HUMAN AND ANIMAL DISEASE
Toxoplasmosis is most often clinically asymptomatic in immunocompetent patients (around 80% of cases) and translates biologically via seroconversion. When it is symptomatic, the most observed clinical sign is in the lymph nodes (15-20% of cases), with the presence of painless and soft cervical or occipital lymphadenopathy. Fever and weakness are often associated; muscle weakness can last for several months. Symptoms regress spontaneously without treatment. These forms are seen most often in adolescents and young adults. Ocular forms were considered rare in acquired infections; generally active chorioretinitis. Their frequency was probably underestimated outside of specific epidemic contexts and diagnosing these ocular forms is often difficult when the lesion is not typical or symptomatic.
However, severe visceral forms can be observed and are mainly due to an infection by virulent strains with an atypical genotype that are present notably in South America. Pulmonary forms have also been observed in Guyana; their prognosis is generally grave when treatment is not initiated quickly.
Toxoplasmosis in immunocompromised patients
Severe forms of toxoplasmosis are generally seen in immunocompromised patients (cellular immunosuppression); in this case, it is most often toxoplasmosis due to the reactivation of an old infection (reactivation of cerebral cysts). Cerebral forms are the most common; in AIDS patients, ocular infection is associated in 10 to 20% of cases. Pulmonary or disseminated forms are also seen in patients with severe cellular immune deficiency. In transplantation, reactivated toxoplasmosis can occur in patients immunized further to immunosuppressive therapy.
Congenital toxoplasmosis is secondary to placental passage of the parasite when a non-immunized pregnant woman contracts the infection during pregnancy. The risk of mother-to-child transmission increases with how far along the pregnancy is when the mother is infected; the global transmission rate is around 29%. The severity of the disease progresses inversely (severe forms in cases of transmission in early pregnancy, infraclinical forms at the end of pregnancy). The potential for the disease to evolve is unpredictable and particularly related to late onset chorioretinitis.
France established a prevention programme for toxoplasmosis by the decree of 14 February 1992, relative to the mandatory screening and monitoring of pregnant women before the end of the first trimester through the end of pregnancy. A Circular from 27 September 1983 details the prescription of safety and hygiene regulations for pregnant women and in immunocompromised patients that are not immunized against toxoplasmosis.
Since 2006, the CNR Toxoplasmosis has collaborated with the InVS (National Health Monitoring Institute) in the monitoring of congenital toxoplasmosis in France (metropolitan and overseas territories) through a network of specialized laboratories in charge of diagnosing the disease (see Epidemiological Pole and Monitoring of congenital toxoplasmosis).
All warm-blooded animals (mammals and birds) can be infected with T. gondii. Their sensitivity varies depending on the species and the infecting dose. In domesticated and wild animals, toxoplasmosis generally presents the same characteristics as in humans. Felides (cats mainly in Europe) are the only definitive hosts for the parasite infection, they are infected by eating meat or ingesting oocysts. Other animals are intermediary hosts and the disease does not seem to be a veterinary problem, except for in small ruminants (goats and sheep), where it can be the cause of abortions, a significant cause of economic loss. Among animals recognized as a source of infection in humans, the prevalence of T. gondii infection varies depending on the animal species and follows in decreasing order for the following species: sheep, goats, free-range pigs, cows, chickens and horses. However, numerous data is old and estimated using different methods, making these studies incomparable and should be updated.
The biological diagnosis of toxoplasmosis depends on the clinical context, isolating the parasite or its DNA through molecular biology, or through revealing specific antibodies (See Activity Poles Serology and Molecular Biology).
Toxoplasma serology depends on various techniques and aims to determine the serological status of patients (former immunity, progressive acquired toxoplasmosis, reactivated toxoplasmosis, etc.). The various commercial kits for diagnosis are currently being evaluated by the CNR. Interpretation guides were recently published by the CNR.
Parasite diagnosis is reserved for severe forms of toxoplasmosis (especially in immunocompromised patients) and congenital toxoplasmosis; it is currently mainly based on DNA research through molecular biology, inoculating mice is mainly reserved for isolating the strains responsible for infection (genotyping).
Few drugs are available for the treatment of toxoplasmosis. They are only active against tachyzoites and have no effect of cysts. There are two main drug families: the first is folinic acid synthesis inhibitors and the second is macrolides. Macrolides alone can be used for benign symptomatic toxoplasmosis (spiramycine, mainly) and the synergistic association of both anti-folates families (pyrimethamine-sulfadiazine or sulfadoxine) is reserved for severe forms and the treatment of congenital toxoplasmosis (antenatal or postnatal).
In France, where there is a monitoring programme for congenital toxoplasmosis, spiramycine is prescribed in the aim to reduce transmission when a pregnant woman contracts the infection. However, its efficacy has not currently been shown and, further to the recommendations by the French High Health Authority (HAS), a clinical hospital research programme is underway, aiming to evaluate this strategy (PHRC Toxogest). When congenital toxoplasmosis is diagnosed, treatment based on a combination of pyrimethamine and sulfamides is prescribed in pregnant women and/or the newborn. Treatment duration in infants is based on empirical data. A national clinical research programme (PHRC Toscane) is underway aiming to evaluate the efficacy of short treatment (3 months) vs long treatment (12 months).