Early-life viral infections are associated with disadvantageous immune and microbiota profiles and recurrent respiratory infections.

The respiratory tract is populated by a specialized microbial ecosystem, which is seeded during and directly following birth. Perturbed development of the respiratory microbial community in early-life has been associated with higher susceptibility to respiratory tract infections (RTIs). Given a consistent gap in time between first signs of aberrant microbial maturation and the observation of the first RTIs, we hypothesized that early-life host-microbe cross-talk plays a role in this process. We therefore investigated viral presence, gene expression profiles and nasopharyngeal microbiota from birth until 12 months of age in 114 healthy infants. We show that the strongest dynamics in gene expression profiles occurred within the first days of life, mostly involving Toll-like receptor (TLR) and inflammasome signalling. These gene expression dynamics coincided with rapid microbial niche differentiation. Early asymptomatic viral infection co-occurred with stronger interferon activity, which was related to specific microbiota dynamics following, including early enrichment of Moraxella and Haemophilus spp. These microbial trajectories were in turn related to a higher number of subsequent (viral) RTIs over the first year of life. Using a multi-omic approach, we found evidence for species-specific host-microbe interactions related to consecutive susceptibility to RTIs. Although further work will be needed to confirm causality of our findings, together these data indicate that early-life viral encounters could impact subsequent host-microbe cross-talk, which is linked to later-life infections.

The amino acid selected for generating mutant TbpB antigens defective in binding transferrin can compromise the in vivo protective capacity.

Haemophilus parasuis is the causative agent of the Glässer's disease (GD), one of the most important bacterial diseases that affect young pigs worldwide. GD prevention based on vaccination is a major concern due to the limited cross-protection conferred by the inactivated whole cell vaccines used currently. In this study, vaccines based on two mutant recombinant proteins derived from transferrin binding protein B of H. parasuis (Y167A-TbpB and W176A-TbpB) were formulated and evaluated in terms of protection against lethal challenge using a serovar 7 (SV7) H. parasuis in a high susceptibility pig model. Our results showed that H. parasuis strain 174 (SV7) is highly virulent in conventional and colostrum-deprived pigs. The Y167A-TbpB and W176A-TbpB antigens were immunogenic in pigs, however, differences in terms of antigenicity and functional immune response were observed. In regard to protection, animals immunized with Y167A-TbpB antigen displayed 80% survival whereas the W176A-TbpB protein was not protective. In conjunction with previous studies, our results demonstrate, (a) the importance of testing engineered antigens in an in vivo pig challenge model, and, (b) that the Y167A-TbpB antigen is a promising antigen for developing a broad-spectrum vaccine against H. parasuis infection.

Safety and efficacy studies on trivalent inactivated vaccines against infectious coryza.

The safety and efficacy of an inactivated oil-emulsion infectious coryza vaccine containing three Avibacterium paragallinarum isolates (one each of Page serovars A, B, and C) was evaluated. The safety of six batches of the vaccine was confirmed by testing with chickens vaccinated with a single large dose or vaccinated repeatedly with a normal dose. Efficacy tests were carried out on three batches of vaccine using both specific pathogen free (SPF) chickens and conventional chickens. In SPF chickens given a single vaccination at 42 days of age, the protection rate against all three serovars of Av. paragallinarum was at least 80% at 30 days post vaccination. The conventional chickens, which were immunized at 42 and 110 days of age, were challenged at 9 months post the second vaccination and the protection rate was at least 80% for all three serovars. The effect of storage on the vaccine was evaluated in SPF chickens using three batches of vaccine stored at 4-8°C for 1 year. The protection rate against challenge from all three serovars (single vaccination at 42 days of age and challenge at 30 days post-vaccination) was at least 80%.

Divergent pro-inflammatory profile of human dendritic cells in response to commensal and pathogenic bacteria associated with the airway microbiota.

