Toxocarosis

Abstract

This chapter discusses the role of Toxocara canis in the syndromes of visceral, ocular, and covert toxocarosis (VT, OT, CT). While the transmission dynamics of T. canis to humans have never been fully elucidated, the potential roles of pet dogs, stray dogs, and foxes, and the influence of their population densities and the age demography of the populations, are compared in relation to contamination of the environment with eggs. Routes of infection for children by geophagia, poor hygiene, fly-borne, and meat-borne ingestion of eggs or larvae are described. The development of prolonged in vitro culture and analysis of the excretions/secretions (ES) and surface of T. canis larvae have gone a long way to explaining the importance of these ES antigens and their rapid production and shedding in the prolonged course of infection and pathogenesis of disease. ES antigens also have greatly improved the sensitivity and specificity of serodiagnosis. Nevertheless, we still have insufficient understanding as to differences in the aetiology of the larvae or differences in immune responses among individuals to account for development of VT versus CT or OT in different individuals. Our understanding that most of the pathology in toxocarosis is due to the immunopathological response of the host to T. canis ES has emphasized the need for vigorous antiinflammatory therapy in treatment; unfortunately, less information is available as to the true efficacy of the anthelmintics currently available. The complexity of the T. canis life cycle in dogs is described and therapeutic regimens to prevent excretion of eggs by pet dogs are given. This, plus adequate control or exclusion of stray or wild canids from a property7 should prevent most cases of VT. Control of the other sources of infection, free-ranging stray dogs and foxes, will be difficult, and more data are needed to clarity the importance of these and of fly-borne and meat-borne transfer of infection to humans to target these for control.