Modified-live Vaccine Research Articles

In silico prediction and ex vivo evaluation of potential T-cell epitopes in glycoproteins 4 and 5 and nucleocapsid protein of genotype-I (European) of porcine reproductive and respiratory syndrome virus

T-cell epitopes of porcine reproductive and respiratory syndrome virus (PRRSV) glycoproteins 4 (GP4), 5 (GP5) and nucleocapsid (N) were predicted using bioinformatics and later tested by IFN-γ ELISPOT in pigs immunized with either a modified live vaccine (MLV) or DNA (open reading frames 4, 5 or 7). For MLV-vaccinated pigs, immunodominant epitopes were found in N but T-epitopes were also found in GP4 and GP5. For DNA-immunized pigs, some peptides were differently recognized. Using a large set of PRRSV sequences it was shown that N contains a conserved epitope and that for GP5, the genotype-I counterparts of previously reported epitopes of genotype-II strains were also immunogenic.

Fièvre catarrhale ovine aux Pays-Bas : aperçu sur trois ans

Since August 2006, the Netherlands has been facing outbreaks of bluetongue (BT) caused by serotype 8 (BTV-8). In this first BT-season about 470 affected holdings were reported in the southern part of the country. It was believed that restrictions to animal movements slowed down the northwards spread of BTV. After a relatively mild winter, BT simultaneously resurfaced in July 2007 at many locations indicating that BTV-8 had survived well. Thousands of affected holdings across the country were reported during that year. After another mild winter, a vaccina­tion campaign for serotype 8 was launched in May 2008, with massive vaccination of sheep, goats and cattle. In 2008, less than 150 outbreaks were reported. The reported BTV-8 cases were in the north-eastern part of the country where the level of natural immunity and the willingness to vaccinate were rela­tively low. This third year with outbreaks was followed by a cold winter. In 2009, no BTV-positive animals were reported from mid-March on. Based on a questionnaire, the willingness of farmers to (re)vaccinate animals tended to decline in 2009, but for cattle farmers this was still at an acceptable level. It is questionable whether farmers will (re)vaccinate again in 2010. Optimism is growing with respect to control, and possibly eradi­cation of BTV-8, but re-emergence after a silent year is a serious possibility. One additional year of vaccination is thus probably required for eradication. In September 2008, because of the enhanced risk of BTV-1 intro­duction, polymerase chain reaction (PCR) positive results were confirmed for BTV-8\net2006 by sequencing the amplicons of the serogroup-specific PCR test and by serotype-specific PCR testing. BTV-6 was found in infected animals in three different herds, irrespective of vaccination. The sequence of genome seg­ment 10 of this virus is genetically close to BTV-2, whereas other segments are all close to those of the modified-live vaccine for serotype 6. This suggests that BTV-6\net2008 is a reassortant of serotypes 2 and 6. Extensive monitoring and additional cases revealed an unusual epidemiology. No other affected animals were detected, but BTV-6 positive animals on a few additional farms were found. The distance between affected holdings was 30-50 kilometres, and there was no epidemiological link between the affected farms. All BTV-6 positive animals were PCR-negative in March 2009, with no new reports of BTV-6 infection. In October 2008, a BTV-1 positive bull was officially reported one month after import. In the same herd, four additional PCR-positive animals were found. Three of these also originated from France and were positive for BTV-8. Detailed investiga­tions revealed a French variant of BTV-8 never found in the Netherlands. We concluded that these animals were infected in France and that BTV-8 appeared to evolve differently in dif­ferent regions in Europe. The fifth animal was positive for BTV-6 and was moved from the BTV-6 affected area. Since no other BTV-positive animals were found in the respective herds and in the one-kilometre radius zone, no spread of BTV-1, BTV-6 and BTV-8 seemed to have occurred in this area. Furthermore, export of Dutch pregnant heifers began again in December 2008, with 2000 to 3000 animals per month. Export is allowed on the basis of vaccination (against serotype 8) before pregnancy and negative PCR testing. Since, no animals were found PCR-positive by the serogroup-specific PCR test, we con­cluded that the Netherlands was free of any BTV circulation in 2009. The situation in 2010 will show whether the Netherlands can be considered as BTV-free again.

