Abstract:
Sri Lanka was certified malaria free by the WHO in 2016. The presence of the malaria vector
in the island, and imported malaria cases pose major risks during the current Prevention of Reestablishment (POR) phase in Sri Lanka. As serological parameters may indicate malaria
transmission dynamics, assessment of antimalarial antibody prevalence/titers in populations
will be indicative of the status of current infections and hence of malaria transmission. Yet,
malaria immunoepidemiology studies in countries successful in eliminating malaria are
nonexistent. We aimed to determine the prevalence of antibodies to Plasmodium vivax vaccine
candidate antigens, PvMSP1-19 and PvAMA1, in residents of two previous high malaria
endemic districts, Hambantota and Kilinochchi; Nuwaraeliya served as the control/malariafree district. Indirect ELISAs assayed antibody responses against two recombinant proteins,
PvMSP1-19 and PvAMA1, on serum samples collected with informed consent from study
participants. In a total of 3129 individuals (Hambanthota-1231, Kilinochchi-1398, and
Nuwaraeliya-500) recruited for the study, Anti-MSP1-19 antibody prevalence was 2.0%, 5.0%
and 1.0% while anti-AMA1 antibody prevalence was 5.0%, 14.0% and 2.0% in Hambanthota,
Kilinochchi and Nuwaraeliya districts, respectively. Compared to the controls, antibody
magnitudes to both PvMSP1-19 and PvAMA1 were significantly higher in Kilinochchi
(p<0.005 and p=0.022, respectively) than in Hambantota (p=0.001 and p<0.005). Previous
exposure to malaria was significantly associated with antibody responses against both
PvMSP1-19 and PvAMA1 among all three districts (p<0.05). In comparison, based on previous
records the prevalence of antimalarial antibodies to MSP1-19 and AMA1 in the Hambantota
district during 1998–2003 were 59% and 54%, respectively. In conclusion, though significant
seroprevalence to P. vivax antigens, MSP1-19 and AMA1, was evident in residents of previous
high malaria endemic areas in comparison to a previous malaria non-endemic area under a POR
setting, compared to malaria pre-elimination data, these have declined to low levels which may
suggest the absence of current malaria transmission.
