Genetic polymorphism of falciparum malaria vaccine candidate antigen genes among field isolates in India.

Abstract

Abstract. The present study was designed to investigate the genetic diversity of Plasmodium falciparum among field isolates from India. A total of 71 clinical isolates were analyzed by the polymerase chain reaction (PCR) for the amplification of repeat regions of malaria vaccine candidate antigen genes, i.e., merozoite surface antigen-1 (MSA-1), MSA-2, and circumsporozoite protein (CSP). All three genes showed variation; MSA-2 has the maximum number of 10 variant forms while MSA-1 and CSP had 8 and 6 variants, respectively. Some variant forms were more common than others among the clinical isolates. There were mixed alleles for each gene in several (27 of (Orissa) not only showed the maximum number of variant forms of each gene but also the maximum number of cases with mixed alleles compared with the non-hyperendemic regions (Madhya Pradesh and Rajasthan). The presence of such large numbers of P. falciparum strains in India should be taken into account in future malaria vaccine programs.Malaria currently remains uncontrolled despite immense efforts being made to contain the disease. The unavailability of a suitable malaria vaccine and emergence of drug-resistant parasites are further complicating the situation in tropical areas. Of the four species of human malaria parasites, Plasmodium falciparum is most lethal and causes epidemics in tropical countries. 1,2 Although several vaccine candidate antigens of P. falciparum have been identified and characterized, the availability of a universal malaria vaccine is still a remote possibility. One reason is the antigenic variation of different geographic isolates of the parasite. The most common and widely characterized vaccine candidate antigens are circumsporozoite protein (CSP) and merozoite surface antigens-1 and -2 (MSA-1 and MSA-1). Allelic forms of these antigen genes have been reported in the literature among several laboratory and wild type field isolates from different parts of the world. 3-8 However, there is limited information on the polymorphic nature of these genes among field isolates from India. Bhattacharya and others have shown only point mutations in MSA-2 gene among Indian laboratory and field isolates. 9,10 In contrast, we show in this report larger deletions/additions (detected by agarose gel electrophoresis) not only for the MSA-2 gene but also for MSA-1 and CSP genes among field isolates from hyperendemic and non-hyperendemic regions of India. The present study also shows an increase in the number of variants and mixed alleles with malaria hyperendemicity. MATERIALS AND METHODSPatients and blood collection. Patients with fever attended malaria clinics at primary health centers (PHCs) or district hospitals. Fingerprick blood was examined for the presence of malarial parasites by light microscopy after Giemsa staining. Approximately 20 l of fingerprick blood was collected from those patients who were confirmed to be positive for the presence of P. falciparum parasites. These patients were informed in the local language about the nature of the expe...

Genetic structure of Plasmodium falciparum field isolates in eastern and north-eastern India

“…Labourers from Orissa, Bihar and other parts of West Bengal come to work in tea gardens of Darjeeling (WB) and Assam and their to and fro movement from native place to work place may be facilitating the gene flow. Observed high proportion of multiclonal isolates was in accordance with the reports of other workers [17,18] on Indian isolates. A comparatively higher proportion of multiclonal isolates as well as multiplicity of infection (MOI) was observed among isolates of district Karbi Anglong (Assam) and district Sundergarh (Orissa).…”

“…Both the districts are highly endemic for malaria with P. falciparum proportion being above 80%. Similar observations that the extent of diversity and multiplicity of infection in an area is related to level of malaria endemicity has been made by Ranjit & Sharma [18], Babiker et al [26] and Zwetyenga et al [27]. …”

Genetic diversity of Plasmodium falciparum merozoite surface protein‐1 (block 2), glutamate‐rich protein and sexual stage antigen Pfs25 from Chandigarh, North India

“…In addition, it has been reported that the difference in the number of alleles for each gene is associated with the degree of endemicity. Thus, highly endemic areas of Asia and Africa reported larger numbers of alleles, whereas a low endemicity areas report small numbers . K1 allele was found in only two samples which could be due to the small number of samples.…”

Genetic polymorphism and amino acid sequence variation in Plasmodium falciparum GLURP R2 repeat region in Assam, India, at an interval of five years

“…The current study has suggested considerable polymorphism and variation in the genetic sequences of P. falciparum GLURP R2 repeat region among the samples collected after an interval of five years in a P. falciparum malaria-endemic setting in the northeastern region of India. Many studies have indicated that genetic diversity and multiplicity of Plasmodium species was responsible for the biological success of the malaria parasite [ 22 – 25 ]. Genetic polymorphism not only confers the malaria parasite with the ability to evade human immune response but also helps in developing resistance to anti-malarial drugs [ 24 , 25 ].…”

“…Malaria parasite P. falciparum has many polymorphic loci that have been used to study genetic diversity [ 21 , 22 , 30 ]. GLURP has been considered an important antigen that has been playing an important role in the induction of protective immunity against P. falciparum malaria [ 7 ].…”