Genetic diversity and allelic variation in MSP3α gene of paired clinical Plasmodium vivax isolates from Delhi, India

Genetic Structure of Introduced Plasmodium vivax Malaria Isolates in Greece, 2015-2019

Greece has been malaria-free since 1974, after an intense malaria control program. However, as Greece hosts migrant populations from P. vivax malaria-endemic countries, there is a risk of introducing the disease to specific vulnerable and receptive areas of the country. Knowledge of the genetic diversity of P. vivax populations is essential for understanding the dynamics of malaria disease transmission in a given region. We used nine highly polymorphic markers to genotype 124 P. vivax-infected archived DNA samples from human blood specimens referred to the NMRL from all over Greece throughout 2015-2019. The genotypic variability of the samples studied was noted, as they comprised several unique haplotypes, indicative of the importation of a large number of different P. vivax strains in the country. However, only a few events of local transmission were recorded. Genotyping revealed and confirmed the same clusters as those identified through epidemiological investigation. In only one introduction event was the index case found. No sustained/ongoing malaria transmissions in/between the studied regions or during consecutive years or additional foci of local transmission were observed. Genotyping is an important component in assisting malaria surveillance, as it provides information concerning the patterns of introduction and the effectiveness of implemented malaria control and elimination measures.

Distinct Allelic Diversity of Plasmodium vivax Merozoite Surface Protein 3-Alpha (PvMSP-3α) Gene in Thailand Using PCR-RFLP

Considering the importance of merozoite surface proteins (MSPs) as vaccine candidates, this study was conducted to investigate the polymorphism and genetic diversity of Plasmodium vivax merozoite surface protein 3-alpha (PvMSP-3α) in Thailand. To analyze genetic diversity, 118 blood samples containing P. vivax were collected from four malaria-endemic areas in western and southern Thailand. The DNA was extracted and amplified for the PvMSP-3α gene using nested PCR. The PCR products were genotyped by PCR-RFLP with Hha I and Alu I restriction enzymes. The combination patterns of Hha I and Alu I RFLP were used to identify allelic variants. Genetic evaluation and phylogenic analysis were performed on 13 sequences, including 10 sequences from our study and 3 sequences from GenBank. The results revealed three major types of PvMSP-3α, 91.5% allelic type A (∼1.8 kb), 5.1% allelic type B (∼1.5 kb), and 3.4% allelic type C (∼1.2 kb), were detected based on PCR product size with different frequencies. Among all PvMSP-3α, 19 allelic subtypes with Hha I RFLP patterns were distinguished and 6 allelic subtypes with Alu I RFLP patterns were identified. Of these samples, 73 (61%) and 42 (35.6%) samples were defined as monoallelic subtype infection by Hha I and Alu I PCR-RFLP, respectively, whereas 77 (65.3%) samples were determined to be mixed-allelic subtype infection by the combination patterns of Hha I and Alu I RFLP. These results strongly indicate that PvMSP-3α gene is highly polymorphic, particularly in blood samples collected from the Thai-Myanmar border area (the western part of Thailand). The combination patterns of Hha I and Alu I RFLP of the PvMSP-3α gene could be considered for use as molecular epidemiologic markers for genotyping P. vivax isolates in Thailand.

Genetic Diversity of Plasmodium vivax Field Isolates from the Thai–Myanmar Border during the Period of 2006–2016

High levels of genetic variants of Plasmodium vivax have previously been reported in Thailand. Circumsporozoite surface protein (CSP), merozoite surface protein (MSP), and microsatellite markers were used to determine the genetic polymorphisms of P. vivax. This study aimed to investigate the molecular epidemiology of P. vivax populations at the Thai–Myanmar border by genotyping the PvCSP, PvMSP-3α, and PvMSP-3β genes. Four hundred and forty P. vivax clinical isolates were collected from the Mae Sot and Sai Yok districts from 2006–2007 and 2014–2016. Polymerase chain reaction with restriction fragment length polymorphism (RFLP) was used to investigate the genetic polymorphisms of the target genes. Based on PCR band size variations, 14 different PvCSP alleles were identified: eight for VK210 and six for VK247. The VK210 genotype was the dominant variant during both sample collection periods. Based on PCR genotyping, three distinct types (A, B, and C) for both PvMSP-3α and PvMSP-3β were observed. Following RFLP, 28 and 14 allelic variants of PvMSP-3α and 36 and 20 allelic variants of PvMSP-3β with varying frequencies were identified during the first and second periods, respectively. High genetic variants of PvMSP-3 and PvCSP were found in the study area. PvMSP-3β exhibited a higher level of genetic diversity and multiple-genotype infection versus PvMSP-3α.

