# Toxoplasma gondii
**Toxoplasma gondii** is a single-celled protozoan parasite that infects most species of warm-blooded animals, including humans, and causes the disease toxoplasmosis.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) It is one of the most common parasitic infections worldwide: a systematic review of 152 studies covering 648,010 people found an average global seroprevalence of 25.7% (95% CI: 25.6 to 25.8%), with country-level rates ranging from 0.5% to 87.7%.[2](https://pubmed.ncbi.nlm.nih.gov/33597463/) Most infected people with healthy immune systems have no symptoms, but the parasite can cause severe disease in pregnant women, their fetuses, and people with weakened immunity.[3](https://www.cdc.gov/parasites/toxoplasmosis/)
| Key fact | Detail |
|---|---|
| Organism | Obligate intracellular protozoan parasite of the phylum Apicomplexa; infects virtually all warm-blooded animals[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) • [4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11148961/) |
| Definitive host | Only members of the cat family (Felidae); sexual reproduction occurs in the feline intestine and unsporulated oocysts are shed in feces[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) |
| Global reach | Average seroprevalence 25.7% worldwide; Africa highest at 61.4%, Asia lowest at 16.4%[2](https://pubmed.ncbi.nlm.nih.gov/33597463/) |
| Persistence | Tissue cysts in muscle, brain, and eye remain for the life of the host; no drug eradicates the encysted stage[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) • [5](https://www.cdc.gov/toxoplasmosis/hcp/clinical-care/index.html) |
| Standard treatment | Pyrimethamine plus sulfadiazine, with folinic acid to protect the bone marrow[5](https://www.cdc.gov/toxoplasmosis/hcp/clinical-care/index.html) |
| Vaccine | No human vaccine exists; the only licensed vaccine, Toxovax, is a live attenuated strain used in sheep[6](https://saeijlab.faculty.ucdavis.edu/toxoplasmosis-the-disease/treatment-and-vaccines/) |
| Congenital burden | Estimated 190,100 new congenital toxoplasmosis cases per year worldwide[7](https://iris.who.int/bitstream/handle/10665/271318/PMC3699792.pdf?sequence=1) |
## Biology and life cycle
The parasite has three infectious stages. The tachyzoite, a rapidly multiplying form about 4 to 8 µm long, characterizes acute infection and invades nucleated cells throughout the body. The bradyzoite multiplies slowly inside tissue cysts, which usually measure 5 to 50 µm in diameter and form most commonly in skeletal muscle, cardiac muscle, the brain, and the eyes; these cysts can persist for the host's lifetime. [Sexual reproduction](https://www.edgepedia.org/sexual-reproduction) in felids produces oocysts that are shed unsporulated in feces; sporozoites develop within these oocysts as they sporulate in the environment.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) • [8](https://pmc.ncbi.nlm.nih.gov/articles/PMC7686686/)
Cats are central to the life cycle. Unsporulated oocysts are shed in cat feces, usually for only 1 to 3 weeks but in large numbers, and take 1 to 5 days in the environment to sporulate and become infective.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) Intermediate hosts such as birds and rodents become infected by ingesting contaminated soil, water, or plant material, and cats become infected by eating prey carrying tissue cysts.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) A single cat can excrete millions of oocysts and spread infection to many hosts.[9](https://www.sciencedirect.com/science/article/pii/S0304401720301254)
## Transmission to humans
Humans acquire infection through several routes: eating undercooked meat containing tissue cysts, especially lamb, pork, and wild game; accidentally ingesting food, water, or soil contaminated with cat feces containing infective oocysts; transplacental passage from a newly infected mother to the fetus; and, rarely, blood transfusion, organ transplantation, or laboratory accidents.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) • [10](https://stacks.cdc.gov/view/cdc/6710/cdc_6710_DS1.pdf) Primary infection also occurs after consuming unwashed fruits or vegetables, contaminated water, or unpasteurized milk containing viable organisms.[11](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/toxoplasmosis)
