Safety and efficacy of the avirulent Mycoplasma gallisepticum strain K5054 as a live vaccine in poultry

A Mycoplasma gallisepticum (MG) isolate from an atypically mild outbreak in turkey breeders was found to be similar to house finch isolates by DNA analyses. A preliminary study in turkeys showed that this isolate (K5054) caused very mild lesions and protected turkeys against subsequent challenge with a virulent MG strain. In this study, K5054 was further evaluated as a potential vaccine strain in commercial layer-type chickens and turkeys. The safety of K5054 was evaluated by aerosol challenge followed by evaluation of gross and histopathologic lesions as well as serologic reactions and isolation of MG from the trachea and air sacs. Infection of chickens (trial 1) and turkeys (trial 2) with K5054 resulted in little evidence of MG lesions. There was weak seroconversion, and K5054 was consistently reisolated from the tracheas of chickens and turkeys. The efficacy of K5054 as a vaccine was evaluated by aerosol challenge of vaccinated chickens (trial 3) and turkeys (trial 4) with virulent R strain. There was evidence of protection from lesions associated with MG.     

Safety and efficacy of the Mycoplasma synoviae MS-H vaccine in turkeys

The live, attenuated, temperature-sensitive Mycoplasma synoviae (MS) vaccine strain MS-H is used to control virulent MS infection in commercial chicken flocks. However, the safety of this vaccine and its potential to prevent disease in turkeys have not been investigated. In this study, MS-H was shown to colonize the upper respiratory system and to induce an antibody response in turkeys but, even at the maximum release dose, was not found to cause air sac, joint, or tracheal lesions typical of wild-type MS infection. Histopathologic examinations of the vaccinated turkeys after exposure to a virulent MS challenge revealed that administration of the vaccine by aerosol, but not eye drop, at the dose recommended for chickens protected the birds against microscopic lesions and colonization of the virulent MS in trachea. It is concluded that MS-H vaccine is safe for use in turkeys and, when used as aerosol at the dose recommended for commercial chickens, can protect turkeys against tracheal lesions caused by a wild-type MS strain.     

Pathogenic effects on domestic poultry of a mycoplasma gallisepticum strain isolated from a wild house finch

Mycoplasma gallisepticum (MG) has been isolated from wild house finches. The pathogenic effects of MG finch strain (K4058) and MG R-strain were compared after exposure of chickens and turkeys. Gross and histologic lesions, reisolation of the organism, serology, and clinical disease were evaluated. Milder histologic and gross lesions, in addition to lower serologic titers, occurred in birds inoculated with the finch strain. Mortality, concurrent with clinical and gross respiratory signs and lesions, was observed only in chickens challenged with R-strain. Both the MG finch strain and MG R-strain were recovered from the respective challenge groups at 14 and 28 days postexposure. The results show that MG isolated from wild house finches may infect domestic poultry species but causes only mild disease and is less virulent than MG R-strain. Commercial enzyme-linked immunosorbent assay kits best detected the serologic response of chickens and turkeys to the MG finch strain.     

Experimental infection of chickens and turkeys with Mycoplasma gallisepticum reference strain S6 and North Carolina field isolate RAPD type B

During an epidemic of mycoplasmosis in chicken and turkey flocks in North Carolina between 1999 and 2001, isolates of Mycoplasma gallisepticum (MG) from affected flocks were characterized by random amplification of polymorphic DNA (RAPD), and eight distinct RAPD types were identified. MG RAPD type B accounted for more than 90% of the isolates and was associated with moderate-to-severe clinical signs and mortality. The virulence of MG RAPD type B for chickens and turkeys was compared with sham-inoculated negative controls and MG S6 (a virulent strain)-inoculated positive controls. Clinical signs occurred in chickens and turkeys inoculated with either MG RAPD type B or MG S6. However, they were not as frequent or severe as those seen in naturally affected flocks, and there was no mortality in the experimental groups. Based on gross and microscopic findings, MG RAPD type B was equal to or more virulent than MG S6. All MG-inoculated birds were culture and PCR positive at 7 and 14 days postinoculation (PI). Among serological tests, the serum plate agglutination test was positive for the majority of chickens and turkeys (58%-100%) infected with either strain of MG at both 7 and 14 days PI. The hemagglutination inhibition test was negative for all birds at 7 days PI and positive for a few chickens (8%-17%) and several turkey sera (40%-60%) at 14 days PI. Only a single serum was positive by enzyme-linked immunosorbent assay (an MG S6-infected turkey) at 14 days PI.     

