Toxoplasmosis in Cats: Risks During Pregnancy and Zoonotic Prevention

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-06-06

Key Takeaways

• Toxoplasma gondii is an obligate intracellular parasite with cats as definitive hosts, completing its sexual cycle in the intestinal epithelium and shedding unsporulated oocysts in feces for 1-3 weeks post-infection.
• Transmission to humans occurs via ingestion of sporulated oocysts from contaminated environments or consumption of undercooked meat containing tissue cysts, with congenital toxoplasmosis being a significant risk during pregnancy.
• Clinical toxoplasmosis in cats, though often subclinical, can manifest as fever, lethargy, lymphadenopathy, ocular disease (uveitis, chorioretinitis), and neurological signs (ataxia, seizures).
• Diagnosis in cats involves serological detection of IgM/IgG antibodies (ELISA, ICS), PCR for parasite DNA in feces or tissues, and histopathology with immunohistochemistry for definitive confirmation.
• Standard treatment for clinical feline toxoplasmosis includes clindamycin (10-12 mg/kg BID for 2-4 weeks), with supportive care and management of concurrent conditions being crucial.
• Zoonotic prevention strategies for cat owners include feeding only commercial/cooked food, keeping cats indoors, daily litter box cleaning (oocysts take 1-5 days to sporulate), and avoiding litter box duty for pregnant/immunocompromised individuals.

Etiology and Life Cycle

Toxoplasmosis is caused by the obligate intracellular apicomplexan parasite Toxoplasma gondii. The definitive host is the domestic cat and other felids, in which the parasite completes its sexual cycle within the intestinal epithelium [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. A single-cell atlas of T. gondii sexual development in the feline intestinal tract has revealed the transcriptional dynamics of pre-sexual stages, demonstrating that proliferating parasites undergo a programmed transition toward gametogenesis [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. The entero-epithelial cycle culminates in the production of unsporulated oocysts that are shed in feces [<a href="#ref-2">2</a>, <a href="#ref-3">3</a>]. Oocyst shedding is temporally restricted, typically occurring for 1 to 3 weeks post-primary infection, after which the cat develops a robust immune response that limits further shedding [<a href="#ref-3">3</a>, <a href="#ref-4">4</a>]. The microRNA expression landscape in the feline small intestine during infection shows dynamic regulation of host and parasite transcripts, which may modulate the intestinal microenvironment to favor parasite replication [<a href="#ref-3">3</a>].

The parasite exists in three infectious stages: tachyzoites (rapidly dividing forms), bradyzoites (slowly dividing forms contained within tissue cysts), and sporozoites (within sporulated oocysts) [<a href="#ref-5">5</a>, <a href="#ref-6">6</a>]. Tachyzoites are responsible for acute dissemination and clinical disease, while bradyzoites establish chronic latent infection in tissues such as skeletal muscle, myocardium, and neural tissue [<a href="#ref-5">5</a>, <a href="#ref-6">6</a>, <a href="#ref-7">7</a>]. Tissue cysts are resistant to gastric digestion and represent a key route of transmission when carnivorous or omnivorous hosts ingest infected tissues [<a href="#ref-8">8</a>, <a href="#ref-9">9</a>, <a href="#ref-10">10</a>]. Oocysts, once sporulated in the environment, are highly resilient and can remain infective for months to years under favorable conditions of moisture and temperature [<a href="#ref-11">11</a>, <a href="#ref-12">12</a>, <a href="#ref-13">13</a>].

Epidemiology and Seroprevalence in Cats

T. gondii infection is distributed globally, with seroprevalence in feline populations varying widely by geographic region, management practices, and diagnostic methodology [<a href="#ref-13">13</a>, <a href="#ref-14">14</a>, <a href="#ref-15">15</a>]. In a study of privately-owned and community cats in Hong Kong, overall seroprevalence was reported at 37.8% using commercial ELISA kits, with higher odds of seropositivity in community cats compared to owned cats [<a href="#ref-14">14</a>]. In Jordan, the first seroprevalence and molecular detection study in cats reported a seroprevalence of 41.2% and detected parasite DNA in 15.3% of fecal samples by PCR [<a href="#ref-15">15</a>]. In urban informal settlements in Brazil, seroprevalence in domestic and companion animals, including cats, was associated with environmental degradation and social marginalization, highlighting the role of socio-ecological determinants in parasite exposure [<a href="#ref-11">11</a>, <a href="#ref-13">13</a>]. In Poland, wild felids showed a seroprevalence of 28.6%, indicating that sylvatic cycles maintain the parasite in natural ecosystems [<a href="#ref-16">16</a>].