Recent studies using culture-independent methods have characterized the human airway microbiota and report microbial communities distinct from other body sites. Changes in these airway bacterial communities appear to be associated with inflammatory lung disease, yet the pro-inflammatory properties of individual bacterial species are unknown. In this study, we compared the immune stimulatory capacity on human monocyte-derived dendritic cells (DCs) of selected airway commensal and pathogenic bacteria predominantly associated with lungs of asthma or COPD patients (pathogenic Haemophillus spp. and Moraxella spp.), healthy lungs (commensal Prevotella spp.) or both (commensal Veillonella spp. and Actinomyces spp.). All bacteria were found to induce activation of DCs as demonstrated by similar induction of CD83, CD40 and CD86 surface expression. However, asthma and COPD-associated pathogenic bacteria provoked a 3-5 fold higher production of IL-23, IL-12p70 and IL-10 cytokines compared to the commensal bacteria. Based on the differential cytokine production profiles, the studied airway bacteria could be segregated into three groups (Haemophilus spp. and Moraxella spp. vs. Prevotella spp. and Veillonella spp. vs. Actinomyces spp.) reflecting their pro-inflammatory effects on DCs. Co-culture experiments found that Prevotella spp. were able to reduce Haemophillus influenzae-induced IL-12p70 in DCs, whereas no effect was observed on IL-23 and IL-10 production. This study demonstrates intrinsic differences in DC stimulating properties of bacteria associated with the airway microbiota.

Bactericidal monoclonal antibody against Moraxella catarrhalis lipooligosaccharide cross-reacts with Haemophilus Spp.

Monoclonal antibodies (MAbs) against lipooligosaccharide (LOS) determinants after immunization of BALB/c mice with heat inactivated Moraxella catarrhalis serotype A were generated. MAb 219A9 was specific for a common epitope of A, B, and C M. catarrhalis serotypes in ELISA and immunofluorescent test (IFT). In both tests it also cross-reacted with whole bacteria and LPS antigens isolated from non-typeable H. influenzae and H. parainfluenzae strains. IgM antibody clone 219A9 possessed a strong bactericidal effect against the three serotypes in the presence of complement. Our results demonstrate that antibodies directed to a single LOS epitope common for A, B, and C serotype could be highly protective. This suggests that the common determinants are very promising in the development of LOS-based vaccine against M. catarrhalis. The cross-reactions of MAb 219A9 with Haemophilus spp. also show that immunization could result in immune response to epitopes conserved in other important respiratory pathogens.

Bacterial capsular antigens. Structural patterns of capsular antigens.

Structural patterns of bacterial capsular antigens including capsular polysaccharides and exoglycans are given in this review. In addition, the immunological activity of capsular antigens and their role in type specificity of bacteria are discussed.

Rat strains differ in antibody response to natural Haemophilus species infection.

Antibody response to Haemophilus species in rat strains was monitored by enzyme-linked immunosorbent assay (ELISA) using antigens of two Haemophilus strains and a Pasteurella pneumotropica strain. Five rat strains from a breeding colony naturally infected by Haemophilus were significantly different in ELISA antibody activity and in the number of seropositive animals. BN and RP rats were (relatively) high and low responders, respectively and BUF, LEW and WAG rats were intermediate. In a second study, five rat strains were exposed to Haemophilus-infected rats, and, after six weeks, were also significantly different in ELISA antibody activity and in numbers of seropositive animals. Here, BN and LEW rats were (relatively) high and low responders, respectively, and BD IX, F344 and WKY rats were intermediate.

Penfigoide ampolloso en lactante tras vacunación / Bullous pemphigoid in an infant after vaccination

El penfigoide ampolloso es una enfermedad que característicamente afecta a personas de edad avanzada aunque se han descrito casos en niños. Presentamos un caso de penfigoide ampolloso en una lactante de 2 meses de vida con lesiones ampollosas en palmas y plantas, que aparecieron una semana después de recibir la primera dosis de la vacuna contra la hepatitis B, poliomielitis, difteria-tétanos-pertussis (DTP) y Haemophilus. Recibió tratamiento con agua sulfatada, dexametasona y ácido fusídico, con lo que desaparecieron las lesiones. Un mes después presentó un nuevo brote, más generalizado, a los 3 días de la segunda dosis de la misma vacuna. La erupción cutánea cedió por completo a los 3 meses de instaurar tratamiento con deflazacort (1 mg/kg/día). Tras 5 años de seguimiento, no ha vuelto a presentar lesiones a pesar de haber recibido el resto de vacunas del calendario oficial

Bullous pemphigoid (BP) is a disease that characteristically affects the elderly, although cases have been described in children. We present a case of BP in a twomonth- old infant with bullous lesions on the palms and soles, which appeared one week after receiving the first dose of the hepatitis B, polio, DTP and HiB vaccine. She was treated with sulphated water, dexamethasone and fusidic acid, and the lesions disappeared. One month later, she presented with a new, more generalized outbreak, three days after the second dose of the same vaccine. The skin eruption completely subsided 3 months after treatment with deflazacort was initiated (1 mg/kg/day). After five years of follow up, the patient has not presented with lesions again, despite having received the rest of the vaccines on the official schedule

Suppurative rhinitis associated with Haemophilus species infection in a cat.

