Developmental stages and viability of Toxocara canis eggs outside the host

Abstract

Introduction: Toxocariasis is a soil-transmitted zoonotic disease caused mainly by ingestion of larvated eggs of Toxocara canis. Objectives: To study the morphology of the intraovular developmental stages of Toxocara canis in culture, characterize non-viable eggs and the sequences of larval molting and compare the viability of eggs at the early stages of division and at reaching full maturation. Material and methods: Observation of developing embryos and characterization of non-viable eggs were done using light microscope. The proportions of viable eggs during embryonation were compared to the proportions of viable mature eggs. Results: Cell division commenced after 24 hours of cultivation. Early stages were found to be present over a period of 3-5 days. The developmental stages identified were eggs with: One cell, two cells, three cells, four cells, early morula, late morula, blastula, gastrula, tadpole, pre-larva, first, second and third stage larva. Two larval molts occurred. Non-viable eggs had degenerated cytoplasm, thin or collapsed shell and the larvae did not move after exposure to light. No significant differences were found between the proportions of viable eggs from day five to day 21 as compared to viability of fully mature eggs (30 days). Conclusion: Developing embryos in the environment may be considered as a potential threat to the public health. The precise identification of developmental stages and the clear differentiation of viable and non-viable eggs can help in determining an accurate baseline rate of development that could be used in studies of ovicidal compounds.

Keywords

• Toxocara canis
• toxocariasis
• zoonoses
• embryonic structures
• larva