Safety and efficacy of vaccination of seronegative bulls with modified-live, cytopathic bovine viral diarrhea viruses

The objectives were to vaccinate peri-pubertal bulls with a modified-live vaccine consisting of cytopathic BVDV strains Singer and 296 and evaluate the resulting: (a) transient shed of modified-live, cytopathic BVDV in semen; (b) risk of prolonged testicular infection; and (c) protection against subsequent testicular infection due to viral challenge. Seronegative, peri-pubertal bulls were vaccinated subcutaneously with a standard dose of vaccine ( n = 11) or were maintained as unvaccinated controls ( n = 11). Forty-nine days after vaccination, all bulls were intranasally inoculated with a noncytopathic field strain of BVDV. Semen and testicular biopsies collected after vaccination and challenge were assayed for BVDV using virus isolation, reverse transcription-nested PCR, or immunohistochemistry, and the identity of viral strains was determined by nucleotide sequencing of PCR products. Vaccination of peri-pubertal bulls with this vaccine caused a short-term, transient shed of only the type 1a strain of modified-live, cytopathic BVDV in semen for up to 10 d after vaccination. The vaccine did not cause prolonged testicular infection. Vaccination with this product prevented development of prolonged testicular infections after subsequent exposure to a field strain of BVDV.

Efficacy of a modified-live virus vaccine administered to calves with maternal antibodies and challenged seven months later with a virulent bovine viral diarrhea type 2 virus

A total of 22 commercial dairy calves were used to determine if vaccination of a modified-live bovine viral diarrhoea virus (BVDV) vaccine with adjuvants in the face of maternal antibody will protect calves from a virulent type 2 BVDV challenge within seven months post-vaccination, following the loss of maternal antibody. Neonatal calves were obtained prior to consuming colostrum and were randomly divided into three groups. Group 1 calves were fed an antibody-free colostrum supplement within six hours of birth. Calves in Group 2 and Group 3 were fed pooled colostrum obtained from cows vaccinated eight weeks prior to calving with a commercial inactivated combination vaccine containing BVDV1 and BVDV2. Group 2 calves were vaccinated at approximately 4.5 weeks of age with a commercial modified-live virus combination vaccine containing BVDV1 and BVDV2. Calves in Groups 1 and 3 were sham vaccinated. Seven months after vaccination, when calves in Group 3 became seronegative to BVDV2, calves in all three groups were challenged intranasally with virulent BVDV2, strain 1373. Calves that received colostrum and were vaccinated had only mild or no clinical diseases. Calves that did or did not receive colostrum and were sham vaccinated, developed severe diseases, with a 33-50% mortality rate. In this study, young calves vaccinated with a modified-live virus vaccine with adjuvants in the face of maternal antibody were protected against a virulent strain of BVDV.

Comparison of the BVDV, BHV-1, and BRSV anamnestic response to modified-live or inactivated vaccines in calves previously vaccinated with a modified-live virus vaccine.

The objective of this study was to compare the serological responses in cattle initially vaccinated with a modified-live virus (MLV) vaccine containing infectious bovine rhinotracheitis (IBR) virus, parainfluenza-3 (PI3) virus, bovine viral diarrhoea virus type 1 (BVDV1), bovine viral diarrhoea virus type 2 (BVDV2), and bovine respiratory syncytial (BRS) virus antigens, and subsequently re-vaccinated with either the same MLV vaccine or inactivated vaccine with oil adjuvants, containing the same viral antigens. A group of 145 nursing calves received an MLV vaccine containing IBR, PI3, BVDV1, BVDV2, and BRSV at one to two months of age. The calves were re-vaccinated with the same MLV vaccine at weaning, three-and-a-half months later. Approximately five months later, 45 of these animals were randomly selected and assigned to one of three treatment groups. Twenty calves received inactivated vaccine with oil adjuvants (IBR, PI3, BVDV1, BVDV2, BRSV); 20 received the same MLV vaccine that they had received as calves (IBR, PI3, BVDV1, BVDV2, BRSV); and five controls received the MLV sterile diluent. Following final vaccination, the animals receiving the inactivated vaccine with oil adjuvants had the highest titre response (P<0.05) for IBRV, BRSV, BVDV1, and BVDV2.

