Allelic diversity of merozoite surface protein-1 (MSP 1) and MSP 2 genes, and clinical manifestations of Plasmodium falciparum malaria cases in Aceh, Indonesia


 Background

Malaria control programme in Indonesia has successfully brought down malaria incidence in many parts of the country, including Aceh Province. Clinical manifestation of reported malaria cases in Aceh varied widely from asymptomatic, mild uncomplicated to severe and fatal complications. The present study aims to explore the allelic diversity of merozoite surface protein genes among the P. falciparum isolates in Aceh Province and to determine their potential correlation with the severity of malaria clinical manifestation.
Methods

Screening of over 500 malaria cases admitted to the 11 districts hospital within Aceh Province during 2013–2015, identified 90 cases of P. falciparum mono-infection without any co-morbidity. The subjects were clinically phenotyped and parasite DNA was extracted and Polymerase Chain Reaction (PCR) amplified for the MSP1 and MSP2 allelic subfamilies.
Results

Analysis of clinical manifestation revealed that fever-chill is the most frequent symptom. Based on WHO criteria showed 19 cases classified as severe and 71 as mild malaria. Analysis of MSP 1 gene revealed the presence of K1 allele subfamily in 34 subjects, MAD20 in 42 subjects, RO33 in 1 subject, and mixed allelic of K1 + MAD20 in 5 subjects, K1 + RO33 in 4 subjects, and MAD20 + RO33 in 4 subjects. Analysis of MSP 2 gene revealed 34 subjects carried the FC27 allelic subfamily, 37 subjects (carried the 3D7 and 19 subjects carried the mixed FC27 + 3D7. Analysis of multiplicity of infection revealed that msp2 alleles is slightly higher than MSP 1 with the mean of MOI were 2.69 and 2.27, respectively. Statistical analysis to determine the association between each clinical manifestation and MSP 1 and MSP 2 alleles revealed that liver function abnormal value was associated with the MSP 2 mixed alleles (p < 0.05; odds ratio = 0.13; CI95%= 0.03–0.53). Malaria severity was associated with the mixed MSP 1 of K1 + RO33 with severe malaria (p < 0.05; odds ratio = 28.50; CI 95%= 1.59-1532.3).
Conclusion

This study found a strong association between severe malaria in Aceh with subjects carrying the MSP 1 mixed alleles of K1 and RO33. The liver function abnormal value associated with the MSP 2 mixed allelic subfamilies. Further study in different geographic areas is recommended.

Malaria remains a major public health problem in Indonesia despite a success in bringing down the incidence within the last few decades. Since the implementation of the malaria elimination program in 2009, the malaria cases in Indonesia dropped signi cantly from 418,439 to 261,617 and the vast majority of the cases occurred in 5 provinces of the eastern parts of country [1]. In Aceh Province, effective monitoring of the implementation of malaria elimination programme has also successfully brought down the Annual parasite incidence (API) from 0.08 in 2015 to 0.06 in 2017. The success of malaria control program relies on three main efforts; early diagnosis and prompt treatment, provision of long-lasting insecticide-treated bednet (LLINs) and insecticide residual spraying. Attempts to develop a suitable vaccine to prevent malaria continue to elude us as several vaccine candidates still fail to provide the required e cacy.
The clinical manifestation of malaria infection in human varies widely, from asymptomatic to fatal infections with cerebral or non-cerebral complications. This phenomenon is associated with factors associated with the malarial parasite, human host and environment. Studies to identify parasite factors that contribute to virulence revealed several candidates such as antimalarial drug resistance, cytoadherence, and antigenic polymorphisms [2]. Clinical manifestation of malaria is directly associated with the repeated cycle of invasion of the red blood cell (RBC) by merozoites, followed by development into schizont which end up in the rupture of the RBC and release of daughter merozoites. During the blood stage, the parasite expresses arrays of proteins and among others are merozoite surface protein 1 (MSP 1) and MSP 2. These proteins are involved in erythrocyte invasion [3] and are targeted by the immune responses [4,5], and therefore have been used as target for vaccine development. MSP 1 and MSP 2 also exhibit high polymorphisms hence play important role in identi cation of genetically distinct P. falciparum parasite sub-populations [3]. MSP 1 gene is located on chromosome 9 and contains 17 blocks of sequences [6]; block 2 is most polymorphic and is grouped into three allelic families MAD20, K1 and RO33 [7]. MSP 2 gene is located on chromosome 2 composed of 5 blocks and block 3 is the most polymorphic [8]. The MSP2 alleles are grouped into two allelic families, FC27 and IC1/3D7) [9].
Many studies have explored the potential roles of MSP 1 and MSP 2 alleles in the modulation of malaria clinical manifestations. In French Guyana, study on the MSP 1 and var genes demonstrated that MSP1 K1 allele and var genes, D allele overexpression associated with severe malaria [10]. Multiple eld studies have tried to characterize virulent strain of Plasmodium falciparum using genetic polymorphisms as markers. Although evidence of differences in virulence among the P. falciparum strains have accumulated, the virulent strains have not yet been characterized in su cient detail to identify suitable virulence markers. The present study aims to explore the allelic diversity of merozoite surface protein genes among the P. falciparum isolates in Aceh Province and their potential association with the severity of clinical manifestation of malaria.

