pGDH is a target malaria antigen that is widely used to develop monoclonal antibodies for non-microscopic immunochromatographic assays (i.e., RDTs). However, little is known about the ability to detect antibodies to pGDH in serum of patients with malaria. Therefore, the sequence variation of pGDH and its antigenicity was investigated among Korean isolates.
Plasmodium vivax has been prevalent in Korea for a long time. However, as the result of a national malaria eradication programme and with help from the World Health Organization, the incidence of vivax malaria rapidly decreased during the 1960s and 1970s [
22‐
25]. Following the report of two cases of malaria in 1985 [
25], there were no additional reported cases in Korea until the emergence of one case in 1993 [
26] and two cases in 1994 [
27]. The incidence of malaria then increased rapidly until approximately 2000 [
28]. After that, reported cases of malaria declined again for several years, owing to nationwide efforts to reduce the incidence of this disease. However, malaria has not been eradicated from the Korean peninsula because many travellers and workers come from areas where malaria is prevalent, including North Korea [
29]. For these reasons, serological diagnostic tools are needed to support both traditional microscopic diagnosis and antibody testing on a population level to gain an estimate of exposure to malaria in Korea. Currently, the immunofluorescence antibody test (IFAT) is used as the standard serological diagnostic method owing to its high sensitivity. However, the sensitivity of this test can be affected by the training and ability of users [
30‐
32]. Therefore, a new antigen is needed for serodiagnosis. Several recombinant proteins cloned from Korean isolates of
P. vivax have been tested for use as antigens for serodiagnosis, including Circumsporozoite protein (CSP) subtypes Pv210 [
18] and Pv247 [
33], merozoite surface protein (MSP) [
34], CSP and MSP chimeric proteins [
35], aldolase [
36], and parasite lactate dehydrogenase [
37]. None of these antigens has enabled replacement of the IFAT method because of their comparatively low sensitivity. Therefore, there has been a focus on pGDH. Monoclonal antibodies against pGDH have been used in several RDTs and exhibit a relatively high sensitivity for detection of malaria parasites. However, in the present study the ELISA detected only 84.8% (39/46) of microscopy-positive samples, even though the
pGDH gene was cloned from a Korean
P. vivax strain (pVKtype3, Fig.
2). Therefore, antibody detection using the recombinant pGDH protein is not superior to antigen detection using monoclonal antibodies against pGDH. Nevertheless, it was worth investigating whether the recombinant pGDH protein could be used to detect antibodies in asymptomatic patients or symptomatic patients with low parasitaemia (under 50/µL), using antibody detection methods such as ELISA or western blotting. The recombinant pGDH protein was evaluated for its usefulness in seroepidemiology using sera collected from Gyodong-myeon, Ganghwa County, Incheon Metropolitan City, in 2012. This study area is an island consisting of several hills surrounded by rice fields and two large irrigation reservoirs. Serum samples from 28.74% of the inhabitants of this island (876 cases) were tested by ELISA with recombinant pGDH protein as antigen. The villages with a positive rate above 10% are adjacent to the main rice field located in the center of the island and the two irrigation reservoirs, which are potential habitats for anopheline mosquitoes. In contrast, villages with a low positive rate are located in coastal areas and are separated by a hill from the main rice field and the two irrigation reservoirs. In conclusion, the results of this study indicate that antibody detection using recombinant pGDH may provide useful information regarding the prevalence of malaria in certain areas and individuals.