced serum BHV-1 antibodies to higher levels and greater duration than one dose.     

Recrudescence of bovine herpesvirus-5 in experimentally infected calves

A latent infection of bovine herpesvirus-5 (BHV-5) was established in 4 calves. These calves, plus 2 controls, were given dexamethasone (DM) to reactivate the latent virus. The 4 principal calves developed antibodies to BHV-5 by postinoculation day (PID) 21. Antibody titers increased until PID 42 before decreasing to low levels of PID 75. After the first DM treatment (started on PID 76), an anamnestic antibody response was demonstrated in the 4 principal calves. Calves, 2, 3, and 4 were euthanatized and necropsied at PID 121, and their antibody titers were again decreasing. The virus BHV-5 was not isolated from the tissues by conventional techniques of viral isolation but was isolated from the trigeminal ganglion and spinal cord of calf 3 by explantation techniques. The BHV-5 was isolated, using conventional viral isolation techniques, from a nasal swab sample of calf 1 on PID 91 (15 days after the first DM treatment) and from the thoracic lymph node 6 days after the start of a 2nd DM treatment. Seemingly, BHV-5 may be latently harbored in the nerve tissues or calves and this virus may be reactivated from the upper respiratory tract following subsequent DM treatment.     

Asymptomatic encephalitis in calves experimentally infected with bovine herpesvirus-5

This study demonstrated that bovine herpesvirus 5 (BoHV)-5 infected calves can develop encephalitis and remain asymptomatic. Seven calves were infected intranasally and monitored for 30 days. Cerebrospinal fluid (CSF) analysis was performed from the onset of neurological signs. Multiple sections of brain and the trigeminal ganglion were submitted to histopathology. Virus detection (PCR and isolation) was performed on CSF and tissues. Four calves developed signs of neurologic disease and died. Three calves remained asymptomatic and were euthanized 30 days post-infection. Cerebrospinal fluid mononuclear pleocytosis occurred in symptomatic and asymptomatic calves. BoHV-5 was isolated and viral DNA was detected in multiple areas of the encephalon of all calves. The viral DNA was detected in the CSF of 2 calves showing neurological signs. Histologically, inflammation was noted in the brain of all calves and confirmed that the encephalitis caused by BoHV-5 may be mild and asymptomatic.     

Comparison of humoral immune responses in dairy heifers vaccinated with 3 different commercial vaccines against bovine viral diarrhea virus and bovine herpesvirus-1

A randomized clinical trial was conducted to compare the humoral immune response to 3 different commercial vaccines in dairy heifers housed in 3 different dairy farms in Quebec. All heifers were seronegative to type 1 bovine viral diarrhea virus (BVDV) (Singer strain), type 2 BVDV (NVSL 125c strain), and bovine herpesvirus-1 (BHV-1) at the beginning of the trial. In addition, control heifers in group 1 remained seronegative to the 2 viruses till the end of the trial. Significant differences in humoral immune responses occurred among the 3 commercial vaccines at 4 weeks and 6 months following vaccination. The vaccine in group 2 elicited higher mean antibody titers and seroconversion rates to both type 1 and type 2 BVDV than that in groups 3 or 4. Vaccines in groups 2 and 3 induced higher mean antibody titers to BHV-1 than did the vaccine in group 4.     

Rationale and perspectives on the success of vaccination against bovine herpesvirus-1

Several characteristics of BHV-1 have contributed to the successful development of both conventional and marker vaccines. BHV-1 is a stable virus, which grows to high titers in vitro, has a limited host range and causes acute viremic infections. Furthermore, the protective antigens, as well as the antigens that are suitable as marker, are present in the predominant virus isolates and induce significant and long-lasting immune responses, both in na?ve and in previously vaccinated animals. In many parts of the world including North-America control of BHV-1 is achieved by vaccination with conventional attenuated or inactivated vaccines. With parts of Europe being BHV-1 free, the ability to differentiate infected from vaccinated animals has become critical as a trading tool. Live and killed gE-deleted marker vaccines are now widely used in Europe, in combination with gE-based diagnostic tests to monitor cattle. However, several issues remain to be resolved. BHV-1 causes latency, which creates a need for stringent management practices in case eradication is to be achieved. Since intramuscular delivery with a syringe and needle leads to considerable tissue damage, needle-free delivery methods should be adopted for beef cattle. Furthermore, conventional inactivated and attenuated vaccines are less efficacious in neonates, so alternative vaccine types such as CpG adjuvanted protein vaccines or DNA vaccines are required for effective vaccination of this age group.     

