A study of virulence parameters for Toxoplasma gondii infections in mice

The correlation of TNF alpha levels with acute phase proteins in acute Toxoplasma gondii infection in mice

Acute Toxoplasma gondii infections can influence the liver as well as other organs. Many cytokines and proteins play a role in the acute response against infection. Tumor necrosis factor alpha (TNF alpha) is a cytokine that plays a key function in stimulating hepatocytes to produce acute phase proteins. In this study, we investigated TNF alpha levels associated with the levels of macroglobulin, haptoglobin, hemopexin, C-reactive protein (CRP), albumin, serum amyloid alpha protein (SAA), and clusterin, which are acute phase proteins, in serum of mice with T. gondii infection. In the experiment, a total of 24 mice were used; 6 mice constituted the control group and 18 mice were infected with the RH strain. On the 2nd, 4th, and 6th days following the infection, 6 animals were euthanized, and their serums were collected. Compared to the control group, we observed a statistically significant decrease in albumin concentration in the group with T. gondii infection on the 6th day. Also, this group displayed a statistically significant, gradual increase in clusterin levels on the 2nd and 6th days, C-reactive protein levels on the 4th day, haptoglobin levels on the 2nd and 4th days, hemopexin levels on the 2nd day, serum amyloid A levels on the 2nd, 4th, and 6th days, and TNF-α levels on the 2nd, 4th, and 6th days (p < 0.05). TNF-α was strongly positively correlated with CRP, SAA, and clusterin, moderately positively correlated with hemopexin, and strongly negatively correlated with albumin. The increase in CRP, SAA, clusterin, and hemopexin levels on the 2nd day after infection, in parallel with the increase in TNF-α levels, indicates that these proteins can be considered as major acute phase proteins in acute T. gondii infection in mice. The data obtained here may be helpful for the diagnosis of T. gondii infection and for monitoring treatments.

Pathogenicity of Cryptosporidium parvum--evaluation of an animal infection model

With the intention of developing a standardised method for assessment of pathogenicity of Cryptosporidium parvum, the CPB-0 isolate was studied by propagation in 1-day-old calves followed by inoculation into specific pathogen free (SPF) piglets. The experiment was repeated. Diarrhoea and shedding of oocysts were seen in all animals infected with the CPB-0 isolate. Clinical signs included depression, inappetence, vomiting (exclusively in the piglets), and death. Histological examination at 17 and 19 days post-infection revealed parasitic stages and microscopic changes primarily restricted to colon and rectum. The unintended presence of rotavirus in some of the experimental animals revealed an additive or synergistic effect between rotavirus and C. parvum as indicated by prolonged diarrhoea, increased oocyst shedding, decreased weight gain and elevated levels of serum haptoglobin and serum amyloid A (SAA) in piglets infected simultaneously with both pathogens. The difference in daily weight gain between infected and control animals was significant only for piglets co-infected with rotavirus. The acute phase response of haptoglobin and SAA was characterised by a large individual variation. In piglets, co-infected with rotavirus, the levels of serum haptoglobin were 3.5 and 4.6 times higher in the infected versus the controls 6 and 9dpi, respectively (mean values: 2411microg/ml+/-S.D. 2023 and 1840 microg/ml+/-S.D. 1697). In the controls infected with rotavirus, peak haptoglobin concentration was seen 3dpi (mean: 1022 microg/ml+/-S.D. 425). Elevated levels of SAA were seen in 1 of 6 piglets infected with C. parvum, and in 5 of 6 piglets co-infected with rotavirus. Tumour necrosis factor alpha (TNFalpha) was undetectable in all serum samples from piglets. The obvious advantages of the SPF pig model are the naturally acquired intestinal microflora, the development of distinct clinical signs similar to cryptosporidiosis in humans and calves, the size of the animals, and the accessibility of individuals born within a short time span. This makes the model ideal for dose-response studies, evaluation of therapeutic agents as well as for assessment of differences in the clinical response to isolates of diverse genetic background. In conclusion, it was shown that the CPB-0 isolate was pathogenic to calves and piglets at a dose of 2.5 x 10(5) oocysts, and that the clinical signs could be replicated during separate experiments. Moreover, diarrhoea, oocyst shedding, body weight changes, histological alterations, and the acute phase response of haptoglobin and SAA were identified as useful parameters for discrimination of isolate-specific differences of pathogenicity.