A young cat with signs of chronic rhinitis was evaluated for underlying anatomical, inflammatory, or infectious disease. Initial diagnostics were significant for the isolation of an unusual pathogen, Haemophilus species. Isolation using a human RapID NH system erroneously identified the isolate as H. segnis, a human pathogen. No database of veterinary pathogens (Haemophilus) are included in the system and animal pathogens will either be erroneously identified or yield a unique biocode not listed. Because of the unique nature of the pathogen we explored the possibility of immunosuppression as a contributory factor to infection. A variety of laboratory tests were employed to evaluate immune function. The clinical indications and utility of immune function testing are discussed. No immune dysfunction was identified.

Efficacy of a new tetravalent coryza vaccine against emerging variant type B strains.

Outbreaks of infectious coryza have been reported in vaccinated flocks in different countries, indicating that new serotype(s) of Haemophilus paragallinarum may have evolved. Several field isolates from vaccinated flocks in the US, Ecuador, Argentina and Zimbabwe were examined and, apart from one serotype C strain, all were typed as serotype B. An inactivated commercial trivalent vaccine, containing serotypes A, B and C, protected against challenge with the serotype C isolate but protection against challenge with serotype B isolates was weaker, suggesting that they might represent a new variant immunotype. An experimental tetravalent oil adjuvant vaccine, containing one of the serotype B isolates, appeared immunogenic against all isolates after one vaccination. Its efficacy and safety were further tested in layer chickens housed under field conditions. Chickens were vaccinated at 8 and 16 weeks of age while controls were unvaccinated. Vaccinates and controls were challenged with type A, B, C and variant type B at 25, 45 or 65 weeks of age. There was good protection (P<0.05) against all four immunotypes after all challenges. No systemic reactions were observed and local reactions were similar to those found with the commercial trivalent vaccine. The tetravalent vaccine may therefore be a good choice for control of new field isolates.

Naturally-farrowed, artificially-reared pigs as an alternative model for experimental infection by Haemophilus parasuis.

The use of naturally-farrowed, artificially-reared piglets as an alternative model to study Haemophilus parasuis infections was evaluated. Two trials were performed in order to evaluate the proposed model. In trial 1, animals were vaccinated and challenged with H. parasuis. Results showed that the proposed model was effectively used to evaluate protective immunity against this organism. In trial 2, animals were challenged with different doses of H. parasuis. Results showed that the severity of clinical signs and lesions tended to increase with higher doses. The reproduction of clinical signs and lesions characteristic of H. parasuis systemic infection was successful in both trials, proving that this model is a viable alternative to specific-pathogen free and cesarean-derived, colostrum-deprived pigs.

The effect of season and vaccination for Glässer's disease and post-weaning Colibacillosis in an outdoor pig unit endemically infected with virulent strain of Haemophilus Parasuis serotype 5 and pathogenic Escherichia coli.

UNLABELLED: The objective of this field trial was to determine if vaccination against Haemophilus parasuis serovar 5 (HPS 5) and pathogenic serotypes of Escherichia coli would improve nursery pig performance in an outdoor unit in different seasons. The unit was concurrently infected with HPS 5 and with different serotypes of E. coli. All piglets were born to HPS 5 vaccinated sows. The trial was carried out in four (two summer and two winter) groups. Group 1 (E. coli and HPS vaccinated, summer season) (n = 362): Piglets were vaccinated pre-weaning with inactivated E. coli-VT2e-toxin and post-weaning against HPS 5. Group 2 (non-vaccinated, summer season) (n = 349): Piglets were not vaccinated. Group 3 (E. coli and HPS vaccinated, winter season) (n = 358): The animals were analogously treated as Group 1. Group 4 (non-vaccinated, winter season) (n = 353): Piglets were not vaccinated. The following parameters were evaluated: A: average daily nursery weight gain (ADG), B: nursery mortality, C: feed efficiency (FE). No significant weight differences were detected within the vaccinated and non-vaccinated summer or winter raised groups of weaners. Summer raised weaners were significantly (P<0.05) heavier from day 35 on than winter raised animals. ADG and FE of summer raised pigs were significantly better (weeks 1-3 P<0.05; fourth week post-weaning P<0.01) during the nursery period than that of the winter raised groups. Winter raised vaccinated weaners showed during the last week of nursing significantly (P<0.05) better daily gain and feed efficiency compared with the non-vaccinated winter raised animals. Non-significant ADG and FE differences were detectable between the summer raised vaccinated or non-vaccinated groups of pig. Winter raised non-vaccinated animals suffered significantly (P<0.05) higher nursery mortality (10.63%) compared to the winter raised vaccinated animals. IMPLICATION: In cases of concurrent infections with HPS 5 and with different serotypes of E. coli, especially during winter season, vaccination against both diseases is suggested.

