A comparative study of live attenuated F strain-derived Mycoplasma gallisepticum vaccines

Commercially available attenuated strains of Mycoplasma gallisepticum (MG) are commonly used within the layer industry to control MG-induced mycoplasmosis. Among these are two live MG vaccines derived from the moderately pathogenic MG "chick F" strain. In the present study, the commercially available F strain derivatives were compared for their ability to elicit seroconversion, persist in vivo, and protect against virulent MG-induced airsacculitis. In addition, a noncommercial laboratory-derived high-passage F strain isolate was included in the study. Commercial (Hy-Line W-36) layers were placed in biological isolation units at 9 wk of age (woa). At 10 woa, birds within each biological isolation unit were treated via eye-drop application with one of the three F strain-derived vaccines at one of four levels (1x, 10(-1)x, 10(-2)x, or 10(-3)x). For the commercially available F strain derivatives, 1x equaled the manufacturer's recommended dose. The 1x dose of the noncommercial laboratory-maintained F strain derivative equaled 20 microl of a 48 hr culture. For wk 1-6 postvaccination (p.v.), sera were collected weekly from each bird, and seroconversion was assessed via serum plate agglutination (SPA). Virulent MG (strain R(low)) challenge occurred via intratracheal inoculation at 7 wk p.v. Necropsies were subsequently performed to assess challenge-associated airsacculitus. For each F strain derivative applied at 1x and 10(-1)x, 100% seroconversion, as measured by SPA, was demonstrated by 6 wk p.v., and rates at the 10(-2)x dosage were 10% and 90% for the commercial vaccines and 60% for the laboratory-derived strain in this period. Following challenge, airsacculitis was observed in 66.67% of the nontreated controls but not in any 1x- or 10(-1)x-treated bird independent of applied F strain derivative.     

Effects of increased dosages of the Mycoplasma gallisepticum vaccine MYCOVAC-L in layer chickens subsequently challenged with virulent M. gallisepticum: egg production and serologic response

Ten-week-old Hy-Line Commercial W-36 pullets were spray-vaccinated with MYCOVAC-L at the manufacturer's recommended dosage (1x) or at 15 times that rate (15x). At 22 or 45 wk of age, subsets of 1x- and 15x-vaccinated pullets were challenged with the virulent Mycoplasma gallisepticum (MG) strain Rlow. Percent hen-day egg production was determined through week 55. Analyses for treatment effects on overall (22-56 wk) percent hen-day egg production revealed no significant differences between nonchallenged 1x and nonchallenged 15x MYCOVAC-L treatments. Among 1x MYCOVAC-L-vaccinated groups, Rlow challenge at 45 wk corresponded to significantly (P < or = 0.01) lower overall egg production compared with the unchallenged 1x-vaccinated control (70.88% vs. 79.15%, respectively). Conversely, at the 15x MYCOVAC-L dosage level, overall egg production was not significantly affected by virulent MG challenge at 45 wk compared with its unchallenged counterpart (84.09% vs. 81.03%, respectively) and could indicate increased protection from virulent MG challenge. Serologic monitoring indicated the virulent MG challenge was consistently (100%) associated with seroconversion. Comparisons among the nonchallenged experimental treatments indicated that vaccinations at the 15x MYCOVAC-L dosage rate were associated with a greater seroconversion rate at weeks 21, 27, and 44, but not at week 50.     