Virulence of Mycoplasma synoviae strains in experimentally infected broiler chickens

Seven field isolates of German origin and the type strain WVU 1853 of Mycoplasma synoviae (MS) were experimentally investigated for their virulence in mycoplasma-free broiler chickens. Two groups of birds were inoculated at 6 days of age with each isolate, one group into the thoracic air sac and the other group intravenously and all surviving birds were examined at necropsy 17 days post inoculation (pi). Groups of negative control birds received sterile Frey's broth medium by intravenous and intra-air sac inoculation, respectively. Variation in virulence was evaluated on the basis of significant differences in incidence, severity and extend of MS-induced airsacculitis and synovitis as well as isolation rates of MS especially from parenchymous organs. All the strains tested were pathogenic but varied in their virulence for broiler chickens. Based on differences of the virulence, the isolates were classified to the categories: (1.) highly virulent, (2.) virulent, (3.) moderately virulent and (4.) slightly virulent. (1) Strains WVU 1853 and 246-91 induced a systemic disease associated with multiple synovitis and bilateral airsacculitis (2) Strains 93-92 and 151-77 induced bilateral airsacculitis similar to WVU 1853 and 246-91 but rarely a systemic disease after exposure by intra-thoracic airsac inoculation. (3) In comparison, strains 27-79, 76-93 and 513-83 caused less frequently airsacculitis and even if, then only at the side of intra-airsac exposure. (4) Strain 91-93 has been found to differ significantly from all the other isolates in its capacity to produce disease independently from the inoculation route. After intravenous inoculation, findings gave no indications for strains with selective tropism to the epithelial membranes of the lower respiratory tract or to those of the joints, tendon sheaths and bursae. However, the presented data of the experiments suggest that the MS strains tested differ in their potential capacity to invade systemically and produce acute septicaemia.     

Pathogenicity of two strains of Mycoplasma gallisepticum in broilers

Strains F and R of Mycoplasma gallisepticum (MG) were compared in two laboratory trials for their relative pathogenicity in terms of inducing airsacculitis and antibody production to MG. Chickens exposed to the R strain had significantly higher incidence of air-sac lesions (P less than 0.05) and greater severity of airsacculitis than did chicks exposed to the F strain. In both trials, chickens vaccinated simultaneously with Newcastle disease-infectious bronchitis vaccine and exposed to MG had more severe lesions than did chickens exposed to mycoplasma alone. chickens exposed to the F strain had significantly lower geometric mean hemagglutination-inhibition antibody titers to MG than did chicks exposed to the R strain. Chickens vaccinated simultaneously with Newcastle disease-infectious bronchitis vaccine and exposed to R strain had significantly lower body weights than did chickens in the other group.     

Pulmonary clearance and lesions of lung and air sac in passively immunized and unimmunized turkeys following exposure to aerosolized Escherichia coli

Two groups of young turkeys, one passively immunized with homologous hyperimmune serum and the other unimmunized but receiving normal turkey serum, were aerosolized with Escherichia coli. Clearance of bacteria from lung and gross and microscopic lung and air-sac lesions were determined after necropsy at timed intervals. The group mean bacterial count in lungs of passively immunized turkeys was significantly less than the mean count in unimmunized turkeys. Lung lesions were generally similar in both groups and were focused in lymphoid nodules, at the junction of primary and secondary bronchi, and at the ostia to the air sacs. Unimmunized birds developed grossly evident purulent airsacculitis by 72 hours after aerosol exposure, whereas passively immunized birds did not.     

Prophylactic efficacy of 3-acetyl-4'-isovaleryl tylosin in a Mycoplasma gallisepticum-induced airsacculitis infection

Formulations of 3-acetyl-4'-isovaleryl tylosin (AIV) were evaluated for oral efficacy in a Mycoplasma gallisepticum (MG) airsacculitis infection. AIV administered by gavage, feed, or water was more effective than tylosin in preventing airsacculitis. An AIV tartrate formulation administered in drinking water to chickens infected with a macrolide-sensitive or macrolide-resistant strain of MG resulted in no detection of mycoplasma in the air sacs and in MG-negative sera.     

