Comparative virulence of Haemophilus parasuis serovars 1 to 7 in guinea pigs.

Reference strains for Haemophilus parasuis serovars 1 to 7 were examined for virulence by inoculation of guinea pigs. Guinea pig response to intraperitoneal inoculation was similar for the 7 reference strains. However, apparent differences in virulence were detected after intratracheal inoculation. Cells of the references strains for serovars 1 and 5 were most invasive, causing moribundity or death at higher doses and a persistent septicemia at lower doses. Haemophilus parasuis could be isolated from respiratory and systemic sites; purulent bronchopneumonia, pericarditis, and pleuritis were apparent in infected guinea pigs. Inoculation of cells of the reference strains for serovars 2 and 6 also resulted in bronchopneumonia and moribundity or death in some guinea pigs; however, reisolation of H parasuis and microscopic lesions at necropsy were less pronounced than those observed with serovars 1 and 5. Inoculation of cells of serovars 3, 4 and 7 induced only transient clinical signs and minimal evidence of H parasuis infection at necropsy. The data from intratracheal inoculation of guinea pigs are similar to data from other investigations in swine, indicating differences in the pathogenic potential of H parasuis strains. Thus, guinea pigs may be useful as a laboratory animal model for examining cellular factors associated with virulence and immunogenicity of H parasuis.

Prevalence of Haemophilus parasuis serovars among isolates from swine.

Two hundred sixty Haemophilus spp isolates that had been obtained from the respiratory tract and other sites of swine were acquired from diagnostic laboratories, primarily in the United States and Canada. The majority of isolates (243/260) were biochemically characterized as H parasuis; however, a few isolates of taxa distinct from H parasuis (taxa "minor group," D, E, and F) were identified. Fourteen H parasuis serovars were identified, and of those previously described, the most prevalent were 5 (24.3% of isolates), 4 (16.1%), 2 (8.2%), and 7 (3.7%). Three new serovars that were also prevalent included ND4 (11.1%), ND3 (8.6%), and ND5 (6.6%). Serovars 1, 3, 6, C, D, and new serovars ND1 and ND2 were infrequently identified, and 15.2% of isolates were nontypeable. It was not uncommon to isolate multiple serovars from swine of the same herd or related herds. Distribution of serovars among isolates from the United States and Canada was generally similar; however, a higher prevalence of serovar 5 and a lower prevalence of serovars 2, ND3, and ND5 were evident in isolates from Canada. Comparison of isolates obtained from the respiratory tract of swine without polyserositis with those obtained from swine with polyserositis revealed an increased frequency of serovars 4 and 5, and a decreased frequency of serovar 2, among isolates from swine with polyserositis. However, all prevalent serovars were isolated from swine with polyserositis, and data were not indicative of an association between serovar, site of isolation, or pathogenic potential.

Simple hemagglutination inhibition test for the diagnosis of toxoplasmosis.

A simple hemagglutination inhibition (HI) test for the serological diagnosis of toxoplasmosis has been developed and evaluated. A total of 84 human and 120 mouse serum samples were tested by the newly developed HI test and compared with an immunoglobulin G-indirect fluorescent antibody test. Statistical analysis of serum titers obtained by using the HI test and the immunoglobulin G-indirect fluorescent antibody test showed a correlation coefficient of 0.89. The diagnostic efficacy of HI when compared with the immunoglobulin G-indirect fluorescent antibody diagnostic test results was 96.43% for human sera and 100% for mouse sera. The unique hemagglutination antigen, derived from Toxoplasma gondii (Rh strain) exotoxin, spontaneously binds with mouse or rat erythrocytes, causing the hemagglutination reaction. In this study, 2, 4, or 8 hemagglutinating units of T. gondii exotoxin was used with Swiss/Webster mouse erythrocytes as an indicator for the HI assay. The results indicate that 8 hemagglutinating units is optimal because this concentration has the least unexplained variability. T. gondii exotoxin was stable for at least 18 months at -70 degrees C. The Toxoplasma HI test we report in this paper is shown to be a fast, easy, highly specific, and sensitive test for the diagnosis of toxoplasmosis.

Toxoplasma gondii: growth in ovine fetal kidney cell cultures.