Vaccination of turkeys with an avian pneumovirus isolate from the United States

Four-week-old poults obtained from avian pneumovirus (APV) antibody-free parents were vaccinated with different serial 10-fold dilutions of cell culture-propagated APV vaccine. The birds were vaccinated with 50 microl into each conjunctival space and nostril (total of 200 microl). Each poult of each group was vaccinated in groups that received doses of 4 x 10(4), 4 x 10(3), 4 x 10(2), 4 x 10(1), or 4 x 10(0) 50% tissue culture infective dose (TCID50) of APV vaccine, respectively. Respiratory signs were seen between 3 and 12 days postvaccination (PV) in the poults that were vaccinated with 4 x 10(4), 4 x 10(3), and 4 x 10(2) TCID50, respectively. In these groups, APV was detected from swabs collected at 5 days PV and seroconversion was detected at 2 wk PV. The groups that were originally vaccinated with 4 x 10(1) and 4 x 10(0) TCID50 developed mild clinical signs after vaccination, but neither virus nor antibody was detected PV. At 2 wk PV (6 wk of age), birds from each group, along with five unvaccinated controls, were challenged with APV. Upon challenge, the 4 x 10(4) and 4 x 10(3) TCID50 groups were protected against development of clinical signs and were resistant to reinfection. The group previously vaccinated with 4 x 10(2) TCID50 developed clinical signs after challenge that were considerably milder than those seen in the groups that had previously been vaccinated with lower doses or no virus. Even though 4 x 10(2) TCID50 vaccine dose administered by intranasal ocular route resulted in infection, incomplete protection resulted with this pivotal dose. Upon challenge, the 4 x 10(1) and 4 x 10(0) TCID50 groups exhibited milder disease signs than those seen in the challenged unvaccinated controls. In these groups, APV was detected in preparations of swabs collected at 5 days postchallenge (PC) and seroconversion was detected at 2 wk PC. These results indicate that the dose of APV vaccine that causes protection is higher than that required to produce infection.     

Floor pen study to evaluate the serological response of broiler breeders after vaccination with ts-11 strain Mycoplasma gallisepticum vaccine

To determine the Mycoplasma gallisepticum (MG) rapid serum plate agglutination (RSPA) test response of broiler breeders after ts-11 strain vaccination, 55 Cobb pullets derived from a nonvaccinated, MG-negative, commercial, broiler breeder grandparent flock were monitored from 8 to 20 wk of age (over a 12-wk trial period). To evaluate the effect of lateral spread of the ts-11 vaccine strain on RSPA test results from commingled and adjacently penned birds, treatment groups included (A) birds vaccinated with ts-11strain MG at 8 wk of age, (B) commingled nonvaccinates in the same pen as the vaccinated birds, (C) nonvaccinates in a second pen separated from the first pen by a distance of 2 m, and (D) birds vaccinated with ts-11 strain MG at 8 wk of age and kept in a separate room. Rapid serum plate agglutination tests were performed once a week for 6 wk and then every 2 wk for 6 more wk, postvaccination. A polymerase chain reaction (PCR) assay specific fbr ts-11 strain MG was used to confirm vaccination, and a second PCR specific for non-ts-11 strain MG was used to confirm the absence of field infection. Seroconversion was first detected by the RSPA test 2 wk postvaccination and attained maximum positive rates of 58% at 12 wk postvaccination in treatment A and 60% at 8 wk postvaccination in treatment D. Seroconversion rates in nonvaccinated, commingled pullets was 10% at 5 wk and 30% at 12 wk after the vaccination of pen mates. The ts-11-specific PCR detected the vaccine strain in 80%-100% of the vaccinated birds 2 wk after vaccination. One of 15 nonvaccinated birds penned 2 m from vaccinated birds yielded ts-11 by PCR assay 12 wk after vaccination, which indicates that the spread of ts-11 over short distances may be possible in situations in which there is a common caretaker. PCR on tracheal swabs taken 12 wk postvaccination detected ts-l1 in 50% and 60% of the vaccinated birds in treatments A and D, respectively; in 30% of the commingled nonvaccinates; and in 6.6% of the separately penned nonvaccinates. In contrast, choanal swabs collected from vaccinated birds at 12 wk were 21% and 40% PCR positive for ts-11 strain MG, while those from nonvaccinates were negative. All samples were PCR negative for field strain MG. The pattern of seroconversion as measured by RSPA test in small groups of broiler breeders was different from that previously reported for leghorns. Lateral spread of the ts-11 strain to commingled pen mates occurred rapidly, causing RSPA seroconversion patterns that mimicked those of the vaccinated pen mates.     

