Toxoplasmosis in Cats: Risks to Pregnant Women and Immunocompromised Individuals

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

Key Takeaways

• _Toxoplasma gondii_ is an obligate intracellular parasite with felids as definitive hosts, shedding unsporulated oocysts in feces that become infectious after 1-5 days of environmental sporulation. Transmission to humans primarily occurs via ingestion of sporulated oocysts from contaminated environments or consumption of undercooked meat containing tissue cysts.
• Pregnant women are at risk of transmitting _T. gondii_ to their fetus, potentially causing congenital toxoplasmosis, with risk increasing with gestational age, though severity decreases. Immunocompromised individuals, including transplant recipients and those with malignancies, are susceptible to severe reactivation of latent infections.
• Feline toxoplasmosis is often subclinical, but clinical signs can include fever, lethargy, anorexia, respiratory distress, ocular inflammation (uveitis, chorioretinitis), and neurological deficits such as seizures or ataxia.
• Diagnostic methods include serology (IgG/IgM ELISA, immunochromatographic strips), molecular detection (PCR targeting B1 gene or repetitive elements), and histopathology with immunohistochemistry. MIC17A antigen detection shows promise for differentiating infection stages.
• Treatment for acute feline toxoplasmosis typically involves clindamycin or trimethoprim-sulfonamide combinations, often with folinic acid. Prevention strategies focus on feeding cats cooked food, keeping them indoors, daily litter box cleaning (before sporulation), and avoiding litter box duties for pregnant or immunocompromised individuals.
• No licensed vaccine for feline toxoplasmosis exists, but gene-edited live-attenuated vaccines and mRNA technologies are under development. A One Health approach integrating veterinary, medical, and environmental health is crucial for global toxoplasmosis control.

Etiology and Parasite Biology

_Toxoplasma gondii_ is an obligate intracellular apicomplexan parasite that infects virtually all warm-blooded vertebrates, with felids serving as the definitive hosts [<a href="#ref-1">1</a>]. The parasite life cycle comprises both sexual and asexual phases. Sexual reproduction (gametogony) occurs exclusively within the feline intestinal epithelium, culminating in the shedding of unsporulated oocysts in feces [<a href="#ref-2">2</a>]. Following sporulation (1-5 days in the environment), oocysts become infectious to intermediate hosts, including humans and livestock [<a href="#ref-3">3</a>]. A single cat can excrete millions of oocysts during primary infection, making environmental contamination a key driver of transmission [<a href="#ref-2">2</a>].

The pre-sexual and sexual stages of _T. gondii_ in the feline gut have been characterized using single-cell transcriptomics, revealing distinct merozoite and gametocyte populations [<a href="#ref-2">2</a>]. Recent work using retinal epithelial cells and intestinal organoids has further elucidated the differentiation pathways leading to sexual commitment [<a href="#ref-4">4</a>]. Microneme protein MIC17A has been identified as a potential marker for both entero-epithelial stages and chronic tissue cysts, offering new targets for diagnostic detection of feline infections [<a href="#ref-5">5</a>].

Three main clonal lineages (Types I, II, III) predominate in North America and Europe, though diverse genotypes circulate globally [<a href="#ref-6">6</a>]. Strain virulence varies considerably; for instance, Type II strains are commonly associated with human congenital toxoplasmosis, while atypical strains may cause severe ocular disease [<a href="#ref-7">7</a>, <a href="#ref-8">8</a>].

Epidemiology

Feline seroprevalence of _T. gondii_ varies widely by geographic region and management practices. In Hong Kong, seroprevalence in privately-owned cats was 12.3% versus 23.7% in community cats [<a href="#ref-9">9</a>]. A study in Jordan reported seroprevalence of 45.1% with associated risk factors including outdoor access and raw meat feeding [<a href="#ref-10">10</a>]. In stray cats from Bangkok, Thailand, PCR-based detection of _T. gondii_ DNA in feces yielded a prevalence of 7.8% [<a href="#ref-11">11</a>]. In Poland, wild felids showed lower seroprevalence (4.0%) compared to domestic cats [<a href="#ref-12">12</a>]. Urban informal settlements in Brazil demonstrate high exposure in both cats and other domestic animals due to environmental degradation and social marginalization [<a href="#ref-3">3</a>, <a href="#ref-13">13</a>].

Risk factors for feline infection include unrestricted outdoor roaming, consumption of raw or undercooked meat, hunting behavior, and contact with contaminated soil [<a href="#ref-9">9</a>, <a href="#ref-10">10</a>]. The AB blood group phenotype in cats does not appear to influence susceptibility to infection [<a href="#ref-14">14</a>].

