Toxoplasmosis in Cats: Risks to Pregnant Women and Immunocompromised Individuals

Introduction

Toxoplasmosis is a globally distributed zoonotic disease caused by the obligate intracellular apicomplexan parasite Toxoplasma gondii [1, 2, 3]. Felids, particularly domestic cats (Felis catus), serve as the definitive hosts in which the parasite completes its sexual life cycle and sheds environmentally resistant oocysts into the environment [4, 5, 6]. Infection in intermediate hosts, including humans and other warm-blooded animals, occurs through ingestion of sporulated oocysts from contaminated soil, water, or food, or through consumption of tissue cysts in undercooked meat [7, 8, 9]. The seroprevalence of T. gondii in cat populations varies widely by geographic region, management practices, and exposure to outdoor environments [10, 11, 12]. Studies in Hong Kong, Jordan, and Brazil report feline seroprevalences ranging from 20% to over 60% depending on the population surveyed [10, 11, 12]. Understanding the epizootiology of T. gondii in cats is critical for public health, given the potential for zoonotic transmission to pregnant women and immunocompromised individuals [13, 14, 15].

Etiology and Life Cycle

Toxoplasma gondii exists in three infectious stages: tachyzoites, bradyzoites (in tissue cysts), and sporozoites (within oocysts) [4, 16]. The sexual cycle occurs exclusively within the intestinal epithelium of felids, leading to the production of unsporulated oocysts that are shed in feces [4, 5, 6]. After excretion, oocysts sporulate in the environment within one to five days, becoming infectious [16, 12].

graph TD
    A[Definitive host: Felids], >|Oocyst shedding in feces| B[Environment: soil, water, food]
    B, >|Sporulated oocysts| C[Intermediate hosts: mammals, birds]
    C, >|Tissue cysts in meat| D[Humans: ingestion]
    B, >|Direct ingestion| D
    D, >|Congenital transmission| E[Fetus]
    D, >|Reactivation| F[Immunocompromised host]
    C, >|Predation or ingestion of tissue cysts| A
    A, >|Oocyst shedding| B

The pre-sexual stages undergo prolific cell division within the feline enterocytes, a process characterized by endodyogeny and endopolygeny [4, 5]. A single-cell atlas of the feline intestinal tract during infection has revealed the transcriptional landscape of sexual commitment and gametocyte development [5]. MicroRNA expression in the feline small intestine is dynamically regulated during infection, with specific miRNAs implicated in modulating host cell responses to facilitate parasite replication [6]. The host range for sexual development is restricted to felids; no other mammal supports the complete sexual cycle [5, 6].

Transmission to Humans

Zoonotic transmission occurs primarily through two routes: ingestion of sporulated oocysts from the environment and consumption of tissue cysts in raw or undercooked meat [7, 8, 9, 16]. Cats that roam outdoors or hunt are more likely to acquire infection and shed oocysts [10, 11, 12]. Oocyst shedding typically occurs for one to three weeks after primary infection, after which the cat develops immunity and generally does not re-shed unless reinfected or immunosuppressed [4, 5].

Environmental contamination with oocysts is a major risk factor in informal settlements and rural areas where cat populations are high and sanitation is poor [1, 12]. In urban informal settlements in Brazil, T. gondii exposure was associated with social marginalisation and environmental degradation, highlighting the interplay between socio-economic factors and parasite transmission [1]. Similarly, high seroprevalence has been documented in cats from the Pantanal region of Brazil and in stray cats in Bangkok, Thailand [17, 18].

Risks During Pregnancy and Immunocompromised Individuals

Pregnant women who acquire a primary T. gondii infection during gestation are at risk of transmitting the parasite transplacentally to the fetus, leading to congenital toxoplasmosis [19, 13, 15]. The risk and severity of fetal infection depend on the trimester of maternal infection; first trimester infections are less likely to transmit but cause more severe disease, whereas third trimester infections transmit more frequently but are often subclinical [19, 13]. A history of abortion or stillbirth has been associated with seropositivity for T. gondii in women in Turkey and in equine and caprine studies, supporting the role of this parasite in reproductive failure across species [7, 19, 9, 20]. Seronegative pregnant women who own cats should receive counselling to avoid exposure to cat feces and contaminated environments [13, 15].