Serial, in vitro passage of Toxoplasma gondii (Rh strain) was successfully performed in a cell line derived from ovine fetal kidney cells. Invasion of this parasite into the kidney cells was easily discernible 1 hr after inoculation. The subsequent proliferation of the parasite was followed in the cytoplasm of the kidney cells. Very active endodyogeny and rosette formations, as many as 13 in a cell, were observed in the cytoplasm of the kidney cells 48 hr postinoculation. After 96 hr of incubation, the parasite population had increased about 132-fold. The virulence of T. gondii against mice was not attenuated after 2 years of in vitro growth which represented 100 serial passages through the kidney cell cultures. Although no "exotoxin" was produced by T. gondii grown in vitro, a Toxoplasma sp. agar gel immunodiffusion test antigen was isolated from the cell-free supernatant fluid of the kidney cell cultures which was identical to an antigen isolated from "toxogenic" organisms harvested from infected mice.

Preparation of a Toxoplasma gondii agar gel immunodiffusion test antigen from ovine fetal kidney cell cultures.

A toxoplasma gondii antigen prepared from the cell-free supernatant of ovine fetal kidney (OFK) cell cultures produced a sharp precipitation line against anti-Toxoplasma serum in an agar-gel immunodiffusion (AGID) test. Results obtained from the AGID and indirect hemagglutination (IHA) tests on 46 human and nine rabbit sera were compared. Thirty-three percent of the serum samples, which were negative for the Toxoplasma IHA test, were positive when assayed by the AGID method. The AGID test appears to be superior to the IHA test for detecting low titers of antibodies against T. gondii. After 70 generations of serial passages through the OFK cell cultures, T. gondii still produced the AGID test antigen.

A survey of domestic animals to detect serological responses against Legionella spp. by indirect fluorescent antibody.

One hundred ninety-six (196) animal sera were examined for antibodies against heat-killed antigens of Legionella pneumophila serogroups 1 to 5, L. bozemanii, L. dumoffii, L. gormanii and L. micdadei by the indirect fluorescent antibody technique. Only two animals (1%), both sheep, reacted against L. pneumophila serogroups at a titer of 256. However, 29% of the horses and 24% of the sheep tested were reactive to at least one non-L. pneumophila Legionella spp. antigen at a titer of 256. At a titer of 128, 72% of the pigs, 56% of the sheep and 50% of the horses were reactive to at least one Legionella spp. antigen. Despite the presence of high antibody titers against Legionella antigens, conclusive evidence of infection by these agents in animals is dependent upon further studies.

Analysis of ovine colostrum to detect antibody against progressive pneumonia virus.

Immunoglobulins were isolated and purified from the colostrum and serum of progressive pneumonia virus infected sheep and also from non-infected control sheep. Four classes of immunoglobulins were isolated from sheep colostrum (IgG1, IgG2, IgA and Ig10s). Three classes of immunoglobulins were isolated from sheep serum (IgG1, IgG2 and IgM). Low levels of virus neutralizing activity were demonstrated only in the whole serum and purified serum IgG1 preparations. No complement fixing activity was detected in any of the antibody preparations from colostrum.

Effect of Corynebacterium granulosum immunopotentiation on the pathogenesis of herpes simplex virus type 2 in BALB/c mice.

Treatment of 4- to 6-week-old, 18- to 22-g male BALB/c mice with 0.6 mg of Corynebacterium granulosum resulted in a significant decrease in mortality due to challenge with herpes simplex virus type 2 (HSV-2). Optimal protection occurred when C. granulosum was injected 1 week before HSV-2 infection. C. granulosum-induced resistance to HSV-2 lasted up to 4.5 weeks. Studies involving immune spleen cell transfer and treatment with antilymphocyte serum demonstrated the importance of cell-mediated immunity in HSV-2 infection. However, C. granulosum protection was not transferable with spleen cells from C. granulosum-treated animals nor was C. granulosum treatment capable of completely overcoming the increased mortality which resulted from antilymphocyte serum treatment of HSV-2 infected mice. Under our experimental conditions, silica did not affect the mortality in BALB/c mice due to HSV-2 but significantly reduced the protective effects induced by C. granulosum. Attempts to transfer protection of HSV-2 challenge in suckling mice by using either glass-adherent or mixed peritoneal cells from either HSV-2-immunized or C. granulosum-treated animals were unsuccessful.