Immunity conferred by Aro- Salmonella live vaccines

The specificity of protection conferred by Aro- salmonellae was studied in BALB/c mice challenged 3 months after intravenous (i.v.) vaccination, more than 1 month after the vaccine had been cleared. Oral challenge showed better protection than i.v. challenge. Salmonella typhimurium aroA SL3261 conferred very good protection against wild-type S. typhimurium C5 (over 10,000 x LD50). Cross protection experiments were performed using S. typhimurium, S. enteritidis and S. dublin for vaccination and challenge, including variants of S. typhimurium and S. enteritidis of similar virulence differing in the main LPS antigen (O-4 or O-9). Salmonella typhimurium aroA conferred solid protection against S. typhimurium (O-4), but no protection against wild-type S. enteritidis (O-9). However challenge with LPS variant strains showed that although protection was generally better to strains of the homologous LPS type, specificity of protection was determined more by the parent strain background (S. typhimurium or S. enteritidis) of the challenge than by O-factors 4 or 9, suggesting that other antigens are involved. The nature of the protective antigen(s) in this model is unclear, but it does not appear to be the main O-specific antigen. A S. enteritidis Se795 aroA vaccine gave good protection against wild-type S. enteritidis Se795 2 weeks after vaccination, but much less at 3 months (approximately 10-200 x LD50), although the persistence of the S. enteritidis aroA vaccine in the liver and spleen was similar to that of the S. typhimurium vaccine, and the wild-type Se795 challenge strain was of similar virulence to S. typhimurium C5. A S. dublin aroA vaccine conferred similar protection against wild-type S. dublin (approximately 300 x LD50).     

Immunity induced by live attenuated Salmonella vaccines

Studies on the degree and specificity of protection conferred by immunization with aroA salmonella live vaccines in BALB/c mice are described. Animals were immunized i.v. and challenged orally 3 months later to ensure that the vaccine had been cleared from the tissues. Vaccination with Salmonella typhimurium aroA SL3261 conferred very good protection against virulent S. typhimurium C5 (over 10,000 x LD50). The specificity of cross protection was studied using S. typhimurium, Salmonella enteritidis and Salmonella dublin for vaccination and challenge, including challenge with variants of S. typhimurium and S. enteritidis of similar virulence which differed in the main LPS (lipopolysaccharide) antigen (0-4 or 0-9). S. typhimurium SL3261 gave very good protection against S. typhimurium C5 (0-4), but no protection against S. enteritidis Se795 (0-9). However, challenge with strains differing in the main 0 antigens showed that, although protection was generally better to strains expressing the same LPS type as the vaccine, specificity of protection was determined more by the background (S. typhimurium or S. enteritidis) of the parent strain used for the challenge than by 0 factors 4 or 9, suggesting that other factors could be involved. The nature of the antigen(s) responsible for protection in this model is unclear, but it would not appear to be the main 0-specific antigen. An S. enteritidis Se795 aroA vaccine was far less effective than S. typhimurium SL3261; it conferred good protection against the homologous wild type at 2 weeks post-vaccination, but far less at three months (approx 10-200 x LD50). This was unexpected, as the persistence of the S. enteritidis vaccine in the liver and spleen was similar to that of S. typhimurium SL3261, and the S. enteritidis and S. typhimurium challenge strains were of similar virulence. An S. dublin aroA vaccine conferred similar protection against wild type S. dublin (approx 300 x LD50).     

Comparative Immunogenicity of Heat-Killed and Living Oral Salmonella Vaccines

CD-1 mice were vaccinated intragastrically or intramuscularly with one or two doses of 200 mug of heat-killed Salmonella enteritidis 5694. Control mice were vaccinated with sublethal doses of living S. enteritidis Se795. The mice were challenged intragastrically with approximately 10(6)S. enteritidis 5694 SM(R) 7 to 14 days later, and the growth of the challenge population in the liver, spleen, mesenteric lymph nodes, lungs, and intestine was measured quantitatively. Mice receiving two doses of heat-killed vaccine by mouth were able to delay the systemic emergence of a gastrically introduced salmonella infection by 1 to 2 days. The corresponding liver and spleen populations were slightly lower than those seen in the normal controls. On the other hand, mice receiving the living, attenuated vaccine (either intravenously or intragastrically) developed an effective anti-salmonella immunity against subsequent reinfection.     

