Protective efficacy of live Salmonella gallinarum 9R vaccine in commercial layer flocks.

Salmonella enterica serovar Gallinarum (S. Gallinarum) is the causative agent of fowl typhoid, a severe systemic disease of chickens that results in high mortality. In this study we re-evaluated the ability of live S. Gallinarum 9R vaccine to protect from wild-type S. Gallinarum challenge. In laboratory trials, there was a significant difference between the vaccinated and unvaccinated control groups in mortality and the re-isolation rate of the challenge strain from the tissues (P<0.05). In field trials, efficacy of the 9R vaccine by one inoculation at the age of 18 weeks and two inoculations at the age of 6 weeks and 18 weeks was persistent throughout the duration of the study from 21 weeks old to 61 weeks old. The results from this study indicate that the protection against mortality and organ invasion in highly susceptible chickens exposed to virulent strains of S. Gallinarum may be severely limited by 9R vaccine.     

Safety and efficacy of a virulence gene-deleted live vaccine candidate for fowl typhoid in young chickens

The safety and efficacy of a live lon-and-cpxR-deleted Salmonella enterica serovar Gallinarum (SG) vaccine candidate (JOL916) was evaluated in young layer chickens. Vaccinated (n=25) and unvaccinated (n=25) groups were organized, respectively, at 1, 2, 3, and 4 weeks of age. One-week-old and 2-week-old chickens were orally inoculated with 2×10⁷ colony-forming units of JOL916, and orally challenged with 2 x 10⁶ colony-forming units of a wild-type SG strain at the third week post vaccination (w.p.v.). Doses of vaccination and challenge were increased 10-fold for 3-week-old and 4-week-old chickens. SG-antigen-specific peripheral lymphocyte proliferation response and concentrations of plasma IgG and secretary IgA in the intestine were examined at the second w.p.v. Gross lesions of the liver and spleen and recovery of the vaccine strain from the spleen were also examined at the second w.p.v. No evidence of side effects was detected by observation of general condition and body weight gain in all vaccinated groups. No, or very mild, gross lesions in the chickens were observed in the liver and/or spleen after vaccination. Significant cellular immune responses and systemic IgG responses were induced after vaccination in all age groups. Elevation of secretary IgA concentration was significant in the group, vaccinated at the age of 1 week. Depression scores after challenge were significantly lower in the vaccinated groups, as compared with the corresponding control groups. Significant reductions of death rates were observed in all vaccinated groups, as compared with the equivalent unvaccinated groups. Thus, the oral vaccination of young chickens with JOL916 was demonstrated to be safe. Moreover, it offered efficient protection against fowl typhoid.     

The effect of a live vaccine on the horizontal transmission of Mycoplasma gallisepticum.

The effect of a live Mycoplasma gallisepticum vaccine on the horizontal transmission of this Mycoplasma species was quantified in an experimental animal transmission model in specific pathogen free White Layers. Two identical trials were performed, each consisting of two experimental groups and one control group. The experimental groups each consisted of 20 birds 21 weeks of age, which were housed following a pair-wise design. One group was vaccinated twice with a commercially available live attenuated M. gallisepticum vaccine, while the other group was not vaccinated. Each pair of the experimental group consisted of a challenged chicken (10(4) colony-forming units intratracheally) and a susceptible in-contact bird. The control group consisted of 10 twice-vaccinated birds housed in pairs and five individually housed non-vaccinated birds. The infection was monitored by serology, culture and quantitative polymerase chain reaction. The vaccine strain and the challenge strain were distinguished by a specific polymerase chain reaction and by random amplified polymorphic DNA analysis. In both experiments, all non-vaccinated challenged chickens and their in-contact 'partners' became infected with M. gallisepticum. In the vaccinated challenged and corresponding in-contact birds, a total of 19 and 13 chickens, respectively, became infected with M. gallisepticum. Analysis of the M. gallisepticum shedding patterns showed a significant effect of vaccination on the shedding levels of the vaccinated in-contact chickens. Moreover, the Cox Proportional Hazard analysis indicated that the rate of M. gallisepticum transmission from challenged to in-contact birds in the vaccinated group was 0.356 times that of the non-vaccinated group. In addition, the overall estimate of R (the average number of secondary cases infected by one typical infectious case) of the vaccinated group (R = 4.3, 95% confidence interval = 1.6 to 49.9) was significantly lower than that of the non-vaccinated group (R = infinity, 95% confidence interval = 9.9 to infinity). However, the overall estimate of R in the vaccinated group still exceeded 1, which indicates that the effect of the vaccination on the horizontal transmission M. gallisepticum is insufficient to stop its spread under these experimental conditions.     