Serum resistance and virulence of Escherichia coli isolated from turkeys

Twenty-five strains of Escherichia coli isolated from turkeys were characterized for their serum resistance and virulence. An in vitro bactericidal assay was used to determine the serum resistance of E coli. Virulence was determined by survival time after IV inoculation of each strain into 3-week-old turkeys. Serum-resistant E coli strains were generally found to be virulent for turkeys, whereas serum-sensitive E coli strains were avirulent. Of the 25 strains, 18 strains were placed in the 2 categories of serum-resistant/virulent and serum-sensitive/avirulent. Five strains were serum-resistant and avirulent, and 2 strains were serum-sensitive and virulent. Serum resistance appears to be an important determinant of virulence for E coli in turkeys; however, the requirement for other virulence factors, in addition to serum resistance, was suggested by the finding that 5 serum-resistant strains were avirulent in turkeys.     

Experimental Escherichia coli respiratory infection in broilers

This study determined optimal conditions for experimental reproduction of colibacillosis by aerosol administration of avian pathogenic Escherichia coli to 2-to-4-wk-old broiler chickens. The basic model for reproducing disease was intranasal administration of approximately 10(4) mean embryo infectious dose of infectious bronchitis virus (IBV) followed by aerosol administration of an 02 or an 078 strain of E. coli in a Horsfall unit (100 ml of a suspension of 10(9) colony-forming units/ml over 40 min). Scores were assigned to groups of infected chickens on the basis of deaths; frequency and severity of lesions in the air sacs, liver and heart; and recovery of the challenge E. coli 6 days post-E. coli infection. An interval of 4 days between the IBV and E. coli challenges was best whether the chickens received the IBV at 8 or 20 days of age. Typically, 50%-80% of the chickens developed airsacculitis and 0 to 29% of the chickens developed pericarditis or perihepatitis, with little or no mortality. Escherichia coli alone resulted in no deaths and 0 to 20% airsacculitis, but these percentages increased to 0 to 5% and 52%-60% when the E. coli aerosol was administered through a cone-shaped chamber. Administration of IBV alone failed to induce lesions. Recovery of the challenge E. coli from chickens did not correlate well with lesions. On the basis of these data, administration of IBV to 20-day-old chickens followed 4 days later by exposure to an avian pathogenic E. coli reproduces avian colibacillosis with the low mortality, high percentage of airsacculitis, and low percentage of septicemic lesions characteristic of the conditions seen in the natural disease.     

Isolation and characterization of Ornithobacterium rhinotracheale from chickens in Brazil

Ornithobacterium rhinotracheale (ORT) is a recently described species of bacterium associated with respiratory disease, growth retardation, mortality, and decreased egg production in chickens and turkeys. Pneumonia, pleuritis, and airsacculitis characterise the infection. ORT has been isolated in many countries but it is still considered exotic in Brazil. Up to date it is prohibited to import and produce reagents for diagnostic and vaccination control. The aim of this study was to isolate and identify the bacteria in chickens. Four isolates were obtained from tracheal swabs of broilers. They were isolated in blood agar with gentamicin and showed biochemical, morphological, antigenic and genetic characteristics of ORT. The results confirm that ORT is present in Brazil.     

Virulence and toxigenicity of capsular serogroup D Pasteurella multocida strains isolated from avian hosts

Five capsular serogroup D strains of Pasteurella multocida isolated from avian hosts were examined for virulence and toxigenicity. Virulence was based on development of lethal infections or lesions following intramuscular exposure of turkey poults. The four strains isolated from turkeys varied from slightly to moderately virulent; the strain isolated from a chicken was avirulent. Poults exposed by intra-airsac inoculation with relatively few organisms of the more virulent of the strains had a high mortality rate; however, intranasal exposure of poults with this strain did not cause clinical disease or establish infections. All strains from turkeys were toxigenic, producing heat-labile toxins that killed poults when administered intraperitoneally and caused focal dermal lesions when administered intradermally. Using these criteria, the strain from a chicken was not toxigenic. The demonstration of virulence, particularly the high mortality in poults exposed via air sacs, indicates avian capsular serogroup D strains are a potential cause of fowl cholera.     

