Development of the serological response in rabbits infected with Toxocara canis and Toxascaris leonina.

The indirect fluorescent antibody test using frozen sections of infective Toxocara canis and Toxascaris leonina eggs, and the enzyme linked immunosorbent assay using homogenized Toxocara canis embryonated egg extract and T canis excretory-secretory products as adsorbed antigens were used to determine the specificity and development of circulating antibodies in rabbits. Frozen sections were subdivided into four morphologically distinct compartments for analysis of the development of the circulating antibody response. The fluid surrounding the larva was the most reactive up to 21 days after infection, and this material was found to be predominantly excretory-secretory in nature. As the infection progressed antibodies directed against 'somatic' tissue materials increased. Cross reactions between sera from rabbits infected with T. canis eggs and Toxascaris leonina frozen sections, and rabbits infected with T. leonina eggs and Toxocara canis frozen sections occurred between both the excretory-secretory fluid and somatic components of the infective eggs. These results were substantiated using the enzyme linked immunosorbent assay. When T. canis excretory-secretory antigen was used, an earlier response (peak day 21) was detected than when using T. canis embryonated egg extract (peak day 35). However, cross reactions between T. canis excretory-secretory antigen and sera from rabbits infected with Toxascaris leonina occurred, indicating that the serodiagnosis of visceral larva migrans using Toxocara canis excretory-secretory antigen may still prove unsatisfactory when considering the role of Toxascaris as a possible causative agent.