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Background  Merozoite surface protein 1 (MSP1) plays an essential role in erythrocyte invasion by malaria parasites. The C-terminal 19-kDa region of MSP1 has long been considered one of the major candidate antigens for a malaria blood-stage vaccine against  Plasmodium falciparum . However, there is limited information on the C-terminal 19-kDa region of  Plasmodium ovale  MSP1 (PoMSP1 19 ). This study aims to analyze the genetic diversity and immunogenicity of PoMSP1 19 .    Methods  A total of 37 clinical  Plasmodium ovale  isolates including  Plasmodium ovale curtisi  and  Plasmodium ovale wallikeri  imported from Africa into China and collected during the period 2012–2016 were used. Genomic DNA was used to amplify  P. ovale curtisi  (poc)  msp1   19    (pocmsp1   19  ) and  P. ovale wallikeri  (pow)  msp1   19   ( powmsp1   19  ) genes by polymerase chain reaction. The genetic diversity of  pomsp1   19   was analyzed using the GeneDoc version 6 programs. Recombinant PoMSP1 19  (rPoMSP1 19 )-glutathione S-transferase (GST) proteins were expressed in an  Escherichia coli  expression system and analyzed by western blot. Immune responses in BALB/c mice immunized with rPoMSP1 19 -GST were determined using enzyme-linked immunosorbent assay. In addition, antigen-specific T cell responses were assessed by lymphocyte proliferation assays. A total of 49 serum samples from healthy individuals and individuals infected with  P. ovale  were used for the evaluation of natural immune responses by using protein microarrays.    Results  Sequences of  pomsp1   19   were found to be thoroughly conserved in all the clinical isolates. rPoMSP1 19  proteins were efficiently expressed and purified as ~ 37-kDa proteins. High antibody responses in mice immunized with rPoMSP1 19 -GST were observed. rPoMSP1 19 -GST induced high avidity indexes, with an average of 92.57% and 85.32% for rPocMSP1 19  and rPowMSP1 19 , respectively. Cross-reactivity between rPocMSP1 19  and rPowMSP1 19  was observed. Cellular immune responses to rPocMSP1 19  (69.51%) and rPowMSP1 19  (52.17%) induced in rPocMSP1 19 - and rPowMSP1 19 -immunized mice were found in the splenocyte proliferation assays. The sensitivity and specificity of rPoMSP1 19 -GST proteins for the detection of natural immune responses in patients infected with  P. ovale  were 89.96% and 75%, respectively.    Conclusions  This study revealed highly conserved gene sequences of  pomsp1   19  . In addition, naturally acquired humoral immune responses against rPoMSP1 were observed in  P. ovale  infections, and high immunogenicity of rPoMSP1 19  in mice was also identified. These instructive findings should encourage further testing of PoMSP1 19  for rational vaccine design.    Graphical abstractSupplementary Information  The online version contains supplementary material available at 10.1186/s13071-021-05086-6.

Genetic diversity and immunogenicity of the merozoite surface protein 1 C-terminal 19-kDa fragment of Plasmodium ovale imported from Africa into China