Vaccination of chickens with strain CVL30, a genetically defined Salmonella enteritidis aroA live oral vaccine candidate.

Newly hatched chicks were vaccinated orally with a genetically defined Salmonella enteritidis aroA candidate, strain CVL30. In chickens immunized with 10(5) or 10(9) CFU and challenged by the intravenous route with 10(8) CFU of S. enteritidis 109 Nalr at 8 weeks old, there were similar reductions in colonization of the spleens, livers, and ceca of vaccinees compared with unvaccinated controls. Two groups of newly hatched female chicks were vaccinated orally with 10(9) CFU of strain CVL30, and one group was revaccinated intramuscularly with 10(9) CFU at 16 weeks old. When challenged intravenously with S. enteritidis 109 Nalr at 23 weeks old, there was a reduction in the colonization of spleens, livers, ovaries, and ceca compared with unvaccinated controls. Inclusion of the intramuscular booster gave increased protection to the ovary, although the vaccine strain was isolated on one occasion from a batch of eggs laid at 20 weeks old. In chickens immunized with 10(9) CFU of strain CVL30 and challenged orally with 10(9) CFU of S. enteritidis 109 Nalr, there was a reduction in intestinal shedding of the challenge strain from vaccines compared with unvaccinated controls. Circulating immunoglobulin G antibodies to lipopolysaccharide (LPS) were detected in unvaccinated controls within 7 to 10 days of oral challenge. In contrast, circulating immunoglobulin G antibodies to LPS in vaccinees were not altered by the oral challenge, which suggested that vaccination reduced or prevented invasion by the challenge strain from the gut or multiplication of the challenge strain in the tissues. Newly hatched chicks were vaccinated orally with ca. 10(9) CFU of strain CVL30, and 1 day later, the vaccines and unvaccinated controls were challenged orally with 10(5) or 10(9) CFU of S. enteritidis 109 Nalr. Colonization of the ceca and invasion from the gut by the S. enteritidis challenge strain was reduced in the vaccines up to 5 days postchallenge compared with controls. In a second trial, vaccinees and controls were challenged orally with 10(7) or 10(9) CFU of S. typhimurium 2391 Nalr. In contrast to the challenge with S. enteritidis, colonization of the ceca and invasion by the S. typhimurium strain were not greatly reduced.     

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.     

Immunogenicity of Living and Heat-Killed Salmonella pullorum Vaccines

Specific pathogen-free CD-1 and C57Bl mice were infected in a hind footpad with 5 x 10(4) viable Salmonella enteritidis cells or 10(7) viable S. pullorum cells. The resulting bacterial growth within the footpad, the draining lymph nodes, and the liver and spleen was followed for 14 days. Mice vaccinated with live S. enteritidis rapidly developed an effective antibacterial resistance to both intravenous and intragastric challenge with S. enteritidis SM(R). The viable inoculum of S. pullorum was rapidly eliminated from the normal mouse tissues and failed to induce a detectable anti-Salmonella resistance to parenteral or oral challenge with S. enteritidis. Heat-killed saline suspensions (200 mug, dry wt) of S. enteritidis or S. pullorum were unable to induce an effective antimicrobial resistance against a subsequent virulent Salmonella challenge. However, when the organisms were suspended in Freund complete adjuvant, both vaccines induced an antibacterial resistance to intravenous and intragastric challenge. Reduction of the antigenic dose from 200 to 40 mug did not greatly affect the protective value of the two killed vaccines against an intravenous challenge, but the level of protection observed with two 40-mug doses of S. pullorum was considerably reduced when the animals were infected intragastrically, suggesting that some quantitative differences existed between the sensitizing antigenic contents of the two test organisms.     