## Clinical disease
In immunocompetent people, acquired infection is generally asymptomatic; 10% to 20% of patients with acute infection may develop cervical lymphadenopathy or a flu-like illness, and symptoms usually resolve within a few weeks to months without treatment.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) • [3](https://www.cdc.gov/parasites/toxoplasmosis/) [Ocular toxoplasmosis](https://www.edgepedia.org/toxoplasmic-chorioretinitis), a retinochoroiditis, can result from congenital infection or infection after birth; in congenital cases, patients are often asymptomatic until the second or third decade of life, when eye lesions develop.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html)
**Immunocompromised patients.** In people with HIV, toxoplasmosis occurs mainly through reactivation of latent tissue cysts from a prior infection and presents most often as Toxoplasma encephalitis (TE), the most common cause of intracerebral mass lesions in patients with AIDS.[11](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/toxoplasmosis) • [1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) Toxoplasma-seropositive people with HIV whose CD4 counts fall below 100 cells/mm³ should receive prophylaxis against TE.[11](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/toxoplasmosis)
**Congenital infection.** [Congenital toxoplasmosis](https://www.edgepedia.org/congenital-toxoplasmosis) results from acute primary infection of the mother during pregnancy, and its incidence and severity vary with the trimester in which infection was acquired.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) A WHO-coordinated systematic review estimated the global annual incidence at 190,100 cases (95% credible interval: 179,300 to higher bound reported in the study).[7](https://iris.who.int/bitstream/handle/10665/271318/PMC3699792.pdf?sequence=1) A global meta-analysis of 250 studies including 723,655 pregnant women found IgG seroprevalence of 32.9% (95% CI: 29.4 to 36.4) and IgM seroprevalence, a marker of recent infection, of 1.9% (95% CI: 1.7 to 2.3).[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC7374101/)
## Diagnosis
Serologic testing is the routine diagnostic method. Initial testing measures Toxoplasma-specific IgG and IgM antibodies: a positive IgG titer indicates infection at some time, while a negative IgM result essentially excludes recent infection. A positive IgM result is difficult to interpret because IgM antibodies may be detectable for as long as 18 months after newly acquired infection, and assay performance varies by laboratory; when timing matters, as in pregnancy, confirmatory panel testing is recommended.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) Congenital infection can be diagnosed by detecting T. gondii DNA in amniotic fluid by PCR, and PCR of cerebrospinal fluid supports diagnosis of toxoplasmic encephalitis in people with HIV.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) • [13](https://pmc.ncbi.nlm.nih.gov/articles/PMC11147977/pdf/12639_2024_Article_1667.pdf)
## Treatment
Most immunocompetent people recover without treatment. When treatment is needed, the standard regimen combines pyrimethamine, considered the most effective drug against toxoplasmosis, with a second drug such as sulfadiazine (or clindamycin for patients with sulfa hypersensitivity), plus folinic acid (leucovorin), which protects the bone marrow from pyrimethamine's dose-related suppression.[5](https://www.cdc.gov/toxoplasmosis/hcp/clinical-care/index.html) • [14](https://www.cdc.gov/toxoplasmosis/treatment/index.html) Trimethoprim-sulfamethoxazole has been used as an alternative, and atovaquone or pyrimethamine plus azithromycin have been tried, though these have not been extensively studied.[5](https://www.cdc.gov/toxoplasmosis/hcp/clinical-care/index.html)
All recommended drugs target the multiplying tachyzoite stage and do not eradicate encysted bradyzoites in tissues; there are no drugs known to eliminate the encysted tissue stage, so a treated infection is controlled rather than cured, and reactivation remains possible if immunity fails.[5](https://www.cdc.gov/toxoplasmosis/hcp/clinical-care/index.html) • [6](https://saeijlab.faculty.ucdavis.edu/toxoplasmosis-the-disease/treatment-and-vaccines/) Immunocompromised patients are treated until their health improves, and some, such as those with HIV, may need suppressive drugs for life or as long as they remain immunosuppressed.[14](https://www.cdc.gov/toxoplasmosis/treatment/index.html)