Characterization of a naturally occurring infection of a Mycoplasma gallisepticum house finch-like strain in turkey breeders

An outbreak of Mycoplasma gallisepticum (MG) in commercial turkeys involving very mild clinical signs was difficult to confirm by routine methods. In the first part of this study (trial A), we conducted a bioassay to increase the likelihood of detecting MG. Susceptible turkeys were inoculated with sinus exudates from four different affected commercial turkey flocks. Turkeys were evaluated for clinical signs, as well as by serology and culture of tracheal swabs, at 21 and 42 days postchallenge. An MG isolate from one of the sinus exudates used for inoculation, designated K5054, was very similar to isolates from house finches when characterized by random amplified polymorphic DNA analysis as well as DNA sequence analysis of portions of the phase-variable putative adhesin protein (pvpA) gene, a lipoprotein gene, and the cytadhesin gapA/mgc1 gene. The turkeys inoculated with the K5054 sinus exudate seroconverted in the absence of severe clinical signs. There was a single reisolation of K5054 from these turkeys 42 days postchallenge. Susceptible contact turkeys were commingled with the K5054-inoculated turkeys at 49 days postchallenge. We found no evidence of transmission of MG to the contacts by culture or serology at 7, 21, or 35 days after commingling. In the second part of this study (trial B), we challenged the contacts and K5054 sinus exudate-inoculated turkeys from trial A with virulent R strain 88 days after the K5054 sinus exudate inoculation. On necropsy 10 days postchallenge, the evaluation of gross and microscopic lesions, serology, and culture showed that the turkeys previously inoculated with K5054 sinus exudate were protected against disease and reinfection.     

Attenutated live fowl cholera vaccine. III. Laboratory and field vaccination trials in turkeys and chickens

Administered via the drinking water, M-3-G, an attenuated strain of Pasteurella multocida of serotype 1, was found to immunize turkeys and chickens against fowl cholera. Immunity was tested by challenging birds intramuscularly, by palatine cleft swab, or orally after 3 vaccinations. No reactions to vaccination were noted in 390 turkeys in 12 laboratory trials, nor in 20,245 vaccinated in field trials. Chickens showed no vaccination reactions, and immunity was elicited by challenge in a laboratory trial and in face of natural outbreaks in the field, where 11,600 chickens were vaccinated. No vaccination reactions were noted, although most birds involved in the trials were carrying Mycoplasma spp. Immunity was found to last about 10 weeks after the last vaccination. The immunizing properties of M-3-G are compared with the CU strain.     

Safety of temperature sensitive mutant Mycoplasma gallisepticum vaccine

A temperature sensitive (ts) vaccine strain designated ts-11 was selected after exposure of a low passage culture of the immunogenic Australian field isolate (strain 80083) of Mycoplasma gallisepticum to 100 mg/ml of N-methyl-N-nitro-N-nitrosoguanidine. Viable counts (assayed as colour changing units (CCU)/25 microliters) of a thawed stock culture of ts-11 were typically log10 3 to log10 5 higher when incubated at 33 degrees C (the permissive temperature) than duplicate viable counts incubated at 39.5 degrees C (the restrictive temperature). Doses of approximately 2 x 10(7) CCU of ts-11 caused no gross lesions or loss of egg production when inoculated into the air sacs of susceptible chickens and no clinical or pathological signs of sinusitis when inoculated into the infraorbital sinuses of susceptible turkey poults, whereas the parent strain 80083 was demonstrably pathogenic. However, 1 of 10 poults inoculated intra-abdominally with approximately 2 x 10(7) CCU of ts-11 did show signs of mild airsacculitis. Eight-week-old pullets were vaccinated by eye drop with up to 1.4 x 10(7) CCU of ts-11 and simultaneously subjected to several stressful management practices, without apparent ill effects. Administration by coarse aerosol of 5 ml of ts-11 vaccine/25 day-old broilers, with or without 25 doses of infectious bronchitis virus vaccine caused no obvious signs of respiratory disease. The non virulent ts phenotype was maintained after 3 passages of strain ts-11 in chickens. Chickens vaccinated 3 weeks previously with ts-11 or with strain 80083 were placed in contact with susceptible chickens for a period of 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adequacy of commercial lentogenic vaccines against Canadian strains of viscerotropic Newcastle disease virus.

