Immunodiagnosis of primary Toxoplasma gondii infection in sheep by the use of a P30 IgG avidity ELISA

Abstract

Toxoplasma gondii is a protozoan parasite with a worldwide distribution. In both sheep and humans, if the parasite is encountered during pregnancy, fetal infection and abortion can occur. Therefore, Toxoplasma infection in sheep has a major economic impact upon sheep farming. Clinically, there is a need to distinguish recent (acute) infections from longstanding (chronic) infections. However, current serological techniques, such as detection of anti-T. gondii IgG, cannot discriminate between acute and chronic infections. Increasing immunoglobulin avidity is a good determining factor of how recent an infection is. In this study, we describe the application and validation of a T. gondii IgG avidity ELISA, based on the use of an affinity-purified, native T. gondii P30 antigen. The assay was used to examine sera from eight sheep experimentally infected with T. gondii and found that all seroconverted within 21 days post-infection (p.i.), beginning with avidities that were initially low but that increased over time, with all sheep reaching high IgG avidity within 10 weeks p.i. In addition, sera from clinically healthy but T. gondii-seropositive lambs and ewes and seropositive ewes with a history of abortion were also subjected to a preliminary serological investigation. High IgG avidities were found in 80% of the seropositive lambs, in 90% of the clinically healthy ewes and in 97% of the ewes with abortion problems. These findings indicate that the animals had most likely contacted the parasite a longer time ago.

Determination of IgG avidity in BALB/c mice experimentally infected with Toxocara canis

“…This difference was observed in Toxoplasma gondii infection, in both humans and sheep, where chronic infection in humans was established when the percentage of IgG avidity was higher than 40%, which occurred after five months of infection (BERTOZZI et al, 1999). In sheep, the percentage of avidity was greater than 35%, which occurred after the fourth week of infection (SAGER et al, 2003).…”

Technical specifications on harmonised epidemiological indicators for biological hazards to be covered by meat inspection of domestic sheep and goats

“…o ELISA using SAG1 (P30) antigen: commercial kits use native antigen (Sager et al, 2003). Recombinant SAG1 antigen is also now available which can be used in a mixture of recombinant antigens .…”

Surveillance and monitoring of Toxoplasma in humans, food and animals - Scientific Opinion of the Panel on Biological Hazards

“…Subsequently, Hill et al (2006) compared six methods for the diagnosis of T. gondii infection in pigs, and they found that the validated ELISA is the most sensitive test for the analysis of sera. An IgG-avidity ELISA which may help in the identification of active or recent T. gondii infections, has been described (Sager et al, 2003).…”