Evaluation of the humoral immune response and fecal shedding in weanling foals following oral and intra-rectal administration of an avirulent live vaccine of Lawsonia intracellularis

Equine proliferative enteropathy (EPE) caused by Lawsonia intracellularis has recently been recognized as an emerging disease in foals. Whilst the clinical entity, diagnostic evaluation and treatment of affected foals have been well established and described, preventive measures for EPE have remained largely unaddressed. The objectives of this study were to investigate the humoral immune response and onset and duration of fecal shedding in foals after oral and intra-rectal administration of a modified-live vaccine of L. intracellularis. Foals were vaccinated twice, 3 weeks apart, via oral drenching after pre-medication with a proton-pump inhibitor (omeprazole; group 1), intra-rectally (group 2) or orally without any pre-medication (group 3). The health status of the foals was monitored daily, with feces and serum collected at regular intervals for Polymerase Chain Reaction (PCR) and serology. All foals remained healthy and no adverse vaccine reactions were observed. Fecal shedding lasted from 1 to 12 days and was mainly detected in foals receiving the intra-rectal vaccine 11-15 days following the first vaccine administration. Serological responses were measured in the majority of the vaccinated foals. All foals vaccinated intra-rectally seroconverted after the first vaccine, compared to 50% and 0% of foals in groups 1 and 3, respectively. Pre-medication with omeprazole prior to oral vaccination in group 1 foals led to an earlier and stronger detectable humoral response compared to non pre-medicated foals.

Efficacy of bovine herpesvirus-1 inactivated vaccine against abortion and stillbirth in pregnant heifers

To evaluate the efficacy of an inactivated bovine herpesvirus-1 (BHV-1) vaccine to protect against BHV-1 challenge-induced abortion and stillbirth. Prospective study. 35 beef heifers. Before breeding, heifers were vaccinated with a commercially available BHV-1 inactivated vaccine SC or IM. The estrous cycle was then synchronized, and heifers were artificially inseminated 30 to 60 days after vaccination. Heifers (n = 21) were challenge inoculated IV at approximately 180 days of gestation with virulent BHV-1. Fourteen control heifers were not vaccinated. Clinical signs of BHV-1 infection were monitored for 10 days following challenge; serologic status and occurrence of abortion or stillbirth were evaluated until time of calving. 18 of 21 (85.7%) heifers that received vaccine were protected from abortion following challenge, whereas all 14 control heifers aborted. Results indicated that an inactivated BHV-1 vaccine can protect against abortion resulting from a substantial challenge infection, with efficacy similar to that of modified-live BHV-1 vaccines.

Vaccinating Calves

For decades, veterinarians have believed that young animals with circulating maternally-derived antibody cannot be effectively vaccinated. However, many investigators have shown that young animals vaccinated in the face of maternal antibody (IFOMA), while not showing evidence of an increase in serum antibody titer typically seen in older animals responding to vaccination, will show evidence of T cell activation or, better yet, protection from disease when they are exposed to infection after maternal antibodies have disappeared. Successful priming for a memory immune response by vaccination IFOMA has repeatedly been shown to be possible in calves. In general, successful vaccination of calves with moderate levels of maternal antibody requires two doses of modified-live vaccine given at least 2-4 weeks apart, but exceptions to this rule have been identified. While two doses are more likely to be successful, in some cases it has been possible to protect calves from disease months later by vaccination with a single dose of modified-live vaccine given intranasally or parenterally when they are within two months of age. However, these findings are not consistent; occasionally young animals vaccinated IFOMA fail to develop a protective immune response to later challenge. Reasons that calves are often but not always successfully protected when vaccinated IFOMA are not completely defined, but are likely related to age of the animal at vaccination, amount of maternal antibody present, type of vaccine the calf receives, virulence of the challenging pathogen, and the outcome used to define success of vaccination. While more research is needed before consistently reliable recommendations for successful vaccination of calves IFOMA can be made, ample evidence suggests that vaccination IFOMA can protect calves from disease when they are exposed to infectious agents after maternal antibodies have disappeared in at least some cases. Thus, vaccination IFOMA may be worthwhile and cost effective practice when young calves are at reasonably high risk of disease due to agents for which effective vaccines are available.

