[Evaluation of the vaccine potentiality of 2 strains from Leptospira interrogans serogroup Ballum]

Two vacine candidate strains from Ballum serogroup were characterized and their immunogenicity and protective power were studied in hamster. The monovalent vaccine formulations obtained showed a high immunogenicity and capacity of homologous protection and, in a lesser degree, of cross protection.

Identification of the hemolysis-associated protein 1 as a cross-protective immunogen of Leptospira interrogans by adenovirus-mediated vaccination

New vaccine strategies are needed for the prevention of leptospirosis, a widespread human and animal disease caused by pathogenic leptospires. Our previous work determined that a protein leptospiral extract conferred cross-protection in a gerbil model of leptospirosis. The 31- to 34-kDa protein fraction of Leptospira interrogans serovar autumnalis was shown sufficient for this purpose. In the present study, N-terminal sequencing of a 32-kDa fraction and Southern blotting of genomic DNA with corresponding degenerated oligonucleotide probes identified two of its constituents: hemolysis-associated protein 1 (Hap1) and the outer membrane Leptospira protein 1 (OmpL1). Adenovirus-mediated Hap1 vaccination induces significant protection against a virulent heterologous Leptospira challenge in gerbils, whereas a similar OmpL1 construct failed to protect the animals. These data indicate that Hap1 could be a good candidate for developing a new generation of vaccines able to induce broad protection against leptospirosis disease.

Control of immunologically crossreactive leptospiral infection by administration of lipopolysaccharides from a nonpathogenic strain of Leptospira biflexa

In our previous paper (Matsuo, K., Isogai, E., and Araki, Y., Carbohydr. Res., 328: 517-524, 2000), antigenic polysaccharides obtained from the lipopolysaccharide (LPS) fraction of a nonpathogenic leptospira, Leptospira biflexa patoc Patoc I, are shown to be broadly crossreactable with most rabbit antisera elicited by immunization with various pathogenic leptospires. The result led us to test a protective effect of the same LPS in a hamster model system by heterologously challenging with a pathogenic leptospira, L. interrogans manilae UP-MMG. Firstly, a similarity in the antigenic epitopes of L. biflexa and L. interrogans was confirmed by the following assays. In the microscopic agglutination test (MAT), a hamster antiserum elicited by immunization with the L. biflexa-LPS preparation was shown to agglutinate cells of L. interrogans. Contrarily, in the enzyme-linked immunosorbent assay (ELISA), the L. biflexa-LPS preparation was shown to crossreact with a hamster antiserum elicited by immunization with whole cells of L. interrogans. These results suggest that the same or closely related antigens may be present on the cell surfaces of both L. biflexa patoc Patoc I and L. interrogans manilae UP-MMG. Furthermore, in a protective assay, the prior administration of a L. biflexa-LPS preparation resulted in raising a protective response in hamsters against challenge by L. interrogans without any side effect. The protective effect was strongly dependent on the dose amounts and/or administration times of L. biflexa-LPS. Thus, L. biflexa-LPS preparations can use as a potent vaccine against leptospirosis caused by various leptospires.

Evidence of cross-protection within Leptospira interrogans in an experimental model

Killed whole-cell preparations were used as bacterins against leptospirosis. As this type of protection is considered to be serogroup-specific, several serogroups were added to the usual vaccines, and the most pathogenic serovar was chosen for each group. Different leptospire extracts were evaluated for their protective capacity against acute lethal leptospirosis in gerbils (Meriones unguiculatus). Total extracts induced complete protection against homologous challenges and partial protection against heterologous challenges. LPS fractions protected against homologous but not heterologous challenges, whereas protein extract induced significant protection against both types of challenge. Thus, cross-protection within L. interrogans was related to the protein extract.