Non-lethal infection parameters in mice separate sheep Type II Toxoplasma gondii isolates by virulence

The zoonotic protozoan parasite Toxoplasma gondii can infect all warm-blooded animals, but virulence of isolates has previously been characterised mainly by the ability to kill mice after experimental infections. In the present study, 15 Type II strains of T. gondii, isolated from five adult sheep, six sheep abortions, two pigs, one cat and one fox were examined for their virulence to young mice by less dramatic parameters. Clinical disease of inoculated mice, directly evidenced by reduced weight gain, was correlated to increase in serum level of haptoglobin and level of specific antibodies. Although Type II T. gondii strains are non-virulent to mice by lethality studies, significant differences in mouse virulence were observed between the strains of T. gondii isolated either from adult sheep or from sheep abortions. It was not possible to characterise strains isolated from sheep abortions as being more or less virulent than strains isolated from adult slaughter sheep.

Transplacental transmission of Toxoplasma gondii in minipigs infected with strains of different virulence

Infections with the zoonotic protozoan Toxoplasma gondii during pregnancy can result in severe fetal infections. To investigate the use of pigs as animal models for congenital toxoplasmosis, tachyzoites of 5 T. gondii strains, with low to intermediate virulence in mice, were intravenously inoculated into pregnant minipig gilts. Two strains caused abortions of uninfected fetuses following severe disease of the mothers. One strain caused no disease in the gilts but slightly elevated anti-T. gondii antibodies in 2 of 9 fetuses. One strain produced clinical disease with 4 mummified fetuses and 2 full-term, congenitally infected piglets in 1 gilt and no clinical disease but elevated specific fetal antibodies in both piglets of the other gilt. Infection with the fifth strain (SVS-O14), which was considered apathogenic to both pigs and mice based on the clinical course of this and previous experiments, resulted in significant numbers of congenitally infected piglets, as indicated by production of anti-T. gondii antibodies in all 12 fetuses; the parasite was identified in 3 of these fetuses. This pattern of infection indicates that pigs infected with SVS-O14 (or a similar strain) are relevant animal models for studies of transplacental transmission and pathogenesis of congenital toxoplasmosis.

Pathogenicity of selected Toxoplasma gondii isolates in young pigs

The pathogenicity in 7-week-old pigs to five different Toxoplasma gondii strains of various host species origin was compared after i.v. inoculation of 10(4) tachyzoites. Additionally, one group of pigs was inoculated i.v. with 10(6) tachyzoites of the reference strain, SSI 119. In response to the infection a significant effect of T. gondii tachyzoite inoculation dose as well as differences among strains could be observed in several parameters. The 10(6)-dose inoculated pigs showed variable degrees of clinical illness and recurrent episodes of fever 4-17 days p.i., while pigs of four of the 10(4) tachyzoite inoculated groups experienced a short-lived rise in body temperature from day 6-8 p.i. without any apparent illness or inappetence. Control pigs and pigs infected with the least pathogenic strain had normal body temperature throughout the experiment. In all inoculated pigs, T. gondii-specific IgM and IgG antibodies appeared from day 8-10 and 10-17 p.i., respectively. Serum levels of alkaline phosphatase and the acute phase protein haptoglobin were decreased or increased, respectively, in response to the infection. Differential leukocyte count on peripheral blood revealed a significant lymphocytopenia on day 6 p.i. equal to both CD4+ and CD8+ T-cells, but shifting towards a reduced ratio of CD4+/CD8+ T-cells from day 8-14 p.i. In the 10(6)-dose inoculated pigs a considerable increase in zymosan induced and spontaneous oxidative burst capacity of peripheral blood leukocytes was observed from 6 days p.i. compared with control pigs. Oxidative burst capacity was not examined for other pigs. In conclusion, several useful parameters to identify differences in T. gondii pathogenicity other than mortality were identified. Furthermore, even at low doses, significant differences between recently collected Danish T. gondii field isolates were demonstrated after i.v. inoculation in young pigs.