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This study was conducted in eleven district hospitals in Aceh Province, Indonesia (Fig. 1). Patients admitted with initials diagnosis of malaria were screened for cases with mono infection of P. falciparum without any co-morbidity. At admission, thick and thin blood lms were obtained using nger prick, stained with Giemsa and examined by accredited microscopists. Any subjects declared positive by microscopy will be further stated in parasite density for microliter blood as previously described. Dried blood spots were made using 3MM Whatman 3M paper (GE Healthcare, Buckinghamshire, UK) and kept in individual plastic ziplock until used.

Determination of malaria severity
Upon admission to the hospital, all subjects underwent physical examination and laboratory assays for complete blood count, thin and thick blood smear, liver and kidney function tests. History taking and consent were obtained from patients or legal guardian. Clinical manifestation of the patients was assessed and classi ed using the World Health Organization (WHO) criteria.

Criteria for severe malaria
Severe falciparum malaria is de ned as one or more of the following [11], occurring in the absence of an identi ed alternative cause and in the presence of P. falciparum asexual parasitaemia: (a) Impaired

Blood collection and DNA Preparation
Blood of the consented subjects were collected using nger prick for making thin and thick blood smears, dried blood spot on Whatman 3M lter paper (GE Healthcare, Buckinghamshire, UK) and kept in individual plastic ziplock bag.

DNA extraction and polymerase chain reaction
The parasite DNA was extracted from the lter paper using Chelex-100 ion exchanger method as described previously [12]. The DNA extract was used as template for the nested PCR using oligos that target the parasite MSP 1 and MSP 2 genes [13]. The second reaction primer set targets speci c allelic families of MSP 1 (MAD20, K1 and R033) or MSP 2 (IC/3D7 and FC27). Reactions for each set of primary and nested primers were performed separately.

Multiplicity of infection (MOI)
MOIs were calculated by dividing the total number of distinct MSP 1 and MSP 2 genotypes by the number of positive samples for each marker. The mean MOI was calculated by dividing the total number of alleles detected in both MSP 1 and MSP 2 by the total number of positive samples for both markers. Samples were considered single infected when harbouring only one allele at each of the genotyped loci. Multiclonal infections were de ned as infections with more than one allele in at least one locus.

Statistical analysis
All data were collected with Epidata and analysed by R version 3.4.0. The allelic subfamily frequency of MSP 1 and MSP 2 was calculated as the proportion of the allele detected for each allelic family out of the total of alleles detected. The frequency of polyclonal infection was calculated using number of samples with more than one ampli ed fragment out of the total samples. The mean multiplicity of infection (MOI) was determined by dividing the total number of alleles detected in both MSP 1 and MSP 2 by the total number of positive samples for both markers. The Chi-square test was used to analyse the association of the clinical manifestations and the allelic subfamilies of the MSP 1 and MSP 2. Statistical signi cance was de ned as P < 0.05.

Results
The study subject's recruitment owchart and the procedures applied to subjects is shown in Fig. 1. Of the total 500 subjects admitted to the hospital with fever, 176 subjects were found positive by microscopy and 117 of which by P. falciparum. Further validation by PCR revealed 90 subjects with P. falciparum mono infection. Among the 90 study subjects, 57.7% of them were male and 42.3% were female with most subjects (46.7%) aged between 21-30 years old (Table 1). Clinical manifestation of the subjects The clinical manifestation, origin and laboratory pro les of each subjects is shown in Tables 2. The commonly observed symptoms and signs includes fever with chill (100%), dyspnoea (75.6%) and spleen enlargement (87.8%). Severe signs such as shock, convulsion and conscious disturbance were observed in few cases. Laboratory assays revealed anaemia in 36.8% of the subjects, abnormalities in the values of liver (63%) and kidney (95.6%) function, and haemoglobinuria (20%). Of the 90 subjects examined 92% had parasite density of 10,000 parasite per microliter blood and the remaining 8% had parasite density of less than 10,000/µl blood. Based on WHO classi cation [11], 19 subjects were classi ed as severe malaria whereas the remaining 71 subjects were mild, uncomplicated malaria.   Table 4). Analysis of the size of amplicons in each subfamily revealed that K1 subfamily had 3 alleles, MAD-20 had 5 alleles and RO33 had 2 alleles. Allelic analysis of the MSP-2 revealed that there were two different allelic subfamilies. Of the total 90 subjects examined, the FC27 subfamily was observed in 41.4%, the 3D7 subfamily in 37.7% of the subjects and 21.2% of the subjects carried the mixed subfamilies of FC27 and 3D7. Analysis of the size of amplicons in each MSP subfamily revealed that FC27 had 4 alleles and 3D7 had 3 alleles (Table 4).