Protection of vaccinated pigs against experimental infections with homologous and heterologous Haemophilus parasuis.

The efficacy of a new Haemophilus parasuis vaccine for pigs was investigated. The vaccine contains H parasuis serotype 5 cells and is adjuvanted with Diluvac Forte (Intervet). Groups of pigs were vaccinated at five and seven weeks with 2 ml and their littermates served as unvaccinated controls. The vaccinated pigs were protected against a challenge with another strain of Hparasuis serotype 5 at two, eight and 17 weeks after the second vaccination, whereas the controls became very ill. The susceptibility of the pigs to the infection decreased with increasing age. After a heterologous challenge with H parasuis serotypes 1, 12, 13 and 14, two weeks after the second vaccination, the vaccine also gave clear protection. The severity of the illness among the control pigs differed with the different serotypes.

Isolation of serovar C-3 Haemophilus paragallinarum from Zimbabwe: A further indication of the need for the production of vaccines against infectious coryza containing local isolates of H. paragallinarum.

Various isolates of Haemophilus paragallinarum, collected from a severe outbreak of infectious coryza in poultry from Zimbabwe, were serotyped and were found to belong to serovar C-3. Previously, isolates were serotyped using polyclonal antiserum produced against serogroup reference strains (0083 for serogroup A, 0222 for serogroup B and Modesto, or H-18 for serogroup C) of H. paragallinarum. In this case, polyclonal antiserum produced against these reference isolates were used, as well as polyclonal antiserum that has been raised specifically against the serovar C-3 isolate 46 C-3. When using the latter serum at a 1 in 50 dilution, no cross-reaction with other members of serogroup C were found. The severity of the disease outbreak in Zimbabwe, the vaccination history of the infected flocks on the sites and the isolation of the uniquely southern African serovar C-3, further highlights the need for vaccines composed of local isolates to control infectious coryza in regions where vaccination failures occur.

Incorporation of N-acetylneuraminic acid into Haemophilus somnus lipooligosaccharide (LOS): enhancement of resistance to serum and reduction of LOS antibody binding.

Haemophilus somnus isolates from cases of thrombotic meningoencephalitis, pneumonia, and other disease sites are capable of undergoing a high rate of phase variation in the oligosaccharide component of their lipooligosaccharides (LOS). In contrast, the LOS of commensal strains isolated from the normal reproductive tract phase vary little or not at all. In addition, the LOS of H. somnus shares conserved epitopes with LOS from Neisseria gonorrhoeae, Haemophilus influenzae, and other species that can incorporate sialic acid into their LOS. We now report that growth of disease isolates of H. somnus with CMP-N-acetylneuraminic acid (CMP-NeuAc) or NeuAc added to the medium resulted in incorporation of NeuAc into the LOS. However, NeuAc was not incorporated into the LOS of commensal isolates and one disease isolate following growth in medium containing CMP-NeuAc or NeuAc. Sialylated LOS was detected by an increase in the molecular size or an increase in the amount of the largest-molecular-size LOS electrophoretic bands, which disappeared following treatment with neuraminidase. Sialylated LOS could also be detected by reactivity with Limax flavus agglutinin lectin, which is specific for sialylated species, by dot blot assay; this reactivity was also reversed by neuraminidase treatment. H. somnus strain 2336 LOS was found to contain some sialic acid when grown in medium lacking CMP-NeuAc or NeuAc, although supplementation enhanced NeuAc incorporation. In contrast strain 738, an LOS phase variant of strain 2336, was less extensively sialylated when the growth medium was supplemented with CMP-NeuAc or NeuAc, as determined by electrophoretic profiles and electrospray mass spectrometry. The sialyltransferase of H. somnus strain 738 was confirmed to preferentially sialylate the Gal(beta)-(1-3)-GlcNAc component of the lacto-N-tetraose structure by capillary electrophoresis assay. Enhanced sialylation of the strain 2336 LOS inhibited the binding of monoclonal antibodies to LOS by enzyme immunoassay and Western blotting. Furthermore, sialylation of the LOS enhanced the resistance of H. somnus to the bactericidal action of antiserum to LOS. Sialylation and increased resistance to killing by normal serum also occurred in a deletion mutant that was deficient in the terminal Gal-GlcNAc disaccharide. LOS sialylation may therefore be an important virulence mechanism to protect H. somnus against the host immune system.