Comparative Efficacies of Three Commercially Available Vaccines against West Nile Virus (WNV) in a Short-Duration Challenge Trial Involving an Equine WNV Encephalitis Model

We used a severe challenge model that produces clinical West Nile virus (WNV) disease to test the efficacy of three commercially available equine WNV vaccines in horses. Twenty-four healthy, WNV-seronegative horses of varying ages and genders were placed, in random and blind manner, into three trial groups consisting of eight horses each; two horses in each group received (i) an inactivated WNV vaccine (K-WN), (ii) a modified-live vaccine (CP-WN) containing the WNV prM and E proteins expressed by a canarypox vector, (iii) a live-chimera vaccine (WN-FV) containing WNV prM and E proteins expressed in a YF17D vector, or (iv) a diluent control. Challenge by this model caused grave neurological signs, viremia, moderate to severe histopathologic lesions in the brain and spinal cord, and an outcome of 0% survivorship in all six control horses. In contrast, challenge in horses at between 28 days postvaccination with the chimera vaccine and 56 days postvaccination with the commercial inactivated or modified-live vaccine resulted in 100% survivorship (protection from the onset of WNV encephalitis and viremia). Horses vaccinated with the live-chimera vaccine showed significantly fewer clinical signs than did the control horses (P </= 0.01) and the horses vaccinated with inactivated vaccine (P = 0.035). Mild residual inflammatory lesions were seen in a few of the vaccinated horses.

Use of a Vectored Vaccine against Infectious Bursal Disease of Chickens in the Face of High-Titred Maternally Derived Antibody

Interference by maternally derived antibody (MDA) is a major problem for the vaccination of young chickens against infectious bursal disease (IBD). The choice of the timing of vaccination and of the type (degree of attenuation) of modified-live vaccine (MLV) to use is often difficult. An IBD vectored vaccine (vHVT13), in which turkey herpesvirus (HVT) is used as the vector, was recently developed. This vaccine is administered once at the hatchery, either in ovo or by the subcutaneous route, to 1-day-old chicks at a time when MDA is maximal. In terms of safety, the vHVT13 vaccine had negligible impact on the bursa of Fabricius when compared with classical IBD MLV. Vaccination and challenge studies demonstrated that this vaccine is able to protect chickens against various IBD virus (IBDV) challenge strains including very virulent, classical, and USA variant IBDV, despite the presence of high-titred IBD MDA at the time of vaccination. These data show that the vector vaccine combines a safety and efficacy profile that cannot be achieved with classical IBD vaccines.

Effect of vaccination with a modified-live porcine reproductive and respiratory syndrome virus vaccine on dynamics of homologous viral infection in pigs