Contribution of Salmonella gallinarum large plasmid toward virulence in fowl typhoid.

Four strains of Salmonella gallinarum isolated from independent cases of fowl typhoid all possessed both an 85-kilobase and a 2.5-kilobase plasmid. Each plasmid was eliminated in turn from one of the strains by transposon labeling and curing at 42 degrees C. Elimination of the small plasmid had no effect on the high virulence of the strain for newly hatched and 2-week-old chickens. Whereas oral inoculation of 2-week-old chickens with the parent strain produced 90% mortality with characteristic signs of fowl typhoid, inoculation of the large-plasmid-minus strain produced 0% mortality. A corresponding increase in the 50% lethal dose from log10 1.1 to greater than log10 7.3 was seen with the large-plasmid-minus strain after intramuscular inoculation. Reintroduction of the large plasmid completely restored virulence. A role for the plasmid-linked virulence genes in both invasion and growth in the reticuloendothelial system is suggested by the failure of the large-plasmid-minus strain to penetrate to the liver and spleen after oral inoculation and by its increased clearance from the reticuloendothelial system after intravenous inoculation. These results clearly demonstrate that the large plasmid of S. gallinarum contributes toward virulence in fowl typhoid of chickens.     

A study of vaccination against Marek's disease with an attenuated Marek's disease virus

Approximately 2,000 day-old white leghorn chickens were distributed into 10 pens and half the pens vaccinated with the attenuated strain of HPRS-16. At 72 weeks of age, mortality from non-specific death and Marek's disease was 17.6% and 15.6% respectively, in vaccinated chickens compared with 14.2% and 51.7% in unvaccinated chickens. Body weights of vaccinated chickens were 5.6% higher at 8 weeks of age than unvaccinated chickens. Vaccinated chickens consumed 2.3% more feed and the hen housed egg production and hen day egg production were 58.7% and 7.0% greater than unvaccinated chickens. Vaccination resulted in a 3.8 fold increase in net margin over food and bird costs per bird housed at 16 weeks. Active antibody production to 'A' antigen occurred later and in a smaller proportion of vaccinated chickens than unvaccinated chickens. Viraemia due to vaccination was detected at 2 weeks of age and viraemia due to field virus was detected at 5 weeks of age. The incidence and titres of viraemia due to field virus were higher in unvaccinated chickens compared with vaccinated chickens. No evidence of spread of vaccine virus to unvaccinated chickens could be found. Acute, classical and apathogenic strains of field virus were isolated from vaccinated chickens and strains of field virus were found to persist throughout the life of the vaccinated chickens. Mild classical and/or apathogenic strains were first apparent at 18 weeks of age and increased in proportion thereafter, forming the majority of isolates from 52 weeks of age. Data on individual birds suggested a direct relationship between virus titre and lesion (or Marek's disease) frequency.     

Immunity to experimental fowl typhoid in chickens induced by a virulence plasmid-cured derivative of Salmonella gallinarum.

Chickens were immunized by two intramuscular inoculations at 1 and 14 days of age with virulence plasmid-cured derivatives of Salmonella gallinarum and were challenged 14 days later by oral inoculation of ca. 50 50% lethal doses (LD50) of fully virulent S. gallinarum 9. Mortality in the nonimmunized and immunized groups were 36 and 3%, respectively. This difference was highly significant (P less than 0.01). A significant reduction in mortality was also produced following oral challenge with 5,000 LD50 doses. The LD50 values by intramuscular inoculation of the challenge organism into nonimmunized and immunized chickens were log10 (0.13 +/- 1.57) and (9.74 +/- 2.72), respectively. Immunization was effective whether chickens were immunized at 1 and 14 days of age or at 21 and 35 days of age. Serum agglutinins were present in immunized chickens. Immunization with plasmid-cured Salmonella pullorum gave less protection, and immunization with Escherichia coli K-12 possessing the virulence plasmid of S. gallinarum gave none. The plasmid-cured S. gallinarum was made both rough by virulent bacteriophage activity and nalidixic acid resistant (Nalr) to produce a strain designated 9VP-phi rNalr. It was compared with a Nalr mutant of the rough 9R vaccine strain designated 9 Nalr for virulence and immunogenicity. 9VP-phi rNalr was slightly less protective and less virulent than was the 9R vaccine strain.     