## Epidemiology
A 2025 meta-analysis of 320 studies from 113 countries and six continents, covering 658,172 individuals between 1959 and 2020, estimated pooled global seroprevalence at 31% (95% CI: 28 to 34%), with Australia highest at 54% and Asia lowest at 25%.[15](https://www.sciencedirect.com/science/article/pii/S0014489425000761) In the United States, age-adjusted antibody seroprevalence among persons over 6 years of age was 12.4% in NHANES 2009 to 2010, down from 22.5% in the 1988 to 1994 survey, and 9.1% among women of childbearing age in the later survey.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) High prevalence in France has been linked to a preference for raw or undercooked meat, while high prevalence in [Central America](https://www.edgepedia.org/central-america) has been related to the frequency of stray cats in a climate favoring oocyst survival.[1](https://www.cdc.gov/dpdx/toxoplasmosis/index.html) In England, 228 confirmed toxoplasmosis cases were reported in 2025, an incidence of 0.38 per 100,000 population.[16](https://www.gov.uk/government/publications/common-animal-associated-infections-2025/common-animal-associated-infections-in-england-2025) The WHO Foodborne Disease Burden Epidemiology Reference Group estimated the foodborne burden of T. gondii at 1,684,414 disability-adjusted life years (95% uncertainty interval: 1,236,005 to 2,452,060) for 2010.[17](https://pmc.ncbi.nlm.nih.gov/articles/PMC4668834/)
## Prevention
[Food safety](https://www.edgepedia.org/food-safety) measures reduce risk substantially. The USDA recommends cooking whole cuts of meat (other than poultry) to at least 145 °F (63 °C) with a three-minute rest, ground meat to 160 °F (71 °C), and all poultry to 165 °F (74 °C); freezing meat for several days at 0 °F before cooking also greatly reduces the chance of infection.[18](https://www.cdc.gov/toxoplasmosis/prevention/) Because oocysts do not become infectious until 1 to 5 days after a cat sheds them, changing the litter box daily removes feces before they pose a risk; other measures include wearing gloves when gardening, rinsing produce, avoiding untreated water and unpasteurized goat's milk, and covering outdoor sandboxes.[18](https://www.cdc.gov/toxoplasmosis/prevention/)
## Vaccines
No human vaccine exists despite decades of research.[6](https://saeijlab.faculty.ucdavis.edu/toxoplasmosis-the-disease/treatment-and-vaccines/) • [19](https://pubmed.ncbi.nlm.nih.gov/42188907/) The only licensed vaccine, Toxovax, is a live attenuated strain derived from the S48 isolate that cannot form cysts, used since the early 1990s to prevent toxoplasmosis-induced abortions in sheep.[6](https://saeijlab.faculty.ucdavis.edu/toxoplasmosis-the-disease/treatment-and-vaccines/) Full and lasting protection in animal studies has come only from live-attenuated parasites, which cannot be given to people because the parasite is zoonotic and a weakened strain could in principle revert to virulence.[6](https://saeijlab.faculty.ucdavis.edu/toxoplasmosis-the-disease/treatment-and-vaccines/) Recent work applies CRISPR-Cas9 gene editing to delete virulence genes such as rop18: a WH3 Δrop18 strain vaccinated mice survived lethal challenge with type I, type II, and Chinese 1 strains and showed greatly reduced brain cyst counts, though no such candidate has reached human use.[20](https://www.nature.com/articles/s41541-024-00996-9) A 2026 review identifies mRNA and adjuvanted subunit formulations targeting multistage conserved antigens as the most realistic near-term human candidates and frames future development around three goals: preventing congenital disease, reducing tissue cysts in livestock, and vaccinating cats to interrupt environmental transmission.[19](https://pubmed.ncbi.nlm.nih.gov/42188907/)
## History
The parasite was first described in 1908 by [Charles Nicolle](https://www.edgepedia.org/charles-nicolle) and Louis Manceaux, working in [Tunisia](https://www.edgepedia.org/tunisia-epzbm6s25e), who isolated it from the gondi (*[Ctenodactylus gundi](https://www.edgepedia.org/ctenodactylus-gundi)*), a North African desert rodent; Alfonso Splendore described it the same year in Brazil.[21](https://pmc.ncbi.nlm.nih.gov/articles/PMC2727930/) • [22](https://parasiteswithoutborders.com/wp-content/uploads/2025/07/PD8-Full-Book-7-14-25-LR_compressed.pdf) Nicolle and Manceaux initially named it *Leishmania gondii* before recognizing it as a separate genus and renaming it *Toxoplasma gondii* in 1909.[23](https://theses.gla.ac.uk/75866/1/13818602.pdf) The full life cycle remained unknown for roughly 60 years after discovery; in 1970, researchers identified felids as the definitive host and the environmentally resistant oocyst shed in cat feces.[24](https://onlinelibrary.wiley.com/doi/full/10.1111/j.1550-7408.2008.00345.x) The parasite later took on a major role as an opportunistic infection in AIDS patients.[25](https://pmc.ncbi.nlm.nih.gov/articles/PMC2693343/)