Evaluation of the bioavailability and pharmacokinetics of two extended-release theophylline formulations in dogs

OBJECTIVE: To evaluate the bioavailability and pharmacokinetic characteristics of 2 commercially available extended-release theophylline formulations in dogs. DESIGN: Randomized 3-way crossover study. ANIMALS: 6 healthy adult dogs. PROCEDURE: A single dose of aminophylline (11 mg x kg(-1) 15 mg x lb(-1)], i.v., equivalent to 8.6 mg of theophylline/kg 13.9 mg x lb(-1) or extended-release theophylline tablets (mean dose, 15.5 mg x kg(-1) [7.04 mg x lb9-1), PO) or capsules (mean dose, 15.45 mg x kg(-1) [7.02 mg x lb(-1)], PO) was administered to all dogs. Blood samples were obtained at various times for 36 hours after dosing; plasma was separated and immediately frozen. Plasma samples were analyzed by use of fluorescence polarization immunoassay. RESULTS: Administration of theophylline i.v. best fit a 2-compartment model with rapid distribution followed by slow elimination. Administration of extended-release theophylline tablets and capsules best fit a 1-compartment model with an absorption phase. Mean values for plasma terminal half-life, volume of distribution, and systemic clearance were 8.4 hours, 0.546 L x kg(-1), and 0.780 mL x kg(-1) x min(1), respectively, after i.v. administration of theophylline. Systemic availability was > 80% for both oral formulations. Computer simulations predicted that extended-release theophylline tablets or capsules administered at a dosage of 10 mg x kg(-1) (4.5 mg x lb(-1)), PO, every 12 hours would maintain plasma concentrations within the desired therapeutic range of 10 to 20 microg x mL(-10. CONCLUSIONS AND CLINICAL RELEVANCE: Results of these single-dose studies indicated that administration of the specific brand of extended-release theophylline tablets or capsules used in this study at a dosage of 10 mg x kg(-1), PO, every 12 hours would maintain plasma concentrations within the desired therapeutic range (10 to 20 microg x mL(-1)) in healthy dogs.     

Monitoring Mycoplasma gallisepticum and Mycoplasma synoviae infection in breeder chickens after treatment with enrofloxacin.

Three experimental strains of breeder chickens were accidentally exposed to Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS), presumably from a newly introduced group of leghorn-type pullets. The experimental strains subsequently became infected and were diagnosed positive for MG and MS by the serum plate agglutination (SPA) test and confirmed by the hemagglutination inhibition (HI) test and the polymerase chain reaction (PCR) of tracheal swabs. Treatment with 10 mg/kg enrofloxacin via drinking water for 14 days was elected. Before and after initiation of treatment, MG and MS were monitored for changes by SPA, HI, PCR, and culture, with sampling intervals ranging from 1 wk to 7 wk. MG and MS SPA, HI, PCR, and culture were performed at each sampling period, with the exception of weeks 1.0 and 6.5. Week 1.0 included SPA and His for MG and MS. Week 6.5 included PCR and culture for MG and MS. The MG and MS SPA results were positive throughout the 29-wk trial period. MG HI titers declined until the last sampling, whereas the MS HI titers did not decline significantly. PCR for MG yielded only one positive result, which occurred before treatment. MS PCR remained positive throughout the trial period. MG was never isolated from any sample; however, one MS organism was isolated during treatment. The treatment regimen was effective for MG on the basis of PCR results. Treatment with enrofloxacin did not eliminate SPA reactions during the 29-wk trial period. MG HI titers remained in the suspicious range throughout the remainder of the trial period. Four weeks after the treatment ended, MG HIs were reduced by approximately 40%, with MS HIs remaining high throughout the 29-wk period. PCR appeared to be a sensitive and specific test on the basis of correlation with HIs. On the basis of the isolation of MS during treatment and continued subsequent PCR positive reactions, the treatment for MS with enrofloxacin was not as efficacious as for MG.     