Salmonella gallinarum gyrA mutations associated with fluoroquinolone resistance.

Salmonella enterica subsp. enterica serovar Gallinarum (S. gallinarum) is the causative organism of fowl typhoid, and an outbreak of fowl typhoid in Korea was confirmed in 1992. The aim of this study was to investigate possible changes in fluoroquinolone susceptibility among S. gallinarum isolates from 1995 to 2001, and to analyse mutations of the gyrA gene in fluoroquinolone-resistant isolates. Among 258 S. gallinarum isolates tested by the disk diffusion method, isolates from 1995 (n=18) were susceptible to all fluoroquinolones tested, whereas a number of isolates from 2001 (n=46) showed reduced susceptibility to enrofloxacin (6.5%), ciprofloxacin (10.9%), norfloxacin (52.5%) and ofloxacin (82.6%). The minimum inhibitory concentration range of enrofloxacin, ciprofloxacin, norfloxacin, ofloxacin and danofloxacin increased from < or =0.06 approximately 0.25 microg/ml in 1995 to 2 approximately 8 microg/ml in 2001. When amino acid changes in the gyrA were analysed by DNA sequencing, 22.5% and 14.7% among 258 isolates had a mutation at the Ser-83 and Asp-87 codons, respectively, and the prevalence of these mutants increased from 5.6% in 1995 to 89.1% in 2001. These mutants contained a change from Ser to Phe or Tyr at codon 83, or a change from Asp to Gly, Tyr or Asn at codon 87, and showed a range of minimum inhibitory concentrations of enrofloxacin from 0.5 to 8 microg/ml, ciprofloxacin from 0.25 to 4 microg/ml, norfloxacin from 2 to 32 microg/ml, ofloxacin from 0.5 to 4 microg/ml, and danofloxacin from 0.5 to 4 microg/ml. These results suggested an important association between the gyrA mutations and fluoroquinolone resistance of S. gallinarum.     

The use of two live attenuated vaccines to immunize egg-laying hens against Salmonella enteritidis phage type 4

Laying hens aged 24 weeks were vaccinated twice, separated by a 2-week interval, with spectinomycin-resistant mutants of either the Salmonella gallinarum 9R vaccine or a rough, aroA insertion mutant of a S. enteritidis phage type 4 strain. The 9R strain was given intramuscularly, the rough, aroA mutant both intramuscularly and orally. Two weeks after the second vaccination the immunized and a control group of unimmunized birds were challenged with a nalidixic acid-resistant mutant of a fully virulent phage type 4 strain. Full post-mortem examinations were carried out and eggs were examined bacteriologically for 3 weeks after challenge. Immunization with the 9R strain produced a marked reduction in the number of isolations of the challenge strain from a number of organs, including the ovaries. In contrast, immunization with the rough, aroA mutant produced little change in the isolation rate from the ovaries with small reductions for the liver and spleen. Both candidate vaccines produced a reduction in the number of isolations from laid eggs. The 9R strain was itself isolated from the ovaries throughout the period of examination whereas the aroA strain was not. Sera taken from the birds immediately prior to challenge were examined by slide agglutination using live S. enteritidis cells. Sera from 9R vaccinated birds contained agglutinins whereas sera from most of the chickens immunized with the rough, aroA mutant did not.     

