Serum Neutralizing Antibody Titers Research Articles

Vaccine therapy for ocular herpes simplex virus (HSV) infection: periocular vaccination reduces spontaneous ocular HSV type 1 shedding in latently infected rabbits

Periocular vaccination of rabbits with preexisting herpes simplex virus type 1 (HSV-1) latent infection with recombinant HSV-2 glycoproteins B and D (gB2 and gD2) plus adjuvant significantly reduced ocular viral shedding. Rabbits were infected in both eyes with HSV-1 strain McKrae. Following HSV-1 infection and the establishment of latency (28 days postinfection), rabbits were given a periocular subconjunctival vaccination three times at 3-week intervals. Beginning 3 weeks after the final vaccination, tear films were collected daily and cultured to detect the presence of HSV-1 and determine the spontaneous HSV-1 ocular shedding rates. Periocular vaccination increased the mean HSV-1 serum neutralizing antibody titer to fivefold above that seen in mock-vaccinated latently infected rabbits. gB enzyme-linked immunosorbent assay (ELISA) antibody titers were increased approximately 8-fold, and gD ELISA antibody titers were increased 60-fold. These increases were all statistically significant (P < 0.0001). In two independent experiments, vaccination reduced the spontaneous shedding rate by approximately 2.5-fold (P < 0.0004). In addition, the percentage of eyes that never shed virus during the 6 week postvaccination test period increased threefold (20% in controls versus 60% in vaccinated animals; P < 0.007). These results show that spontaneous ocular shedding of HSV-1 in latently infected rabbits can be significantly reduced by local periocular vaccination. This is the first report in any animal model of a successful therapeutic vaccine against recurrent HSV-1 ocular shedding. These results support the concept that development of a therapeutic vaccine for ocular HSV-1 recurrence in humans is possible.

Failure of Neutralizing Antibody to Regulate CAE Lentivirus Expression in Vivo

Sequential isolates of caprine arthritis-encephalitis lentivirus (CAEV) were obtained from clinically arthritic carpal joints of three Saanen goats between 36.4 and 44.9 months after infection with biologically cloned CAEV isolate 63. These virus isolates and the CAEV-63 inoculum were evaluated for neutralization by autologous sera. Neutralizing antibody to CAEV-63 persisted throughout the period of virus isolations. Five CAEV isolates from cell-free synovial fluid and six isolates from synovial fluid cells were neutralized by autologous sera at the time of virus isolation and up to 38.7 months prior to virus isolation. Comparison of serum neutralizing antibody titers for CAEV-63 and selected CAEV isolates demonstrated that neutralizing antibody responses were predominantly type-specific. Six virus isolates were resistant to neutralization by coincident autologous sera; however, neutralization assays using postisolation sera indicated that four of these isolates did not elicit detectable neutralizing antibody responses. Results indicate that (i) CAEV replication persists in the presence of neutralizing antibody and (ii) the neutralization phenotype of CAEV variants depends on the relative immunodominance of antigenically variable neutralization epitopes. We suggest that neutralizing antibody responses are a consequence of CAEV antigenic diversity and that variants are not selected based on resistance to neutralization. Enhancement of virus infectivity by nonneutralizing antibody is a possible mechanism of positive selection of antigenic variants.

Rabies in African wild dogs (Lycaon pictus) in the Serengeti region, Tanzania.

Rabies was confirmed as the cause of death of one African wild dog (Lycaon pictus) in the Serengeti region, Tanzania. One adult African wild dog in the same pack showed central nervous signs consistent with rabies infection. Inactivated rabies vaccine was administered intramuscularly to African wild dogs in two packs, by dart or by hand following anesthesia. These individuals comprised all known adults in the Serengeti National Park. In a limited study of seroprevalence of rabies antibody carried out at the time of vaccination, 3 of 12 African wild dogs sampled in the Serengeti had rabies serum neutralizing antibody titers before vaccination. Paired serum samples from two individuals sampled after vaccination showed increased antibody titers.