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 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.     

Vaccination route, infectivity and thioglycollate broth administration: effects on live vaccine efficacy of auxotrophic derivatives of Salmonella choleraesuis

An aromatic-dependent, therefore non-virulent, derivative of a mouse-virulent strain of Salmonella choleraesuis previously shown not to be effective as a live vaccine when given intraperitoneally (i.p.) to Itys mice, was administered to BALB/c mice. Two doses given i.p. or by feeding did not protect against i.p. or oral challenge with 50 to 5000 LD50 of the virulent ancestor strain. By contrast two doses given intravenously (i.v.) gave almost complete protection against i.p. or oral challenge with 500 LD50 and some protection against larger doses. The number of live bacteria (cfu) in the liver and spleen 24 h after administration of the live vaccine was less than 1% of the number inoculated i.p., but c. 25% of the number injected i.v. The number of cfu in the gut 24 h after oral vaccine administration was only c 10(-5) of the number fed. Administration of thioglycollate broth i.p. 5 days before i.p. vaccination increased recovery of live vaccine cfu in the liver and spleen and its protective efficacy. In each case the live vaccine did not multiply extensively in vivo. We have previously shown that a purine- and a thymine-requiring derivative of S. choleraesuis were each considerably attenuated but unlike the aro derivative were effective as i.p. live vaccines in mice. Doses of these strains (c. 10(4) cfu) found protective were administered i.p. to BALB/c mice. Each strain multiplied extensively in the liver and spleen to c. 10(7) cfu by day 6. All these results are in agreement with a correlation of protective efficacy of a live vaccine with the persistence of a large number of the vaccine bacteria in the liver and spleen for several days.     

Mice vaccinated with a non-virulent, aromatic-dependent mutant of Salmonella choleraesuis die from challenge with its virulent parent but survive challenge with Salmonella typhimurium

BALB/c mice given a live vaccine of an aroA mutant of Salmonella choleraesuis by intraperitoneal (i.p.) injection were not protected against i.p. challenge with its virulent parental strain but were protected against i.p. challenge with either of two virulent strains of Salmonella typhimurium (O [1], 4, [5], 12). Vaccination with a live vaccine of S. typhimurium aroA protected against challenge with S. typhimurium but not with S. choleraesuis. Intraperitoneal administration of either aroA strain evoked high levels of serum antibody against the homologous lipopolysacharide (LPS) as determined by an enzyme immunoassay. Sera from vaccinated mice also reacted with heterologous LPS but at dilutions at least seven-fold lower than homologous endpoint titres. The vaccination schedule employed with either live-vaccine strain conferred an equal degree of resistance to challenge with Listeria monocytogenes. After mixed infection of mice with equal numbers of virulent S. typhimurium and S. choleraesuis by the i.p. route, the former was isolated in numbers at least 50,000 times greater than the latter from the liver and spleen between days 1 and 5. When mice were vaccinated i.p. with S. choleraesuis aroA, L. monocytogenes or P. multocida before mixed infection, neither serotype showed more than a slight predominance in the liver and spleen during the same period. Thus, in relative terms, vaccination with S. choleraesuis aroA or inoculation with unrelated bacteria suppressed the growth of virulent S. typhimurium in mice but allowed virulent S. choleraesuis to multiply. These results clearly show that S. choleraesuis 38(1) can multiply to kill immunised BALB/c mice.     

Invasiveness and persistence of Salmonella enteritidis, Salmonella typhimurium, and a genetically defined S. enteritidis aroA strain in young chickens.