Adjuvant effect of ginsenoside-based nanoparticles (ginsomes) on the recombinant vaccine against Eimeria tenella in chickens

An experiment was conducted to study the adjuvant effect of ginsomes on the recombinant profilin in coccidian-infected breeding birds. Three-day-old chickens were vaccinated with Eimeria tenella recombinant profilin antigen (10, 50, and 100 μg per chicken) with or without 50 μg ginsomes per chicken. The boost vaccination was carried out 14 days later. Two weeks after the booster, the chickens were challenged with 1.5?×?10(4) homologous sporulated oocysts. The specific antibody response, lymphocyte proliferation, and IL-1 release from lymphocyte were measured at 1-42 days after boost vaccination. Seven days post-challenge, the rate of survival, body weight gains (BWG) were examined then all chickens were sacrificed and lesion scores and oocysts per gram were monitored to evaluate the protective effects of the vaccination after challenge. Compared with the group of vaccinating with profilin only, groups of 50 and 100 μg antigen plus ginsomes significantly enhanced lymphocyte proliferation and IL-1 secretion. The profilin specific antibody level in the four vaccinated groups was significantly higher than in the control group and in groups vaccinated with profilin containing ginsomes than profilin only. In the groups vaccinated with profilin plus ginsomes, the BWG was significantly higher than that of group of profilin only, but there was no significant difference between profilin plus adjuvant ginsomes, diclazuril medicated and uninfected-unmedicated-unvaccinated control groups. The lesion scores in groups immunized with profilin plus ginsomes was significantly lower than that both of groups unimmunized-challenged-unmedicated control and group vaccinated with profilin only. Oocyst excretion in groups vaccinated with 50 or 100 μg profilin plus ginsomes was lower than that of groups vaccinated with profilin only. These results demonstrate that the adjuvant ginsomes can promote subunit vaccine to induce a strong immune response and protective effects.     

Development and evaluation of an experimental vaccination program using a live avirulent Salmonella typhimurium strain to protect immunized chickens against challenge with homologous and heterologous Salmonella serotypes.

A stable live avirulent, genetically modified delta cya delta crp Salmonella typhimurium vaccine strain, chi 3985, was used in several vaccination strategies to evaluate its use in the control of Salmonella infection in chickens. Oral vaccination of chickens at 1 and at 14 days of age with 10(8) CFU of chi 3985 protected against invasion of spleen, ovary, and bursa of Fabricius and colonization of the ileum and cecum in chickens challenged with 10(6) CFU of virulent homologous Salmonella strains from group B. Chickens challenged with heterologous Salmonella strains from groups C, D, and E were protected against visceral invasion of spleen and ovary, while invasion of the bursa of Fabricius and colonization of ileum and cecum was reduced in vaccinated chickens. Oral vaccination at 2 and at 4 weeks of age induced an excellent protection against challenge with virulent group B Salmonella serotypes and very good protection against challenge with group D or E Salmonella serotypes, while protection against challenge with group C Salmonella serotypes was marginal but significant. Vaccination at 2 and at 4 weeks of age also protected vaccinated chickens against challenge with 10(8) CFU of highly invasive S. typhimurium or S. enteritidis strains. The protection of chickens vaccinated with chi 3985 against challenge with homologous and heterologous Salmonella serotypes is outstanding, and the complete protection against ovarian invasion in chickens challenged with 10(8) CFU of highly invasive S. typhimurium or S. enteritidis strains suggests that vaccination of chickens with chi 3985 can complement the present hygiene- and sanitation-based Salmonella control measures. This paper reports a breakthrough in the use of live avirulent vaccine to control Salmonella carriers in chickens.     

Field evaluation of <Emphasis Type="Italic">Eimeria tenella</Emphasis> (local isolates) gametocytes vaccine and its comparative efficacy with imported live vaccine,LivaCox®

