Analysis of Seroreactivity and Seropositivity in Balb/c Mice Experimentally Infected with Toxocara canis Using Two Recombinant (rTc-CTL-1 and rTES-120) Antigens.

INTRODUCTION

Toxocarosis in human beings is currently diagnosed by serological assay based on the detection of antibodies against Toxocara antigens. Toxocara canis larvae do not reach the adult stage in paratenic hosts like humans and mice. Therefore experimental infection in mice, which mimics the biology of human infection, might be relevant to get a better understanding of human toxocarosis.

METHODS

Two recombinant antigens viz. rTc-CTL-1 and rTES-120 were developed by expression of respective genes in Escherichia coli. The Balb/c mice were divided into 3 groups; Group I and group II (n = 8 mice each) were infected orally with 100 and 1000 T. canis embryonated eggs, respectively and Group III, mice served as uninfected control mice. The serum samples were obtained from all mice at 0, 7, 14, 28, 45, 60, 90, 120 and 150 days post infection (dpi) were tested by indirect ELISA for detecting seroreactivity to Toxocara and at 28 dpi sera of mice was used for confirming seropositivity of toxocarosis in experimentally infected mice.

RESULTS

The rTc-CTL-1 antigen based ELISA showed the antibody response in both the infected groups were increased from 7 dpi, reached maximum at 28 dpi, then gradually declined but it was maintained up to 150 dpi where as the rTES-120 antigen based ELISA detected antibody only at 28 dpi with a maximum at 60 dpi, then moderately declined but it was observed up to 150 dpi. The antibody response of group II mice were significantly higher than the group I mice throughout the observation period when compared to control group (P < 0.01). Statistical analysis showed a highly significant difference in the antibody response between the group I and group II mice from 14 to 150 dpi with rTc-CTL-1 ELISA and from 28 to 150 dpi with rTES-120 based ELISA (P < 0.01). The seropositivity in mice sera samples at 28 dpi using rTc-CTL-1 based ELISA revealed 87.5% in group I and 100% in group II mice were positive. The rTES-120 ELISA revealed 12.5% in group I and 25% in group II mice were positive. Statistically highly significant difference in the seropositivity between the recombinant antigens (P < 0.01) was observed, but, there was no significant difference between the infected group of mice.

CONCLUSION

It was concluded that rTc-CTL-1 antigen based ELISA detect antibody in early infections compared to rTES-120 ELISA and also the antibody response was directly proportional to the dosage of infective eggs. The diagnostic efficacy of rTc-CTL-1 antigen based ELISA was better when compared to rTES-120 antigen based ELISA.