To determine effects of vaccination protocols with modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine on persistence and transmission of virus in pigs infected with a homologous isolate and determine clinical and virologic responses following heterologous viral challenge. Four hundred forty 6- to 8-week-old PRRSV-naïve pigs. Pigs were allocated into 5 groups. Groups A to D were inoculated with wild-type PRRSV VR2332. Group A (positive control pigs) received PRRSV only. Groups B, C, and D received modified-live PRRSV vaccine (1, 2, or 3 doses). Group E served as a negative control group. To evaluate viral transmission, sentinel pigs were introduced into each group at intervals from 37 to 67, 67 to 97, and 97 to 127 days postinoculation (DPI). To evaluate persistence, pigs were euthanized at 37, 67, 97, or 127 DPI. To assess clinical and virologic response after challenge, selected pigs from each group were inoculated at 98 DPI with a heterologous isolate (PRRSV MN-184). Mass vaccination significantly reduced the number of persistently infected pigs at 127 DPI. Vaccination did not eliminate wild-type PRRSV; administration of 2 or 3 doses of modified-live virus vaccine reduced viral shedding after 97 DPI. Previous exposure to wild-type and vaccine virus reduced clinical signs and enhanced growth following heterologous challenge but did not prevent infection. Findings suggest that therapeutic vaccination may help to reduce economic losses of PRRSV caused by infection; further studies to define the role of modified-live virus vaccines in control-eradication programs are needed.

Investigation of the Molecular Detection of Vaccine-Derived Equine Herpesvirus Type 1 in Blood and Nasal Secretions from Horses Following Intramuscular Vaccination

The objective of this study was to investigate whether intramuscular vaccination of healthy adult horses with a killed or a modified live equine herpesvirus type 1 (EHV-1) vaccine could induce transient positive PCR results in either blood or secretions collected on a nasopharyngeal swab. Four horses in each group received either a single killed or a modified-live vaccine intramuscularly. Two local commingled and 2 distant nonvaccinated controls were included for each group. All horses were observed daily for evidence of clinical abnormalities throughout the study periods. Blood and nasopharyngeal swabs were collected twice before vaccination and once weekly for 4 weeks after vaccination and submitted for PCR testing for EHV-1 by 2 independent laboratories using different real-time PCR methodologies. Serum samples collected from all horses on the vaccination day and 21 days later were tested for antibodies against EHV-1 using a serum neutralization test. Whereas the 2 vaccine strains tested positive in both EHV-1 PCR assays, nasopharyngeal swabs and whole blood collected from vaccinated and control horses had negative PCR test results for EHV-1 during the entire study period. Serum neutralization testing revealed a 2- to 4-fold increase in titers for all vaccinated horses, whereas titers in control horses were largely unchanged. The use of seropositive horses before immunization and the sampling frequency of 7 days may have prevented the occasional molecular detection of the vaccine virus in whole blood and nasopharyngeal secretions. However, the study results demonstrate that detection of EHV-1 DNA by PCR in vaccinated and unvaccinated healthy horses is not a common event.

Feline herpesvirus

Feline herpesvirus (FHV-1; felid herpesvirus 1 (FeHV-1)) is an alphaherpesvirus of cats closely related to canine herpesvirus-1 and phocine herpesvirus-1. There is only one serotype of the virus and it is relatively homogenous genetically. FeHV-1 is an important cause of acute upper respiratory tract and ocular disease in cats. In addition, its role in more chronic ocular disease and skin lesions is increasingly being recognised. Epidemiologically, FeHV-1 behaves as a typical alphaherpesvirus whereby clinically recovered cats become latently infected carriers which undergo periodic episodes of virus reactivation, particularly after a stress. The primary site of latency is the trigeminal ganglion. Conventional inactivated and modified-live vaccines are available and protect reasonably well against disease but not infection, although viral shedding may be reduced. Genetically engineered vaccines have also been developed, both for FeHV-1 and as vector vaccines for other pathogens, but none is as yet marketed.