Newly hatched chicks were dosed orally with a Salmonella typhimurium wild-type strain, an S. enteritidis wild-type strain, and a genetically defined S. enteritidis aroA vaccine candidate, strain CVL30. The S. typhimurium strain, 2391 Nalr, was virulent in newly hatched chicks and caused deaths in 7 of 20 chicks after an oral dose of 10(5) organisms. The S. enteritidis wild-type strain, LA5, caused death in 1 of 25 chicks and gross pathology including pericarditis and perihepatitis in 6 of the 24 survivors after an oral dose of 10(9) organisms. S. enteritidis aroA CVL30, attenuated by ca. 6.5 log10 in BALB/c mice, was nonvirulent when administered orally to chicks and did not cause morbidity. When newly hatched chicks were dosed, the pattern of invasion and colonization of the reticuloendothelial system by strain CVL30 was similar to that of its parent strain, LA5, irrespective of the dose. Oral inoculation of newly hatched chicks with < 10 organisms of S. enteritidis LA5 or CVL30 was followed by multiplication in the cecal contents. Within 3 days of hatching, the pH of the cecal contents was reduced from ca. 7 to 5. Samples of gut contents were inoculated in vitro. The S. enteritidis strains multiplied in samples taken from the ileum and duodenum irrespective of age but multiplied in the cecal samples from newly hatched chicks only. Invasion from the gut by S. enteritidis LA5 and CVL30 was both age and dose dependent.     

Plasmid-cured Salmonella enteritidis AL1192 as a candidate for a live vaccine.

We report the immunizing capacity of Salmonella enteritidis AL1192, a strain that has been cured of a 36-megadalton plasmid, to protect ddY mice against subsequent challenge with virulent salmonellas. This strain, which was given subcutaneously at a dose of 10(6) organisms, provided significant protection against oral, subcutaneous, or intraperitoneal challenge by virulent wild-type strains of not only S. enteritidis, but also S. dublin, S. naestved, and S. typhimurium.     

Role of T cells, TNF alpha and IFN gamma in recall of immunity to oral challenge with virulent salmonellae in mice vaccinated with live attenuated aro- Salmonella vaccines.

The SL3261 Salmonella typhimurium aroA live vaccine strain confers solid protection against oral challenge with virulent salmonellae, immunity persisting long after the vaccine has been cleared from the tissues. BALB/c mice immunized with SL3261 and later subjected to in vivo depletion of both CD4+ and CD8+ T cells had impaired recall of immunity to oral challenge with the virulent S. typhimurium C5, with increased mortality and higher bacterial loads in the reticuloendothelial system (RES). Selective depletion of CD4+ cells alone significantly impaired resistance both 8 and 14 weeks after vaccination as determined by estimation of bacterial numbers in organ homogenates. Depletion of CD8+ cells alone had less effect on immunity when performed at 8 weeks than at 14 weeks after immunization. Administration of anti-IFN gamma or anti-TNF alpha antibodies also impaired recall of immunity, exacerbating a secondary infection in vaccinated mice. Challenge of T cell-depleted immune mice with virulent salmonellae caused hepatosplenomegaly with minute grossly visible focal lesions, and a marked increase in the number and severity of necrotic foci in spleen, liver and lymph nodes. A widespread mononuclear cell infiltrate was present. The histopathology in anti-IFN gamma-treated mice was qualitatively similar to that seen in T-cell depleted mice. In contrast, in the anti-TNF alpha-treated mice splenomegaly was much less than in T cell-depleted mice. Granulomas were absent, no mononuclear infiltration was observed and there was severe necrosis; the lesions appeared similar to or worse than those seen in na?ve mice. Surprisingly, IFN gamma was detectable in sera of both controls and T cell-depleted mice on day 8 of the secondary infection, as well as in sera of anti-TNF alpha-treated mice on day 6 of infection. The results indicate that T cells, IFN gamma and TNF alpha are all important in the specific recall of immunity to virulent salmonellae conferred by immunization with live vaccines, with the effect of T cell and IFN gamma depletion (marked macrophage infiltration) being qualitatively very different from that of TNF alpha neutralization (no mononuclear infiltrate or granuloma formation).     

