First Report on Toxoplasma gondii Infection in Bosnia and Herzegovina: Study in Blood Donors

T oxoplasma gondii is one of the most successful parasites on Earth, estimated to infect one-third of the global human population. Although infection is generally mild and self-limiting, it may cause life-threatening disease in populations with an incompetent immune system, including the unborn baby and immunosuppressed individuals, such as those infected by HIV or organ and tissue transplant recipients (Remington et al. 2001, Weiss and Dubey 2009). Toxoplasma infection is preventable (Montoya and Remington 2008), but a prerequisite for a prevention program to be adequate for a particular population is insight into the specific local epidemiological parameters of infection (Bobić et al. 1998).

There are virtually no published data on Toxoplasma infection in Bosnia and Herzegovina (B&H). According to official data a mean three cases per year were reported in the past 10 years (Institute for Public Health of B&H, 2005–2014), but the definition of “case” is not clear. A recent prediction analysis of the incidence of congenital toxoplasmosis (CT) estimated 2 cases per 1000 live births per year in B&H (McDonald et al. 2015). With 30,268 live births in 2014 (Agency for Statistics of Bosnia and Herzegovina 2015), this implies 60 CT cases only in that year, indicating CT as a significant public health issue. The aim of this study was to assess the prevalence of Toxoplasma infection and identify the basic demographic risk factors in the region of Banja Luka.

B&H is a Balkan country composed of two entities, the Federation of Bosnia and Herzegovina and the Republika Srpska (RS). The capital of RS is the city of Banja Luka, the greater area of which has a population of 300,000. Thus, the study sample of 320 consecutive blood donors involved 1% of the population. Routine medical examination, collection of personal data (gender, age, and residential address), and blood sampling were all performed at the Institute for Transfusion Medicine of RS in Banja Luka during February 2015.

Serology was performed in the National Reference Laboratory for Toxoplasmosis of Serbia, at the Institute for Medical Research in Belgrade. Specific IgG antibodies were detected by an in-house high-sensitivity direct agglutination assay (HSDA) (Desmonts and Remington 1980), using formalin-fixed tachyzoites as antigen, kindly provided by Isabelle Villena (Reims, France). A sample was considered positive if the test was positive at a serum dilution of 1:40 (corresponding to 2 IU/mL according to both a WHO reference serum and a laboratory standard).

The study was approved by the Institute for Medical Research Ethics Committee (decision no. EO111-2015).

The differences in the prevalence of infection between subgroups were analyzed by the chi-square test. The association between infection and gender, age (stratified into 10-year age groups), and area of residence (urban/rural) was analyzed by logistic regression (Wald forward stepwise method). The level of statistical significance was 5%.

Among the 320 blood donors (age range 18–55 years, mean age 35.9 years), the overall prevalence of Toxoplasma infection was 30.6% (95% confidence interval [CI] = 25.5–35.6), but differing significantly between the genders and according to age. In men, the prevalence of 36.6% was significantly (χ² = 6.31, p = 0.012) higher than in women, where it was 23.6%. Analysis of the overall seropositivity by age showed a significant (χ² = 8.44, p = 0.036) age-associated increase, from 21.5% to 44.4%. In women, however, this age-associated increase in seropositivity (from 18.6% to 33.3%) was not significant (χ² = 1.92, p = 0.166). In contrast, in men, the prevalence significantly (χ² = 7.71, p = 0.005) increased with age (from 26.3% to 54.2%). Finally, a higher (χ² = 4.46, p = 0.034) prevalence of infection was found among residents of rural areas.

Since gender, age, and area of residence were also shown to be significantly associated with infection in univariate analysis (Table 1), they were all included in the multivariate regression model. The analysis confirmed all three as risk factors for Toxoplasma infection in the studied population. The risk increased with age, and was significantly higher in men than in women, as well as in individuals residing in rural than in those from urban areas (Table 1). Gender and residence were further analyzed according to their modalities, and this analysis showed that for women, the area of residence was a risk factor (OR = 2.39; 95% CI = 1.08–5.30; p = 0.032), whereas for men this was age (OR = 1.45; 95% CI = 1.07–1.95; p = 0.015).

Owing to its clinical relevance, and also for more adequate comparison with the published data in the regional context, it was considered of importance to analyze the seroprevalence in women of childbearing age. Of the 148 examined women, 121 were aged between 18 and 45 (mean age 31.7 years), of which Toxoplasma antibodies were detected in 27 (22.3%, 95% CI = 14.9–29.7).

There has been a declining trend of Toxoplasma infection across the Balkan region over the past 20 years. As reviewed by Bobić et al. (2011), the most recent prevalence rates (obtained in women of childbearing age) of 27%, 29%, and 31% in the neighboring countries of, respectively, Montenegro, Croatia, and Serbia, are similar to the 30% overall prevalence and 22% in childbearing age women determined in this first ever study in B&H. Interestingly, infection was significantly more prevalent in males than in females. Although data on toxoplasmosis in males are generally scarce, a similar study carried out in 2000–2001 in Croatia also showed a higher prevalence (53.8%) in male than in female (47.8%) blood donors (Đaković-Rode et al. 2010).

Demographic factors including gender, age, and residence area were all shown as predictors of infection in blood donors in the Banja Luka region. An age-associated increase in the prevalence of infection may be expected as a result of the length of exposure to the infection. However, this study showed a significant age-associated increase only in men. The higher prevalence in men, as well as the significant increase with age, suggests that male lifestyle habits lead to exposure to infection more than female. In contrast, living in rural areas had a significant influence particularly among women, possibly as a result of exposure to soil through farming/gardening.

Variations in the prevalence of Toxoplasma infection are a result of sociocultural habits, which determine the influence of particular transmission routes in a population. Differences in demographic predictors of toxoplasmosis in neighboring countries (i.e., age was a predictor of infection in Serbia but not in FYR Macedonia, residence in highly urban areas was particularly significant in Serbia and Albania) may be explained by differences in the main routes of infection (consumption of undercooked meat in Serbia and Albania and contact with soil in FYR Macedonia) (Bobić et al. 2011).

On the local level, the presented data are a basis for future work on the transmission risk factors that should lead to a locally adequate prevention program, whereas on the global level, these data represent another piece in the jigsaw puzzle of the epidemiology of toxoplasmosis.