The present paper describes the field evaluation of local gametocyte vaccine and its comparative efficacy with commercial anticoccidial vaccine, LivaCox, used in breeder and broiler flocks in Pakistan. Humoral immune response in vaccinated and control chickens was monitored by enzyme-linked immunosorbent assay. Results demonstrated significantly elevated antibody titres in vaccinated groups as compared to control groups conducted both in Laboratory and field experiments. Significantly (P < 0.01) higher antibody titres in local gametocyte-vaccinated group as compared to LivaCox-vaccinated chickens were recorded. Splenic cell migration inhibition assay was used to detect the cell-mediated immune (CMI) response, and results were expressed in terms of per cent migration index. Lower per cent migration index in LivaCox-vaccinated chickens indicated the higher CMI response, as compared to local gametocyte-vaccinated chickens, although the difference was statistically non-significant (P > 0.05). Results of the challenge studies in laboratory experiments revealed significantly higher (P < 0.05) oocyst count in LivaCox-vaccinated group as compared to local gametocyte-vaccinated chickens.Maximum protection (75%) against mixed species of genus Eimeria was recorded in chickens vaccinated with gametocyte vaccines as compared to LivaCox-vaccinated group. The mean body weight gains in chickens vaccinated with local gametocyte vaccine were significantly better (P < 0.05) than in chickens vaccinated with LivaCox vaccine, both in laboratory and field experiments. Majority of the chickens (70-72%) in control group demonstrated severe lesions (3.0-4.0), while 20-26% chickens showed moderate lesions (2.0). On the other hand, local gametocyte- and LivaCox-immunized chickens developed 78% and 85% mild to moderated lesions (1.0-2.0), respectively. Results of the present study provide a probable explanation for cross-protection induced by Eimeria tenella gametocyte vaccines against other species of genus Eimeria.     

Long-term protection against a virulent field isolate of infectious laryngotracheitis virus induced by inactivated,recombinant, and modified live virus vaccines in commercial layers

Infectious laryngotracheitis (ILT) is an acute respiratory disease of chickens controlled through vaccination with live-modified attenuated vaccines, the chicken embryo origin (CEO) vaccines and the tissue-culture origin (TCO) vaccines. Recently, novel recombinant vaccines have been developed using herpesvirus of turkey (HVT) and fowl pox virus (FPV) as vectors to express ILTV immunogens for protection against ILT. The objective of this study was to assess the protection efficacy against ILT induced by recombinants, live-modified attenuated, and inactivated virus vaccines when administered alone or in combination. Commercial layer pullets were vaccinated with one or more vaccines and challenged at 35 (35 WCH) or 74 weeks of age (74 WCH). Protection was assessed by scoring clinical signs; and by determining the challenge viral load in the trachea at five days post-challenge. The FPV-LT vaccinated birds were not protected when challenged at 35 weeks; the HVT-LT and TCO vaccines in combination provided protection similar to that observed in chickens vaccinated with either HVT-LT or TCO vaccines when challenged at 35 weeks, whereas protection induced by vaccination with HVT-LT followed by TCO was superior in the 74 WCH group compared with the 35 WCH group. Birds given the inactivated ILT vaccine had fewer clinical signs and/or lower viral replication at 74 WCH when combined with TCO or HVT-LT, but not when given alone. Finally, the CEO-vaccinated birds had top protection as indicated by reduction of clinical signs and viral replication when challenged at 35 weeks (74 weeks not done). These results suggest that certain vaccine combinations may be successful to produce long-term protection up to 74 weeks of age against ILT.     

Protection of chickens against very virulent infectious bursal disease virus (IBDV) and Marek's disease virus (MDV) with a recombinant MDV expressing IBDV VP2.

To develop a herpes virus vaccine that can induce immunity for an extended period, a recombinant Marek's disease (MD) virus (MDV) CVI-988 strain expressing infectious bursal disease virus (IBDV) host-protective antigen VP2 at the US2 site (rMDV) was developed under the control of an SV40 early promoter. Chickens vaccinated with the rMDV showed no clinical signs and no mortality and 55% of the chickens were considered protected histopathologically after challenge with very virulent IBDV (vvIBDV), whereas all of the chickens vaccinated with the conventional IBDV vaccine showed no clinical signs and were protected. Chickens vaccinated with the CVI-988 or chickens in the challenge control showed severe clinical signs and high mortality (70-75%) and none of them were protected. Also, the rMDV conferred full protection to chickens against vvMDV just as the CVI-988 strain did, whereas 90% of the challenge control chickens died of MD. Antibody levels against IBDV and MDV following the vaccination increased continuously for at least 10 weeks. No histopathological lesions in the rMDV-vaccinated chickens and no contact transmission of the rMDV to their penmates were confirmed. These results demonstrate that an effective and safe recombinant herpesvirus-based IBD vaccine could be constructed by expressing the VP2 antigen at the US2 site of the CVI-988 vaccine strain.     