Pharmacokinetics and dosage regimen of 2-pyridine aldoxime in Bubalus bubalis intoxicated with fenitrothion

In the present study, the pharmacokinetics of 2-pyridine aldoxime (2-PAM, 30 mg/kg, i.v.) alone and in conjunction with atropine (0.3 mg/kg; 1/4 i.v., 3/4 i.m.) was investigated in 10 Bubalus bubalis intoxicated with a single oral lethal dose of fenitrothion (435 mg/kg). Based on the kinetic parameters, an appropriate dosage regimen of 2-PAM in B. bubalis was calculated. There was no significant difference between plasma levels and pharmacokinetic parameters of 2-PAM in the two groups of animals, given 2-PAM alone and in conjunction with atropine. The peak plasma concentration of 2-PAM at 1 min was in the range of 189.5-196.6 microg/mL which declined to 9.22-9.98 microg/mL at 4 h. The values of elimination half-life, Vd(area) and total body clearance were 2.41-2.67 h, 0.77-0.95 L/kg and 227.5-245.7 mL/kg/h, respectively. The binding capacity of 2-PAM to plasma proteins of fenitrothion-intoxicated buffalo calves and dissociation rate constant of protein drug complex were 0.015 x 10(-6) mol/g and 2.367 x 10(-6) mol, respectively. Approximately 63% of 2-PAM was bound with plasma proteins. In the treatment of organophosphate insecticide (OPI) toxicity in B. bubalis, an appropriate i.v. dosage regimen of 2-PAM in conjunction with atropine would be 18 mg/kg followed by 15 mg/kg at 4 h interval.     

A chronicle of serologic response in commercial layer chickens to vaccination with commercial F strain Mycoplasma gallisepticum vaccine

Vaccination of multi-age layer operations, wherein one million plus commercial layer chickens are housed, has been spurious until the development of a self-propelled, constant-speed spray vaccinator. Still, even with its use, live Mycoplasma gallisepticum (MG) vaccinations have been questionable in terms of seroconversion. Using the vaccinator as a research tool over the past 5 yr, factors have been elucidated which impact seroconversion to one live MG vaccine in particular, the F strain of MG (FMG). These factors include the type of nozzle used to spray the vaccine, the temperature of the water used to rehydrate and administer the vaccine, and the pH and osmolarity of the fluid used to apply the vaccine. In the present study, one farm was monitored for its seroconversion rates over 4 1/2 yr, during which time the FMG vaccination protocol was amended as factors were identified that enhanced seroconversion rates. The results of this study showed that implementation and inclusion of the optimized factors into the vaccination protocol for FMG enhanced seroconversion rates because they went from an initial 50%-55% positive seroconversion rate to a consistent 100% positive seroconversion rate over the 56-mo study period.     

Sensitivity and specificity of Mycoplasma gallisepticum agglutination antigens prepared from medium with artificial liposomes substituting for serum

Three batches of strain A5969 Mycoplasma gallisepticum (MG) serum-plate-agglutination (SPA) antigen grown in regular Frey's medium with 12% swine serum, three batches grown in Frey's medium containing artificial liposomes instead of serum, and one commercial SPA antigen were evaluated for sensitivity and specificity. Sensitivity was measured using chickens exposed to MG by intraocular and intranasal inoculation. Specificity was measured in uninoculated controls and in groups inoculated with the oil-emulsion vaccines Haemophilus paragallinarum, infectious bursal disease inactivated virus vaccine, or Staphylococcus aureus. Sera were tested 1 to 8 weeks postinoculation. All SPA antigens had a perfect sensitivity score, except one liposome-grown antigen batch (LC). The two other liposome-grown antigen batches (LA and LB) maintained significantly higher specificity by yielding significantly (P less than 0.01) fewer false positive (FP) agglutination reactions than did the other antigens. The three antigen batches produced in medium with serum had intermediate levels of FP agglutination reactions. When known MG-negative sera were tested, MG SPA antigens LC and commercial SPA antigen yielded significantly (P less than 0.01) higher numbers of FP agglutination reactions than the other SPA antigens.     