[The evaluation of the reactogenicity and immunogenic activity of a new concentrated inactivated leptospirosis vaccine]

In the controlled field trial the reactogenicity, safety and antigenic activity of a new concentrated inactivated leptospirosis vaccine after its administration in one and two injections of 0.5 ml were studied in comparison with those of the existing commercial vaccine, introduced in two injections in doses of 2.0 and 2.5 ml. The new experimental vaccine exhibited low reactogenicity and was found to be safe and highly immunogenic when introduced in a single injection of 0.5 ml. As shown in this trial, the immunogenic characteristics of immunization made in a single injection were not inferior than those obtained as the result of immunization made in two injections, yielding high percentage of seroconversions (89.8% to 98.3%) with respect to 4 Leptospira serogroups and leading to the production of the protective titers of corresponding antibodies. The existing commercial vaccine was inferior to the experimental one in antigenic activity (the frequency of seroconversions, antibody titers). The results of the trial make it possible to recommend the experimental concentrated leptospirosis vaccine for use in medical practice in a dose of 0.5 ml introduced in a single injection.

[The reactogenicity and immunogenicity of the first Cuban vaccine against human leptospirosis]

A controlled double-blind trial was conducted with the participation of 80 adult volunteers of both sexes, who were randomly divided into groups of 40 individuals each one. The case-base study received the vaccine and the control group was administered placebo to know the safety, the behaviour of reactogenicity, and to star the immunogenicity studies of the first Cuban vaccine against human leptospirosis. The vaccine used in the case-base study was an inactivated and trivalent vaccine containing strains of Leptospira canicola, icterohaemorrhagiae and pomona, since they have the highest circulation in the country. The results obtained showed the inocuity of the vaccine as no adverse severe reactions were detected. The general symptomatology observed was low, where as febricula was the most common general symptom. It appeared during the first 3 days of observation and there were no significant differences between the 2 group. Only a mild pain at the site of the injection was reported as a local symptom, which was more frequent in the vaccinated group than in the control group (7.8 against 1.5%, respectively). The seroconversion obtained was of 29% by microagglutination, and of 34.2% by ELISA. The final results allowed to conclude that this vaccine is safe for human adults at the ages under study, and give the possibility to continue other studies in more advanced stages to complete the requirements for obtaining its license.

[Immunoprotection in guinea pigs using DNA recombinant plasmid rpDJt and expressed protein P68 in L. interrogans serovar lai]

Immunoprotection against the infection by Leptospira interrogans serogroup Icterohemorrhagiae serovar lai strain 017 was demonstrated in guinea pigs vaccinated with DNA recombinant plasmid rpDJt and expressed protein P68 derived from genomic library of Leptospira strain 017. Thirty days after active immunization, each group received intraperitoneally (1/2 dose) and subcutaneously (1/2 dose) inoculum of L. interrogans serovar lai stain 017; cultures were adjusted to 5 x 10(8) cells/ml. All guinea pigs were observed for 10 days after challenge. Survival (%) of P68 group was 100(7/7); P23 group was 75(3/4); group rpDJt was 77(10/13); group lack recombinant (control) pT7-7 was 25 (3/12), and group with whole-cell inactivated vaccine was 93(13/14). Although the protective antigen in the leptospires has yet to be determined, it is evident that expressed protein P68 conferred a high degree of immunoprotection in guinea pigs.

PCR amplification, molecular cloning, DNA sequence analysis and immuno/protection in BALB/C mice of the 33 kDa endoflagellar protein of L. interrorgans serovar lai

A pair of oligonucleotide primers were designed to amplify the endoflagella gene of L. interrogans serovar lai. An approximately 840 bp fragment was generated with PCR and inserted into plasmid pUC8, after the fragment and pUC8 were digested respectively with BamHI and PstI. A recombinant plasmid (designated as pLF1) was obtained. SDS-PAGE analysis indicated that a 33 kDa was expressed in E. coli JM103 harboring pLF1 and the expression level of the protein was 11% of the total bacterial soluble proteins. Western blot analysis showed that the protein band could be recognized by the antiserum against the endoflegella (Axial filament) of Leptospira interrogans serover lai. Nucleotide sequence data showed an open reading frame encoding 282 aminoacids residues, corresponding to a protein of molecular weight 33.6 kDa. Comparison of the deduced endoflagellar subunit protein (flaB) amino acid sequence with flagellins from other bacteria revealed a high level of identity with the Treponema pallidum flaB proteins. Immunization/protection experiment was performed on the model of BALB/C mice and showed that there was higher survival rate in the group JM103-pLE1 than in the group JM103-pUC8.