Three field strains of Newcastle Disease virus, designated S20, S21 and S23, isolated from chickens or turkeys in Ontario during the 1971-72 epizootic, were characterized as velogenic viscerotropic viruses. No significant antigenic differences were demonstrated among B1, LaSota and a field strain (S23) of velogenic vescerotropic virus by haemagglutination inhibition or protection tests. Primary water vaccination of chicks with commercial B1 and LaSota vaccines at five weeks of age and aerosol revaccination with the same strains four weeks later resulted in protection that lasted 16 weeks after revaccination against experimental challenge with strain S23. The differences in haemagglutination inhibition titres noted when the homologous or the heterologous viruses were used as haemagglutinating antigen were not statistically significant. The rates of decay of virus neutralizing and haemagglutination inhibition antibodies in vaccinated birds showed a divergence indicating the possible duality of antibodies measured in serum neutralization and haemagglutination inhibition tests.     

Evaluation of the effectiveness of two infectious bronchitis virus vaccine programs for preventing disease caused by a California IBV field isolate

Infectious bronchitis virus CA99 serotype was isolated from several broiler flocks in Northern California. The virus caused late-onset respiratory disease and increased airsacculitis condemnation in affected flocks despite the use of an established infectious bronchitis virus vaccination program. An experimental study compared Holland/Arkansas and Massachusetts/Arkansas vaccination protocols to determine the efficacy of commercial infectious bronchitis virus vaccines in reducing respiratory disease and airsacculitis lesions found at processing that were associated with a CA99 field isolate. All vaccination groups were given Massachusetts/Connecticut strains of infectious bronchitis virus vaccines at age 1 day followed by vaccination with either Holland/ Arkansas or Massachusetts/Arkansas vaccine strains at 18 days of age. Birds were challenged at age 31 days with a CA99 field isolate. Gross pathology, histopathology, and virus isolation were evaluated. Chickens vaccinated with Holland/Arkansas had marginally better protection against CA99 challenge than chickens vaccinated with Massachusetts/Arkansas, although differences were not statistically significant.     

Humoral immune response of turkeys to strain S6 and a variant Mycoplasma gallisepticum studied by immunoblotting.

Two putative variant Mycoplasma gallisepticum (MG) strains (M876 and M35), originally isolated from commercial turkeys, were compared with eight well-characterized MG strains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). SDS-PAGE protein profiles indicated that the variant strains were correctly classified as MG based on homologous patterns in species-specific regions of the electrophoretic profiles. However, differences in protein profiles also indicated that variant strains M876 and M35 were different from each other and the other MG strains tested. Immunoblotting was used to assess the humoral immune response of turkeys to infection with the S6 reference strain or M876 variant strain of MG. Immunoblots using antisera to M876 showed that seroconversion to this isolate was slower, and to fewer MG proteins when compared with immunoblots using antisera to S6. Immunoblot analyses further indicated that pooled antisera from turkeys inoculated with either S6 or M876 reacted with each of 10 MG strains tested. However, pooled S6 antisera reacted with greater intensity and with more MG proteins than did pooled M876 antisera. The species-specific immunodominant proteins with the greatest potential for use as antigens in serologic tests appeared to be those of 64 (p64) and 56 (p56) kilodaltons molecular mass.     

Pathogenicity of recent isolates of infectious bursal disease virus in specific-pathogen-free chickens: protection conferred by an intermediate vaccine strain

The pathogenicity of recent isolates of infectious bursal disease virus and the protection conferred against them by a commercial vaccine strain of intermediate virulence were examined in specific-pathogen-free chickens. Based on clinical signs, mortality, and macroscopic lesions in susceptible chickens, the isolates designated as A-Delmarva and U-28 were distinct from a previously known serotype I virulent isolate (Edgar). Histopathological analysis of the bursa of Fabricius did not establish differences between the field isolates. Although the vaccine strain produced some degree of bursal damage in antibody-free chickens, it was significantly less severe than the damage caused by the field isolates. The active immune response induced by vaccination was cross-protective against the pathological effects produced by the different isolates used in this study.     

Vaccination of turkeys against air-sac infection with a temperature-sensitive mutant of Mycoplasma gallisepticum

Turkeys were vaccinated with temperature-sensitive (TS) mutants of Mycoplasma gallisepticum (MG) to determine pathogenicity and immunogenicity. TS 37 was apathogenic yet immunogenic to turkeys, TS 100 was highly pathogenic, and TS 102 was slightly pathogenic and nonimmunogenic. Five or 7 weeks after intranasal vaccination of turkeys with the TS 37 mutant, a highly statistically significant resistance against intra-air-sac challenge with the S6 strain of MG was observed.