Determination of the effective dose of the live Mycoplasma synoviae vaccine, Vaxsafe MS (strain MS-H) by protection against experimental challenge

The minimum effective dose of the Mycoplasma synoviae-H (MS-H) vaccine was determined through protection against experimental challenge. Chickens were vaccinated by eyedrop with the following doses of a vaccine: 1.2 x 10(5), 2.4 x 10(5) 4.8 x 10(5), 9.6 x 10(5), 1.92 X 10(6), and 3.84 X 10(6) color change units (CCU), then challenged 6 wk after vaccination. Rapid serum agglutination results indicated that 100% of birds receiving an MS-H dose of > or = 4.8 x 10(5) CCU had antibodies to MS and enzyme-linked immunosorbent assay results showed that 60% of birds receiving a dose of 4.8 x 10(5) or 9.6 x 10(5) CCU and 100% of birds receiving a dose of 1.92 x 10(6) or 3.84 x 10(6) had antibodies to MS. At postmortem after challenge, the following parameters were significantly lower in birds vaccinated with an MS-H dose of > or = 4.8 x 10(5) CCU: air sac (AS) lesion severity; incidence of AS lesions; mucosal thicknesses in the upper trachea, middle trachea, and lower trachea (LT); and MS colonization of the LT and AS. It was concluded that an MS-H dose of 4.8 x 10(5) CCU was sufficient to elicit an antibody response in birds, prevent MS colonization in the LT and AS, and protect against AS lesions caused by an experimental MS and infectious bronchitis virus challenge.     

Evaluation of sodium dodecyl sulfate-polyacrylamide gel electrophoresis purified proteins of Mycoplasma gallisepticum and M. synoviae as antigens in a dot-enzyme-linked immunosorbent assay

Selected immunogenic proteins of Mycoplasma gallisepticum (MG) strain R and M. synoviae (MS) isolate F10-2AS were purified from sodium dodecyl sulfate-polyacrylamide gels. Purified MG proteins of 65 to 63 (p64) kilodaltons (kDa), and 26 and 24 (p26/24) kDa, and purified MS proteins of 53 (p53) kDa, 41 (p41) kDa, and 22 (p22) kDa were evaluated as potential antigens for an enzyme-linked immunosorbent assay (ELISA). Chicken antisera to MG, MS, or oil-emulsion vaccines were used to evaluate these purified proteins as antigens in a dot-ELISA. MG antigen p64 detected antibodies 3 days after the serum plate agglutination (SPA) test and 7 days before the hemagglutination-inhibition (HI) test. Antigen p64 detected antibodies to 12 MG isolates, and in sera from field outbreaks of MG. No cross-reactions with MS-positive antisera were seen with antigen p64. MG antigen p26/24 did not perform as well as p64. MS antigen p41 detected antibodies 5 days after the SPA test and at least 11 days before the HI test, and in sera from field outbreaks of MS. However, some MG-positive antisera reacted with p41. MS antigens p53 and p22 did not perform well.     