Dual-viral vector approach induced strong and long-lasting protective immunity against very virulent infectious bursal disease virus

To induce strong protective immunity against very virulent infectious bursal disease virus (vvIBDV) in chickens, two viral vector systems, Marek's disease and Fowlpox viruses expressing the vvIBDV host-protective antigen VP2 (rMDV, rFPV), were used. Most of chickens vaccinated with the rFPV or rMDV alone, or vaccinated simultaneously with both at their hatch (rMDV-rFPV(1d)), were protected against developing clinical signs and mortality; however, only zero to 14% of the chickens were protected against gross lesions. In contrast, gross lesions were protected in 67% of chickens vaccinated primarily with the rMDV followed by boosting with the rFPV 2 weeks later (rMDV-rFPV(14d)). Protection against the severe histopathological lesions of rFPV, rMDV, rMDV-rFPV(1d), and rMDV-rFPV(14d) vaccine groups were 33, 42, 53, and 73%, respectively. Geometric mean antibody titers to VP2 of chickens vaccinated with the rFPV, rMDV, rMDV-rFPV(1d), and rMDV-rFPV(14d) before the challenge were 110, 202, 254, and 611, respectively. Persistent infection of the rMDV in chickens after the booster vaccination with rFPV was suggested by detection of the rMDV genes from peripheral blood lymphocyte DNA at 28 weeks of age. These results indicate that the dual-viral vector approach is useful for quickly and safely inducing strong and long-lasting protective immunity against vvIBDV in chickens.     

Evaluation of vaccination against infectious laryngotracheitis (ILT) with recombinant herpesvirus of turkey (rHVT-LT) and chicken embryo origin (CEO) vaccines applied alone or in combination

ABSTRACT

The chicken embryo origin (CEO) infectious laryngotracheitis (ILT) live attenuated vaccines, although capable of protecting against disease and reducing challenge virus replication, can regain virulence. Recombinant ILT vaccines do not regain virulence but are partially successful at blocking challenge virus replication. The objective of this study was to evaluate the effect of rHVT-LT vaccination on CEO replication and how this vaccination strategy enhances protection and limits challenge virus transmission to naïve contact chickens. The rHVT-LT vaccine was administered at 1 day of age subcutaneously and the CEO vaccine was administered at 6 weeks of age via eye-drop or drinking water. CEO vaccine replication post vaccination, challenge virus replication and transmission post challenge were evaluated. After vaccination, only the group that received the CEO via eye-drop developed transient conjunctivitis. A significant decrease in CEO replication was detected for the rHVT-LT?+?CEO groups as compared to groups that received CEO alone. After challenge, reduction in clinical signs and challenge virus replication were observed in all vaccinated groups. However, among the vaccinated groups, the rHVT-LT group presented higher clinical signs and challenge virus replication. Transmission of the challenge virus to naïve contact chickens was only observed in the rHVT-LT vaccinated group of chickens. Overall, this study found that priming with rHVT-LT reduced CEO virus replication and the addition of a CEO vaccination provided a more robust protection than rHVT alone. Therefore, rHVT-LT?+?CEO vaccination strategy constitutes an alternative approach to gain better control of the disease.     

Effect of vaccination of hens with an avirulent strain of Salmonella typhimurium on immunity of progeny challenged with wild-Type Salmonella strains.

