Serological Detection of Canine Toxocarosis Using Recombinant and Native Toxocara canis Excretory–Secretory Antigens: A Comparative ELISA Study

Toxocara canis is the most prevalent intestinal roundworm of dogs and other canids, with significant zoonotic potential for humans. In the present study, two recombinant antigens, rTc-CTL-1 and rTES-120, were developed from the larvae of T. canis excretory-secretory (TES) antigens by amplifying, cloning and expressing the respective genes in Escherichia coli. The native TES antigen was prepared from in vitro cultivation of larvae. A total of 170 serum samples were collected from dogs above 6 months of age (n = 90) and below 6 months of age (n = 80) in the Chennai region, Tamil Nadu. The serodiagnostic potential of the recombinant rTc-CTL-1 and rTES-120 antigens was compared with that of the native TES antigen using ELISA for the detection of anti-Toxocara IgG antibodies. The rTc-CTL-1 antigen-based ELISA showed that 40% of dogs above 6 months and 28.8% of dogs below 6 months were positive, whereas the rTES-120 antigen detected 35.6% and 22.5% positivity in the respective age groups. In comparison, the native TES antigen-based ELISA detected 58.9% positivity in dogs above 6 months and 38.8% in dogs below 6 months of age. Among the three antigens, the highest percentage of seropositivity as well as the highest antibody titre was detected with the native TES antigen, followed by the recombinant rTc-CTL-1 antigen and the lowest with the TES-120 antigen. Statistical analysis showed a highly significant difference in seropositivity between the recombinant and native TES antigens (χ2 = 15.52, p 2 = 1.09, p > 0.05). However, a highly significant difference was observed between the age groups of dogs when using the native TES antigen (χ2 = 6.87, p < 0.01). Detection of T. canis eggs in faecal samples revealed that only 12.2% of adult dogs were positive, whereas 60% of pups were positive. In contrast, the IgG ELISA test detected more positive cases in adult dogs compared to faecal examination. It was concluded that the IgG-based ELISA using either recombinant or native TES antigens is a reliable tool for detecting migratory larval infection in adult dogs, with a fairly high degree of sensitivity.