The effects of lobenzarit disodium, a novel immunomodulator, upon murine coxsackievirus B3 myocarditis.

The aim of this study is to test the therapeutic efficacy of immunomodulation with lobenzarit disodium (CCA) upon coxsackievirus B3 (CB3) myocarditis. Two-week-old C3H/He mice were inoculated with 10(3) plaque-forming units of CB3. CCA, 2.5 mg/kg per day, was administered subcutaneously daily on days 0-14 (Experiment I; group 2) and days 14-28 (Experiment II; group 4). Both treated groups were compared to infected controls (groups 1 and 3). For the analysis of splenic lymphocyte subsets, additional mice in untreated and treated groups were killed on day 7, and the percentages of Thy 1.2 (CD3), L3T4 (CD4) and, Ly 2 (CD8) subsets were analyzed by laser flow cytometry (Experiment III). In Experiment I, the survival rate did not differ significantly between groups 1 and 2. Cellular infiltration in the CCA group was less severe. Myocardial virus titers and serum neutralizing antibody titers did not differ significantly between the two groups. In Experiment II, the survival rates between the two groups did not differ significantly. Myocardial necrosis in the CCA group was less severe compared to the control. In Experiment III, the percentages of Thy 1.2 (CD3) and L3T4 subsets (CD4) of the treated group were significantly higher than those of the control group. Thus, CCA increased splenic T cells and improved cardiac pathology in acute murine CB3 myocarditis.

Immunopotentiation of bovine respiratory disease virus vaccines by interleukin-1 β and interleukin-2

Three experiments, using 85 crossbred beef calves, were conducted to evaluate the adjuvanticity of single, multiple, and combined doses of recombinant bovine IL-1 β (rBoIL-1 β) and recombinant bovine IL-2 (rBoIL-2), with a modified-live bovine herpesvirus-1/parainfluenza-3 (BHV-1/PI-3) virus vaccine and a killed bovine viral diarrhea (BVD) virus vaccine. Cytokines were administered intramuscularly at vaccination but at different injection sites. All cytokine treatments increased non-major histocompatibility complex (MHC)-restricted cytolytic capability of peripheral blood mononuclear cells (PBMC) against virus-infected target cells and serum neutralizing (SN) antibody titers to BHV-1 and BVD virus. Multiple, consecutive injections of rBoIL-2 generally showed the greatest adjuvant effect, and no additive effect was observed when rBoIL-1 β and rBoIL-2 were administered together. In a challenge experiment, calves were vaccinated with a modified-live BHV-1/PI-3 vaccine and infected with BHV-1 on Day 21. Cytokine-treated calves had higher SN antibody titers to BHV-1 than did the control calves at the time of challenge. Calves that were administered rBoIL-2 on 5 consecutive days shed less BHV-1 and had the highest SN antibody titer to BHV-1 (Day 28). These data suggest that rBoIL-1 β and rBoIL-2 may be useful immunoadjuvants for bovine respiratory disease virus vaccines.

Bovine respiratory syncytial virus protects cotton rats against human respiratory syncytial virus infection

