RESUMEN
REASON FOR PERFORMING STUDY: West Nile virus (WNV) infection is endemic and able to cause disease in naive hosts. It is necessary therefore to evaluate the safety of new vaccines. OBJECTIVES: To establish: 1) the safety of a modified live Flavivirus/West Nile virus (WN-FV) chimera by administration of an overdose and testing for shed of vaccine virus and spread to uninoculated sentinel horses; 2) that this vaccine did not become pathogenic once passaged in horses; and 3) vaccine safety under field conditions. METHODS: There were 3 protocols: 1) In the overdose/shed and spread study, horses were vaccinated with a 100x immunogenicity overdose of WN-FV chimera vaccine and housed with sentinel horses. 2) A reversion to virulence study, where horses were vaccinated with a 20x immunogenicity overdose of WN-FV chimera vaccine. Horses in both studies were evaluated for abnormal health conditions and samples obtained to detect virus, seroconversion and dissemination into tissues. 3) In a field safety test 919 healthy horses of various ages, breeds and sex were used. RESULTS: Vaccination did not result in site or systemic reactions in either experimental or field-injected horses. There was no shed of vaccine virus, no detection of vaccine virus into tissue and no reversion to virulence with passage. CONCLUSIONS: WN-FV chimera vaccine is safe to use in horses with no evidence of ill effects from very high doses of vaccine. There was no evidence of reversion to virulence. In addition, administration of this vaccine to several hundred horses that may have been previously exposed to WNV or WNV vaccine resulted in no untoward reactions. POTENTIAL RELEVANCE: These studies establish that this live attenuated Flavivirus chimera is safe to use for immunoprophylaxis against WNV disease in horses.
Asunto(s)
Anticuerpos Antivirales/sangre , Enfermedades de los Caballos/prevención & control , Vacunas Atenuadas/efectos adversos , Fiebre del Nilo Occidental/veterinaria , Vacunas contra el Virus del Nilo Occidental/efectos adversos , Virus del Nilo Occidental/inmunología , Animales , Quimera , Relación Dosis-Respuesta Inmunológica , Heces/virología , Femenino , Enfermedades de los Caballos/epidemiología , Enfermedades de los Caballos/transmisión , Caballos , Masculino , Seguridad , Factores de Tiempo , Vacunas Atenuadas/administración & dosificación , Vacunas Atenuadas/inmunología , Virulencia , Fiebre del Nilo Occidental/epidemiología , Fiebre del Nilo Occidental/prevención & control , Fiebre del Nilo Occidental/transmisión , Vacunas contra el Virus del Nilo Occidental/administración & dosificación , Vacunas contra el Virus del Nilo Occidental/inmunología , Virus del Nilo Occidental/patogenicidadRESUMEN
REASON FOR PERFORMING STUDY: West Nile virus (WNF) is a Flavivirus responsible for a life-threatening neurological disease in man and horses. Development of improved vaccines against Flavivirus infections is therefore important. OBJECTIVES: To establish that a single immunogenicity dose of live Flavivirus chimera (WN-FV) vaccine protects horses from the disease and it induces a protective immune response, and to determine the duration of the protective immunity. METHODS: Clinical signs were compared between vaccinated (VACC) and control (CTRL) horses after an intrathecal WNV challenge given at 10 or 28 days, or 12 months post vaccination. RESULTS: Challenge of horses in the immunogenicity study at Day 28 post vaccination resulted in severe clinical signs of WNV infection in 10/10 control (CTRL) compared to 1/20 vaccinated (VACC) horses (P<0.01). None of the VACC horses developed viraemia and minimal histopathology was noted. Duration of immunity (DPI) was established at 12 months post vaccination. Eight of 10 CTRL exhibited severe clinical signs of infection compared to 1 of 9 VACC horses (P<0.05). There was a significant reduction in the occurrence of viraemia and histopathology lesion in VACC horses relative to CTRL horses. Horses challenged at Day 10 post vaccination experienced moderate or severe clinical signs of WNV infection in 3/3 CTRL compared to 5/6 VACC horses (P<0.05). CONCLUSIONS: This novel WN-FV chimera vaccine generates a protective immune response to WNV infection in horses that is demonstrated 10 days after a single vaccination and lasts for up to one year. POTENTIAL RELEVANCE: This is the first USDA licensed equine WNV vaccine to utilise a severe challenge model that produces the same WNV disease observed under field conditions to obtain a label claim for prevention of viraemia and aid in the prevention of WNV disease and encephalitis with a duration of immunity of 12 months.