The avirulent Salmonella typhimurium chi3985 was used to vaccinate white leghorn chickens at 16 and 18 weeks of age, and the effect of maternal antibody on Salmonella colonization of progeny of vaccinated hens was assessed with S. typhimurium F98 or chi3985. Progeny of hens that had been vaccinated at 1 and 3 or 2 and 4 weeks of age with chi3985 were used to determine the effect of maternal immunity on vaccine efficacy. Vaccination of hens induced long-lasting Salmonella-specific antibodies which were transferred into eggs and were detected as immunoglobulin G (IgG) in the egg yolk. Maternal antibody was detected in the progeny of vaccinated birds as IgG and IgA in serum and intestinal fluid, respectively. The titer of maternally transmitted IgG or IgA was highest in the first week of life of the progeny and declined with age. Maternal antibodies prevented colonization of the chicks by S. typhimurium chi3985 and reduced colonization by S. typhimurium F98. Overall, chicks from vaccinated hens had significantly higher antibody responses than did the progeny of nonvaccinated hens after oral infection with Salmonella strains. Maternal antibody reduced the efficacy of vaccination of progeny with chi3985 at 1 and 3 weeks of age. But vaccination at 2 and 4 weeks of age induced excellent protection against challenge with S. typhimurium F98 or S. enteritidis 27A PT 8 in birds from vaccinated hens and in specific-pathogen-free chickens. Vaccination of chickens at 2 and 4 weeks of age has been shown to protect the birds against challenge with homologous and heterologous Salmonella serotypes. A combination of vaccination of adult animals and use of the progeny of vaccinated birds will enhance effective control of Salmonella infections in the poultry industry. This will complement the present control of Salmonella-associated food poisoning caused by Salmonella enteritidis in eggs because the avirulent S. typhimurium vaccine strain chi3985 induced excellent protection against S. enteritidis in chickens.     

The efficacy of Mycoplasma gallisepticum K-strain live vaccine in broiler and layer chickens

The efficacy of a live Mycoplasma gallisepticum (MG) vaccine candidate (K-strain) was compared to commercially available vaccines in broiler-type chickens (Trial 1) and layer-type chickens (Trial 2). In Trial 1, three-week-old broiler-type chickens were vaccinated via aerosol with K-strain or an F-strain vaccine. The vaccinated chickens and 10 non-vaccinated controls were subsequently challenged with virulent R-strain via aerosol at six weeks post vaccination; both K-strain and F-strain vaccination resulted in significant protection from air sac and tracheal lesions, as well as R-strain colonization (P ≤ 0.05). In Trial 2, commercial layer-type chickens were vaccinated with ts-11 (via eye drop) or K-strain (via aerosol) at 12 weeks of age. At 25 weeks of age these birds were challenged with R-strain via aerosol. The ts-11 and K-strain vaccinated groups both had significantly lower air sac lesion scores and a lower prevalence of ovarian regression after challenge as compared to non-vaccinated chickens (P ≤ 0.05). K-strain vaccination also prevented significant tracheal lesions and R-strain colonization (P ≤ 0.05). K-strain shows great potential as a highly efficacious live MG vaccine in broiler and layer-type chickens for protection of the respiratory and reproductive systems as well as prevention of infection with field strains.     

Strategies for improving the efficacy of a H6 subtype avian influenza DNA vaccine in chickens

A low-pathogenicity avian influenza H6N2 virus was used to investigate approaches to improve DNA vaccine efficacy. The viral hemagglutinin (HA) gene or its chicken biased HA gene, incorporating a Kozak sequence, was cloned into a pCAGGS vector to produce the pCAG-HAk and pCAG-optiHAk constructs. Following two intramuscular injections, the seroconversion rate in vaccinated chickens with 10, 100 or 300 μg pCAG-HAk were 87.5%, 75% and 75%, respectively. The profile of H6 hemagglutination inhibition (HI) antibodies induced by different doses of pCAG-HAk during the 8-week study period was similar. The HI titer rose significantly in the three different dose groups following the booster and reached a plateau 2-3 weeks post-booster. In a single dose vaccination group with 100 μg pCAG-HAk, a maximum seroconversion rate reached 53.3% at 5 weeks post-vaccination. The earliest time of seroconversion appeared two weeks after DNA immunization. Following two electroporation (EP) vaccinations with 100 μg pCAG-HAk, all birds seroconverted and the HI antibody titers were significantly higher than those using intramuscular immunization, suggesting that EP was more efficient than intramuscular delivery of the DNA vaccines. In comparison, chickens immunized with 10 or 100 μg pCAG-optiHAk showed 37.5% and 87.5% seroconversion rates, respectively, at 3 weeks following the booster. The pCAG-HAk was not significantly different from the pCAG-optiHAk in either the seroconversion rate or H6 HI titer, suggesting that the codon-optimized HA DNA vaccine did not achieve significantly better immunogenicity than the pCAG-HAk vaccine.