Transmission Transmission of Toxocara to humans is usually through ingestion of infective eggs. T. canis can lay around 200,000 eggs per day. These eggs are passed in cat or dog feces, but the defecation habits of dogs cause T. canis transmission to be more common than that of T. cati. Both Toxocara canis and Toxocara cati eggs require a several week incubation period in moist, humid weather outside a host before becoming infective, so fresh eggs cannot cause<unk> . Many objects and surfaces can become contaminated with infectious Toxocara eggs. Flies that feed on feces can spread Toxocara eggs to surfaces or foods. Young children who put contaminated objects in their mouths or eat dirt (pica) are at risk of developing symptoms. Humans can also contaminate foods by not washing their hands before eating. Humans are not the only accidental hosts of Toxocara. Eating undercooked rabbit, chicken, or sheep can lead to infection; encysted larvae in the meat can become reactivated and migrate through a human host, causing<unk> . Special attention should be paid to thoroughly cooking giblets and liver to avoid transmission. Incubation period The incubation period for Toxocara canis and cati eggs depends on temperature and humidity. T. canis females, specifically, are capable of producing up to 200,000 eggs a day that require 2–6 weeks minimum up to a couple months before full development into the infectious stage. Under ideal summer conditions, eggs can mature to the infective stage after two weeks outside of a host. Provided sufficient oxygen and moisture availability, Toxocara eggs can remain infectious for years, as their resistant outer shell enables the protection from most environmental threats. However, as identified in a case study presented within the journal of helminthology, the second stage of larvae development poses strict vulnerabilities to certain environmental elements. High temperatures and low moisture levels will quickly degrade the larvae during this stage of growth. Reservoir Puppies are the major source of environmental contamination with roundworm eggs Dogs and foxes are the reservoir for Toxocara canis, but puppies and cubs pose the greatest risk of spreading the infection to humans. Infection in most adult dogs is characterized by encysted second stage larvae. However, these larvae can become reactivated in pregnant females and cross the placental barrier to infect the pups. Vertical transmission can also occur through breastmilk. Infectious mothers, and puppies under five weeks old, pass eggs in their feces. Approximately 50% of puppies and 20% of adult dogs are infected with T. canis. Cats are the reservoir for Toxocara cati. As with T. canis, encysted second stage larvae in pregnant or lactating cats become reactivated. However, vertical transmission can only occur through breastfeeding. Flies can act as mechanical vectors for Toxocara, but most infections occur without a vector. Most incidents with<unk>  result from prokaryotic expression vectors and their transmission through direct physical contact with feces that results in the contraction of the illness. Morphology Both species produce eggs that are brown and pitted. T. canis eggs measure 75-90 µm and are spherical in shape, whereas the eggs of T. cati are 65-70 µm in diameter and oblong. Second stage larvae hatch from these eggs and are approximately 0.5mm long and 0.02mm wide. Adults of both species have complete digestive systems and three lips, each composed of a dentigerous ridge. Adult T. canis are found only within dogs and foxes and the males are 4–6 cm in length, with a curved posterior end. The males each have spicules and one “tubular testis.” Females can be as long as 15 cm, with the vulva stretching one third of their bodylength. The females do not curve at the posterior end. T. cati adult females are approximately 10 cm long, while males are typically 6 cm or less. The T. cati adults only occur within cats, and male T. cati are curved at the posterior end. Life cycle thumb Cats, dogs and foxes can become infected with Toxocara through the ingestion of eggs or by transmission of the larvae from a mother to her offspring. Transmission to cats and dogs can also occur by ingestion of infected accidental hosts, such as earthworms, cockroaches, rodents, rabbits, chickens, or sheep. Eggs hatch as second stage larvae in the intestines of the cat, dog or fox host (for consistency, this article will assume that second stage larvae emerge from Toxocara eggs, although there is debate as to whether larvae are truly in their second or third stage of development). Larvae enter the bloodstream and migrate to the lungs, where they are coughed up and swallowed. The larvae mature into adults within the small intestine of a cat, dog or fox, where mating and egg laying occurs. Eggs are passed in the feces and only become infective after three weeks outside of a host. During this incubation period, molting from first to second (and possibly third) stage larva takes place within the egg. In most adult dogs, cats and foxes, the full lifecycle does not occur, but instead second stage larvae encyst after a period of migration through the body. Reactivation of the larvae is common only in pregnant or lactating cats, dogs and foxes. The full lifecycle usually only occurs in these females and their offspring. Second stage larvae will also hatch in the small intestine of an accidental host, such as a human, after ingestion of infective eggs. The larvae will then migrate through the organs and tissues of the accidental host, most commonly the lungs, liver, eyes, and brain. Since L2 larvae cannot mature in accidental hosts, after this period of migration, Toxocara larvae will encyst as second stage larvae.
Toxocariasis
Filariasis
Acariasis
Helminthiasis
Paragonimiasis
Metagonimiasis
Leishmaniasis
Isosporiasis