112 - Ascarids

Abstract

•First Described: Toxocara canis and T. cati have been recognized since the late 1700s. Toxascaris leonina was first described in 1902. Baylisascaris procyonis was first described in raccoons (Procyon lotor) in Poland in 1951, and first reported in dogs in 1988 (Michigan, United States).•Cause: Ascarids (order Ascaridida) are large robust nematodes that primarily infect the small intestine of their definitive hosts. The anterior end of this group of nematodes has three prominent lips and males lack copulatory bursa. Representatives of this group include important pathogens of several domestic animals, wildlife species, and humans. This chapter will focus on the four primary ascarid species that infect dogs and cats: Toxocara canis and Toxascaris leonina in dogs, Toxocara cati and T. leonina in cats, and Baylisascaris procyonis (raccoon roundworm) which rarely occurs in dogs.•Affected Hosts: Domestic dogs and wild canids can become infected with T. canis and T. leonina, whereas domestic cats and wild felids are the hosts of T. cati and T. leonina. Although the raccoon is the primary host of B. procyonis, domestic dogs can develop patent infections.•Paratenic Hosts: An intermediate host is not required for ascarids, but many species utilize paratenic hosts. Rodents are the primary paratenic host species, although birds can also become infected with Toxocara spp. and B. procyonis.•Geographic Distribution: Toxocara canis, T. cati, and T. leonina have cosmopolitan distributions. Baylisascaris procyonis is native to many regions of the United States and Canada but has been introduced to parts of Asia and Europe through translocation of raccoons.•Route of Transmission: Toxocara canis can be transmitted to canids by ingestion of embryonated eggs or paratenic hosts or by transplacental or transmammary routes. Toxocara cati can be transmitted to felids by ingestion of embryonated eggs or paratenic hosts and through the transmammary route. Toxascaris leonina is transmitted to canids or felids by ingestion of embryonated eggs or paratenic hosts. Baylisascaris procyonis is transmitted to canids by ingestion of embryonated eggs or paratenic hosts.•Major Clinical Signs: Young dogs and cats are more likely to develop signs which may include unthriftiness, lethargy, abdominal tenderness, rough haircoat, poor body condition and potbellied appearance, cough, and mucoid diarrhea. Adult animals are less likely to develop signs, as are those animals with low parasite burdens.•Differential Diagnoses: Parasitic ova of other GI helminths must be differentiated from ascarid eggs. In dogs and cats, other large parasitic helminths or pseudoparasites (e.g., Physaloptera spp., free-living planarian Bipalium, horsehair worms/nematomorpha) may be passed in feces or vomitus that must be differentiated from ascarids.•Human Health Significance: Toxocara spp. and B. procyonis are zoonotic. Infections are acquired by ingestion of embryonated eggs in the environment.