Immunocompromised individuals, including those with HIV/AIDS, organ transplant recipients, and patients on immunosuppressive therapy, are at risk of reactivation of latent toxoplasmosis, which most commonly manifests as cerebral toxoplasmosis [14, 21, 22]. In renal transplant recipients, cerebral toxoplasmosis is a rare but severe complication often resulting from reactivation of a prior infection [14]. Ocular toxoplasmosis can also occur in immunocompetent and immunocompromised adults, manifesting as retinochoroiditis [21, 22]. Seroprevalence studies in sickle cell disease patients suggest that blood transfusion history may contribute to T. gondii exposure, further complicating risk management in immunocompromised populations [23].

Clinical Signs in Cats

Most cats infected with T. gondii remain subclinical [10, 11]. Clinical disease is more common in kittens and immunocompromised cats. Signs of acute toxoplasmosis may include fever, lethargy, anorexia, dyspnea (due to pneumonia), and neurological deficits such as ataxia or seizures [6, 20]. Ocular signs, including uveitis and chorioretinitis, are also reported [21]. The severity of disease correlates with the stage of infection and the parasitic load [5, 6]. Feline reproductive tissues can harbor the parasite, and infection has been documented in tissues collected from cats in neutering programs [20].

Diagnostics

Diagnosis of feline toxoplasmosis relies on serological detection of antibodies and molecular detection of parasite DNA [2, 24, 25, 26].

Point-of-care immunochromatographic strips have been developed for rapid detection of T. gondii antibodies in cats and other species, facilitating field studies and clinical screening [2, 24]. Molecular detection using PCR on fecal samples is particularly useful for identifying shedding cats, as seropositivity does not correlate with current oocyst excretion [17, 26].

Treatment

Treatment in cats is indicated for clinical toxoplasmosis, especially when signs are severe or in immunocompromised animals [20]. Standard therapy involves a combination of clindamycin hydrochloride at 10-12 mg/kg orally twice daily for two to four weeks [20]. Alternative regimens include trimethoprim-sulfonamide combinations or azithromycin [20]. Treatment does not eliminate tissue cysts and does not prevent latent infection. For oocyst shedding, treatment with clindamycin or ponazuril may reduce the duration and intensity of shedding, but does not prevent it entirely [4, 5].

In pregnant women and immunocompromised individuals, treatment involves spiramycin (if seroconversion during pregnancy) or pyrimethamine with sulfadiazine and folinic acid (for confirmed fetal infection or reactivation), but these are human medical decisions [14, 15]. Veterinary guidance for cat owners includes reassuring that the risk from a pet cat can be managed through hygiene practices [15].

Prevention

Prevention strategies focus on reducing environmental contamination and modifying risk behaviors in vulnerable individuals [1, 13, 15, 16].

• For cat owners: Keep cats indoors to prevent hunting and scavenging. Feed only cooked or commercial food. Clean litter boxes daily (oocysts require >24 hours to sporulate). Use gloves and wash hands thoroughly after handling litter. Pregnant women should delegate litter box cleaning to another household member or wear disposable gloves [13, 15].
• For pregnant women and immunocompromised individuals: Avoid stray cats and kittens. Do not handle stray or unknown cats. Avoid gardening or contact with soil in areas where cats may defecate. Wash fruits and vegetables thoroughly. Cook meat to safe internal temperatures [19, 13, 8].
• For the community: Proper management of stray cat populations reduces oocyst burden in the environment [1, 17, 12]. Vaccination of cats remains an area of active research but no licensed vaccine is currently available for cats [3, 27]. Gene-edited live-attenuated vaccines and mRNA vaccine platforms are being explored but have not yet reached commercial application [3, 27].

Conclusion

Toxoplasma gondii infection in cats represents a significant zoonotic risk, particularly for pregnant women and immunocompromised individuals [23, 14, 15]. The parasite's life cycle, with the cat as the definitive host, drives environmental contamination with oocysts. Seroprevalence studies across multiple continents confirm widespread exposure in cat populations [10, 11, 12]. Advances in diagnostic tools, including immunochromatographic strips and antisense PCR, facilitate rapid detection of infection in cats [2, 24, 26]. Veterinary guidance remains the cornerstone of prevention: keeping cats indoors, feeding cooked diets, and practicing rigorous hygiene around litter boxes [13, 15]. Ongoing research into vaccines and host-parasite interactions at the molecular level offers hope for future control strategies [3, 27, 5].