The efficacy of three commercial Mycoplasma gallisepticum vaccines in laying hens

The efficacy of three commercial Mycoplasma gallisepticum (MG) immunizing agents-a bacterin, a recombinant fowlpox-MG vaccine, and a live F-strain vaccine-was compared in specific-pathogen-free hens in egg production. Three groups of 25 chickens were vaccinated with one of the vaccines at 10 wk of age and 25 birds were not vaccinated. At 25 wk of age (and approximately 50% egg production), 20 birds from each of the three vaccinated groups and 15 nonvaccinated controls were challenged with virulent R-strain via aerosol; the birds were necropsied and evaluated at 10 days post-challenge. The MG bacterin and live F-strain vaccinations were both protective and resulted in significant differences in air sac lesions, tracheal lesions, and ovarian regression compared to the nonvaccinated controls and the recombinant fowlpox-MG vaccine (P < or = 0.05). The evaluation of ovarian regression is a useful method of testing the efficacy of MG vaccines in laying hens.     

Avian titer development against West nile virus after extralabel use of an equine vaccine.

West Nile virus affects many animals, but the highest prevalence of morbidity and mortality is observed in birds, horses, and humans. The purpose of this study was to determine a protocol in birds of prey and corvids, using a vaccine developed for horses. The birds were assigned to five groups. Groups 1-4 received 0.25 ml, 0.5 ml, 0.75 ml, and 1.0 ml, respectively, and group 5 served as a control group. The greatest percentage of seroconversion (58.3%) was observed in the vaccine group that received a dose of 1.0 ml administered thrice, 3 wk apart. This report demonstrates that a vaccine developed for equines against West Nile virus can be administered to birds.     

Evaluation of the specificity and sensitivity of two commercial enzyme-linked immunosorbent assay kits, the serum plate agglutination test, and the hemagglutination-inhibition test for antibodies formed in response to Mycoplasma gallisepticum

Two commercial enzyme-linked immunosorbent assay (ELISA) kits, seven serum plate agglutination (SPA) antigens, and the hemagglutination-inhibition (HI) test for antibodies to Mycoplasma gallisepticum (MG) were compared for sensitivity and specificity using known MG-positive and MG-negative sera from leghorn chickens. All SPA antigens proved to be highly sensitive when testing MG-positive sera. Laboratory-prepared SPA antigens yielded fewer positive reactions when testing MG-negative sera than commercial SPA antigens. Both MG ELISA kits showed high rates of positive reactions when testing sera from birds given commercial M. synoviae bacterin, fowl coryza (Haemophilus paragallinarum) bacterin, inactivated infectious bursal disease virus vaccine, and to a lesser extent fowl cholera (Pasteurella multocida) bacterin. Immunization with Frey's medium with 12% swine serum-in-oil or Staphylococcus aureus-in-oil resulted in sera which yielded numerous positive ELISA reactions. During the first 1 to 3 weeks, antibodies induced by experimental infection with MG were better detected by the SPA test than by the ELISAs and the HI test, thus confirming the SPA test's importance in Mycoplasma diagnostic serology. The HI test can serve to confirm positive SPA results.     

Effect of vaccination with a monovalent Leptospira interrogans serovar hardjo type hardjo-bovis vaccine on type hardjo-bovis infection of cattle.

Effectiveness of 2 concentrations of a monovalent vaccine containing Leptospira interrogans serovar hardjo type hardjo-bovis was evaluated for protection of heifers from infection with type hardjo-bovis. Nine heifers were given 2 doses of low-dose vaccine (8.32 x 10(8) cells/dose); 9 heifers were given 2 doses of high-dose vaccine (8.32 x 10(9) cells/dose); and 1 steer and 1 heifer were maintained as nonvaccinated controls. Groups of vaccinated cattle were challenge-exposed with serovar hardjo type hardjo-bovis at 7 (n = 6), 11 (n = 6), or 15 (n = 6) weeks after completion of vaccination. All cattle were challenge-exposed by conjunctival instillation of 1 x 10(5) hardjo-bovis cells on 3 consecutive days. Both control and all vaccinated cattle became infected and shed serovar hardjo type hardjo-bovis in their urine. Leptospires were detected in 15 of 16 (94%) urine samples from control cattle and in 124 of 143 (87%) samples from vaccinated cattle. Leptospires were detected in kidneys of 17 of 18 vaccinated cattle and 2 of 2 control cattle and in the uterus or oviducts of 13 of 18 vaccinates and the 1 control heifer.     