Asunto(s)
Anticuerpos Antivirales/sangre , Enfermedades de los Caballos/prevención & control , Vacunas Atenuadas/inmunología , Fiebre del Nilo Occidental/veterinaria , Vacunas contra el Virus del Nilo Occidental/inmunología , Virus del Nilo Occidental/inmunología , Animales , Quimera , Relación Dosis-Respuesta Inmunológica , Femenino , Enfermedades de los Caballos/epidemiología , Caballos , Masculino , Distribución Aleatoria , Seguridad , Índice de Severidad de la Enfermedad , Factores de Tiempo , Resultado del Tratamiento , Vacunas Atenuadas/administración & dosificación , Vacunas Atenuadas/efectos adversos , Viremia/veterinaria , Virulencia , Fiebre del Nilo Occidental/epidemiología , Fiebre del Nilo Occidental/prevención & control , Vacunas contra el Virus del Nilo Occidental/administración & dosificación , Vacunas contra el Virus del Nilo Occidental/efectos adversos , Virus del Nilo Occidental/patogenicidadRESUMEN
The ability of pseudorabies virus (PrV) to down-modulate expression of major histocompatibility complex class I antigens in murine and porcine cells was investigated. When quantified by flow cytometry, surface expression of class I Kk and Dk antigens on PrV-infected cells decreased by 60% or more. Down-modulation was associated with a decrease in total cellular class I antigens, indicating regulation at the transcriptional or posttranscriptional level. PrV did not suppress expression of transferrin receptor, suggesting a selective regulatory mechanism.
Asunto(s)
Regulación hacia Abajo , Herpesvirus Suido 1/fisiología , Antígenos de Histocompatibilidad Clase I/inmunología , Animales , Herpesvirus Suido 1/genética , Tolerancia Inmunológica , Rabia/inmunología , Receptores de Transferrina/inmunología , Transcripción GenéticaRESUMEN
A monoclonal antibody specific for the gI glycoprotein of virulent pseudorabies virus was produced and used to affinity purify gI glycoprotein. The purified gI was used in an enzyme-linked immunosorbent assay (ELISA) that identified and differentiated field virus-exposed animals from animals vaccinated with gI-deleted virus. The gI ELISA was evaluated by comparing it with the virus neutralization test and with a standard ELISA which does not distinguish between vaccinated and naturally infected animals. Pigs vaccinated with a gI-deleted vaccine were seropositive by the virus neutralization or standard ELISA but were seronegative in the gI ELISA. Nonvaccinated and vaccinated animals were detected as seropositive in the gI ELISA only after exposure to gI-containing field virus. Exposed animals were detected as early as day 7 and for as long as 141 days after field virus exposure. As little as 10(2.7) PFU of field virus was sufficient to seroconvert negative animals in the gI ELISA. Pseudorabies virus-seronegative animals which received multiple doses of gI-deleted vaccine remained seronegative in the gI ELISA. The use of this test to monitor swine for pseudorabies virus infection would offer significant benefits towards eradication of the disease.
