Ascarids - species, hosts, importance

ASCARIDOIDEA

Species, hosts and importance

The superfamily is divided into 5 families only one of which, the Acarididae is of major importance in domestic animals. One other family, the Anisakidae, is a large group of nematodes widely distributed in marine mammals, birds, fishes and reptiles as definitive hosts. The anisakids require water for transmission and usually involve fish and aquatic invertebrates as paratenic or intermediate hosts. Anisakis simplex is of medical importance because its larvae can cause a severe enteritis in humans after eating undercooked marine fish and squid that serve as paratenic hosts for Anisakis simplex. Pseudoterranova decipiens is economically important because its intermediate and paratenic hosts include fish that are of commercial importance such as the Atlantic cod and American plaice.

Anisakids of marine mammals
Species	Definitive hosts	Transmission	Comments
*Anisakis simplex*	Marine mammals - primarily cetaceans (dolphin, porpoise, whales) but also pinnipeds (seals)	Ingestion of L3s in marine crustaceans such as shrimps (intermediate hosts) or paratenic hosts such as fish (herring, cod, salmon, mackerel and halibut) and squid.	Humans may become infected by eating fish or squid that is raw, undercooked, pickled, smoked or salted. Other Anisakis species may also be involved.
*Pseudoterranova decipiens*	Pinnipeds - seals, sea lions and walruses	Ingestion of larvae in fish intermediate hosts	May also be implicated in enteritis in humans.

Ascarids of domestic animals
Species	Definitive hosts	Transmission	Comments
*Ascaris suum*	Pigs	1. Ingestion of eggs containing second stage larvae.	Global distribution
*Parascaris equorum*	Horses and donkeys	1. Ingestion of eggs containing second stage larva.	Global distribution
*Toxocara canis*	Dogs	1. Ingestion of eggs containing second stage larvae. 2. Ingestion of mice paratenic hosts. 3. Prenatal transmission. 4. Transmammary transmission.	Global distribution
*Toxocara cati*	Cats	1. Ingestion of eggs containing second stage larvae. 2. Ingestion of mice paratenic hosts. 3. Transmammary transmission.	Global distribution
*Toxascaris leonina*	Dogs and cats	1. Ingestion of eggs containing second stage larvae. 2. Ingestion of mice intermediate hosts.	Global distribution
*Toxocara vitulorum*	Mainly cattle but also sheep and goats	1. Ingestion of eggs containing second stage larvae. 2. transmammary transmission.	Global distribution. In North America, mainly in the southern U.S.
*Baylisascaris procyonis*	Raccoons primarily but occasionally in dogs.	1. Ingestion of eggs containing second stage larvae. 2. Ingestion of intermediate hosts.	Implicated in serious neurologic disease (larval migrans) in domestic animals and humans