Seroprevalences of Toxoplasma gondii and Neospora caninum in pet rabbits in Japan

Abstract

The potential contamination of Toxoplasma gondii and Neospora caninum oocysts in the human environment is a concern from the public health viewpoint. However, estimation of their seroprevalences in humans cannot be performed in a manner that distinguishes between oocysts and tissue cysts as a source of infection. Rabbits are considered popular pet animals in Japan that can acquire natural infections by the aforementioned parasites only through the ingestion of oocysts. Therefore, this study was conducted to estimate the seroprevalences of T. gondii and N. caninum in pet rabbits in Japan as an indicator of the possible oocyst contamination in the environment surrounding human beings. Serum samples of 337 rabbits were examined by different serological methods. Enzyme-linked immunosorbent assays were performed to measure the titer of IgG and IgM antibodies. Samples revealed to be seropositive by ELISA were further analyzed by a latex agglutination test, Western blotting and an indirect immunofluorescence assay. The rates of seropositivity for T. gondii were 0.89% (3/337) and 0.29% (1/337) in IgG and IgM ELISA, respectively. SAG1 and SAG2 were detected as major antigens by the positive rabbit sera in Western blotting associated with strong staining observed by IFA in T. gondii tachyzoites. Regarding N. caninum, none of the serum samples showed a specific reaction in both Western blotting and the IFA. The results of this study indicate low seroprevalences of toxoplasmosis and neosporosis in pet rabbits in Japan, suggesting low oocyst contamination in the human environment.

Fig. 1.

Western blot analysis. A) Lanes 1, 2 and 3 represent seropositive rabbit samples for T. gondii. Lane 4 represents a seronegative sample. The analysis was performed by using an equal volume of purified T. gondii tachyzoite lysate of the ME49 strain as the antigen. B) Specific bands of SAG1 can be observed at 30 kDa (left panel), and those of SAG2 can be observed at 22 kDa (right panel). Lane 1 shows seropositive rabbit sample naturally infected with T. gondii. Lane 2 shows mouse anti-SAG1 monoclonal (left panel) and mouse anti-SAG2 polyclonal (right panel) antibodies, respectively. Purified T. gondii lysate of the ME49 strain was used as the antigen.

Fig. 2.

Immunoprecipitates of either seronegative (lane 2) or seropositive (lane 3) samples reacted with either the mouse anti-SAG1 monoclonal antibody (left panel) or mouse anti-SAG2 polyclonal antibody (right panel). Lane 1, T. gondii lysate. The black arrow represents the specific band of SAG1 (left) and SAG2 (right) precipitated only by the positive sera. Arrowheads represent IgG heavy (upper) and light (lower) chains, respectively.

Fig. 3.

IFA. Detection of specific antibodies in RH strain tachyzoites of T. gondii. Rows 1, 2 and 3 represent T. gondii-seropositive samples (left panel, red). Row 4 represents a seronegative sample. The mouse anti-T. gondii IMC1 antibody (green) was used for counterstaining.