References

[1] Eyre MT, Wang JY, Carneiro IO, et al. Social marginalisation, environmental degradation and Toxoplasma gondii exposure in urban informal settlements in Brazil. PLoS Negl Trop Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42330015/

[2] Mu X, Chen C, Pu X, et al. Development and Field Validation of a Double-Antigen Sandwich Colloidal Gold Immunochromatographic Strip for Detection of Toxoplasma gondii Antibodies in Multiple Host Species. Transbound Emerg Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42253330/

[3] Sang X, Zhang H, Zhang Y, et al. Gene-edited live-attenuated vaccines against Toxoplasma gondii: recent advances and future frontiers. Parasit Vectors. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42252477/

[4] Sena F, Hakimi M-A, Francia ME. Proliferating toward sex: characterization of cell division of Toxoplasma gondii's pre-sexual stages. mBio. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42153709/

[5] Alrubaye HS, Reilly SM, da Silva R, et al. A single-cell atlas of Toxoplasma sexual development in the feline intestinal tract. Nat Microbiol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42020723/

[6] Zhai B, Bao B, Xie SC, et al. Dynamic landscape of microRNA expression in the feline small intestine during Toxoplasma gondii infection. Parasit Vectors. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41965856/

[7] Pinto GOA, Silva RAD, Oliveira PRF, et al. Molecular detection of Toxoplasma gondii in an aborted equine fetus and serological evidence of infection in mares enrolled in embryo transfer programs in Brazil. J Equine Vet Sci. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42252005/

[8] Muhammad AS, Kudi AC, Mohammed A, et al. Public health significance of prevalence and risk factors associated with Toxoplasma gondii infection in goats sampled from two quarantine facilities and an institutional farm in Maiduguri metropolis, Borno state, Nigeria. Sci Rep. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42020619/

[9] Ait Issad N, Mohamed Cherif A, Mebkhout F, et al. First report of molecular and histopathological detection of Toxoplasma gondii in aborted fetal goat myocardium in Algeria with associated risk factors. Parasitol Int. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41864556/

[10] Elsohaby I, Zubair M, Baqar Z, et al. Seroprevalence of Toxoplasma gondii and associated demographic factors in privately-owned dogs, cats, and community cats in Hong Kong. BMC Vet Res. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42135800/

[11] Alkhatatbeh SK, Lafi SQ, Hammad HB, et al. The first seroprevalence and molecular detection of toxoplasmosis infecting cats in Jordan with associated risk factors. Vet Parasitol Reg Stud Reports. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41741047/

[12] Bazan L, Argibay HD, Borges-Silva W, et al. Seroprevalence and risk factors for Toxoplasma gondii infection in wild, domestic and companion animals in urban informal settlements from Salvador, Brazil. PLoS Negl Trop Dis. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41401226/

[13] Henriette BA, Jémima EK, Jean-Sébastien MA, et al. First report of knowledge and practices towards toxoplasmosis among pregnant women in primary care in Abidjan, Côte d'Ivoire. Trop Parasitol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42199683/

[14] Mihaljević D, Sitaš Z, Hanulak J, et al. Cerebral Toxoplasmosis in a Renal Transplant Recipient-A Rare Complication. Life (Basel). 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41900989/

[15] Gharbi M, Yera H, Dupouy-Camet J. [The cat, the women and the toxoplasma: What advice should be given to a pregnant woman who is seronegative for toxoplasmosis and owns a cat?]. Gynecol Obstet Fertil Senol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41628830/

[16] Biswas PK, Aryal D, Tarak AN, et al. Genotype distribution and risk factors of Toxoplasma gondii infection in animals of Trishal, Bangladesh. PLoS One. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41528989/

[17] Kengradomkij C, Chimnoi W, Kamyingkird K, et al. PCR detection of Toxoplasma gondii DNA in fecal samples from stray cats in Bangkok Metropolitan, Thailand. Food Waterborne Parasitol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42094705/