[Homology of the recombinant DNA of plasmid pDJH2 with the recombinant DNA probe of L. alstoni and analysis of its expression in Escherichia coli]

Dig-labeled recombinant DNA probe of L. alstoni which contains the entire structural OmpL1 gene was hybridized with the recombinant DNA of the plasmid named pDJH2 of the gene library of L. interrogans serovar lai strain 017. The result showed a high degree of homology among them; expression of recombinant DNA of pDJH2 was achieved by beta-D-galactosidase (IPTG) induction in E. coli. The molecular weight of this product is 68kd. Then they were treated with proteinase K and subjected to SDS-PAGE. The results showed it is a protein in nature. Using the specific monoclonal antibody E4B7D5 on immunoblotting and specific polyclonal antibody on dot-ELISA assay, we investigated the immune reaction and noticed that protein 68kd might be an antigen in character. E. coli which contains the recombinant plasmid pDJH2 were injected into BALB/c mice. Then the mice were challenged by leptospires of the strong virulence strain 017, but all the infected mice survived. In this paper, we first report the expression of recombinant DNA of L. interrogans serovar lai strain 017 in E. coli when injected with IPTG, and immunoprotection of BALB/c mice which were injected with the expression against the infection of L. interrogans serovar lai strain 017. pDJH2 may be the first recombinant for which the gene has been cloned and its expression product 68kd may be the immunoprotective antigens.

Protective effects of serum thymic factor to Leptospira interrogans serovar Copenhageni infection in Mongolian gerbils

The susceptibility to Leptospira interrogans serovar copenhageni in Mongolian gerbils treated with 10 micrograms of serum thymic factor (FTS) 1 day before infection was examined. Susceptibility of gerbils treated 5 times with 10 micrograms of FTS was also investigated. Mortality of FTS-treated gerbils was significantly lower than that of controls when small challenge doses were used. To analyse the FTS-induced resistance to leptospiral infection, natural killer (NK) cell activity and macrophage activity were studied. Macrophage activity was unaltered but NK cell activity was enhanced in FTS-treated gerbils, with or without leptospiral infection. Since no side-effects of FTS were observed, this compound should be considered for the treatment of leptospirosis.

Recognition of Leptospira interrogans antigens by vaccinated or infected dogs

Antigenic recognition of leptospiral antigens by vaccinated or infected dogs was studied by microagglutination test (MAT) and by western blots. In western blots, serovar specific antigens detected by MAT migrated in the 18-31 kDa zone. The 25-31 zone seemed to be linked to antigens indicating virulence of the strain. These antigens are LPS. The first antibodies made after infection are produced against LPS migrating in the 14 kDa zone. Many protein antigens are common in leptospires belonging to different serogroups. Virulent strains exhibited specific antigens in the 45 and 32-34 kDa zones.

Understanding of Weil's disease among canoeists

Although the risks of contracting Weil's disease in the UK are small, it can be a serious illness. Recently the disease has attracted public interest. This interest has prompted confusion and anxiety among recreational water user groups such as canoeists who had not previously seen themselves as being particularly at risk. In this paper, the experience of symptoms associated with Weil's disease among canoeists, their understanding and perceptions of the disease, and their compliance with preventive advice on the British Canoe Union (BCU) warning card, have been studied. Gaps in understanding and of adherence to preventive advice were identified. Accordingly, it was concluded that health education for canoeists could be improved. Consideration is being given by the BCU to the value of preparing a canoeist instructors' training pack.