PvMSP-3α and PvMSP-3β genotyping reveals higher genetic diversity in Plasmodium vivax parasites from migrant workers than residents at the China-Myanmar border

BACKGROUND

The genetic diversity of malaria parasites traces the origin and spread of new variants and can be used to evaluate the effectiveness of malaria control measures. Therefore, this study aims to improve the understanding of the molecular epidemiology of Plasmodium vivax malaria at the China-Myanmar border by genotyping the PvMSP-3α and PvMSP-3β genes.

METHODS

Blood samples were collected from P. vivax malaria patients along the China-Myanmar border. The PvMSP-3α and PvMSP-3β genes were amplified by polymerase chain reaction (PCR) and the genetic polymorphism and haplotype of the two genes were analyzed.

RESULTS

A total of 422 blood samples were used for this study, of which 224 were analyzed at PvMSP-3α and 126 at PvMSP-3β. Samples mainly were from young adults aged 18-45 years, although local patients were significantly younger than migrant laborers crossing the border at Tengchong (P < 0.0001). Molecular evolutionary analysis revealed that PvMSP-3α and PvMSP-3β underwent diversifying natural selection, and intragenic recombination contributed to the diversity of the isolates. Based on the length of the genes, we identified three types of PvMSP-3α [1.9-2.0 kb (Type-A), 1.4-1.5 kb (Type-B), and 1.1-1.3 kb (Type-C)] and two types of PvMSP-3β [1.7-2.2 kb (Type-A) and 1.4-1.5 kb (Type-B)]. Migrant laborers returning to China through Tengchong bore P. vivax infections displaying significantly higher genetic diversity than local residents.

CONCLUSIONS

Both PvMSP-3 paralogs were subjected to diversifying selection in each sample population. Clustering of alleles supports ephemeral endemic differentiation of alleles, but the broader phylogeny suggests that alleles transit the globe, perhaps accelerated by movements of migrants such as those transiting Tengchong.

Allelic variation of msp-3α gene in Plasmodium vivax isolates and its correlation with the severity of disease in vivax malaria

Malaria is a global socio-economic burden of which Plasmodium vivax contributes for about 70-80 million cases on an annual basis worldwide and 60-65% cases in India. Diversity observed in highly polymorphic Merozoite Surface Protein-3α (msp-3α) encoded by MSP-3 gene family, has been used efficiently for genotyping of P. vivax infection. This study aims to correlate the severity of clinical symptoms with parasite load, genotype of P. vivax and multiplicity of infection. Based on clinical symptoms classification, 31 (67.9%) out of 46 cases were found to be severe while 15 (32.6%) were non-severe and correlation of the severity of vivax infection with parasite load was not observed. Analysis of msp3-α allele genotype showed that out of 31 severe cases, 19 (61.2%) were single-clone infection cases whereas 12 (38.7%) were multi-clone infections. Similarly, out of 15 non-severe cases, 9 (60%) were single clone and 6 (40%) were multi-clone infections indicating the absence of a correlation between the multiplicity of infection and disease severity. Allele frequency observed was 65.9%, 23.4%, 23.4%, and 28.2% for allele A, B, C and D, respectively. An important finding was the greater distribution of allele D than alleles B and C, which has been reported as a rare allele otherwise. Further, of 13 cases with allele D, 76.9% (10/13) cases were severe. This study showed the absence of a correlation between the severity of clinical symptoms with parasite load and multiplicity of infection but at the same time drives a possibility of severe vivax malarial symptoms to have an association with the persistence of allele D in the population. This upon exploration can lead to the development of a target in detection of severe cases of malaria.