Human respiratory syncytial virus (HRSV) is the most frequent cause of severe respiratory infections in infancy. No vaccine against this virus has yet been protective, and antiviral drugs have been of limited utility. Using the cotton rat model of HRSV infection, we examined bovine respiratory syncytial virus (BRSV), a cause of acute respiratory disease in young cattle, as a possible vaccine candidate to protect children against HRSV infection. Cotton rats were primed intranasally with graded doses of BRSV/375 or HRSV/Long or were left unprimed. Three weeks later, they were challenged intranasally with either BRSV/375, HRSV/Long (subgroup A), or HRSV/18537 (subgroup B). At intervals postchallenge, animals were sacrificed for virus titration and histologic evaluation. Serum neutralizing antibody titers were determined at the time of viral challenge. BRSV/375 replicated to low titers in nasal tissues and lungs. Priming with 10(5) PFU of BRSV/375 effected a 500- to 1,000-fold reduction in peak nasal HRSV titer and a greater than 1,000-fold reduction in peak pulmonary HRSV titer upon challenge with HRSV/Long or HRSV/18537. In contrast to priming with HRSV, priming with BRSV did not induce substantial levels of neutralizing antibody against HRSV and was associated with a delayed onset of clearance of HRSV upon challenge. Priming with BRSV/375 caused mild nasal and pulmonary pathology and did not cause exacerbation of disease upon challenge with HRSV/Long. Our findings suggest that BRSV may be a potential vaccine against HRSV and a useful tool for studying the mechanisms of immunity to HRSV.

Enhancement of coxsackievirus B3 myocarditis in mice by lobenzarit disodium through inhibition of splenic pan T cells

The aim was to test the efficacy of the immune system modulator lobenzarit disodium in the treatment of coxsackievirus B3 myocarditis. Two week old C3H/He mice were inoculated with 10(3) plaque forming units of coxsackievirus B3. Lobenzarit disodium, 25 mg.kg-1.d-1, was given subcutaneously daily on days 0-14 (experiment I; group 2) and days 14-28 (experiment II; group 4). Both treated groups were compared to infected controls for each experiment (groups 1 and 3). For the analysis of splenic lymphocyte subsets, additional mice in untreated and treated groups were killed on d 7, and the percentages of Thy 1.2 (CD3), L3T4 (CD4), Ly 2 (CD8) subsets were analysed by laser flow cytometry (experiment III). In experiment I, the survival rate in the lobenzarit treated group was significantly lower than in the controls (2/11 v 8/11). Cellular infiltration and myocardial necrosis in the lobenzarit group were more severe. Myocardial virus titres and serum neutralising antibody titres did not differ significantly between the two groups. In experiment II, the survival rate (7/9 v 13/13) and cardiac pathology between the two groups did not differ significantly. In experiment III, the percentage of the Thy 1.2 subset (CD3) in the treated group was significantly lower (p < 0.05) than in the control group, at 36.0(SD 2.9)% v 42.8(5.8)%. Lobenzarit disodium decreased splenic pan T cells and aggravated both clinical course and cardiac pathology in acute murine coxsackievirus B3 myocarditis.

Pilot evaluation of influenza virus vaccine (IVV) combined with adjuvant

The safety of licensed influenza virus vaccine (IVV) combined with a novel adjuvant containing muramyl tripeptide (MTP) conjugated to phosphatidylethanolamine (PE) was evaluated in a randomized pilot study. Ten healthy 23–30-year-old men were given a single intramuscular dose of IVV combined with saline ( n = 5) or with 100 μg of MTP PE in the MF59 adjuvant emulsion (MF59-100) ( n = 5). Evaluations were performed on days 0, 1, 2, 4, 7 and 28 after inoculation. IVV alone was well tolerated. All volunteers immunized with IVV/MF59-100 experienced moderate to severe local and systemic reactions which interfered with usual activities. Discomfort at the injection site was first noted at 2–6 h; induration (5/5), erythema (3/5), and regional adenopathy (3/5) persisted for up to 4 days. Systemic symptoms including chills (5/5), fever (3/5), nausea (3/5) and/or dizziness (2/5) developed within 12 h of inoculation and resolved by 48 h. Elevated white blood cell count (days 1 and 2), erythrocyte sedimentation rate and serum fibrinogen were transiently observed. Although peak serum neutralizing antibody titres versus influenza A/H3N2 and influenza B antigens were higher in the group given IVV with MF59-100, these unexpected reactions indicate that this dose of adjuvant is unsuitable for use in combination with this IVV.

