Pattern of malaria imported by foreign residents under active survey.

An active of imported malaria was carried out on 1432 foreign residents entering Czechoslovakia between 1986-1989. The survey group consisted of adult aged 18-35 years who arrived from malaria endemic regions. Of 660 people surveyed who were from regions of Africa south of the Sahara, 10% were positive for Plasmodium falciparum. Whereas, those arriving from South East Asia had a relatively low prevalence of malaria (2.6%), predominantly P. vivax. Of the 10% of cases testing positive for P. falciparum, 85% had less than 10,000 asexual stages/microliters of blood and 75% were asymptomatic carriers. By contrast, 93.8% of P. vivax/ovale infections were diagnosed because of the onset of symptoms. Both the frequency of seropositivity and the geometrical mean reciprocal titre (IgG), using P. falciparum antigen, were higher in those people arriving from Africa (79% and 1,307) compared with those arriving from S.E. Asia (44.4% and 628). Malaria was confirmed, by blood smear examination, in only 23.8% of the seropositive cohort. There was a positive correlation between the percentage of P. falciparum-positive blood smears and the level of antibody titre. There was no correlation between serum reactivity and level of parasitaemia.