## Research neglect
A 2025 analysis in *PLOS Neglected Tropical Diseases* found that toxoplasmosis meets the WHO criteria for a neglected tropical disease. Drawing on United States National Institutes of Health data, toxoplasmosis research was funded at $177 per disability-adjusted life-year for 2018 to 2024, compared with $283 per DALY for trachoma and $337 per DALY for Chagas disease.[26](https://journals.plos.org/plosntds/article?id=10.1371%2Fjournal.pntd.0014425)
## References
1. [CDC DPDx – Toxoplasmosis](https://www.cdc.gov/dpdx/toxoplasmosis/index.html)
2. [Molan A et al. Global status of Toxoplasma gondii infection: systematic review and prevalence snapshots. Tropical Parasitology 2019](https://pubmed.ncbi.nlm.nih.gov/33597463/)
3. [CDC – About Toxoplasmosis](https://www.cdc.gov/parasites/toxoplasmosis/)
4. [ABCD guidelines on Toxoplasma gondii infection in cats, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11148961/)
5. [CDC – Clinical Care of Toxoplasmosis](https://www.cdc.gov/toxoplasmosis/hcp/clinical-care/index.html)
6. [Saeij Lab, UC Davis – Toxoplasmosis treatment and why there is no vaccine](https://saeijlab.faculty.ucdavis.edu/toxoplasmosis-the-disease/treatment-and-vaccines/)
7. [Torgerson PR & Mastroiacovo P. The global burden of congenital toxoplasmosis: a systematic review. Bulletin of the WHO](https://iris.who.int/bitstream/handle/10665/271318/PMC3699792.pdf?sequence=1)
8. [The life-cycle of Toxoplasma gondii reviewed using animations, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC7686686/)
9. [All about toxoplasmosis in cats: the last decade, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0304401720301254)
10. [CDC – Diagnosis and Management of Foodborne Illnesses: A Primer for Physicians](https://stacks.cdc.gov/view/cdc/6710/cdc_6710_DS1.pdf)
11. [NIH – Guidelines for Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV: Toxoplasmosis](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/toxoplasmosis)
12. [Bigna JJ et al. Global, regional, and country seroprevalence of Toxoplasma gondii in pregnant women. Scientific Reports 2020](https://pmc.ncbi.nlm.nih.gov/articles/PMC7374101/)
13. [Molecular diagnosis of human toxoplasmosis: the state of the art, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11147977/pdf/12639_2024_Article_1667.pdf)
14. [CDC – Treatment of Toxoplasmosis](https://www.cdc.gov/toxoplasmosis/treatment/index.html)
15. [Exploring global trends in human toxoplasmosis seroprevalence by meta-analysis. Experimental Parasitology 2025](https://www.sciencedirect.com/science/article/pii/S0014489425000761)
16. [UKHSA – Common animal-associated infections in England: 2025](https://www.gov.uk/government/publications/common-animal-associated-infections-2025/common-animal-associated-infections-in-england-2025)
17. [WHO estimates of the global and regional disease burden of 11 foodborne parasitic diseases, 2010, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC4668834/)
18. [CDC – Preventing Toxoplasmosis](https://www.cdc.gov/toxoplasmosis/prevention/)
19. [Advances and Translational Challenges in Toxoplasma gondii Vaccine Development, PubMed 2026](https://pubmed.ncbi.nlm.nih.gov/42188907/)
20. [Wang C et al. Toxoplasma WH3 Δrop18 acts as a live attenuated vaccine against acute and chronic toxoplasmosis. npj Vaccines 2024](https://www.nature.com/articles/s41541-024-00996-9)
21. [The early years of Toxoplasma research, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC2727930/)
22. [Parasites Without Borders – Toxoplasma gondii (Nicolle and Manceaux 1908)](https://parasiteswithoutborders.com/wp-content/uploads/2025/07/PD8-Full-Book-7-14-25-LR_compressed.pdf)
23. [University of Glasgow thesis – History of Toxoplasma gondii](https://theses.gla.ac.uk/75866/1/13818602.pdf)
24. [Dubey JP. The History of Toxoplasma gondii – The First 100 Years. Journal of Eukaryotic Microbiology 2008](https://onlinelibrary.wiley.com/doi/full/10.1111/j.1550-7408.2008.00345.x)
25. [A century of Toxoplasma research, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC2693343/)
26. [Toxoplasmosis meets the World Health Organization criteria for a neglected tropical disease. PLOS NTD 2025](https://journals.plos.org/plosntds/article?id=10.1371%2Fjournal.pntd.0014425)
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*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Other microbial eukaryotes › Parasitic protists and protozoal disease › Apicomplexa*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license