Efeito pró-inflamatório do vírus da febre aftosa em cobaias imunes e não imunes

A estirpe O1Campos do vírus da febre aftosa (VFA) usada como agente indutor do teste de pleurisia foi capaz de desencadear um efeito pró-inflamatório em cobaias normais e imunes. A atividade pró-inflamatória do VFA, detectada em dois intervalos de pleurisia (24 e 48 horas) foi demonstrada, somente por quimiotaxia de leucócitos mononucleares (MN), no primeiro intervalo e por efeito edematogênico, migração de MN e polimorfonucleares (PMN), no último intervalo de reação. Os perfis de reação inflamatória induzida pelo VFA em cobaias imunes (imunizadas com vacinas oleosas anti-VFAO1Campos), aos 7 e aos 30 dias pós-vacinação (PV) apresentaram imensidades mais baixas do que as observadas em cobaias normais, embora nas cobaias com 7 dias de vacinação a quimiotaxia de leucócitos totais e de PMN tenha sido similar àquela encontrada nos animais normais, no intervalo de 48 horas de reação. Ademais, nas cobaias com 30 dias PV, o VFA induziu um aumento significante no volume de exsudato e na infiltração de MN, no intervalo de 24 horas, sendo que os valores de todos os parâmetros do exsudato inflamatório caíram a níveis normais, no segundo intervalo de reação. Nas cobaias imunes foi observada uma associação negativa entre o aumento no título de anticorpos soro-neutralizantes, de 7 para 30 dias PV e as intensidades dos parâmetros inflamatórios pleurais. O teste de pleurisia revelou-se um procedimento adequado para avaliar a atividade próinflamatória do VFA.

Evidence that Protection against Rotavirus Diarrhea after Natural Infection Is Not Dependent on Serotype-Specific Neutralizing Antibody

This case-control study sought to determine whether protection against clinically significant rotavirus diarrhea in children aged 4-35 months correlated with titers of serum neutralizing antibody and, if so, whether this protection was serotype-specific. Titers of acute-phase sera from 156 cases of treated rotavirus diarrhea in rural Bangladesh were contrasted with titers from 312 contemporaneously selected, age-matched controls. Analyses of the culture-adapted rotaviruses from the cases revealed that 24%, 15%, 43%, and 17% belonged to serotypes 1-4, respectively. Titers of both homologous and heterologous neutralizing antibody in acute blood specimens of cases were significantly lower than those of matched controls. However, multivariate logistic regression models demonstrated that only antibody titers to heterotypic rotaviruses were independently associated with protection against rotavirus disease. These data, which indicate that the correlation of protection with neutralizing antibody titers is not serotype-specific, suggest that immunity to rotavirus disease may be mediated by other factors.

Clinical evaluation of the efficacy of inoculating cattle with a vaccine containing Tritrichomonas foetus

Summary To test the efficacy of a polyvalent Tritrichomonas foetus vaccine, 130 nulliparous heifers were randomly assigned to either receive the test T foetus vaccine or to serve as nonvaccinated controls. The polyvalent test vaccine consisted of a Campylobacter fetus/Leptospira canicola-grippotyphosa-hardjo-icterohaemorrhagiae-pamona bacterine containing 5 × 107 killed T foetus/dose. The polyvalent control vaccine consisted of the aforementioned formulation without T foetus. Heifers were administered 2 doses of control or experimental vaccine at 3-week intervals. Heifers were bred to T foetus-infected bulls and their conception and pregnancy rates were determined throughout gestation. In addition, serum samples were analyzed to determine induced concentrations of antitrichomonal antibodies and vaginal secretions were sampled to determine T foetus infection rates in control and vaccinated animals. One week after each of the 15-day breeding periods, 60% (6 of 10) of tested vaccinates and 80% (8 of 10) of tested control animals were T foetus culture-positive. The mean duration of infection of vaccinates was 3.8 weeks (± 7.5 days), compared with 5.4 weeks (± 7.5 days) of infection for control heifers. All vaccinates developed increased immunofluorescence and serum neutralizing antibody titers following the first immunization, and had additional increases of at least fourfold in response to the second injection. In contrast, no consistent increase in immunofluorescence or serum neutralizing antibodies was observed in control animals. Conception rates were 89.2% for vaccinates and 85.9% for control animals 30 days after breeding and 80 to 90% of these remained pregnant 60 days after breeding. However, within the next 4 months, the pregnancy rate of control heifers decreased to 30% for those that had conceived. During the same 4-month period, more than 60% of vaccinated heifers remained pregnant. Significantly, 62.5% of heifers vaccinated against T foetus produced calves, whereas only 31.5% of control heifers produced calves. These findings indicate that the polyvalent test vaccine induced an immune response that was effective in lowering the rate of T foetus infection, decreasing the duration of infection, and reducing losses in calf production attributable to early fetal death and abortion caused by T foetus infection.

