Seroprevalence of Bovine Viral Diarrhea Virus in Wild Pigs (Sus scrofa) in 17 States in the USA.

Wild pigs (Sus scrofa) are among the most detrimental invasive species in the USA. They are damaging to crops and agriculture, pose a public health risk as reservoirs of zoonotic pathogens, and may also spread disease to livestock. One pathogen identified in wild pigs is bovine viral diarrhea virus (BVDV), a virus that causes an economically important disease of cattle (Bos taurus and Bos indicus). We sought to determine the BVDV seroprevalence in wild pigs in 17 states across the US and to determine whether age category, sex, or location were associated with a positive antibody titer. Serum samples from 945 wild pigs were collected from 17 US states. Virus neutralization assays were performed to determine antibody titers against BVDV-1b and BVDV-2a. Total BVDV seroprevalence for the study area was 5.8% (95% confidence interval [CI], 4.11-8.89). Seroprevalence across all evaluated states was determined to be 4.4% (95% CI, 2.48-6.82) for BVDV-1b and 3.6% (95% CI, 1.54-5.60) for BVDV-2a. The seroprevalence for individual states varied from 0% to 16.7%. There was no statistical difference in median antibody titer for BVDV-1b or BVDV-2a by sex or age category. State seroprevalences for both BVDV-1b and BVDV-2a were associated with wild pig population estimates for those states.

Intranasal booster vaccination of beef steers reduces clinical signs following experimental coinfection with BRSV and BHV-1 without reducing shedding of BRD-associated bacteria.

OBJECTIVE: To determine the efficacy of primary or booster intranasal vaccination of beef steers on clinical protection and pathogen detection following simultaneous challenge with bovine respiratory syncytial virus and bovine herpes virus 1. METHODS: 30 beef steers were randomly allocated to 3 different treatment groups starting at 2 months of age. Group A (n = 10) was administered a single dose of a parenteral modified-live vaccine and was moved to a separate pasture. Groups B (n = 10) and C (10) remained unvaccinated. At 6 months of age, all steers were weaned and transported. Subsequently, groups A and B received a single dose of an intranasal modified-live vaccine vaccine while group C remained unvaccinated. Group C was housed separately until challenge. Two days following vaccination, all steers were challenged with bovine respiratory syncytial virus and bovine herpes virus 1 and housed in a single pen. Clinical and antibody response outcomes and the presence of nasal pathogens were evaluated. RESULTS: The odds of clinical disease were lower in group A compared with group C on day 7 postchallenge; however, antibody responses and pathogen detection were not significantly different between groups before and following viral challenge. All calves remained negative for Histophilus somni and Mycoplasma bovis; however, significantly greater loads of Mannheimia haemolytica and Pasteurella multocida were detected on day 7 postchallenge compared with day -2 prechallenge. CLINICAL RELEVANCE: Intranasal booster vaccination of beef steers at 6 months of age reduced clinical disease early after viral challenge. Weaning, transport, and viral infection promoted increased detection rates of M haemolytica and P multocida regardless of vaccination status.

Multivariate Analysis as a Method to Evaluate Antigenic Relationships between Bovine Viral Diarrhea Virus 1b Isolates and Vaccine Strains.

The antigenicity of bovine viral diarrhea virus (BVDV) has been evaluated using virus-neutralizing titer data analyzed by principal component analysis (PCA) and has demonstrated numerous isolates to be antigenically divergent from US vaccine strains. The lack of BVDV-1b strains in currently licensed vaccines has raised concerns regarding the lack of protection against BVDV-1b field strains. The aim of this study was to evaluate the antigenic diversity of BVDV-1b strains and better understand the breadth of antigenic relatedness using BVDV-1b antisera and antisera from vaccine strains. Results from this analysis demonstrate the antigenic diversity observed among BVDV-1b isolates and genetic assignment into the BVDV-1b subgenotype is not representative of antigenic relatedness. This is demonstrated by BVDV-1b isolates (2280N, SNc, Illc, MSU, and 2337) observed to be as antigenically dissimilar as BVDV-2a isolates when using BVDV-1b antisera. Additionally, when BVDV-1a vaccine antisera was used for comparisons, a greater percentage of BVDV-1b isolates clustered with BVDV-1a vaccine strains as part of PC1, suggesting antigenic relatedness and potentially partial protection. Collectively, data from this study would suggest that while most BVDV-1b isolates are antigenically similar, there are antigenically dissimilar BVDV-1b isolates as determined by the lack of cross-reactivity, which may contribute to the lack of protection.

The titers, duration, and residual clinical protection of passively transferred nasal and serum antibodies are similar among beef calves that nursed colostrum from vaccinated or unvaccinated dams and were challenged experimentally with bovine respiratory syncytial virus at three months of age.

OBJECTIVES: To compare initial titers, duration, and residual clinical protection of passively transferred bovine respiratory syncytial virus (BRSV) nasal immunoglobulin (Ig) G-1 and IgA, and serum neutralizing (SN) antibodies. ANIMALS: 40 three-month-old beef steers born either to unvaccinated or vaccinated cows. PROCEDURES: During the last trimester of gestation, cows were assigned randomly to either vaccinated or unvaccinated groups. Calves were grouped on the basis of whether they nursed colostrum from unvaccinated dams (NO-VACC group; n = 20) versus dams vaccinated with 2 doses of an inactivated BRSV vaccine (VACC group; n = 20). At 3 months of age, calves were challenged with BRSV. Respiratory signs were scored. Nasal BRSV IgG-1 and IgA and SN antibodies were compared before and after the challenge. The presence of BRSV in nasal secretions was evaluated by reverse transcription-PCR assays. RESULTS: Respiratory scores after BRSV challenge were similar between treatment groups. Nasal BRSV IgG-1 and SN antibodies were significantly greater in VACC calves at 48 hours of life; however, by 3 months of age, titers had decayed in both groups. Nasal BRSV IgA titers were minimal after colostrum intake and before the BRSV challenge, and increased in both groups after the challenge. The NO-VACC group had a significantly greater probability of shedding BRSV compared with VACC calves. CLINICAL RELEVANCE: At 3 months of age, titers of passively transferred BRSV antibodies in VACC and NO-VACC calves had decayed to nonprotective levels. Calves born to vaccinated dams had a decreased probability of BRSV shedding; however, this was not related to differences in SN or nasal BRSV antibody titers.

Local and Systemic Antibody Responses in Beef Calves Vaccinated with a Modified-Live Virus Bovine Respiratory Syncytial Virus (BRSV) Vaccine at Birth following BRSV Infection.

Maternal antibodies interfere with BRSV vaccine responses and efficacy in young calves. The objective of this study was to determine if vaccination before the complete absorption of colostral antibodies results in adequate immune priming and clinical protection of beef calves. Within 6 h of life, calves were randomly assigned to 2 different treatment groups. Group Vacc (n = 25) received a single dose of a modified-live virus (MLV) BRSV vaccine intranasally (IN) and group Control (n = 25) received 2 mL of 0.9% saline IN. At approximately 3 months of age, all calves were experimentally challenged with BRSV. Serum and nasal secretion samples were collected before and after challenge for BRSV real-time RT-PCR and antibody testing. Respiratory signs were not observed before challenge. After challenge, respiratory scores were similar between groups. On the challenge day, >40% of calves in each group were febrile. The mean serum and nasal BRSV-specific antibody titers indicated natural BRSV exposure before the experimental challenge in both groups. All calves tested positive for BRSV and had a similar duration of shedding after challenge. Based on these results, vaccination at birth does not offer advantages for immune priming or clinical protection for beef calves in BRSV-endemic cow-calf herds.