Response of calves to challenge exposure with virulent bovine respiratory syncytial virus following intranasal administration of vaccines formulated for parenteral administration

To determine whether single-fraction and combination modified-live bovine respiratory syncytial virus (BRSV) vaccines commercially licensed for parenteral administration could stimulate protective immunity in calves after intranasal administration. Randomized controlled trial. 39 calves. Calves were separated from dams at birth, fed colostrum with a minimal concentration of antibodies against BRSV, and maintained in isolation. In 2 preliminary experiments, 9-week-old calves received 1 (n = 3) or 2 (3) doses of a single-component, modified-live BRSV vaccine or no vaccine (8 control calves in each experiment), and were challenged with BRSV 21 days after vaccination. In a third experiment, 2-week-old calves received combination modified-live virus (MLV) vaccines with or without BRSV and calves were challenged with BRSV 8 days later. Calves were euthanized, and lung lesions were measured. Immune responses, including serum and nasal antibody and nasal interferon-alpha concentrations, were assessed. BRSV challenge induced signs of severe clinical respiratory tract disease, including death and pulmonary lesions in unvaccinated calves and in calves that received a combination viral vaccine without BRSV. Pulmonary lesions were significantly less severe in BRSV-challenged calves that received single or combination BRSV vaccines. The proportion of calves that shed virus and the peak virus titer was decreased, compared with control calves. Protection was associated with mucosal IgA antibody responses after challenge. Single and combination BRSV vaccines administered intranasally provided clinical protection and sparing of pulmonary tissue similar to that detected in response to parenteral delivery of combination MLV and inactivated BRSV vaccines previously assessed in the same challenge model.

Compatibility of a bivalent modified-live vaccine against Bordetella bronchiseptica and cpiV, and a trivalent modified-live vaccine against cpv, cdv and cav-2

Eight puppies (group 1) were vaccinated once with a bivalent modified-live vaccine against infectious tracheobronchitis by the intranasal route and at the same time with an injectable trivalent vaccine against...

Correlation between the nature of immunity induced by different immunogens and the establishment of latent infection by wild-type pseudorabies virus

To assess the correlation between the nature of immunity induced by different types of immunogens and the establishment of latent infection by wild-type pseudorabies virus (PrV), we used a murine model immunized with different immunogens, the PrV modified live vaccine (MLV), inactivated vaccine (IAV), and commercial oil-adjuvant subunit vaccine (OSV), via either intranasal (i.n.) or intramuscular (i.m.) route. Both MLV and IAV induced a different nature of immunity biased to Th1- and Th2-type, respectively, as judged by the ratio of PrV-specific IgG isotypes (IgG2a/IgG1) and the profile of cytokine IL-2, IL-4, and IFN-γ production. In contrast, the OSV induced a lower isotype IgG2a to IgG1 ratio and higher level of IL-2 production. The MLV (inducing Th1-type) provided more effective protection against a virulent wild-type PrV challenge than IAV and OSV (inducing Th2- and mixed type, respectively). In addition, the MLV impeded the establishment of a latent infection with wild-type PrV, and the decrease in the PrV latency load by immunization with the MLV appeared to be mediated by the immune T-cells. These results demonstrate the substantial role of the immune responses driven by preceding vaccination in modulating the establishment of PrV latency caused by the post-infection of a field virus.

Evaluation of protection against virulent bovine viral diarrhea virus type 2 in calves that had maternal antibodies and were vaccinated with a modified-live vaccine

To evaluate the efficacy of an adjuvanted modified-live bovine viral diarrhea virus (BVDV) vaccine against challenge with a virulent type 2 BVDV strain in calves with or without maternal antibodies against the virus. Challenge study. 23 crossbred dairy calves. Calves were fed colostrum containing antibodies against BVDV or colostrum without anti-BVDV antibodies within 6 hours of birth and again 8 to 12 hours after the first feeding. Calves were vaccinated with a commercial modified-live virus combination vaccine or a sham vaccine at approximately 5 weeks of age and challenged with virulent type 2 BVDV 3.5 months after vaccination. Clinical signs of BVDV infection, development of viremia, and variation in WBC counts were recorded for 14 days after challenge exposure. Calves that received colostrum free of anti-BVDV antibodies and were vaccinated with the sham vaccine developed severe disease (4 of the 7 calves died or were euthanatized). Calves that received colostrum free of anti-BVDV antibodies and were vaccinated and calves that received colostrum with anti-BVDV antibodies and were vaccinated developed only mild or no clinical signs of disease. Results indicated that the modified-live virus vaccine induced a strong protective immune response in young calves, even when plasma concentrations of maternal antibody were high. In addition, all vaccinated calves were protected against viral shedding, whereas control calves vaccinated with the sham vaccine shed virus for an extended period of time.