Effects of vaccination against 18 immunogens in beef replacement heifers at weaning

Summary Humoral immune responses to vaccination, mean daily body-weight gains, morbidity, and mortality were compared in groups of beef replacement heifers from weaning to 4 months after weaning. The only difference in management among groups of heifers was the number and type of vaccines they received. Heifers were vaccinated at weaning (mean age, 205 days) and again 28 days later against 0, 1,9, 10, 17, or 18 antigens, using commercially available monovalent and multivalent vaccines. The common vaccine component in all treatment groups was a modifed-live bovine respiratory syncytial virus. Mean daily gain, morbidity, mortality, and serum neutralization antibody titers to bovine respiratory syncytial virus did not differ among treatment groups. Although the study revealed the safety of vaccinating beef heifers against 18 antigens at weaning, our data emphasized the need for serial vaccination to induce a measurable serum antibody response.

Response of colostrum-deprived cynomolgus monkeys to intragastric challenge exposure with simian rotavirus strain SA11

Summary The infectivity and pathogenic potential of a cell culture-adapted simian rotavirus was evaluated in colostrum-deprived newborn and infant cynomolgus macaques (Macaca fascicularis). Intragastric challenge exposure with the simian rotavirus strain SA11 on postpartum day 2 induced diarrhea in 5 of 5 colostrum-deprived newborn monkeys. Compared with sham-inoculated controls, 3 of the 5 inoculated monkeys also manifested reduced body weight gain during the initial 5 days after challenge exposure. Rotavirus was detected in feces of 3 challenge-exposed monkeys for up to 2 days after inoculation. Evaluation of antibody response after rotavirus inoculation was obscured by high but variable prechallenge-exposure serum titers of rotavirus-specific antibody. Preexisting serum titer of neutralizing antibody in newborn monkeys was not predictive of clinical response to inoculation with rotavirus SA11. Two 90-day-old infant monkeys with low serum neutralizing antibody titer did not have diarrhea, reduced weight gain, or antibody response after oral inoculation with rotavirus SA11. Results of these challenge-exposure studies in newborn cynomolgus monkeys were consistent with a heterologous host-rotavirus model and indicate that neonatal serum antibody of maternal origin may not be associated with resistance to rotavirus-induced disease.

Evidence that active protection following oral immunization of mice with live rotavirus is not dependent on neutralizing antibody

Studies were performed to determine whether active immunity against murine rotavirus (EDIM) infection of mice correlated with titers of neutralizing antibody to the challenge virus. Neonatal mice administered either murine or heterologous rotaviruses all developed diarrhea and high titers of serum rotavirus IgG. However, only mice given EDIM, the murine EB, or simian SA11-FEM strains were protected against EDIM infection when challenged 60 days later. Other serotype 3 strains (RRV, SA11-SEM), as well as strains belonging to serotypes 5 and 6 (OSU, NCDV, WC3), were not protective. Serum neutralizing antibody titers to EDIM were almost undetectable after rotavirus infection with any strain and could not, therefore, be correlated with protection. Likewise, intestinal neutralizing antibody titers were extremely low 21 days after EDIM infection, and by 60 days after inoculation, EDIM-infected mice had no greater intestinal neutralizing antibody titers than uninoculated controls. Mice inoculated with SA11-FEM as neonates had much higher serum rotavirus IgG responses than mice inoculated as adults, and only those infected with this virus as neonates were protected. Thus, although immunity to EDIM did not correlate with the presence of neutralizing antibody to EDIM, it did correlate with the overall magnitude of the immune response after inoculation with SA11-FEM.