Assay for measuring relative potency of leptospiral bacterins containing serovar pomona

An enzyme-linked immunosorbent assay (ELISA) was developed for the quantitation of leptospiral antigen in bacterins containing Leptospira interrogans serovar pomona type kennewicki. A monoclonal antibody (MAb), 2D7, which is directed against a surface antigen on whole cells of L. interrogans serovar pomona type kennewicki, was used in the assay. The capture of antigen in bacterins by a polyclonal antiserum was followed by the addition of the 2D7 ascites fluid, an anti-mouse conjugate and substrate. Biologicals evaluated with this system included preparations containing type kennewicki antigen (homologous) and those not containing type kennewicki antigen (heterologous). Heterologous bacterins gave optical density (OD) values comparable to those of blank wells. Homologous bacterins yielded OD values equal to or greater than those of the National Veterinary Services Laboratories (NVSL) reference pomona bacterin. The relative potencies (RP) of 84 licensed commercial Leptospira pomona bacterin serials were evaluated against the NVSL reference pomona bacterin using the NVSL Relative Potency computer program. Random samples of 1, 2, 3 and 5 ml dose products were selected for evaluation with this system. All products tested passed the hamster potency assay required for leptospiral bacterins. This ELISA system enables detection of antigen in bacterins containing L. interrogans serovar pomona type kennewicki and demonstrates the potential for in vitro testing of leptospiral bacterins.

[A field study on the post-inoculation reaction and immunological effects in vaccinated population immunized with "Zhejiang type-D" leptospiral vaccine]

A comparative study on the post-inoculation and antibody responses after inoculation with two different dosage (1ml, 2ml) of "zhejiang type-D" leptospiral vaccine was carried out. There was no general reaction in all of the vaccinated people after immunization. The GMT values of antibody against leptospire were 3.08-7.91 times in 1ml dose group and 3.48-9.57 times in 2ml dose group more than pre-vaccination respectively. 3 months after immunization the levels of specific antibody still were high in most vaccinated people, whatever in 1ml dose or 2ml dose of immunization. However the antibody couldn't be detected in part of vaccinated people at that time, but there was no difference between the two different dosages. During the epidemic season, there was no leptospirosis case (0/3260) in the 1ml group, 1 case (1/625) in the 2 ml group while there was 9/3970 in the control group.

Potency of leptospiral vaccines and protection against chronic infection in golden hamsters

Seven vaccines prepared from pathogenic strains of different origin of Leptospira interrogans [serovars icterohaemorrhagiae (one strain) and copenhageni (6 strains)] were examined in protection tests on golden hamsters. Two of the copenhageni strains were used for challenge. The organs (kidneys, spleen, liver) in the vaccinated animals surviving challenge were protected to a varying degree. Low rates of survival were associated with a high incidence of Leptospira-positive findings, partly connected with focal lesions of the kidneys. On the other hand, in the groups in which all the animals survived, it was not possible to culture leptospires from their organs or to detect leptospiral antigen in these organs by immunohistochemical investigation. A protection of the organs that prevents vaccinated animals from shedding leptospires after infection clearly depends on the vaccine dose administered and the efficacy of the vaccine which can be measured in potency tests based on the survival rate as the relevant parameter.

Immunological reactivity and passive protective activity of monoclonal antibodies against protective antigen (PAg) of Leptospira interrogans serovar lai

Monoclonal antibody (MAb) AG1 against the protective antigen (PAg) was produced and characterized. It had been extracted from Leptospira interrogans serovar lai by the chloroform-methanol-water method and was of glycolipid nature (23-30Kd). The fact that the PAg was a serogroup-specific antigen was shown by MAb AG1, because MAb AG1 agglutinated serovars of serogroup Icterohaemorrhagiae. Purified MAb LW2 and LW3 which are agglutinating antibodies of serovar lai and AG1 passively protected hamsters from leptospiral infection. Induction of the reactive oxygen intermediates by MAbs from peritoneal exudate macrophages of mice were observed in the chemical luminescence assay and the MAbs reacted with the PAg in the dot enzyme-linked immunosorbent assay. However, MAb LW4a against the genus-specific antigen present in the sub-surface of leptospiral cells did not show protective and reactive-oxygen-inducing activities; they reacted with the non-protective glycolipid antigen of low molecular weight (Fr I, 10-15Kd) in the dot enzyme-linked immunosorbent assay. These results indicated that anti-PAg antibody exhibited opsonic activity against Leptospira and the production of reactive oxygens by macrophages led to leptospiricidal action as one of the defence mechanisms of the host against leptospiral infection. However, the antibody against the genus-specific glycolipid antigen may not be important for protection against leptospiral infection.