Longevity of protective immunity to experimental bovine herpesvirus-1 infection following inoculation with a combination modified-live virus vaccine in beef calves

OBJECTIVE: To determine whether a combination viral vaccine containing modified-live bovine herpesvirus-1 (BHV-1) would protect calves from infection with a recent field isolate of BHV-1. DESIGN: Randomized controlled trial. ANIMALS: Sixty 4- to 6-month-old beef calves. PROCEDURE: Calves were inoculated with a placebo 42 and 20 days prior to challenge (group 1; n = 10) or with the combination vaccine 42 and 20 days prior to challenge (group 2; 10), 146 and 126 days prior to challenge (group 3; 10), 117 and 96 days prior to challenge (group 4; 10), 86 and 65 days prior to challenge (group 5; 10), or 126 days prior to challenge (group 6; 10). All calves were challenged with BHV-1 via aerosol. Clinical signs, immune responses, and nasal shedding of virus were monitored for 14 days after challenge. RESULTS: Vaccination elicited increases in BHV-1-specific IgG antibody titers. Challenge with BHV-1 resulted in mild respiratory tract disease in all groups, but vaccinated calves had less severe signs of clinical disease. Extent and duration of nasal BHV-1 shedding following challenge was significantly lower in vaccinated calves than in control calves. In calves that received 2 doses of the vaccine, the degree of protection varied with the interval between the last vaccination and challenge, as evidenced by increases in risk of clinical signs and extent and duration of viral shedding. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that this combination vaccine provided protection from infection with virulent BHV-1 and significantly reduced nasal shedding of the virus for at least 126 days after vaccination.     

Response of proinflammatory and anti-inflammatory cytokines in calves with subclinical bovine viral diarrhea challenged with bovine herpesvirus-1

The aim of this work was to investigate the susceptibility of calves infected with bovine viral diarrhea virus (BVDV) against secondary infections. For this purpose, the profile of cytokines implicated in the immune response of calves experimentally infected with a non-cytopathic strain of BVDV type-1 and challenged with bovine herpesvirus 1.1 (BHV-1.1) was evaluated in comparison with healthy animals challenged only with BHV-1.1. The immune response was measured by serum concentrations of cytokines (IL-1β, TNFα, IFNγ, IL-12, IL-4 and IL-10), acute phase proteins (haptoglobin, serum amyloid A and fibrinogen) and BVDV and BHV-1.1 specific antibodies. BVDV-infected calves displayed a great secretion of TNFα and reduced production of IL-10 following BHV-1 infection, leading to an exacerbation of the inflammatory response and to the development of more intense clinical symptoms and lesions than those observed in healthy animals BHV-1-inoculated. A Th1 immune response, based on IFNγ production and on the absence of significant changes in IL-4 production, was observed in both groups of BHV-1-infected calves. However, whereas the animals inoculated only with BHV-1 presented an IFNγ response from the start of the study and high expression of IL-12, the BVDV-infected calves showed a delay in the IFNγ production and low levels of IL-12. This alteration in the kinetic and magnitude of these cytokines, involved in cytotoxic mechanisms responsible for limiting the spread of secondary pathogens, facilitated the dissemination of BHV-1.1 in BVDV-infected calves.     

Attempted reactivation of latent bovine herpesvirus 1 infection in calves by infection with ruminant pestiviruses

Three calves, latently infected with bovine herpesvirus 1 (BHV 1), were each inoculated intranasally with 9 strains of ruminant pestivirus (BVDV). All three calves developed a biphasic pyrexia and a lymphopenia followed by a neutrophilia. They did not shed BHV 1 in their nasal secretions in the 14 days following BVDV inoculation, and their BHV 1 antibody levels remained static, as did those of 2 control calves not given BVDV. All five calves were subsequently shown to be latently infected with BHV 1 by the production of recrudescent infections following the administration of dexamethasone. BHV 1 was recovered from nasal secretions and there was a marked rise in BHV 1 antibody titres in the second week after dexamethasone administration.     

Vaccination of calves with contaminated batches of bovine herpes virus 1 vaccines did not result in infection with bovine virus diarrhea virus

The aim of the experiment was to study whether bovine herpesvirus 1 (BHV1) marker vaccine batches known to be contaminated with bovine virus diarrhoea virus (BVDV) type 1 could cause BVD in cattle. For this purpose, four groups of cattle were used. The first group (n = 4 calves, the positive control group), was vaccinated with vaccine from a batch contaminated with BVDV type 2. The second group (n = 4 calves, the negative control group), was vaccinated with vaccine from a batch that was not contaminated with BVDV. The third group (n = 39 calves), was vaccinated with a vaccine from one of four batches contaminated with BVDV type 1 (seronegative experimental group). The fourth group (n = 6 seropositive heifers), was vaccinated with a vaccine from one of three batches known to be contaminated with BVDV type 1. All cattle were vaccinated with an overdose of the BHV1 marker vaccine. At the start of the experiment, all calves except those from group 4 were seronegative for BVDV and BHV1. The calves from group 4 had antibodies against BVDV, were BVDV-free and seronegative to BHV1. After vaccination, the positive control calves became severely ill, had fever for several days, and BVDV was isolated from nasal swabs and white blood cells. In addition, these calves produced antibodies to BVDV and BHV1. No difference in clinical scores of the other groups was seen, nor were BVDV or BVDV-specific antibody responses detected in these calves; however, they did produce antibodies against BHV1. The remainder of each vaccine vial used was examined for the presence of infectious BVDV in cell culture. From none of the vials was BVDV isolated after three subsequent passages. This indicates that BVDV was either absent from the vials or was present in too low an amount to be isolated. Thus vaccination of calves with vaccines from BHV1 marker vaccine batches contaminated with BVDV type 1 did not result in BVDV infections.