Restriction of serological cross-reactivity between blood stages of Plasmodium falciparum and P. vivax following single malaria infections

Serology is valuable for assessing malarial transmission levels, monitoring the effectiveness of control measures, detecting latent foci and screening blood donors in malaria-free areas. Only a Plasmodium falciparum antigen, obtained from culture, is commercially available for serological testing, the rational being the cross-reactivity among blood stages of different Plasmodium species. We have compared the frequency of cross-reactivity of sera from individuals who had recovered from clinical malaria caused by P. vivax (group Pv) or P. falciparum (group Pf) with blood stage antigens of either parasite. In both groups, a higher seropositivity, detected using indirect fluorescent antibody test (IFAT), was observed with the homologous antigen. Since the cross-reactivity observed with the heterologous antigen could reflect previous malaria infections, we analysed the reactions with sera from mono-infected individuals with either Pf or Pv and observed a low level of cross-reaction (∼ 20%). Our results suggest that the Pf antigen used in the routine of serology does not replace the Pv antigen, and that the two antigens should be used simultaneously to avoid false negative reactions, especially in primary infections.