Risk factors for feline seropositivity include outdoor access, hunting behavior, raw meat consumption, and increased age [<a href="#ref-10">10</a>, <a href="#ref-14">14</a>, <a href="#ref-15">15</a>]. Stray cats in Bangkok Metropolitan, Thailand, had a PCR detection rate of 8.7% in fecal samples, confirming active oocyst shedding in free-roaming populations [<a href="#ref-12">12</a>]. The AB blood group system phenotype in cats does not appear to play a role in susceptibility to T. gondii infection, as demonstrated by a study that found no significant association between blood type and seropositivity [<a href="#ref-17">17</a>].

Clinical Signs and Pathology in Cats

Most immunocompetent cats infected with T. gondii remain subclinical [<a href="#ref-4">4</a>, <a href="#ref-18">18</a>]. When clinical disease occurs, it is most frequently observed in kittens, immunocompromised adults, or cats with concurrent infections [<a href="#ref-18">18</a>, <a href="#ref-19">19</a>]. The most common clinical manifestations include fever, lethargy, anorexia, and lymphadenopathy [<a href="#ref-18">18</a>, <a href="#ref-19">19</a>]. Ocular toxoplasmosis presents as uveitis, chorioretinitis, and retinal detachment, and can occur as a sequela of either acute or reactivated latent infection [<a href="#ref-19">19</a>, <a href="#ref-20">20</a>]. Neurological signs, including ataxia, seizures, circling, and behavioral changes, result from encephalitis and meningoencephalitis caused by tachyzoite proliferation in neural tissue [<a href="#ref-7">7</a>, <a href="#ref-19">19</a>]. Respiratory signs such as dyspnea and tachypnea may arise from interstitial pneumonia [<a href="#ref-19">19</a>]. Hepatic and pancreatic involvement can lead to icterus and vomiting [<a href="#ref-18">18</a>].

Pathologically, the hallmark lesions are multifocal necrosis and inflammation in affected organs, particularly the lungs, liver, spleen, and central nervous system [<a href="#ref-18">18</a>, <a href="#ref-19">19</a>]. Tissue cysts are often observed in skeletal and cardiac muscle without associated inflammation in chronic infections [<a href="#ref-18">18</a>]. In the feline reproductive tract, T. gondii DNA has been detected in ovarian and uterine tissues from cats enrolled in neutering programs, suggesting potential for vertical transmission [<a href="#ref-18">18</a>]. Abortion and stillbirth have been documented in experimentally infected queens, and similar findings have been reported in other species such as goats and horses [<a href="#ref-9">9</a>, <a href="#ref-18">18</a>, <a href="#ref-21">21</a>, <a href="#ref-22">22</a>].

Diagnostics

Diagnosis of feline toxoplasmosis relies on a combination of serological, molecular, and histopathological methods [<a href="#ref-4">4</a>, <a href="#ref-23">23</a>, <a href="#ref-24">24</a>, <a href="#ref-25">25</a>]. Serological detection of anti-T. gondii antibodies, particularly IgM and IgG, is the most common approach [<a href="#ref-23">23</a>, <a href="#ref-24">24</a>, <a href="#ref-26">26</a>]. Commercial ELISA kits and colloidal gold immunochromatographic strips (ICS) have been developed for rapid serological screening in multiple host species, including cats [<a href="#ref-23">23</a>, <a href="#ref-24">24</a>]. A double-antigen sandwich colloidal gold ICS demonstrated high sensitivity and specificity for field detection of antibodies in diverse animal populations [<a href="#ref-23">23</a>]. Similarly, a SAG1-based colloidal gold ICS has been validated for swine and shows cross-species applicability [<a href="#ref-24">24</a>].

Molecular diagnostics, particularly PCR, offer higher sensitivity for detecting active infection and oocyst shedding [<a href="#ref-12">12</a>, <a href="#ref-15">15</a>, <a href="#ref-25">25</a>]. An antisense PCR assay targeting the B1 gene has been developed specifically for domestic cats, improving detection limits in fecal and tissue samples [<a href="#ref-25">25</a>]. PCR detection of T. gondii DNA in fecal samples from stray cats provides direct evidence of environmental contamination [<a href="#ref-12">12</a>]. Real-time PCR assays can quantify parasite burden and differentiate between acute and chronic infection stages [<a href="#ref-25">25</a>]. Histopathological examination of biopsy or necropsy tissues, combined with immunohistochemistry, remains the gold standard for confirming tissue-phase infection [<a href="#ref-4">4</a>, <a href="#ref-9">9</a>]. The MIC17A antigen has been identified as a potential marker for both entero-epithelial and chronic stage infection, offering a target for improved diagnostic assays [<a href="#ref-4">4</a>].