[The improvement of immunobiological preparations against leptospirosis. An experimental study of a new concentrated purified vaccine against icterohemorrhagic leptospirosis for human immunization]

The findings of the study of immunological structure of the population in regions endemic for leptospirosis indicate that the immune status of humans makes it impossible to obtain titrated blood sera for the preparation of antileptospirosis immunoglobulin. The data obtained in the study of the immunobiological properties of a new concentrated vaccine against icterohemorrhagic leptospirosis show the possibility of using this vaccine for the immunization of donors with the aim of obtaining blood sera to be used as raw material for the production of immunobiological preparations.

An experimental study with a Leptospira interrogans serovar bratislava vaccine

The intramuscular vaccination of pigs with two doses, two weeks apart, of a Leptospira interrogans serovar bratislava bacterin, protected pigs against renal infection when challenged with bratislava strains six weeks later but did not protect pigs challenged after 26 weeks.

Immunological characteristics of the glycolipid antigen of Leptospira interrogans serovar lai

The protective antigen (PAg), a glycolipid substance, was extracted from Leptospira interrogans serovar lai strain 017 with a chloroform-methanol-water (1:2:0.8 [vol/vol/vol]) solution and partially purified by silica gel column chromatography. The PAg was not detected by Coomassie brilliant blue staining in sodium dodecyl sulfate-polyacrylamide gel electrophoresis but was observed as a smearlike band, which corresponded to a 24- to 30-kilodalton standard protein, by silver staining. The outer envelope (OE) fraction showed the same band, suggesting that the PAg was one of the chemical components of the OE. The immunogenicity and protective activity of the PAg were compared with those of the OE. The PAg as well as the OE and whole cells was able to induce agglutinating antibody against L. interrogans. Furthermore, the immune sera exhibited opsonic activity against L. interrogans, as observed by measurement of chemical luminescence derived from reactive oxygen. The PAg exhibited protective activity in hamsters challenged with lethal doses of L. interrogans. Therefore, the antigen may be useful as a component vaccine against leptospiral infection.

Experimental immunisation of hamsters with lipopolysaccharide antigens of Leptospira interrogans

Hamsters were immunised with leptospiral lipopolysaccharide (LPS) or the polysaccharide (PS) fraction of LPS from Leptospira interrogans serovar copenhageni and the antibody responses were measured by agglutination tests. Maximum titres were observed approximately 6 weeks after immunisation and protection against lethal challenge with the homologous strain was afforded by immunisation with as little as 2.5 micrograms of LPS or PS. All animals produced IgM agglutinins but a higher proportion of-animals immunised with PS produced IgG agglutinins than did those immunised with LPS. Immunisation of guinea-pigs with autoclaved PS showed that the preparation retained some but not all of its immunogenic activity.

Effect of vaccination with a pentavalent leptospiral vaccine on Leptospira interrogans serovar hardjo type hardjo-bovis infection of pregnant cattle

Effectiveness of a pentavalent leptospiral vaccine to protect cattle from infection and reproductive problems caused by Leptospira interrogans serovar hardjo type hardjo-bovis was evaluated. Seven cows were vaccinated once and 8 cows were vaccinated twice with a USDA-licensed pentavalent leptospiral vaccine. Five cows were maintained as nonvaccinated controls. Cows were bred 1 to 2 months after the last vaccination. During the 4th to 6th month of gestation, all cows were challenge exposed on 4 occasions by conjunctival instillation of 10(8) serovar hardjo type hardjo-bovis organisms and on 3 occasions by conjunctival instillation of urine from a cow shedding hardjo-bovis. All control cows and 13 of 15 vaccinated cows became infected and shed leptospires in the urine. Leptospires were detected in fewer urine samples collected from vaccinated cows, compared with those collected from control cows. Four stillborn calves and 3 weak calves were born to control and vaccinated cows. Leptospires were detected in the kidneys of 11 apparently healthy calves born to vaccinated and control cows. Agglutinating antibodies were not detected in the precolostral serum of these calves.

