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Sheelagh Lloyd

and Eric R. Morgan

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date: 07 December 2021

Toxocara canis and the syndromes of visceral and ocular larva migrans (VLM, OLM), covert toxocarosis, and neurological toxocarosis are described. Other potential agents, particularly Toxocara cati and Baylisascaris procyonis , are described. The transmission dynamics of toxocarosis to humans have never been fully elucidated, but the potential roles of pet and stray dogs, foxes, cats, and the influence of their population densities, and age demographies, are discussed in relation to contamination of the environment with eggs. Routes of infection with eggs by geophagia, poor hygiene outdoors and with dogs, and fly-borne contamination of food, and meat-borne ingestion of larvae are described. The development of prolonged in vitro culture and analyses of T. canis larval excretions/secretions (TES) and surface antigens helped explain the importance of the rapid production and shedding of TES in the prolonged course of infection and pathogenesis of disease. TES also have greatly improved serodiagnosis. However, we still have insufficient understanding of differences in the aetiology of the larvae or differences in immune responses among individuals to account for development of VLM, covert toxocarosis, or OLM in different individuals. Our understanding of the immunopathological response of the host to TES has emphasized the need for anti-inflammatory therapy in treatment; unfortunately, less information is available on the true efficacy of the anthelmintics 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 property could prevent most cases of VLM. Control of infection from free-ranging stray dogs, cats and foxes, will be difficult and more data are needed to clarify the importance of these and of fly-borne and meat-borne transfer of infection to humans for control.

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