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Toxoplasmosis
Introduction
- Cause: Toxoplasma 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.
Presenting signs
- Uveitis.
- Pyrexia.
- Dyspnea.
- Hyperesthesia.
- Myocarditis.
- Weight loss.
- Central or peripheral nervous system signs (ataxia, seizures).
- Icterus.
- Diarrhea.
Acute presentation
Generalized infection
- Depression.
- Respiratory distress.
- Anorexia.
- Diarrhea.
- Peritoneal effusion.
- Icterus.
- Pyrexia followed by hypothermia.
- Progresses to death.
Geographic incidence
- Worldwide.
Age predisposition
- All ages, severe disease more likely in cats less than 1 year old.
Public health considerations
- Potential zoonotic, but shedding is rare (1 in 250 cats) and not prolonged (typically lasting 3-10 days). Oocysts are not infectious until 1-5 days after being shed.
- Infection in man is usually thought to result from eating/handling undercooked meat.
Pathogenesis
Etiology
- Toxoplasma gondii: Toxoplasma gondii coccidian protozoal parasite.
- Obligate intracellular parasite.
Predisposing factors
General
- Undercooked meat.
- Scavenging/hunting.
- Cat feces in soil.
- Feline litter tray if not cleaned daily.
Specific
- Clinical toxoplasmosis most severe in transplacental or lactogenically infected kittens, with pulmonary or hepatic signs being the most common finding.
- Immunosuppression activates subclinical infection.
Pathophysiology
- 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.
Epidemiology
- 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).
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
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 4 (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 1 (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.