# Food and Drinking Water as Sources of Pathogenic Protozoans: An Update
## 6 _Toxoplasma gondii_
### Diseases Caused by T. gondii  
In immunocompetent individuals, _T. gondii_ infection is mostly asymptomatic or mild and self-limiting, but it can be life-threatening in fetuses and immunocompromised individuals [158; 160; 163]. Severe toxoplasmosis in immunocompromised individuals mainly manifests as central nervous system (CNS) disease, myocarditis, or pneumonitis [157; 159; 164]. Latent infection may be associated with specific neuropsychiatric conditions [165]. Infection during pregnancy can cause congenital infection and lead to miscarriage, stillbirth, prematurity, neonatal death, and clinical manifestations in the newborn in both humans and animals. In Europe, 75% of children with congenital _T. gondii_ infection were asymptomatic at birth, but--if left untreated--they could develop symptoms later, including chorioretinitis, intracranial calcifications, or hydrocephalus [159].  
When the organism is disseminated throughout the body via macrophages, toxoplasmosis can manifest with fever, pneumonia, or brain cysts. Clinical manifestationsinclude myelopathy, encephalitis, brain abscesses, hydrocephalus, short-term memory loss, cognitive impairment, altered mental status, cachexia, hypercalcemia, and stroke. Rare voluminous lesions mimic primary and metastatic tumors. Central nervous system (CNS) involvement, most commonly acute or chronic meningitis, has been reported in 5-10% of cases and usually occurs both in disseminated or focal CNS infection [163]. In patients with AIDS, toxoplasmosis can manifest as encephalitis [166].  
The bradyzoites form cysts in the heart, liver, kidney, skeletal muscle, and--due to the high affinity for nerve cells--also in the brain. This chronic form of the pathogen may persist even for the whole life of the host and reactivate, leading to a severe pathology in case of weakened immune response, as occurs in patients with dormant toxoplasmosis who receive allogeneic hematopoietic stem cell transplants or grafts [163]. Patients treated with immunosuppressive can develop symptomatic toxoplasmosis as recently reported for a 34-year-old woman treated with izekizumab for chronic psoriasis who regularly consumed rare meat [157]. Moreover, a case-control study based on serological diagnosis showed that rheumatic patients had a significantly higher _T. gondii_ seroprevalence than control subjects. Consumption of raw shellfish was identified through multivariate analysis as being among the risk factors that affected the _T. gondii_ seroprevalence in these patients [167].  
The diagnosis of _T. gondii_ infection is carried out by serological tests, with detection in serum of anti-toxoplasma-specific antibodies and the presence of IgM specific for _T. gondii_ being indicative of acute infection [159]. Laboratory tests are less reliable in immunosuppressive patients, so clinical symptoms are interpreted by investigating possible foodborne transmission routes, such as rare and cured meat, raw shellfish, and unpasteurized milk. In addition, PCR, histological examination, isolation of the organisms, and imaging are carried out. Acute infection can be diagnosed by visualization of tachyzoites and infiltration of inflammatory cells in tissues or body fluids with immunohistochemical or Giemsa staining [157].