Protection conferred by a live Salmonella Enteritidis vaccine against fowl typhoid in laying hens

Fowl typhoid is under control in poultry farms of developed countries, but it still endemically subsists in commercial laying hen farms of some countries. It has been demonstrated that Salmonella live vaccines can elicit cross-immunity against members of the same Kauffmann-White scheme serogroup. In this work, we explored the protection conferred by TAD Salmonella vac E, a live Salmonella enterica serovar Enteritidis vaccine, against fowl typhoid. Three groups of laying hens were vaccinated with different vaccination schedules starting on the first day of life, and afterwards were infected with 2 x 10(5) CFU of a virulent Salmonella Gallinarum strain, either at wk 28 or wk 52. Mortality, fecal shedding, and organ invasion of Salmonella Gallinarum were assessed. In this work we demonstrated that this Salmonella Enteritidis vaccine is able to cross-immunize against Salmonella Gallinarum. At wk 28, hens vaccinated with three oral doses or with two oral doses combined with one subcutaneous dose were protected by the vaccine. At wk 52, when hens were infected 36 wk after the final immunization, the vaccine was not able to confer protection. Thus, revaccination every 3 mo would be highly recommended. In countries where Salmonella Gallinarum subsists together with Salmonella Enteritidis, control programs should include vaccination of laying hens using safe attenuated Salmonella strains.     

Oral vaccination of brushtail possums (Tichosurus vulpecula) with BCG: immune responses, persistence of BCG in lymphoid organs and excretion in faeces

AIMS: To determine immune responses, and the localisation and persistence of Mycobacterium bovis bacille Calmette-Guérin (BCG) in gut-associated lymphoid tissues (GALT) and other organs in possums vaccinated orally with lipid-formulated BCG vaccine. To determine the duration of excretion and longevity of survival of BCG in the faeces of vaccinated animals. METHODS: Possums (n=28) were vaccinated with lipid-formulated BCG (1 x 10(8) colony forming units (cfu) of formulated BCG) by the oral route. Control possums (n=17) were fed oral bait pellets containing formulation medium only. Possums were sacrificed at 3 days and at 1, 3, 6 and 8 weeks after vaccination or ingestion of bait. Proliferation responses to bovine purified protein derivative (PPD) were measured in lymphocytes from blood and mesenteric lymph nodes (MLN) and samples of lung, spleen, liver, MLN and Peyer's patches (PP) were cultured for the presence of BCG. The number of BCG organisms excreted in faeces and the duration of excretion were determined in eight vaccinated possums and eight control possums over a 3-week period. In a separate experiment, a further six possums were vaccinated with oral BCG vaccine (5-10 x 10(8) cfu BCG/possum) and their faeces collected over 48-72 h, for culture of BCG. The longevity of survival of BCG in these faeces was determined by storing faecal samples (n=12) under three different conditions: in an incubator (22.5 degrees C), and conditions which simulated the forest floor and open pasture. A proportion (1-2 g) of these faecal samples was collected after storage for 1, 3, 5, 8 or 20 weeks, and cultured for BCG. RESULTS: Possums vaccinated orally with BCG vaccine showed strong proliferation responses to bovine PPD in peripheral blood lymphocytes at 6-8 weeks post-vaccination (p.v.). Positive lymphocyte proliferation assay (LPA) responses to bovine PPD were first evident in MLN at 3 weeks p.v. BCG was cultured from MLN and PP in a proportion of animals at 3-8 weeks p.v. BCG was not cultured from sections of spleen, lung or liver at any time p.v. BCG was recovered in low to moderate numbers from the faeces of vaccinated possums for up to 7 days, and maximal numbers were cultured in faeces collected 48-72 h p.v. After storage for 1 week, BCG was cultured from all faecal samples placed in the incubator and from a proportion of faeces exposed to conditions similar to those on the forest floor and pasture. With the exception of one faecal sample stored under forest floor conditions which was culture-positive for BCG at 3 and 5 weeks, BCG was not cultured from any other faecal sample stored for more than 1 week. CONCLUSIONS: Ingestion of oral BCG vaccine by possums was associated with the development of strong cell-mediated immunity in both blood and MLN. Following oral vaccination with BCG, the organisms were localised and persisted in GALT but did not spread to the spleen, liver or lungs. BCG was shed in low to moderate numbers in the faeces for up to 7 days p.v. The viability of BCG excreted in faeces decreased rapidly, particularly when faeces were exposed to an open pasture environment. Oral vaccination of possums with formulated BCG is unlikely to result in undue contamination of the environment with BCG.     

