There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
The visceral infection of humans with Toxocara canis is particularly prevalent in
children and may cause a variety of symptoms that commonly persist for 6-24 months.
The ocular infection usually causes permanent loss of visual acuity. Human infection
is acquired by ingestion of embryonated T. canis eggs with contaminated dirt. Review
of recent reports indicates that patent T. canis infection is widely prevalent in
the general population of dogs all over the world (3-81%) and results in a substantial
contamination of the ground (0.3-87%). The results of sensitive and specific serological
tests suggest that about 7% of the clinically healthy human population of the United
States, about 5% of that of Canada, and about 4% of that in Great Britain is infected
with the parasite. Control of transmission of the parasite to man is often attempted
by eliminating the infection in dogs, reducing the population of dogs and the environmental
contamination with their feces, and educating the public about the zoonotic potential
of toxocariasis. The evidence reviewed indicates that these methods are only marginally
effective. Because T. canis relies on congenital and lactogenic transmission to persist
in nature, only a procedure that effects the sustained killing of the reservoir larvae
in the tissues of the bitch, or of newly-acquired parasites, is expected to be successful.
Research with mice, rabbits and dogs demonstrated that prior infections of the host
induce the development of protective immunity to reinfections. This procedure, however,
leaves remnant populations of larvae from the immunizing infections that are resistant
to anthelmintics and to the effect of prior irradiation. Hyperimmunization with partially-purified
extracts of T. canis larvae induced 37% resistance to a challenge in mice when the
extract was administered alone, and 76% resistance when administered with lipopolysaccharide
adjuvant. Production of complete resistance, however, will probably require the prior
control of the immunosuppression induced by the parasite. T. canis infections inhibit
the production of homologous protective immunity and antibody responses to heterologous
antigens, probably by interfering with the activity of helper T-cells, competing with
protective antigens, and suppressing antibody synthesis. The evidence indicates, however,
that an anti-T. canis vaccine to eliminate the parasite in dogs is feasible.