Transmission to humans occurs primarily through ingestion of sporulated oocysts from contaminated soil, water, or produce; consumption of tissue cysts in undercooked meat; and rarely via blood transfusion [<a href="#ref-15">15</a>, <a href="#ref-16">16</a>]. Vertical transmission is a major concern for pregnant women; primary infection acquired during gestation can result in congenital toxoplasmosis, leading to abortion, stillbirth, or neonatal disease [<a href="#ref-16">16</a>, <a href="#ref-17">17</a>]. The risk of fetal infection increases with gestational age, but severity decreases [<a href="#ref-16">16</a>]. Seroprevalence studies in women with histories of abortion or stillbirth in Turkey revealed significantly higher anti-_T. gondii_ antibody positivity compared to controls [<a href="#ref-17">17</a>]. In Côte d'Ivoire, pregnant women exhibited knowledge gaps regarding toxoplasmosis transmission and prevention [<a href="#ref-18">18</a>].

Immunocompromised individuals, including organ transplant recipients, patients with malignancies, and those with sickle cell disease, are at elevated risk for reactivation of latent toxoplasmosis [<a href="#ref-15">15</a>, <a href="#ref-19">19</a>, <a href="#ref-20">20</a>]. Cerebral toxoplasmosis is a rare but severe complication in renal transplant recipients [<a href="#ref-19">19</a>]. Seropositivity in patients with malignancies in Iran reached 39.2% [<a href="#ref-20">20</a>]. Ocular toxoplasmosis can occur in both immunocompetent and immunocompromised individuals, with reactivation of retinochoroidal lesions being more common in the latter [<a href="#ref-7">7</a>, <a href="#ref-8">8</a>].

Clinical Signs and Pathology in Cats

Feline toxoplasmosis often remains subclinical. When disease occurs, clinical signs are typically associated with the acute phase of infection, during which tachyzoites undergo rapid replication in host cells [<a href="#ref-21">21</a>]. Common presentations include fever, lethargy, anorexia, and respiratory distress due to pneumonitis. Ocular signs such as uveitis, chorioretinitis, and anterior chamber inflammation are observed [<a href="#ref-7">7</a>]. Neurological manifestations can include seizures, ataxia, and behavioral changes [<a href="#ref-22">22</a>]. Hepatic and pancreatic involvement may lead to icterus and vomiting.

Pathologically, necrotic foci are found in multiple organs, particularly the lungs, liver, spleen, and lymph nodes. Histological examination reveals tachyzoites and tissue cysts, with associated mononuclear cell infiltration. The intestinal stages in the definitive host cause transient enteritis, but most cats clear entero-epithelial infection without overt diarrhea [<a href="#ref-2">2</a>].

Cat Toxoplasmosis Baby: Zoonotic Risk to Pregnant Women

The phrase "cat toxoplasmosis baby" encapsulates the public health concern that pregnant women may acquire toxoplasmosis from their pet cats and transmit the parasite to the developing fetus. This risk must be contextualized: the primary source of human infection is not direct contact with cats but rather ingestion of oocysts from environmental contamination or consumption of undercooked meat [<a href="#ref-16">16</a>]. Cats only shed oocysts for a brief period (1-3 weeks) following primary infection, and reinfection generally does not lead to renewed shedding [<a href="#ref-9">9</a>]. Proper hygiene, such as daily litter box cleaning (before oocysts sporulate), wearing gloves, and hand washing, virtually eliminates risk [<a href="#ref-16">16</a>]. Nevertheless, seronegative pregnant women should avoid handling litter boxes and adopt preventive measures [<a href="#ref-16">16</a>, <a href="#ref-18">18</a>].

Diagnostics

Diagnostic approaches for feline toxoplasmosis include serological, molecular, histological, and antigen-based methods.

Serology. Detection of anti-_T. gondii_ IgG and IgM antibodies is the most common diagnostic modality. Commercial enzyme-linked immunosorbent assays (ELISAs) are widely used [<a href="#ref-23">23</a>]. A double-antigen sandwich colloidal gold immunochromatographic strip has been developed and field-validated for rapid detection of antibodies across multiple host species, including cats [<a href="#ref-23">23</a>]. This test uses recombinant antigens to achieve high sensitivity and specificity. IgG seropositivity indicates past exposure; rising titers or IgM positivity suggests recent infection [<a href="#ref-5">5</a>]. MIC17A-based serological assays show promise for detecting both entero-epithelial and chronic stage infections [<a href="#ref-5">5</a>].

Molecular detection. Conventional and real-time PCR assays targeting the B1 gene or 529-bp repetitive element are standard for detecting _T. gondii_ DNA in tissues, blood, and feces [<a href="#ref-24">24</a>]. An antisense PCR assay has been developed specifically for domestic cats, improving sensitivity for low-level parasitemia [<a href="#ref-24">24</a>]. Fecal PCR can differentiate active oocyst shedding from past exposure [<a href="#ref-11">11</a>]. PCR detection in stray cat feces in Thailand identified 7.8% positivity, demonstrating the utility of molecular surveillance for environmental risk assessment [<a href="#ref-11">11</a>].