The following table summarizes the principal diagnostic modalities for feline toxoplasmosis:

Treatment and Management

Treatment of clinical toxoplasmosis in cats is indicated when signs are present, particularly ocular, neurological, or respiratory disease [<a href="#ref-19">19</a>]. The standard therapeutic regimen consists of clindamycin administered orally or parenterally at 10 to 12 mg/kg every 12 hours for 2 to 4 weeks [<a href="#ref-19">19</a>]. Alternative therapies include trimethoprim-sulfonamide combinations and pyrimethamine, though the latter is associated with bone marrow suppression and requires folinic acid supplementation [<a href="#ref-19">19</a>]. Supportive care, including fluid therapy, nutritional support, and anti-inflammatory doses of corticosteroids for ocular inflammation, is often necessary [<a href="#ref-19">19</a>, <a href="#ref-20">20</a>].

Prevention of oocyst shedding is a critical public health goal. Cats should be fed only commercially processed or thoroughly cooked food to prevent ingestion of tissue cysts [<a href="#ref-10">10</a>, <a href="#ref-27">27</a>]. Indoor confinement reduces exposure to infected prey and contaminated soil [<a href="#ref-14">14</a>, <a href="#ref-27">27</a>]. Litter boxes should be cleaned daily, as oocysts require 1 to 5 days to sporulate and become infective [<a href="#ref-27">27</a>]. Pregnant women and immunocompromised individuals should avoid handling litter boxes and should delegate this task to another household member [<a href="#ref-27">27</a>, <a href="#ref-28">28</a>].

Zoonotic Transmission and Risks During Pregnancy

The zoonotic potential of T. gondii is well established, with cats serving as the primary source of environmental oocyst contamination [<a href="#ref-11">11</a>, <a href="#ref-12">12</a>, <a href="#ref-27">27</a>]. Humans become infected through ingestion of sporulated oocysts from contaminated soil, water, or food, or through consumption of undercooked meat containing tissue cysts [<a href="#ref-8">8</a>, <a href="#ref-29">29</a>, <a href="#ref-30">30</a>]. The term "cat toxoplasmosis baby" reflects the clinical concern for congenital toxoplasmosis, which occurs when a pregnant woman acquires a primary infection and the parasite crosses the placental barrier [<a href="#ref-22">22</a>, <a href="#ref-27">27</a>, <a href="#ref-28">28</a>]. Seronegative pregnant women who own cats are at risk if they are exposed to oocysts from the cat's litter box or from contaminated gardening soil [<a href="#ref-27">27</a>, <a href="#ref-28">28</a>]. Studies have shown that knowledge and practices regarding toxoplasmosis prevention among pregnant women are often inadequate, particularly in primary care settings [<a href="#ref-28">28</a>, <a href="#ref-31">31</a>]. In a study from Côte d'Ivoire, only 38% of pregnant women knew that cats are the definitive host, and fewer than 25% practiced proper hand hygiene after handling cat litter [<a href="#ref-28">28</a>]. Similar knowledge gaps have been reported among university students in Iraq [<a href="#ref-31">31</a>] and veterinary medicine professionals in Mexico [<a href="#ref-26">26</a>], indicating that educational interventions are needed across multiple populations.

Seroprevalence studies in women with a history of abortion or stillbirth have demonstrated a significant association between T. gondii seropositivity and adverse pregnancy outcomes [<a href="#ref-22">22</a>]. In Kars, Turkey, anti-T. gondii antibodies were detected in 42.3% of women with a history of abortion, with contact with cats identified as a significant risk factor [<a href="#ref-22">22</a>]. In Brazil, seroprevalence in quilombola communities was associated with poor sanitation and close contact with cats, further linking environmental exposure to infection risk [<a href="#ref-32">32</a>]. The risk of congenital transmission is highest when maternal infection occurs during the second and third trimesters, although the severity of fetal disease is greatest with first-trimester infections [<a href="#ref-22">22</a>, <a href="#ref-27">27</a>].

Zoonotic Prevention Strategies

Prevention of zoonotic toxoplasmosis requires a multi-pronged approach targeting both feline and human behaviors [<a href="#ref-5">5</a>, <a href="#ref-6">6</a>, <a href="#ref-27">27</a>]. For cat owners, the following measures are recommended:

• Feed cats only commercial or cooked food to prevent ingestion of tissue cysts [<a href="#ref-10">10</a>, <a href="#ref-27">27</a>].
• Keep cats indoors to reduce hunting and exposure to contaminated soil [<a href="#ref-14">14</a>, <a href="#ref-27">27</a>].
• Clean litter boxes daily and dispose of feces in sealed bags [<a href="#ref-27">27</a>].
• Pregnant women and immunocompromised individuals should avoid litter box duty [<a href="#ref-27">27</a>, <a href="#ref-28">28</a>].
• Wear gloves when gardening and wash hands thoroughly after soil contact [<a href="#ref-27">27</a>].
• Wash all fruits and vegetables before consumption [<a href="#ref-27">27</a>].
• Cook meat to an internal temperature of at least 67 degrees Celsius to inactivate tissue cysts [<a href="#ref-8">8</a>, <a href="#ref-30">30</a>].

