[Inter- and intra-cephalic variations in pathogenicity in Toxoplasma gondii. Clinical and epidemiologic consequences]

Clinical and epidemiological studies, especially the ones conducted in HIV+ patients indicate that the pathogenicity of Toxoplasma gondii varies according to the strain considered. The differences observed among strains are represented by distinct genomic DNA patterns which could be experimentally evaluated by means of the RFLP (Restriction Fragment Length Polymorphism) and the RAPD (Random Amplified Polymorphic DNA). If on the one hand virulent strains present very similar genomic DNA patterns, on the other hand chronic strains are highly polymorphic. These differences may be, at least in part, due to the asexual (clonal) multiplication of virulent strains. The existence of an intraspecific pathogenicity variation and genetic heterogeneity was observed within a single strain either after attenuation (infection in Fischer or Wistar rats), or during reactivation (in immunodepressed animals). In a congenital model of toxoplasmosis, the differences are detected from one animal to another and sometimes, even from one organ to another in the same host. This finding do not seem to be related to the occurrence of mutations but rather to selective pressures, notably of immunological origin, exerted by the infected organism. A better understanding of these phenomena could result in significant therapeutic and prophylactic advances. Our first effort will be directed to the establishment of more precise diagnostic and predictive elements. The accomplishment of this step relies on the use of primers deriving from DNA sequences characteristic of virulence and which will be tested by PCR.

[Infectious diseases and risks in pregnancy: precautions to take and contra-indications]

Prenatal diagnosis of toxoplasmosis, rubella, CMV, varicella and parvovirus B19 are reliable by fetal blood sampling and or amniocentesis. Strategy for improving the management is discussed taking into account the specific therapy and the contraindications.

Biology of Toxoplasma gondii

In conclusion, a large body of new information on the biology and immunology of T. gondii has accumulated in the past several years. Much of this is due to the advent of AIDS and the increased funding made available to researchers interested in opportunistic infections in this patient population. These scientific advances have led to a better understanding of the process by which Toxoplasma infects mammalian host cells, molecular biology and biochemistry of the parasite, antigenic structure and immune response to the infection and approaches to be adopted for drug design and therapeutic strategies. Thus, it is through such recognition of the importance of understanding the basic science of an opportunistic pathogen that such advances can be realized.

Toxoplasmosis in pregnancy

Primary infection with Toxoplasma gondii in pregnant women occurs all over the world with frequencies between 0.1-1%. In approximately 40% of the cases, the unborn child is infected. The risk of fetal infection increases during pregnancy, while at the same time the risk of severe disease decreases. As a result, infants with congenital toxoplasmosis are mostly asymptomatic at birth, but long-term studies indicate that up to 85% of them will develop sequelae including chorioretinitis (leading to severe impairment of vision), hearing loss or mental retardation. Early recognition of maternal infection and treatment with spiramycin or pyrimethamine-sulphadiazine will reduce the parasitic colonization of the placenta by more than 60% and prevent infection in the fetus. If fetal infection has already occurred, maternal treatment modifies the fetal disease. Therapy during the first year of life improves the prognosis. It is possible today to identify infected fetuses by prenatal diagnosis based on detection of the parasite in cord blood, amniotic fluid and placental tissue. Specific antibodies and non-specific signs of infection in fetal blood give additional information. Advances in laboratory techniques have made it feasible to consider serological surveillance of pregnant women. The present recommendation is that each country should provide data on the incidence of toxoplasma infection in pregnancy and thereby decide whether it represents a problem and what measures should be adopted. This paper summarizes the present knowledge of the parasite and its implication for the mother and unborn child. The effect and problems of primary and secondary prevention in pregnancy are discussed as well as the efficacy of treatment. The need for future research including long-term follow-up studies are emphasized.

[Toxoplasmosis and important virus infections in pregnancy-- diagnosis and management]

Toxoplasmosis and viral infections such as rubella, cytomegaly and parvovirus B19 are much feared risk during pregnancy. The rate of connatal toxoplasmosis and of subclinically infected infants at birth with the risk of late manifestation is still unclear, whereas such data are fairly well-known for rubella-, CMV- and parvovirus-B19-infections. The respective major diagnostic issues in pregnancy, the laboratory diagnosis, and its rational use in combination with clinical information are presented. Also the value of passive prophylaxis, therapy, and prenatal diagnosis as well as the possible management for diminishing the infection problems in pregnancy are discussed.

[Toxoplasmosis in AIDS]

Toxoplasmosis is one of the major opportunistic infections observed in France in 15 to 37 percent of HIV-infected patients. Its main manifestation is encephalitis. Other, less frequent manifestations are chorioretinitis, pneumonia or disseminated toxoplasmosis. The conventional treatment is a combination of pyrimethamine 50-75 mg/day and sulfadiazine 6-8 g/day. Acute therapy should be pursued for at least 3 weeks or until optimal response is achieved, i.e. 6 to 8 weeks in most cases. The pyrimethamine-clindamycin combination in doses of at least 2.4 g/day is a possible alternative. Other drugs are being studied, but there is still a need for new drugs active against the parasite, that could be used in humans. In HIV-infected patients treatment should be maintained lifelong to prevent relapses. Maintenance regimens use the same drugs as acute therapy but in lower doses. The main field of research is primary prophylaxis of toxoplasmosis in HIV-infected patients.