Immunologic responses in healthy random-source cats fed N,N-dimethylglycine-supplemented diets

Summary The immunomodulatory capacities of N,N-dimethylglycine (dmg) were examined in random-source cats. Blood mononuclear leukocytes of healthy adult cats that had negative results to tests for FeLV and feline immunodeficiency virus were exposed in vitro to various concentrations of dmg (10 to 1,000 μg/ml) and were evaluated for proliferative responses to T- or B-cell phytomitogens. Although increased, mean lymphocyte blastogenic responses to phytolectins in dmg-treated cultures did not differ significantly from responses of untreated cultures. For in vivo studies, cats were given a solution containing either 100 mg of dmg or a control solution without dmg orally at 8 am and 6 pm for 40 consecutive days. On posttreatment day 24 and 25, mean blastogenic responses to phytolectins in dmg-treated and control cats inoculated 10 days earlier with an inactivated feline virus vaccine were similar. Cats given dmg and inoculated twice in a 3-week interval with a commercial vaccine containing inactivated feline herpesvirus-1 and feline calicivirus had significantly (P = 0.045) lower virus neutralizing serum antibody titers against feline herpesvirus-1, compared with titers of control cats, whereas feline calicivirus titers were similar in both groups. On day 25, mean serum interferon activity, induced after iv inoculation of Newcastle disease virus, was significantly (P = 0.021) lower in the dmg-treated cats. Results of this study of dmg in healthy cats failed to demonstrate enhancement of either specific or nonspecific immunity.

Protective effect of serum antibody on respiratory infection of influenza C virus in rats

The effects of serum antibody on the replication of influenza C virus in the nose and lung were evaluated in rats challenged with the virus by the intranasal and endotracheal routes, respectively. Convalescent rat serum administered intraperitoneally prior to infection suppressed virus replication significantly in both the nasal and pulmonary tissues. Resistance achieved was however much greater in the lung than in the nose. Rats with a serum neutralizing antibody titer of 1:800 showed almost complete resistance to pulmonary virus infection, and virus yield from the lung was reduced 10- to 100-fold in animals with the antibody titer of 1:80-160 or less. In contrast, significant decrease in virus shedding from the nose was observed only in animals with a serum antibody titer of 1:800 or greater. The effect of adoptive transfer of monoclonal antibodies (MAbs) to haemagglutinin-esterase (HE) glycoprotein and matrix (M) protein on pulmonary virus replication was also examined. Anti-HE MAbs with neutralization activity prevented virus shedding from the lung almost completely whereas non-neutralizing anti-HE MAb and anti-M Mab showed no inhibitory effect.

Field Trials on a Live Bovine Respiratory Syncytial Virus Vaccine in Calves.

Field trials were carried out in calves using a live bovine respiratory syncytial (BRS) virus vaccine prepared from the attenuated BRS virus, strain rs-52. Two hundred seventy-five and 353 calves were vaccinated intranasally and intramuscularly, respectively. No undesirable postvaccinal reactions were observed in the vaccinated calves. Of the serum neutralizing (SN) antibody negative calves 89.7% (26/29) and 92.8% (90/97) developed SN antibody 1 month after intranasal and intramuscular vaccination, respectively. Most of the calves having SN antibody titers of 1:1 or 1:2 at the time of vaccination showed a significant increase in SN antibody titer. About 70% and 90% of the calves vaccinated intranasally and intramuscularly, respectively, maintained SN antibody for 6 months after vaccination. In a field trial, a natural BRS virus infection occurred about 5 months after the start of the trial. Ten of the 16 unvaccinated control calves showed respiratory symptoms due to BRS virus infection. On the contrary, all of the 68 vaccinated calves exhibited no symptoms at all, indicating efficacy of the vaccine.