The effect of a homologous bacterin given to sows prefarrowing on the development of Glässer's disease in postweaning pigs after i.v. challenge with Haemophilus parasuis serotype 5.

UNLABELLED: The trial was carried out to evaluate the impact of maternal antibodies on the development of Glässer's disease after i.v. exposure of weaned pigs with a homologous serovar of Haemophilus parasuis (HPS). Two groups of weaned pigs were formed. Group one VI (n = 10): born to vaccinated sows, weaners i.v. challenged one week postweaning and euthanatized 14 days postweaning. Group two NVI (n = 10 wearners): born to non vaccinated sows, i.v. challenged one week postweaning euthanatized 14 days postweaning. One week postweaning all weaners were i.v. inoculated with HPS serovar 5. The following parameters were evaluated: clinical signs (depression, centralnervous signs, fever, lameness), macroscopic lung, pleura, peritoneum, liver and joint changes, and mortality. All trial sows were HPS seronegative prior to vaccination. The HPS vaccinated sows were proven seropositive on day 3 p.p. (values > 0.24), the non vaccinated ones were tested seronegative (values < 0.23). The progeny of sows vaccinated prefarrowing with two doses of HPS serovar 5 bacterin were partially protected against HPS caused clinical and pathological signs. The majority of clinical signs as fever, depression, recumbency, lack of response to verbal stimuli and lameness showed significant (P < 0.05) milder clinical symptoms in VI than in NVI animals. Respiratory signs (P = .169) and involvement of the central nervous system as ataxia, muscular tremor, incoordination of hind legs and convulsions (P = 1) showed no significant differences between the groups. Except lesions of pericard (VI vs. NVI, P = .14) and pleura (VI vs. NVI, P = .14) there were significant (P < 0.05) macroscopic differences at necropsy in lung, liver, joints and cerebrospinal fluid between the offspring of vaccinated sows and the ones of non vaccinated dams. No HPS were isolated from the nasal mucosa of the pigs prior to inoculation. HPS serovar 5 was recovered at necropsy from the nasal mucosa of all pigs in both groups. One pig from group VI presented in all examined organs the presence of HPS serovar 5. The remaining animals in group VI revealed in lung, pericard, pleura, liver, joints and cerebrospinal fluid no presence of HPS. The rate of isolation between VI and NVI groups revealed a significant (P < 0.05) difference. All the survived piglets of group NVI showed positive ELISA titres against HPS serovar 5 (values > .24). The piglets that died or were euthanatized before the end of the study have not been subjected to ELISA serological testing. One piglet died in group VI before the end of the study. Non of the remaining animals in group VI showed seroconversion to HPS serovar 5. IMPLICATIONS: Vaccination of sows did not influence the colonisation of nasal mucosa, but progeny of sows vaccinated prefarrowing with two doses of HPS serovar 5 bacterin were partially protected against HPS caused diseases.

Experimental nephropathy induced by Haemophilus parainfluenzae antigens.

BACKGROUND: We have demonstrated that outer membrane antigens of Haemophilus parainfluenzae (OMHP) are potentially involved in IgA nephropathy (IgAN). In this study, we established an experimental model of IgAN using OMHP antigens and investigated the nephritogenicity of OMHP antigens. METHODS: One hundred and twenty C3H/HeN mice were administered OMHP antigens orally (PO group) or intraperitoneally (IP group). Mice were sacrificed at 10, 20, 30, 40, and 50 weeks of age to examine sequential glomerular changes and to measure levels of IgG, IgA, and IgM antibody against OMHP by ELISA. RESULTS: Glomerular deposition of IgA and increases in the amount of mesangial matrix were observed in the PO group and the IP group from 40 and 30 weeks of age, respectively. Mice in both groups showed glomerular deposition of OMHP antigens from 30 or 40 weeks of age. Levels of IgA antibodies against OMHP were significantly increased in the PO and IP groups compared with controls. There was a significant correlation between mesangial proliferation and glomerular deposition of IgA. CONCLUSIONS: Administration of OMHP antigens to mice may induce glomerular deposition of IgA and mesangial proliferation, resembling the changes seen in IgAN, with increases in IgA antibodies against OMHP antigens. This is the first use of OMHP antigens to establish an active model of IgAN.