Asunto(s)
Seudorrabia/diagnóstico , Enfermedades de los Porcinos/diagnóstico , Proteínas del Envoltorio Viral/inmunología , Animales , Anticuerpos Antivirales/aislamiento & purificación , Antígenos Virales/aislamiento & purificación , Línea Celular , Ensayo de Inmunoadsorción Enzimática , Herpesvirus Suido 1/inmunología , Seudorrabia/inmunología , Seudorrabia/prevención & control , Porcinos , Enfermedades de los Porcinos/inmunología , Enfermedades de los Porcinos/prevención & control , Proteínas del Envoltorio Viral/aislamiento & purificación , Vacunas Virales/farmacologíaRESUMEN
Quantitative enzyme-linked antibody centrifuge (ELAC) assays have been developed for measuring Escherichia coli adhesion pilus antigens K99, K88, 987P and F41 in E. coli bacterins used for protecting newborn animals against neonatal enteric colibacillosis. The test consists of reacting an alkaline phosphatase conjugate of specific pilus antigen antibody directly with dilutions of the bacterin on test and a standard reference bacterin. Following incubation the unbound conjugate is removed by two centrifugation steps and the bacteria with bound conjugate are reacted with substrate. The optical density is measured at 405 nm. Unknown samples are compared to a standard bacterin known to develop sufficient immunity in sows to provide protective levels of passive maternal immunity to their piglets. A relative potency (RP) value is calculated and used for standardizing bacterial concentrates and for final potency testing. The advantages to be realized are: shortening of the test period, specificity, and reduction in test animal usage.
Asunto(s)
Antígenos Bacterianos/análisis , Vacunas Bacterianas/normas , Escherichia coli/inmunología , Fimbrias Bacterianas/inmunología , Animales , Animales Recién Nacidos , Infecciones por Escherichia coli/prevención & control , Infecciones por Escherichia coli/veterinaria , Técnicas para Inmunoenzimas , PorcinosRESUMEN
Bacterial ability to obtain iron in bovine serum or in media containing transferrin (Tr) or conalbumin (Ca) was investigated by using serum-resistant (virulent) and serum-sensitive (avirulent) strains of Escherichia coli and Salmonella typhimurium. Bacteria growing in bovine serum enriched with radioactive iron-saturated Tr or with radioactive iron-saturated enterobactin (E) did not acquire radioactive iron. It has been found that the passage of siderophore (Si)-iron complexes into bacteria is blocked in serum by Tr and in Ca-containing medium by Ca. The investigation of bacterial ability to take iron in synthetic media showed that bacteria take in Si-bound but no Tr-bound radioactive iron. In the absence of free iron, the growth of serum-exposed virulent bacteria was supported by their stored iron. Virulent bacteria passaged in medium void of usable iron became depleted in stored iron and did not grow in animal sera unless sera were enriched by the addition of exogenous iron. Experiments with serum-exposed avirulent bacteria showed that their growth in Si-enriched serum should not be attributed to the iron-providing activity of Si but to the stimulating effect of Si which facilitates the use of stored iron. As distinct from avirulent bacteria, virulent bacteria used stored iron without the stimulating activity of extracellular Si.
Asunto(s)
Escherichia coli/crecimiento & desarrollo , Hierro/metabolismo , Salmonella typhimurium/crecimiento & desarrollo , Sangre , Medios de Cultivo , Enterobactina/metabolismo , Escherichia coli/metabolismo , Ácidos Hidroxámicos/metabolismo , Radioisótopos de Hierro , Piperazinas/metabolismo , Salmonella typhimurium/metabolismo , Transferrina/metabolismo , VirulenciaRESUMEN
Two smooth and six rough strains of Salmonella typhimurium with progressively smaller amounts of sugar and protein in their outer membrane were tested for degree of virulence in normal and iron-injected mice and for ability to acquire iron in mammalian sera. The rate of mortality showed that bacterial virulence for mice was lowered with progressive decrease of outer-membrane sugar and protein. Iron injections increased the rate of mortality in mice infected either with smooth strains or with superficially rough strains but were without effect in mice infected with deep rough strains. In in vitro experiments, iron promoted with equal effectiveness the growth of all serum-exposed bacterial strains, whereas enterobactin (E) was much more effective in promoting the growth of smooth and superficial rough than in promoting that of deep rough strains. Various experiments showed that deep rough strains cannot grow in E-supplemented serum because they are not able to use the transferrin-iron-E complexes that E forms with transferrin-iron. This failure to use transferrin-iron-E complexes by deep rough strains was found to be due to the inability of these strains to absorb iron containing complexes to their outer membrane. Adsorption studies with chemically treated bacteria showed that the receptor of transferrin-iron-E or E-iron complexes is a protein of the outer membrane of bacterial cells.