A monoclonal antibody reacting with a determinant on leptospiral lipopolysaccharide protects guinea pigs against leptospirosis

An IgA monoclonal antibody (MUM/F1-1/copenhageni) was produced from a mouse immunised with Leptospira interrogans serovar copenhageni. The antibody showed partial serogroup specificity by agglutination and by reaction in enzyme immunoassay, and opsonised homologous leptospires for phagocytosis by cultured mouse macrophages. Immunodiffusion and Western-blotting experiments indicated that MUM/F1-1/copenhageni reacted with a carbohydrate determinant in the leptospiral lipopolysaccharide. Daily administration of purified MUM/F1-1/copenhageni IgA before and after challenge with 2 X 10(8) virulent homologous leptospires passively protected newborn guinea pigs against lethal leptospirosis.

Leptospirosis in Hawaii: shifting trends in exposure, 1907-1984

Leptospirosis was first recognized as an occupational disease of sugar plantation workers in Hawaii in 1907. Since then, shifts have been noted in the animal transmission cycles, the occupational groups at risk, and an increasing recognition of cases associated with avocational exposure. Surveys of the small mammal populations indicate rats, mice, and mongooses are the most important vectors in Hawaii. Serologic surveys of workers in high-risk occupations show antibody prevalence rates ranging from 12 to 82 percent. The epidemiology of leptospirosis in Hawaii is described, based on 182 cases reported to the Hawaii Department of Health from 1970-1984. The most common infecting serovar was mankarso in the Icterohaemorrhagiae serogroup; other serovars in the Icterohaemorrhagiae group were also frequently implicated as causing disease. The manifestations of disease noted by physicians in Hawaii are similar to those observed in the continental U.S. Fever, myalgia, and headache were the most common symptoms reported in the majority of cases in Hawaii; jaundice was noted in the records of 24 percent. Recommendations made to interrupt the cycle of transmission and reduce the chances of exposure in occupational settings include the control of rodent populations and vaccination of domestic animals. Personal hygiene among workers is to be encouraged, and the development of prophylactic measures is suggested either by immunization or by chemoprophylaxis.

Doxycycline prophylaxis for experimental leptospira infection in non-human primates and hamsters

Doxycycline was effective as a chemoprophylactic agent for experimental Leptospira infection in non-human primates and hamsters. Monkeys injected intraperitoneally with Leptospira bataviae, and receiving only diluent as treatment developed a leptospiremia during the first week and later leptospires were cultured from the cerebrospinal fluid and urine. Monkeys treated daily with oral doxycycline for 10 days beginning one day before infection had a shortened period of detectable leptospiremia, and organisms were never detected in the cerebrospinal fluid or urine. Even an oral dose of doxycycline 2 hours before infection and on day 7 prevented the later infection of the cerebrospinal fluid and urine. In hamsters, doxycycline treatment prevented deaths from acute Leptospira infection and when hamsters were treated daily for 4 or more days, renal infection was prevented. The results of animal studies, the susceptibility of LC0475 and the five other isolates to doxycycline in vitro, and lack of evidence for antibiotic resistance in culture suggests this antibiotic may be useful as a prophylactic drug for high risk groups and an effective treatment for leptospirosis in Thailand.

The long term efficacy of a hardjo-pomona vaccine in preventing leptospiruria in cattle exposed to natural challenge with Leptospira interrogans serovar hardjo

The long term efficacy of a commercially prepared bivalent vaccine against Leptospira interrogans serovar hardjo and L. interrogans serovar pomona was evaluated in a group of 82 dairy heifers exposed to natural challenge with L. interrogans serovar hardjo for up to 55 weeks after calfhood vaccination. Nineteen heifers were vaccinated twice with a one-month interval, at calfhood (9 to 10 months). A further 18 heifers received a similar calfhood vaccination regimen plus a third injection at adulthood (22 to 23 months), while 19 heifers were vaccinated twice at adulthood only and finally 22 heifers were used as unvaccinated controls. At 55 weeks after calfhood vaccination and prior to adulthood vaccination, only 2.7% of the vaccinated heifers were found to have leptospiruria compared with 58.5% of the unvaccinated heifers (p less than 0.0001). Microscopic agglutination (MA) titres at the same time in the unvaccinated heifers ranged from 32 to 4096 while those vaccinated at calfhood ranged from 32 to 64. Adult vaccination of infected animals did not significantly reduce leptospiruria . Prior to adulthood vaccination, 9 of 19 heifers had leptospiruria , in comparison to 4 of 15 after adulthood vaccination. At the same sampling periods 15 of 22 controls had leptospiruria in comparison to 4 of 9 subsequently tested.