[18] Artiaga-Silva GL, de Lima Ruy Dias ÁF, Carvalho MR, et al. High Seroprevalence Rates of Toxoplasma gondii and Neospora caninum in Dogs in the Pantanal Region of Mato Grosso, Brazil. Acta Parasitol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41843222/

[19] Karacali B, Mor N. Investigation of anti-Toxoplasma gondii antibody seropositivity and possible risk factors in women with abortion or stillbirth history in Kars, Turkey. Afr J Reprod Health. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42202767/

[20] Murata FHA, Barboza JP, de Souza CAG, et al. Investigation of Toxoplasma gondii in reproductive tissues of companion animals from a municipal neutering program. Vet Parasitol Reg Stud Reports. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41651631/

[21] Askaryanzardak A, Kakkassery V, Tartaglione Gracia GP, et al. [Ocular toxoplasmosis in adults : Refresher course]. Ophthalmologie. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41603939/

[22] Filho SCC, Moron SE, Ferreira RG, et al. Risk Factors and Ocular Health Associated with Toxoplasmosis in Quilombola Communities. Microorganisms. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41597614/

[23] Orish VN, Tetteh RE, Adzah D, et al. Toxoplasma gondii seropositivity among patients with sickle cell disease: Prevalence and association with blood transfusion history. PLoS One. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41931585/

[24] Chen XX, Sun H, Liang Y, et al. Development of a SAG1-based colloidal gold immunochromatographic strip for rapid serological detection of swine Toxoplasma gondii. Parasit Vectors. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42169035/

[25] Günay-Esiyok Ö, Koçkaya ES, Yılmaz R, et al. The Potential of MIC17A both as an Entero-epithelial and Chronic Stage Marker for Detection of Feline Toxoplasmosis. Curr Microbiol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41874672/

[26] Li YY, Bai SY, Yu HQ, et al. Development and evaluation of an antisense PCR assay for Toxoplasma gondii detection in domestic cats. Vet Parasitol. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41724116/

[27] Qadeer A, Tharwat M, Khan MZ, et al. Advances and Translational Challenges in Toxoplasma gondii Vaccine Development: From Antigen Discovery to mRNA and One Health Strategies. Vet Sci. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42188907/

[28] de Velasco-Reyes I, Torres-García SE, Hernández-Rangel JJ, et al. Seroprevalence of Toxoplasma gondii Infection in Veterinary Medicine Professionals and Students in Aguascalientes, Mexico. Epidemiologia (Basel). 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42201205/

[29] Chalabi KN, Jabar Bakr E. Toxoplasmosis - knowledge among university students in Erbil, Iraq: a cross-sectional study. Int J Environ Health Res. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41873025/

[30] Hanedan B, Taş BZ, Yıldırım E, et al. Investigation of Toxoplasma gondii seroprevalence and associated risk factors in dairy cattle in the Eastern Anatolia region of Türkiye. Vet Parasitol Reg Stud Reports. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41819961/

[31] Marín-García PJ, Ballesteros-García O, Martínez-Sáez L, et al. Low seroprevalence of Toxoplasma gondii in pig farms (Sus scrofa domesticus) of eastern Spain in intensive farms with control of animal entry. Vet Parasitol Reg Stud Reports. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41741032/

[32] Spada E, Tattarletti G, Proverbio D, et al. The AB Blood Group System Phenotype Does Not Play a Role in Toxoplasma gondii Infection in Cats. Pathogens. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41471183/

[33] Didkowska A, Kołodziej-Sobocińska M, Matusik K, et al. Toxoplasma gondii in wild felides in Poland. BMC Vet Res. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41387866/

[34] Kołodziej-Sobocińska M, Holec-Gąsior L, Ferra B, et al. A long-term serological survey of Toxoplasma gondii in European bison (Bison bonasus) - the largest european herbivore. Vet Res Commun. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41359089/

[35] Villa-Mancera A, Vargas-Tizatl E, Robles-Robles JM, et al. High Seroprevalence of Toxoplasma gondii and Neospora caninum Infections Among Goats in Mexico Is Associated with Climatic, Environmental, and Risk Factors. Pathogens. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41305406/ *** Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.