Felis ISSN 2398-2950


Contributor(s): Stephen Barr, SandyTrees, Kim Willoughby, Kerry Simpson


  • CauseToxoplasma gondii Toxoplasma gondii, a protozoan parasite of the cat; dogs, humans, etc, are intermediate hosts.
  • Infection via sporulated oocysts from cat feces, undercooked meat or transplacental.
  • Signs: usually subclinical, occasional severe multisystemic or central nervous system (CNS) infection.
  • Diagnosis: typically based on serology.
  • Treatment: clindamycin.
  • Prognosis: fair to good.
  • Predominate risk to humans is from consumption of undercooked meat, or soil/litter tray containing cat feces contaminated with sporulated oocysts (sporulation does not occur until 1-5 days after being passed).
  • Primary infection of women during pregnancy can cause fetal malformation/miscarriage.
    Print off the Owner factsheet on toxoplasmosis and risks to pregnant women Toxoplasmosis and risks to pregnant women to give to your client.



  • Toxoplasma gondiiToxoplasma gondii coccidian protozoal parasite.
  • Obligate intracellular parasite.

Predisposing factors


  • Undercooked meat.
  • Scavenging/hunting.
  • Cat feces in soil.
  • Feline litter tray if not cleaned daily.


  • Clinical toxoplasmosis most severe in transplacental or lactogenically infected kittens, with pulmonary or hepatic signs being the most common finding. 
  • Immunosuppression activates subclinical infection.


  • Infection by carnivorous feeding  →  tissue infection  →  oocysts released into the gut and passed in feces.
  • Cat is definitive host and, as such, is the main reservoir of infection. 
  • Cats shed unsporulated oocysts, which can become infectious (sporulated) 1-5 days after shedding.
  • Ingestion of sporulated oocysts or tissue cysts  →  organisms invade and multiply in tissues  →  intracellular pseudocysts  →  pseudocysts rupture  →  release numerous tachyzoites  →  spread throughout body  →  chronic phase.
  • Bradyzoites divide slowly within parasitic membrane  →  tissue cyst, especially in muscles and brain.
  • 2-7 days after ingestion, formation of oocysts occurs in the cat, followed by shedding (shedding typically lasts for 3-10 days but in rare cases can last up to 21 days).
  • Once tissue cysts form, host has developed immunity  →  resistant to reinfection with that strain, but may be infected with other strains.
  • Tissue cysts persist for months/years.
  • There are 3 possible modes of transmission; congenital infection, ingestion of infected tissue and ingestion of oocyst-contaminated food or water.
  • Most natural infections acquired by eating infected meat (hence feral cats greater risk to man than domestic).

Clinical infection

  • This is dependant on the host/parasite interaction and may occur in:
    • Neonates/kittens.
    • Immunosuppressed individuals (reactivation of chronic infection).
    • If a poor immune response is mounted after primary infection.
  • Some strains of Toxoplasma gondii appear to be more pathogenic than others and some appear to demonstrate specific tissue affinities.
  • Immune complex formation and deposition in tissues, as well as delayed hypersensitivity reactions, can be involved in chronic forms of toxoplasmosis.


  • Definitive hosts are Felidae.
  • Intermediate hosts: mammals, amphibians, reptiles, fish.
  • Seroprevalence: cats 40% (0-100%, the higher prevalence being in cats which hunt for their food), dogs 30-40%, humans 30-60%.
  • Cats ingest oocysts/tissue cysts  →  enteroepithelial cycle  →  shed oocysts within 3 days to 3 weeks  →  sporulate in environment in 1-3 days  →  ingested by intermediate host.
  • Dogs/man infected via:
    • Ingestion of meat containing pseudocysts or tissue cysts.
    • Ingestion of sporulated oocysts.
    • Transplacental infection (dam/mother develops parasitemia during pregnancy).


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hartmann K, Addie D, Belák S et al (2013) Toxoplasma Gondii Infection in Cats: ABCD guidelines on prevention and management. J Feline Med Surg 15 (7), 631-637 PubMed.
  • Lappin M R (2010) Update on the diagnosis and management of Toxoplasma gondii infection in cats. Top Companion Anim Med 25 (3), 136-141 PubMed.
  • Last R D, Suzuki, Y, Manning T et al (2004) A case of fatal systemic toxoplasmosis in a cat being treated with cyclosporin A for feline atopy. Vet Dermatol 15 (3), 194-198 PubMed.
  • Brownlee L & Sellon R K (2001) Diagnosis of naturally occurring toxoplasmosis by bronchoalveolar lavage​ in a cat. JAAHA 37 (3), 251-255 PubMed.
  • Powell C C & Lappin M R (2001) Clinical ocular toxoplasmosis in neonatal kittens. Vet Opthalmol (2), 87-92 PubMed.
  • Davidson M G (2000) Toxoplasmosis. Vet Clin North Am Small Anim Pract 30 (5), 1051-1062 PubMed.
  • Davidson M G (1998) Feline ocular toxoplasmosis. Vet Ophthalmol (2-3), 71-80 PubMed.
  • Lappin M R (1996) Feline toxoplasmosis - interpretation of diagnostic test results. Seminars Vet Med Surg (Small Anim) 11 (3), 154-160 PubMed.
  • Dubey J P (1994) Toxoplasmosis. JAVMA 205 (11), 1593-8 PubMed.
  • Dubey J P & Carpenter J L (1993) Neonatal toxoplasmosis in littermate cats. JAVMA 203 (11), 1546-1549 PubMed.
  • Peterson J L, Willard M D, Lees G E et al (1991) Toxoplasmosis in two cats with inflammatory intestinal disease. JAVMA 199 (4), 473-476 PubMed.
  • Heidel J R, Dubey J P, Blythe L L et al (1990) Myelitis in a cat infected with Toxoplasma gondii and feline immunodeficiency virus. JAVMA 196 (2), 316-318 PubMed.

Other sources of information

  • Taboada J & Merchant S R (1995) Protozoal and miscellaneous infections. In: Ettinger, S J and Feldman, E C (eds) Textbook of Veterinary Internal Medicine.4th edition. Philadelphia: W B Saunders. p 384. (Brief but comprehensive review.)
  • Ramsey I & Tennant B (2001) Manual of Canine and Feline Infectious diseases. BSAVA Publications, Gloucester.
  • Dubey J P & Lappin M R (1998) Toxoplasmosis and neosporosis.In:Infectious diseases of the Dog and Cat. 2nd edn. Ed. Greene CE. WB Saunders Co. pp. 493-509.