Differentiation between field and vaccine strain of bluetongue virus serotype 16

In August 2000, bluetongue virus (BTV) appeared for the first time in Sardinia and, since then, the infection spread across Sicily and into the mainland of Italy involving at the beginning serotypes 2 and 9 and then, from 2002, 4 and 16. To reduce direct losses due to disease and indirect losses due to new serotype circulation, the 2004 Italian vaccination campaign included the modified-live vaccines against BTV-4 and 16 produced by Onderstepoort Biological Product (OBP), South Africa. Few months after the end of the campaign, BTV-16 was reported broadly in the country and the need of differentiating field from the BTV-16 vaccine isolate became crucial. In this study, the gene segments 2, 5, 6 and 10 of both the Italian and vaccine BTV-16 strains were sequenced and their molecular relationship determined. As sequences of segment 5 were those showing the highest differences (17.3%), it was possible to develop a new diagnostic tool able to distinguish the Italian BTV-16 NS1 gene from that of the homologous vaccine strain. The procedure based on the use of a RT-PCR and the subsequent sequencing of the amplified product showed a high degree of sensitivity and specificity when samples from either BTV-16 vaccinated or infected sheep were tested.

A DNA vaccine coding for gB and gD of pseudorabies virus (suid herpes type 1) primes the immune system in the presence of maternal immunity more efficiently than conventional vaccines

DNA vaccines are capable of priming the immune system of neonates in the presence of maternal antibodies. However, it is still not clear whether the extent of priming and protection against challenge infections induced by a DNA vaccine in maternally immune newborns is better than that induced by conventional vaccines. To study this, we used the pseudorabies virus (PRV) infection model in the natural host, the pig. We compared the efficacy of a DNA vaccine with the efficacy of a conventional modified live vaccine (MLV) and an inactivated vaccine (IV) in maternally immune newborn piglets. We measured the priming of the immune response and the degree of protection against challenge infection for all vaccine types. We vaccinated piglets with or without maternal immunity twice, at the age of 5 and 9 weeks, and we assessed protection by challenge infection with virulent PRV at the age of 15 weeks. Vaccination with DNA or conventional vaccines induced both humoral and cell-mediated immune responses in maternally immune animals. DNA vaccination seemed not to suffer from suppression by maternal immunity and resulted in similar or stronger immune responses in maternally immune piglets as compared in naïve piglets. In contrast, vaccination with conventional vaccines resulted in weaker immune responses in maternally immune piglets than in naïve piglets. Moreover, DNA vaccination provided better protection against challenge infection in maternally immune piglets than in naive piglets, whereas vaccination with conventional vaccines did not.

Effect of Two Commercially Available Multivalent Modified-Live Viral Vaccines on Milk Production of Holstein Dairy Cows

Vaccination of lactating dairy cows is a common practice among US dairy herds. The objective of vaccination during lactation is to bolster immunity against common agents that may cause failure to conceive, fetal loss, or respiratory disease. The viruses commonly included in these vaccines are bovine viral diarrhea virus (BVDV), bovine herpes virus 1 (BHV-1), bovine respiratory syncytial virus (BRSV) and parainfluenza-3 virus (PI-3). The vaccines may contain inactivated virus or modified-live virus (Compendium of Veterinary Products 2004). In addition to the cost of vaccine and labor to administer the vaccine, producers should consider the cost of lost production when evaluating the economic benefits of vaccinating a lactating cow. Vaccination with an inactivated viral vaccine in combination with leptospiral bacterin produced a significant decrease in production compared to controls (Scott 2001). The effect of modified-live viral vaccines on milk production has not been reported. The objective of this study was to determine the effect of two commercially available multivalent modified-live viral vaccines on milk productionof Holstein dairy cows.