Toxoplasmosis in pregnancy: an emerging concern for family physicians

Toxoplasmosis is usually asymptomatic in pregnant women but poses a risk of severe effects on the fetus. One to eight of every 1,000 pregnant women become infected, and the infection is transmitted to the fetus in approximately 40 percent of these cases. The risk of transmission rises with increasing gestational age at the time of initial infection. Congenital infection with toxoplasmosis may lead to serious sequelae, such as blindness, mental retardation, neurologic deficits and deafness. Prevention of morbidity from toxoplasmosis depends on prevention of the infection in pregnant women, plus early recognition and aggressive treatment of maternal infections.

[Toxoplasmosis: new aspects, diagnosis and treatment]

The position of visceral toxoplasmosis in HIV infection has changed in the late 1980's. The strong prevalence of toxoplasmosis in the French population and the regression of pneumocystosis due to generalization of primary prophylaxis have made cerebral toxoplasmosis the initial manifestation of AIDS in about 20% of the cases. At the same time, a better management of AIDS patients has made it possible to hope for a longer survival, even in patients with very deep immunodeficiency. Altogether, these various elements are in favour of developing a primary prophylaxis in patients at high risk for visceral toxoplasmosis. During the last few years, other visceral forms of this infection have emerged, which are either localized (chorioretinitis, diffuse encephalitis) or disseminated, affecting the lung, liver, heart, muscles, bone marrow and other viscera. These forms usually imply a very severe immunodeficiency. Because of the toxicity of the reference therapy, sulfadiazine-pyrimethamine, attempts are being made at developing more effective and better tolerated treatments. At the moment, the clindamycin-pyrimethamine combination is a possible alternative. Other compounds, and in particular macrolids, are still under study.

Coccidian infections in AIDS. Toxoplasmosis, cryptosporidiosis, and isosporiasis

Cryptosporidium sp. and Isospora belli are coccidian protozoan parasites that were long recognized as pathogens for many animal species. The medical community became acquainted with these organisms with the advent of AIDS. Both parasites are associated with persistent, debilitating enteritis and, in the case of Cryptosporidium, biliary tract involvement in patients with AIDS. For the immunocompetent host, infection with these two pathogens usually results in self-limited diarrhea. Cryptosporidiosis appears to occur more often than isosporiasis, but the true prevalence of both infections for various populations of humans is unknown. Clinically, cryptosporidiosis is indistinguishable from isosporiasis. Diagnosis is based on finding the acid-fast (red staining oocyst in stained fecal specimens). There is no known effective therapy for cryptosporidiosis, whereas patients with isosporiasis respond promptly to treatment with trimethoprim-sulfamethoxazole. Patients with AIDS and isosporiasis have a high relapse rate after achieving complete remission and therefore need to be maintained on suppressive therapy. Much more needs to be learned about these two fascinating, "newly recognized" parasites.

A review of 58 patients in Singapore with significantly high anti-Toxoplasma serotitres

Over a 42-month period, 58 patients presenting at the Singapore General Hospital were identified to have IgG anti-Toxoplasma serotitres of 1:1024 or higher by the indirect immunofluorescence test. This retrospective study examines the clinical presentation and management of these 58 patients. About 60% of these 58 patients had presented with lymphadenopathy, 20% with ocular symptoms and 14% with bad obstetric history. Almost all patients with IgG anti-Toxoplasma serotitres exceeding 1:1024 had presented with lymphadenopathy (with a modal titre of 1:4096). In contrast, most of the patients who presented with ocular symptoms or bad obstetric history had lower modal titres. The majority of patients who had presented with lymphadenopathy were Chinese, aged 21 to 35. Typically, they presented with a painless, mobile, solitary cervical node of three to four weeks duration as the only symptom, had biopsies where the histopathology was suggestive of toxoplasmosis, received no treatment and experienced no sequelae. The study concludes that: acute toxoplasmosis is common in Singapore and presents typically as asymptomatic cervical lymphadenopathy in a young Chinese; the incidence of congenital infection is also believed to be high, based on the number of cases presenting with fetal wastage and the prevalence of ocular toxoplasmosis; pigs in Singapore may constitute an important reservoir for the transmission of this disease to man.

Current diagnosis and management of toxoplasmosis in cancer patients

Toxoplasmosis should be considered as a potential pathogen in cancer patients who have clinical syndromes, especially lymphadenopathy, for which the cause is not clear. Patients with reticuloendothelial malignancies or solid cancers treated with systemic chemotherapy or with progressive disease appear to be at particular risk for life-threatening toxoplasmosis. There has also been an explosion in the number of cases of toxoplasmic encephalitis in patients infected with HIV. Diagnosis rests on demonstration of trophozoites in tissue or body fluids, demonstration of characteristic serologic test results, and, in cases of lymphadenopathy, characteristic histologic features.

[Complex treatment of toxoplasmosis in women with a history of severe obstetric problems]

A total of 43 females with chronic required toxoplasmosis and habitual abortion were exposed to comprehensive investigation and etiological treatment with regard to toxoplasmosis. In the majority of cases combined involvement of various organs and systems was revealed. Treatment of 14 pregnant women in presence of threatened abortion positively affected not only the course and outcomes of advancing pregnancies but the development of future pregnancies as well.