A potency test method for foot and mouth disease vaccine based on the serum neutralizing antibody response produced in cattle.

A method is described for converting a mean serum neutralizing antibody titre after primary vaccination directly into a percentage protection value using a single regression slope. This has advantages over the indirect method in which a potency value is first estimated on the log antigen dose scale before conversion to a percentage protection value, since to do this requires the use of three separate regression slopes. Test designs for the serological method have been formulated that meet the 1975 Recommendations of the Office International des Epizooties, and which possess minimum potency standards at least as high as those of the European Pharmacopoeia's vaccine dose extinction endpoint method.

Experimental inoculation of raccoons (Procyon lotor) with rabies virus of skunk origin.

To determine raccoon (Procyon lotor) susceptibility and serum neutralizing antibody response to a skunk salivary gland rabies virus, raccoons were inoculated with a rabies virus isolated from a naturally-infected striped skunk (Mephitis mephitis). Raccoons were divided into four groups of three animals each. A dilution of the rabies virus suspension, 10(2.4), 10(3.4), or 10(4.8), mouse intracerebral lethal dose50 (MICLD50), was administered into the masseter muscles of each animal. Three negative control animals received only diluent. Saliva and sera were collected on post-inoculation days 35, 63 and 92 for virus isolation and determination of serum neutralizing antibody titer. All animals survived the 92 day observation period and none exhibited the behavioral changes classically associated with clinical rabies virus infections. Rabies virus was not detected in the saliva of any raccoon and two of the three animals receiving the highest inoculum developed serum neutralizing antibodies (SNA). On day 92, a challenge suspension of New York City/Georgia (NYC/GA) strain rabies virus in fox salivary glands (10(3.2) MICLD50) was administered to all 12 raccoons. All animals succumbed to rabies virus except the two animals that had earlier developed SNA. The results of this study provided evidence about the susceptibility of raccoons to a skunk rabies virus and demonstrated that exposed raccoons could survive for at least 92 days following exposure. Furthermore, animals developing SNA under such circumstances were capable of withstanding challenge with rabies virus that was fatal for seronegative raccoons.

Outbreaks in Quebec pig farms of respiratory and reproductive problems associated with encephalomyocarditis virus.

Encephalomyocarditis virus (EMCV) was isolated from tissues of aborted fetuses and weaned and suckling piglets from 4 different pig farms in Quebec. The farms were experiencing reproductive failure in sows of different parities concomitant to respiratory problems in suckling and postweaning piglets. At necropsy, gross lesions were confined to the lung and consisted of pulmonary congestion and edema of various degrees. Lesions of multifocal interstitial to proliferative pneumonia were found in the lungs of these piglets. Bacteriologic examination of various tissues from necropsied pigs yielded no pathogens in most cases. No significant antibody titers against 3 swine viruses (transmissible gastroenteritis virus, porcine parvovirus, and swine influenza virus) and two bovine viruses (bovine viral diarrhea and infectious bovine rhinotracheitis viruses) were detected in the sera of convalescent pigs. The Quebec EMCV isolates were antigenically related to the reference ATCC-VR129 strain of EMCV, as demonstrated by indirect immunofluorescence, serum neutralization (SN), and Western immunoblotting. However, one of the Quebec isolates could be distinguish by SN. EMCV-specific SN antibody titers up to 1:12,800 were detected in thoracic and ascitis fluids of aborted fetuses and in sera of convalescent pigs. A possible pneumotropic EMCV variant in swine may exist.