Sublingual vaccination with sonicated Salmonella proteins and mucosal adjuvant induces mucosal and systemic immunity and protects mice from lethal enteritis

Salmonella enteritidis is one of the most common pathogens of enteritis. Most experimental vaccines against Salmonella infection have been applied through injections. This is a new trial to explore the effect of sublingual administration of Salmonella vaccines on systemic and mucosal immunity. Adult BALB/c mice were sublingually vaccinated with sonicated Salmonella proteins (SSP) alone, or plus adjuvant CpG DNA (CpG) or cholera toxin (CT). They were boosted 2 weeks later. Saliva specific secretory IgA (SIgA) antibody responses were significantly stimulated in the mice vaccinated with SSP only or together with CpG or CT. Whereas the mice sublingually vaccinated with SSP and CpG had higher spleen cell IFN-γ production and serum specific IgG2a antibody responses, those receiving SSP and CT showed enhanced spleen cell IL-4, IL-5 and IL-6 production, and serum specific IgG1 antibody responses. After oral challenge with live S. enteritidis, the same strain of the source of SSP, immune protection in those sublingually vaccinated with SSP and CpG or CT was found to prevent intestinal necrosis and to render a higher survival rate. In conclusion, sublingual vaccination together with mucosal adjuvant CpG or CT is a simple but effective way against enteric bacterial pathogens.     

Efficacy of inactivated infectious bursal disease (IBD) vaccines: Comparison of serology with protection of progeny chickens against IBD virus strains of varying virulence

The efficacy of inactivated infectious bursal disease vaccines was determined by measuring both the antibody response of vaccinated chickens and clinical protection of progeny chicks from vaccinated dams. Similar virus neutralizing (VN) antibody titres were obtained in 4-week-old chickens and mature hens after vaccination with one vaccine dose. VN titres below 10 log 2 increased considerably between the fourth and seventh week after vaccination in 4-week-old chickens as well as in mature chickens. All 2-week-old progeny chicks with serum VN antibody titres of at least 9 log 2 were clinically protected against the classical virulent 52/70 infectious bursal disease virus (IBDV) strain, as well as against the very virulent IBDV (vvIBDV) strain D6948. However, vaccination often did not prevent subclinical infection in these 2-week-old progeny chicks, which often resulted in severe lymphocyte depletion in the bursa of Fabricius. Even a serum VN titre of 11 log 2 was not always sufficient to prevent severe bursal damage. Although 52/70 IBDV and vvIBDV were equally pathogenic in 2-weekold specific pathogen free chickens, significant higher maternal antibody titres were required to prevent the adverse effects of vvIBDV in comparison with 52/70 IBDV. The relation between the serological response of chickens after application of inactivated IBD vaccines and the protection of progeny chicks of vaccinated dams depended on both the virulence of the IBDV challenge strain and the IBDV strain in the vaccine.     

Study on the local effect of eye-drop vaccination against infectious bronchitis in 1-day-old chicks with maternal antibodies

One-day-old chicks with maternal antibodies to infectious bronchitis virus (IBV) were vaccinated by eye-drop with H120 vaccine strain of IBV. Four weeks later the chicks were challenged by eye-drop or intratracheally with virulent IBV (Massachusetts-type field strain). The chicks were resistant to ocular challenge, but highly susceptible to an intratracheal challenge. After intratracheal challenge the birds showed clinical signs of infectious bronchitis (IB). The immunofluorescence test on IBV was positive. Macroscopical and microscopical lesions were present in the trachea. From these observations it was concluded that the protection against virulent IBV after eye-drop vaccination is localised mainly in the conjunctival and nasal tissues. Thus in vaccination studies with IBV the result of challenge depended highly on the route of application of the challenge virus. Ten days after challenge the neutralisation index of serum for IBV was significantly higher in the intratracheally-challenged chicks as compared with their eye-drop challenged or/and unchallenged mates.     