Histopathology. Tissue biopsy with histochemical staining (e.g., hematoxylin and eosin, periodic acid-Schiff) or immunohistochemistry using monoclonal anti-_T. gondii_ antibodies can identify tachyzoites and tissue cysts in clinical specimens [<a href="#ref-25">25</a>]. Histopathological detection of _T. gondii_ in aborted fetal myocardium has been reported in goats, with analogous applications in feline pathology [<a href="#ref-25">25</a>].

Antigen detection. Double-antigen sandwich immunochromatographic strips provide point-of-care detection of antibodies without species restriction [<a href="#ref-23">23</a>]. Western blot analysis can confirm serological results.

Diagnostic method comparison

Treatment and Control in Cats

Treatment. The standard therapeutic regimen for acute feline toxoplasmosis consists of a combination of clindamycin (10-12 mg/kg orally every 12 hours for 2-4 weeks) or a trimethoprim-sulfonamide combination, often supplemented with folinic acid to mitigate bone marrow suppression [<a href="#ref-21">21</a>]. For ocular disease, topical corticosteroids may be used in conjunction with systemic antiprotozoals to control inflammation. Clindamycin is commonly prescribed; however, resistance and tolerability concerns remain. Alternative agents include pyrimethamine plus a sulfonamide, though feline toxicity limits use.

Vaccine development. No licensed vaccine currently exists for feline toxoplasmosis. Gene-edited live-attenuated vaccines (e.g., _T. gondii_ strains with deletion of essential virulence genes) represent a promising avenue, inducing protective immunity while preventing reversion to virulence [<a href="#ref-21">21</a>]. Advances in mRNA vaccine technology and One Health strategies are being explored for both veterinary and human applications [<a href="#ref-26">26</a>]. Pre-sexual stage antigens are potential targets for blocking oocyst shedding [<a href="#ref-1">1</a>].

Control measures. Prevention of feline toxoplasmosis centers on management practices:

• Feed cats only commercial cooked or canned food to prevent ingestion of tissue cysts [<a href="#ref-9">9</a>].
• Prevent hunting and scavenging by keeping cats indoors [<a href="#ref-9">9</a>, <a href="#ref-10">10</a>].
• Clean litter boxes daily; dispose of feces in sealed bags.
• Pregnant women and immunocompromised individuals should avoid litter box duties [<a href="#ref-16">16</a>].
• Reduce environmental contamination through proper disposal of cat feces.
• Stray cat population management reduces oocyst contamination in high-risk areas [<a href="#ref-10">10</a>, <a href="#ref-11">11</a>].

Mermaid decision tree for feline toxoplasmosis diagnosis and management

flowchart TD
 A["Cat with suspected toxoplasmosis"] --> B["Serology: ELISA IgG/IgM"]
 B --> C{"Acute infection?"}
 C -->|"IgM positive or rising IgG"| D["PCR on blood/feces"]
 D --> E["Positive"] --> F["Start clindamycin therapy"]
 D --> G["Negative"] --> H["Consider other causes"]
 C -->|"IgG only, low titer"| I["Chronic infection - no treatment unless clinical signs"]
 C -->|"Clinical signs present"| J["Tissue biopsy or PCR"]
 J --> K["Positive"] --> F
 J --> L["Negative"] --> M["Re-evaluate diagnosis"]
 F --> N["Recheck serology/PCR after therapy"]
 N --> O["Resolution"] --> P["Preventive management: indoor, cooked food"]
 N --> Q["Persistent"] --> R["Switch antiprotozoal or investigate resistance"]

Prevention flowchart for pregnant women and immunocompromised individuals

flowchart LR
 A["Owner at risk: pregnant or immunocompromised"] --> B{"Owns a cat?"}
 B -->|"Yes"| C["Cat indoor-only, fed cooked food"]
 C --> D["Owner avoids litter box"]
 D --> E["Daily litter cleaning by another person"]
 E --> F["Wear gloves and wash hands if unavoidable"]
 F --> G["Serological testing of cat if unknown status"]
 G --> H["If cat seronegative, maintain prevention"]
 G --> I["If cat seropositive, no additional risk if no active shedding"]
 B -->|"No"| J["General prevention: cook meat thoroughly, wash produce"]

Conclusion

_Toxoplasma gondii_ infection in cats is a significant zoonotic concern for pregnant women and immunocompromised individuals due to the potential for congenital transmission and severe disease. The risk can be effectively managed through education, proper hygiene, and veterinary preventive care. Advances in diagnostics, including antisense PCR and multi-species immunochromatographic strips, enable more accurate detection of infection in cats. Continued research into vaccines and strain epidemiology will further refine control strategies. A One Health approach integrating veterinary, medical, and environmental health is essential for reducing the burden of toxoplasmosis globally [<a href="#ref-26">26</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