Toxascaris spp

From Dog
Eggs of T. leonina as visualized under light microscopy[1]

Toxascaris spp are a large parasitic cold-weather nematode of dogs, cats and foxes[2].

Adult can be up to 10 cm in length, with a very short prepatent period of 1 - 2 weeks.

Species which are pathogenic to dogs include:

  • Toxascaris leonina

Dogs become infected by eating intermediate hosts (usually rodents) where encysted larvae reside within the intestinal epithelium[3]. Larvae become proteolytically activated in the dog stomach. In the small intestine, they penetrate the mucosa and develop into adults, activatng a Th-2 helper cell response by the host[4]. They finally return to the lumen of the intestine as adult, where they lay eggs[5].

The short life cycle enables this parasite to persist in even well-sanitized colonies of dogs. Fecal eggs can be detected in pups from 6 weeks of age in kennels endemically infected with this parasite[6].

Infections in young dogs normally result in characteristic underweight, pot-bellied puppies, which are often anemic[7]. Deaths associated with heavy infestations in young dogs is uncommon, compared with Toxocara canis and Ancylostoma caninum.

Adult dogs are often asymptomatically infected, although poor coat, polyphagia and anemia can also occur[8].

Diagnosis is usually based on coprological examinations using fecal floatation devices[9].

Supportive diagnosis can be made with ELISA assays of feces and blood samples, and PCR assays can be used for accurate speciation of the parasite[10].

Treatment is usually effective with milbemycin oxime[11], emodepside[12], moxidectin, selamectin[13], ivermectin and most proprietary benzimidazoles or thiophenes (e.g. febantel[14]).


  1. Kim YH & Huh S (2005) Prevalence of Toxocara canis, Toxascaris leonina and Dirofilaria immitis in dogs in Chuncheon, Korea (2004). Korean J Parasitol 43(2):65-67
  2. Mirzaei M & Fooladi M (2012) Prevalence of intestinal helminthes in owned dogs in Kerman city, Iran. Asian Pac J Trop Med 5(9):735-737
  3. Dubey JP (1969) Migration and development of Toxascaris leonina larvae in mice. Trop Geogr Med 21(2):214-218
  4. Cho MK et al (2009) Identification of host immune regulation candidate genes of Toxascaris leonina by expression sequenced tags (ESTs) analysis. Vet Parasitol 164(2-4):242-247
  5. Bowman, DD (2009) Georgis' parasitology for veterinarians. 9th edn. Elsevier Saunders, Missouri. pp:200-201
  6. Fisher MA et al (2002) Epidemiology of Toxascaris leonina infection post-weaning within a colony of dogs. J Helminthol 76(1):27-29
  7. Qadir S et al (2011) Intestinal helminths induce haematological changes in dogs from Jabalpur, India. J Helminthol 85(4):401-403
  8. Rep BH (1980) Roundworm infection (Toxocara and Toxascaris) in dogs in the Netherlands. Tijdschr Diergeneeskd 105(7):282-289
  9. Becker AC et al (2012) Prevalence of endoparasites in stray and fostered dogs and cats in Northern Germany. Parasitol Res 111(2):849-857
  10. Li MW et al (2007) PCR tools for the verification of the specific identity of ascaridoid nematodes from dogs and cats. Mol Cell Probes 21(5-6):349-354
  11. Schnitzler B et al (2012) Confirmation of the efficacy of a combination tablet of spinosad and milbemycin oxime against naturally acquired infections of canine intestinal nematode parasites. Vet Parasitol 184(2-4):279-283
  12. Altreuther G et al (2009) Field evaluation of the efficacy and safety of emodepside plus praziquantel tablets (Profender tablets for dogs) against naturally acquired nematode and cestode infections in dogs. Parasitol Res 105(1):S23-S29
  13. McTier TL et al (2000) Efficacy of selamectin against experimentally induced and naturally acquired ascarid (Toxocara canis and Toxascaris leonina) infections in dogs. Vet Parasitol 91(3-4):333-345
  14. Clark JN et al (1992) Efficacy of ivermectin and pyrantel pamoate combined in a chewable formulation against heartworm, hookworm, and ascarid infections in dogs. Am J Vet Res 53(4):517-520