Vaccine development for T. gondii is an active area of research, with gene-edited live-attenuated vaccines and mRNA-based platforms showing promise in animal models [<a href="#ref-5">5</a>, <a href="#ref-6">6</a>]. A live-attenuated vaccine based on CRISPR-Cas9 deletion of virulence genes has been shown to induce protective immunity in mice and is being evaluated for use in cats [<a href="#ref-5">5</a>]. The One Health framework, which integrates human, animal, and environmental health, is essential for effective toxoplasmosis control [<a href="#ref-6">6</a>, <a href="#ref-27">27</a>].

The following Mermaid diagram illustrates the decision tree for managing toxoplasmosis risk in households with pregnant women and cats:

flowchart TD
 A["Household with cat and pregnant woman"] --> B{"Is the woman seronegative?"}
 B -->|"Yes"| C["Test cat for T. gondii shedding"]
 B -->|"No"| D["No additional precautions needed"]
 C --> E{"Is cat shedding oocysts?"}
 E -->|"Yes"| F["Isolate cat from litter box duty"]
 F --> G["Delegate litter box cleaning"]
 G --> H["Daily litter box cleaning"]
 H --> I["Feed cat commercial diet only"]
 I --> J["Keep cat indoors"]
 E -->|"No"| K["Maintain standard hygiene"]
 K --> L["Wash hands after handling cat"]
 L --> M["Avoid raw meat for cat"]
 M --> N["Monitor for clinical signs in cat"]

Public Health Implications and One Health Considerations

The public health significance of T. gondii extends beyond congenital toxoplasmosis. Ocular toxoplasmosis is a leading cause of posterior uveitis worldwide and can result in permanent visual impairment [<a href="#ref-20">20</a>, <a href="#ref-32">32</a>]. In immunocompromised individuals, such as transplant recipients and those with sickle cell disease, reactivation of latent infection can cause severe cerebral toxoplasmosis [<a href="#ref-29">29</a>, <a href="#ref-33">33</a>]. Seroprevalence in patients with sickle cell disease has been associated with blood transfusion history, suggesting a potential iatrogenic transmission route [<a href="#ref-29">29</a>]. In renal transplant recipients, cerebral toxoplasmosis is a rare but life-threatening complication that requires a high index of suspicion for diagnosis [<a href="#ref-33">33</a>].

Environmental contamination with oocysts is a persistent challenge, particularly in regions with large populations of free-roaming cats [<a href="#ref-11">11</a>, <a href="#ref-12">12</a>, <a href="#ref-13">13</a>]. Studies in Brazil have demonstrated that social marginalisation and environmental degradation are associated with higher T. gondii exposure in both humans and animals [<a href="#ref-11">11</a>, <a href="#ref-13">13</a>]. In Bangladesh, genotype distribution and risk factor analysis in animals revealed a predominance of Type II and III strains, with stray cats serving as a major reservoir [<a href="#ref-10">10</a>]. In Spain, intensive pig farms with strict biosecurity measures showed low seroprevalence, indicating that management practices can effectively reduce transmission [<a href="#ref-30">30</a>]. In Nigeria, goats sampled at quarantine facilities had a seroprevalence of 34.7%, with risk factors including age and source of animals [<a href="#ref-8">8</a>]. In Algeria, molecular and histopathological detection of T. gondii in aborted fetal goat myocardium confirmed transplacental transmission in small ruminants [<a href="#ref-9">9</a>]. In Turkey, seroprevalence in dairy cattle was 18.2%, with grazing on pasture identified as a significant risk factor [<a href="#ref-34">34</a>]. In the Pantanal region of Brazil, high seroprevalence rates in dogs (68.4%) suggest widespread environmental contamination [<a href="#ref-35">35</a>]. These findings underscore the importance of a One Health approach that includes veterinary surveillance, public education, and environmental management to reduce the burden of toxoplasmosis [<a href="#ref-6">6</a>, <a href="#ref-27">27</a>].

References

Related Clinical & Scientific Guides

• Tick-Borne Diseases in Dogs: Pathogens, Clinical Signs, Diagnosis, and Prevention
• Toxoplasmosis in Cats and the Risk of Brain Infection in Humans
• Dog Heartworm and Tick-Borne Disease Prevention