Haemophilus somnus bronchopneumonia in American bison (Bison bison).

Immunoperoxidase assays were performed on 21 archived formalin-fixed, paraffin-embedded tissues from from American bison (Bison bison) with bronchopneumonia. Seven of the 21 bison had positive staining for Haemophilus somnus in alveolar exudate, visceral pleura, lung parenchyma, and chronic necrotic lesions, and H. somnus was isolated from tissues from 1 of these 7 animals. Results suggest that H. somnus is a respiratory pathogen in bison.

Phosphorylcholine-dependent cross-reactivity between dental plaque bacteria and oxidized low-density lipoproteins.

Antibodies reactive with phosphorylcholine (PC) are ubiquitous in human sera, but the antigens stimulating their production and their function are not clear. Previous studies have shown that a significant proportion of dental plaque bacteria contain PC as determined by reactivity with PC-specific mouse myeloma proteins and monoclonal antibodies. Additionally, serum antibody concentrations of immunoglobulin (IgG) G anti-PC are higher in sera of individuals who have experienced periodontal attachment loss than those who are periodontally healthy. These data implicate the oral microflora as a source of antigen-stimulating anti-PC responses. Recent data also indicate that antibodies with specificity for PC are elevated in ApoE-deficient mice, a model for studies of athersclerosis, and that such antibodies bound oxidized low-density lipoproteins (LDL) (oxLDL) in atherosclerotic plaques. These data prompted the hypothesis that human anti-PC could bind to both oral bacteria and human oxLDL, and that these antigens are cross-reactive. We therefore examined the ability of human anti-PC to bind to PC-bearing strains of oral bacteria using enzyme-linked immunosorbent inhibition assays and by assessment of direct binding of affinity-purified human anti-PC to PC-bearing Actinobacillus actinomycetemcomitans. Our results indicated that PC-bearing strains of Streptococcus oralis, Streptococcus sanguis, Haemophilus aphrophilus, Actinomyces naeslundii, Fusobacterium nucleatum, and A. actinomycetemcomitans, as well as a strain of Streptococcus pneumoniae, absorbed up to 80% of anti-PC IgG antibody from human sera. Furthermore, purified anti-PC bound to a PC-bearing strain of A. actinomycetemcomitans but only poorly to a PC-negative strain. OxLDL also absorbed anti-PC from human sera, and oxLDL but not LDL reacted with up to 80% of the anti-PC in human sera. Furthermore, purified anti-PC bound directly to oxLDL but not to LDL. The data indicate that PC-containing antigens on a variety of common oral bacteria are cross-reactive with neoantigens expressed in oxLDL. We propose that PC-bearing dental plaque microorganisms may induce an antibody response to PC that could influence the inflammatory response associated with atherosclerosis.

The relationship between the occurrence of undifferentiated bovine respiratory disease and titer changes to Haemophilus somnus and Mannheimia haemolytica at 3 Ontario feedlots.

The association between exposure to Haemophilus somnus and Mannheimia haemolytica (formerly Pasteurella haemolytica) and the risk of undifferentiated bovine respiratory disease (UBRD) was investigated using serological evidence of exposure coupled with a factorial design vaccine field trial. Measures of previous exposure (titer at arrival) and current exposure (titer increase in the study period) to these agents were used. The vaccine field trial involved systematic allocation of animals into groups that received either a M. haemolytica vaccine, an H. somnus vaccine, a combined M. haemolytica and H. somnus vaccine, and an unvaccinated control group. Serum was collected from the 852 animals enrolled to determine titers to H. somnus, M. haemolytica, bovine coronavirus and bovine viral diarrhea virus. Vaccination with H. somnus in combination with M. haemolytica and with M. haemolytica alone reduced the risk of UBRD. The odds ratio for vaccination with H. somnus alone and UBRD risk suggested some sparing effect, but the 95% confidence limits included unity. There was no association between serological evidence of concurrent exposure to M. haemolytica and UBRD occurrence. There was an association between titer change to H. somnus and UBRD risk. However, the association changed with time of BRD treatment; animals diagnosed and treated for UBRD on or after day 10 showed little evidence of exposure to H. somnus, despite evidence of natural H. somnus exposure in the unvaccinated group. The association between titer change to H. somnus and UBRD occurrence seen in this study may be a consequence of prolonged exposure to antibiotics, rather than a causal association.