Vaccination of chickens against a Belgian nephropathogenic strain of infectious bronchitis virus B1648 using attenuated homologous and heterologous strains

White Leghorn chicks without and with maternally derived antibodies (MDA) to infectious bronchitis virus (IBV) and broiler chicks with MDA were vaccinated at 1 day of age either with H120 vaccine, combined H120 and D274 vaccines or with a non-commercial attenuated strain derived from the virulent Belgian nephropathogenic IBV strain, B1648. Protection following challenge with virulent B1648 was assessed 4 weeks later by virus isolation from the trachea, antigen detection in the kidney by immunofluorescence and mortality rates. Vaccination with either homologous or heterologous vaccines reduced the duration of virus replication in the trachea of all groups compared to unvaccinated controls. Homologous vaccination reduced the incidence of virus replication in the kidney. Heterologous vaccination (H120 to D274) did not reduce kidney infection in the MDA + groups; however, partial kidney-protection was found in the MDA - group. There was no correlation between serum antibody titres measured by ELISA and the degree of kidney protection.     

Differences in resistance to Salmonella enterica serovar Gallinarum infection among indigenous local chicken ecotypes in Tanzania.

A study was conducted to evaluate the disease resistance potential in 105 chickens of six indigenous local chicken ecotypes in Tanzania by orally challenging 1-week-old chicks with 2.5 x 10(8) colony-forming units of virulent S. Gallinarum. For 14 days post infection, clinical signs, necropsy findings, antibody titres, packed cell volume, leukocyte population count, and viable bacterial cell counts in the liver and spleen were recorded. Clinical signs were recorded daily but other parameters were recorded on the day of infection, then on days 3, 6, 10 and 14 after infection. Clinical signs of fowl typhoid were evident in chickens from day 3 post infection and disappeared by day 9 post infection. Pathological lesions on sacrificed birds included enlargement of the liver and spleen with foci of necrosis on the liver, spleen and myocardium. The mean viable bacterial cell counts in the liver and spleen varied between ecotypes, although the differences were not statistically significant. There were significant differences in the leukocyte population in the peripheral blood, with one ecotype (Morogoro-medium) showing a consistent and significantly higher heterophil count compared with other ecotypes. It was concluded that there is a selectable resistance potential to S. Gallinarum among the local chicken ecotypes in Tanzania that may be attributable to non-specific host immune responses. Further studies are suggested.     

Genetic manipulation of Salmonella serotype Bovismorbificans to aromatic-dependence and evaluation of its vaccine potential in mice

The generation of smooth aromatic-dependent Salmonella serotype Bovismorbificans (Group C2, O6, 8) from a smooth wild-type parent strain by transduction with phage P1, and conjugation with Salmonella serotype Typhimurium carrying F'-8gal is described. The smooth aromatic-dependent S. serotype Bovismorbificans was non-lethal for mice at an oral challenge dose of 2 x 10(9) cfu (equivalent to 200 LD50 of the parent, wild-type strain). The safety of the auxotrophic mutant was further substantiated by comparing its multiplication kinetics in vivo with that of its virulent parent organisms. Mice immunised with live, smooth aromatic-dependent S. serotype Bovismorbificans by either the oral or intraperitoneal (i.p.) route were protected against oral challenge with virulent S. serotype Bovismorbificans; the degree of protection was significantly better (p less than 0.05) at a challenge dose of 100 or 200 LD50 in mice receiving two rather than one vaccination. In contrast, mice immunised with three doses of the formalin-killed virulent, parent organisms by the i.p. route were not protected, in spite of high antibody titres. Only those mice immunised with the live, smooth aromatic-dependent S. serotype Bovismorbificans i.p. developed significant (p less than 0.01-0.05) delayed-type hypersensitivity.