Evaluation of Mycoplasma gallisepticum K-strain as a live vaccine in chickens

We evaluated the pathogenicity of three live Mycoplasma gallisepticum (MG) vaccine candidates by infection via aerosol of 3-wk-old chickens with log phase broth cultures (trial 1). Two of the candidates (K3020 and K4649A) colonized only 10% and 20% of the chickens, respectively, unlike K2101 (K-strain), which was reisolated from all of the vaccinated chickens tested. K-strain inoculation did not result in significant air sac or tracheal lesions in chickens at 10 and 39 days postinfection (P < or = 0.05). The efficacy of K-strain as a live vaccine was evaluated in trial 2, by challenge of vaccinated chickens with virulent R-strain via aerosol at 6 wk postvaccination. K-strain vaccination resulted in significant protection from air sac and tracheal lesions (P < or = 0.05). The K-strain was further investigated to evaluate transmissibility (trial 3), colonization and persistence of infection following aerosol administration (trial 4), genetic and phenotypic stability following back passage through chickens (trial 5), and vertical transmission (trial 6). The K-strain had a low rate of horizontal transmission; it remained primarily in the respiratory system of inoculated birds and persisted in the upper respiratory tract for the duration of the trial 4 (5 mo). There was no increase in virulence of K-strain when it was back passaged five times through chickens, and no vertical transmission of K-strain was detected. K-strain showed great potential as a safe and effective live MG vaccine.     

Use of a live attenuated Salmonella typhimurium vaccine to protect hens against Salmonella enteritidis infection while undergoing molt

Previous studies demonstrated that Salmonella enteritidis infections in hens undergoing molt via feed withdrawal were more severe than in full fed hens. We conducted two trials to determine if immunizing specific-pathogen-free, Salmonella-culture-negative hens via aerosol exposure to MeganVacl, a commercially available attenuated Salmonella typhimurium vaccine, would reduce transmission of S. enteritidis from infected hens to uninfected but contact-exposed hens during a molt. In trial 1, one group of hens received two aerosol doses of vaccine 2 wk apart whereas a second group of hens remained nonvaccinated. In trial 2, the vaccinated group received only one dose of vaccine. Two weeks after the final immunization, feed was removed from all the hens, and on day 4, the center hen in rows of 11 hens received a dose of 3 x 10(5) (trial 1) or 1.3 x 10(6) (trial 2). Transmission to the unchallenged hens was followed 3, 10, 17, and 24 days later. Vaccination reduced the horizontal spread of S. enteritidis in vaccinated hens compared with their nonvaccinated counterparts, with vaccinated hens shedding significantly less S. enteritidis on day 10 postchallenge in trial 1 and on days 3, 10, 17, and 24 in trial 2. Recovery of S. enteritidis from ovaries was significantly reduced in the vaccinated hens in trial 1 and from livers/spleens, ovaries, and cecum in trial 2. These studies indicate that immunization of hens with a live S. typhimurium vaccine could help reduce S. enteritidis problems during a molt situation.