Genetic polymorphism in msp-2, ama-1 and csp genes in Plasmodium falciparum field isolates from north and north-western India.
OBJECTIVE
Malaria is a major public health problem in tropical and sub-tropical countries. Malaria vaccine is highly desirable as an adjunct to existing malaria control measures. The polymorphism in vaccine candidate antigens might be a hurdle in developing an effective vaccine. Merozoite surface protein-2, apical membrane antigen-1 and circumsporozoite protein of Plasmodium falciparum are vaccine candidate antigens. The aim of this study was to detect extent of genetic polymorphism in potential vaccine candidate antigen genes, i.e. msp-2, ama-1 and csp of P. falciparum isolates prevalent in northern and north-western parts of India.


METHODS
Overall 88 parasite isolates of P. falciparum were collected during July 1998-March 2002 from different parts of northern and north-western India. DNA was extracted and analyzed for genetic polymorphism by PCR-RFLP method. For msp-2 gene, family-specific (FC-27 and 3D7) nested PCR was also performed.


RESULTS
PCR showed size polymorphism in all the target genes. Three alleles were observed in msp-2 and ama-1, while only two in csp. RFLP of ama-1 and csp with Dra-1 and Ssp-1 endonucleases respectively, failed to differentiate isolates in sub-allelic types, while Hinf-I digestion of msp-2 amplicons differentiated three alleles into two distinct allelic families, i.e. FC-27 and 3D7. The allelic family-specific PCR generally confirmed the results of PCR-RFLP except in a few isolates, which showed mixed (two) clones of msp-2 gene.


CONCLUSIONS
There was extensive polymorphism in msp-2 gene while ama-1 and csp genes showed low polymorphism which may be due to the functional constraints of these proteins. The low level transmission of malaria in the study area may also be a factor for low polymorphism.
Farooq
Umar
U
Department of Parasitology, Post Graduate Institute of Medical Education and Research, Chandigarh, India.
Malla
N
N
Dubey
M L
ML
D000483:Alleles; D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics*; D016054:DNA, Protozoan / Q000032:analysis; D006801:Humans; D007194:India; D017780:Malaria Vaccines / Q000235:genetics; D016778:Malaria, Falciparum / Q000469:parasitology*; D008565:Membrane Proteins / Q000235:genetics*; D010963:Plasmodium falciparum / Q000235:genetics* / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D012150:Polymorphism, Restriction Fragment Length; D015800:Protozoan Proteins / Q000235:genetics*
D000953:Antigens, Protozoan; D016054:DNA, Protozoan; D017780:Malaria Vaccines; D008565:Membrane Proteins; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium; C041595:circumsporozoite protein, Protozoan