Pregnancy as a risk factor for acute toxoplasmosis seroconversion

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Abstract

Objective: To test the hypothesis that pregnancy is a risk factor for toxoplasmosis seroconversion. Materials and methods: A prospective observational study of women at child-bearing age vulnerable to Toxoplasma gondii. Serological reactions with indirect immunofluorescent antibody and immunoenzyme tests were used. The risk estimate used limits of reliability at 95%, and the results were validated by χ2 and RR tests. Results: Acute infection among pregnant women was 8.6% (45/522), and pregnancy was confirmed to be a risk factor for seroconversion (P=0.001). Living in close contact with host animals and vehicles of oocyst transmission proved to be a statistical risk for pregnant women to seroconvert, which was aggravated in adolescents. Conclusion: Gestation, potentiating susceptibility to this infection, points to the need of primary and secondary prevention for all pregnant women at risk.

Introduction

Toxoplasmosis is a zoonosis widely spread in nature, caused by a coccidian protozoan, Toxoplasma gondii. Its importance is due to the possibility of transplacental transmission, damaging the fetus [1].

In most areas of the world, 50–90% of the population carry antibodies against the parasite, demonstrating previous exposure. Some countries with low prevalence (<20%) are Thailand (3%), Japan, and USA. Australia (23%), UK (35%), Poland (36%), and Belgium (53%), show average prevalence. Tahiti (77%) and France present high prevalence (>60%) [2], [3], [4].

The rate of pregnancy damage depends on the infection prevalence among women at child-bearing age, among the animals they eat, the level of contact between vulnerable pregnant women and the sources of protozoan transmission, and on the time of gestation when the transmission occurs; the earlier in gestation transmission occurs, the greater the severity of sequelae in the fetus or newborn is [5].

In different geographical regions, annual seroconversion rates range from 0.6 to 1.5% [6], [7], [8]. The incidence of infection increases with age, and several studies have shown high prevalence among women at child-bearing age, although the children are more exposed to the sources of transmission of this parasite [3]. Some studies present conflicting results. A study by Walpole et al. [5], in Australia, could not relate exposure of women with seroconversion to any known risk factors. In the Netherlands, there was an inexplicable rise in infection rate at the end of pregnancy, despite the prophylactic measures adopted [5].

In pregnancy, there are alterations in the mother’s T-lymphocyte sub-populations, mainly at the end of pregnancy, with CD4 lymphocytes decreasing and CD8 lymphocytes increasing, and depletion of the function of NK cells as to the immune function of neutrophils, monocytes, and macrophages. The phagocytic function and the chemotaxis of polymorphonuclear neutrophils are depleted in women between the 30th and 34th weeks of gestation, thus justifying a higher vulnerability to the invasion of this micro-organism during the third trimester of pregnancy [10], [11], [12], [13]. The immune mechanisms, which are altered in pregnancy, are exactly the ones that protect her against T. gondii [1], [2], [3]. These immunological alterations could explain the higher vulnerability of pregnant women to the protozoan found in Australia [4] and the failure of prophylactic measures in the Netherlands [9].

Although there are many studies about the risk factors for seroconversion and its effects on pregnancy, no studies on the risk of pregnancy itself were found.

Section snippets

Methods

The study was carried out between January 1997 and 1999, in Goiânia (GO), a capital city in the midwestern region of Brazil.

Women of child-bearing age (12–49 years old) were identified via parental clinics, birth control groups, communitarian work groups, religious congregations, or public night elementary and high schools, and invited for meetings. Volunteers who consented to be followed for 6–12 months had blood samples collected, totalling 3564 women. The result of the serological screening

Results

Table 1 shows the percentage of women who were pregnant for the seroconverters and seronegative groups separately.

Table 2 shows the relation between low family income and low level of formal education, and seroconversion for different age groups.

In Table 3, we show the relation between various other factors and seroconversion, and in Table 4 the effect of pregnancy on these relationships.

In Table 5, we show the risk of seroconversion associated with environmental risk factors in pregnant and

Discussion

The prevalence of this infection varies in different regions of the world and even of the same city, which could be observed in Goiânia during the period of this study [11]. The north-western region of the city, where the population has lower family income, had already shown a statistical risk of seroconversion before the prevention program started. This city is located in the midwestern region of Brazil and presents tropical weather, which favours the survival of T. gondii oocysts, a fact that

Conclusion

The most important evidences found in this study were the identification of the adolescents as the group with the highest risk among the pregnant women, principally when they live in environments contaminated by host animals and vehicles of oocyst transmission, and the higher risk of acute infection for older pregnant women that consume contaminated food, such as raw meat, raw eggs and non-pasteurised goat’s milk. Daunter [19] showed that the presence of alterations in the balance

Acknowledgements

The authors would like to thank all the institutions and the people that have helped in the course of this research, collaborating in financial support, data collection, and sample processing. Financial support: National Foundation for Research Support; State Health Secretary of Goiás; Municipal Health Secretary of Goiânia; Technical laboratory support: Department of Parasitology, Institute of Tropical Pathology and Public Health, Federal University of Goiás; Laboratory of Immunology, Institute

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    Institutions associated with the research: Medical School of the Federal University of Goiás (FM-UFG), Institute of Tropical Pathology and Public Health of the Federal University of Goiás (IPTESP-UFG), National Foundation of Support to Research (FUNAPE), State Secretary of Health of Goiás, and Municipal Secretary of Health of Goiânia (GO). Study accomplished between January 1997 and 1999.

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