Protection of pregnant swine by vaccination against Leptospira infection

The protection conferred on pregnant gilts by 2 commercially available leptospira interrogans serovars pomona and tarassovi bacterins was evaluated. Gilts vaccinated either 3, 6 or 12 months prior to natural challenge with L. interrogans serovar pomona had significantly lower abortion rates (2% vs 69%) and foetal mortality rates (14% vs 57%) than unvaccinated controls. One vaccine was significantly superior to the other and contained approximately twice the number of L. interrogans serovar pomona organisms per vaccine dose. Neither vaccine protected against renal colonisation but vaccination reduced urinary excretion of leptospires. Both vaccines reduced agglutinating antibody response to infection, as measured by the microscopic agglutination (MA) test. This may prevent the detection of a carrier animal by serology. Foetal pigs did not develop specific MA titres. Cultural methods were not reliable in making a diagnosis of foetal infection. Histopathology of foetal liver and kidneys helped in making a diagnosis of foetal infection.

[Analysis of the antigeno-immunologic activity of heated leptospirosis vaccine in vaccinees and in an experimental study]

The comparative analysis of the immunological effectiveness of heat-killed polyvalent leptospirosis vaccine has shown the low immunological effectiveness of the whole preparation (17.8%) and its components with the exception of the antigen of the Grippotyphosa serogroup. Antibodies could be detected in the vaccinees for not more than 10 months, and they showed the properties of 19S-macroglobulin antibodies. In experiments on rabbits newly isolated Leptospira strains from human patients and wild rodents, homologous to the vaccinal strains, were found to considerably surpass the latter in their immunogenic properties; this was particularly manifest in strain "Tundra vole No. 180". The use of newly isolated Leptospira strains as vaccinal antigens is recommended. A modified heat-killed polyvalent leptospirosis vaccine should have less antigens, and the antigenic and immunogenic properties of the remaining antigens must be equivalent to those of the vaccinal antigen of Leptospira belonging to the Grippotyphosa serogroup.

Susceptibility of mice treated with cyclophosphamide to lethal infection with Leptospira interrogans Serovar pomona

Mice not normally susceptible to infection with Leptospira interrogans serovar pomona were rendered susceptible to lethal infections by treatment with a single dose of 300 mg of cyclophosphamide (Cy) per kg administered optimally from 4 days before to 1 day after infection. Cy-treated mice with either passively or actively acquired antibody were protected from death. Blood levels of leptospires in infected untreated and in Cy-treated mice remained similar until 2 days after infection, when untreated mice cleared the leptospires. Soon afterwards, opsonizing and agglutinating antibody appeared. Cy-treated mice given spleen cells from other normal or specifically immune mice were protected from infection. An important factor in the natural resistance of mice to leptospiral infection appears to be their capacity to produce circulating antibody within 48 to 72 h. Applications are suggested for this animal model in vaccination and protection studies.

Immunizing effects of structural components of Leptospira icterohaemorrhagiae

The protective attributes of the structural components of Leptospira icterohaemorrhagiae strain Shibaura were examined. Guinea pigs were immunized with the outer envelope, the cell wall, the type-specific main antigen, and the protein constituent of the outer envelope respectively. Of the 4 preparations, the outer envelope, the cell wall and the type-specific main antigen showed a considerable protective effect in this order. The protein constituent of the outer envelope was less effective. Immunization with 200 mug of the outer envelope protected guinea pigs from lethal infection but no completely from the renal carrier state. The rate of protection from renal leptospirosis by the preparations of leptospiral components and lyophilized whole cells was always inferior to the survivor rate.