Discussion
Analysis of the clinical manifestation of the malaria cases admitted to the hospitals in Aceh revealed that the classical symptoms such as fever with chill is still the primary symptom experienced by the patients, followed by dyspnoea and spleen enlargement. Majority of the malaria cases are classi ed as mild, uncomplicated malaria but over 20% of which are severe according to WHO criteria [11]. The ndings are in accordance with the report of the Ministry of Health where malaria in many parts of Aceh Province continues to decrease, making the risk to having malaria also diminishing and affect mainly adults who stay or travel to remaining endemic foci in the Province or other parts of the country [14]. This situation is completely different with the malaria cases found in eastern parts of the country where children are still the most vulnerable group and adults are usually asymptomatic [15,16].
Analysis of the MOI based on the allelic diversity of MSP1 and MSP2 revealed a value of 2.27 and 2.67 for the MSP1 and MSP2 respectively. This nding is slightly higher than the MOI data from Myanmar [17] and Southwest Paci c [18] but lower than Thailand, Kenya and Burkina Faso [19][20][21][22]. The difference in MOI can be attributed to several factors such as differences in geographical areas, intensity of malaria transmission, and difference in age of study population and mean parasite density in the study population [23][24][25]. In our study, all subjects are adult with symptomatic malaria and therefore with a relatively higher parasite density. Several studies reported con icting results in which the MOI correlates with ages, parasite density [25,26] and intensity of malaria transmission [27] but others studies failed to demonstrate this correlation [28,29]. The low MOI reported in our study might also be attributed to the decreasing malaria transmission intensity in Aceh, following the implementation of the malaria elimination program in the area. It is of interest to note that despite a signi cant reduction of malaria in the area, a challenge of zoonotic malaria is currently increasing [30].
Analysis on the genetic diversity pro les of P. falciparum with the malaria clinical manifestation may provide useful information about parasite characteristics to design speci c intervention strategies targeting the virulence factors [31] as well as to the evaluation of drug e cacy [32]. To our knowledge, this study is the rst study in Indonesia that provides information about genetic diversity of MSP 1 and MSP 2 alleles of Plasmodium falciparum among the hospitalized malaria cases. Analysis to determine the association between allelic subfamilies of the MSP 1 and MSP 2 with malaria severity revealed a strong association between mixed MSP 1 K1 + RO33 with severe malaria. The ndings is slightly different with that of Ariey et al [10] where K1 allele subfamily and the D allele of var gene overexpression associated with severe malaria. Others ndings reported a high proportion of subjects carrying the FC27 allele subfamily among the uncomplicated malaria patients [33]. This difference might be associated with the multifactorial nature of severe malaria with diverse clinical manifestation [2]. The difference in geographic setting, age of the subjects, and genetic background of the parasites and host certainly contribute substantial role. This nding is in accordance with the ndings in previous studies in Bobo-Dioulasso [34]. Another study has also investigated genetic diversity of P. falciparum isolates, which was conducted in Libreville, Gabon. In the study, extensive genetic polymorphism within MSP 1 allelic families (30 alleles identi ed) has been observed. This is consistent with the diversity found in Bakoumba (25 alleles) in 1999, Senegal (33 alleles) in 1995, and in Mauritania (27 alleles) in 2010 [35,36]. Our study on the distribution of MSP 2 allele subfamilies showed the presence of two allelic subtypes in the study area, which is similar to the results of study conducted by Kang et al in Myanmar where the geographical areas are alike. Their study also found only two allelic subtypes in Myanmar, which are the FC27 and 3D7. The difference between their study and our study is that the number of patients infected by mixed allelic subtypes is higher than patients affected by single infections; while our study has demonstrated contrasted nding where single infection, either by FC27 or 3D7 alleles is higher [37]. This study also evaluated each clinical manifestations and symptoms among patients with falciparum malaria in Aceh Province and found out association between liver function abnormal value with nixed allelic MSP2 infection. This nding has never been analysed in previous studies except for the severe malarial anaemia [33]. Despite different results found, a closer observation on the phenotypes deserve further exploration in the other geographic areas. We also acknowledge several limitation of this study such as the inadequate amount of sample size, di culties to precisely estimate the allelic frequencies and genetic diversity due to the detection limit of the PCR technique used in the study. Alleles with short differences in length (less than 10 bp) might not be clearly distinguished.

Conclusion
Allelic subfamilies analysis of the MSP 1 and MSP2 genes among the hospitalized uncomplicated and severe malaria cases in Aceh have been analysed. Association between liver function abnormal value with the mixed allelic type of MSP 2 was observed. Mixed allelic infection of MSP 1 K1 and RO33 is strongly associated with severe malaria. Further study to explore more subjects in different geographic setting is recommended. Availability of data and materials

Declarations
All relevant data are within the manuscript.

Competing interests
The authors declare that they have no con ict of interest. and DS molecular assays, data analysis, and manuscript writing. KFJ, S and DS designed the study and responsible for management and fund raising for this study. All authors read and approved the nal manuscript.