How toxoplasmosis is transmitted

10/12/2025

Toxoplasmosis is a disease caused by a protozoan (Toxoplasma gondii) that is distributed globally in the environment. It is estimated that around one third of the world’s population is infected.

The life cycle of the protozoan takes place in the digestive tract of domestic and wild felines, which infect humans by contaminating water and food with their faeces. Infection occurs mainly through:

Undercooked meat
Poorly washed fruit and vegetables

What symptoms does toxoplasmosis cause?

During the acute phase of infection, most patients remain asymptomatic. However, a small percentage develop symptoms similar to glandular fever:

Cervical lymphadenopathy
Myalgia
Odynophagia (pain on swallowing)
Fever

These symptoms usually resolve, but the organism remains latent in the body for life.

Severe forms of toxoplasmosis: when complications occur

Congenital toxoplasmosis

This occurs in newborns born to infected mothers. It may affect the eyes and/or the nervous system, and its consequences can be very severe:

Blindness
Hydrocephalus
Psychomotor delay
Epilepsy
Toxoplasmic encephalitis

In immunocompromised adults, toxoplasmosis may present either as a primary infection or as reactivation of a latent infection, as seen in patients with AIDS or other immunodeficiency disorders.

Ocular toxoplasmosis: how it affects the retina

Also known as toxoplasmic retinochoroiditis, it presents with:

Localised white retinal lesions
Episodes of severe vitritis during reactivations
Frequent association with old scars

Treatment of ocular toxoplasmosis

Treatment is based on the combined use of:

Antibiotics: pyrimethamine plus sulfadiazine is the most commonly used regimen; alternatively, trimethoprim–sulfamethoxazole may be used. The regimen is continued for six weeks.
Anti-inflammatory treatment (corticosteroids).

In cases of infection involving the nervous system or the eye, glucocorticoids are added as anti-inflammatory therapy.

Visual consequences

Lesions may leave serious sequelae if they affect the macular area (the region of greatest visual acuity). This occurs more frequently in congenital toxoplasmosis, although it may also occur in adults.

Can ocular inflammation recur?

Yes. The risk of recurrence of retinal inflammation:

Is higher after the age of 40
Increases during the five years following a previous inflammatory episode

Prevention remains the best tool

In cases of immunosuppression, prolonged prophylactic antibiotic regimens may be used, but prevention remains fundamental to healthcare. Food hygiene and hand hygiene are basic pillars in the control of infectious diseases, and their importance should never be underestimated.

Dr Ramón Rey, Internal Medicine consultant at the Barraquer Ophthalmology Centre