The deep vascular sequestration of parasitized erythrocytes is a central pathological event in falciparum malaria. Variant surface antigens are encoded mainly by three multi-copy gene families, namely, var, stevor, and rifín. Var is one of the most important families that plays a crucial role in antigenic variation and immune evasion. Clinical and epidemiological studies have shown that severe or complicated malaria is manifested in a limited number of patients. This indicates that a subset of these multigene families could be determinants in the manifestation of different malaria phenotypes. Recent studies have indicated the possible role of stevor (sub-telomeric variable open read), a multi-gene family, in erythrocyte invasion, antigenic variation and host cell modification, of infected erythrocytes. In this study, we describe the repertoire and diversity of members of the stevor multigene family in patients with complicated and uncomplicated malaria in India.
Materials and methods
Plasmodium falciparum complicated isolates (n=8) from Odisha and uncomplicated isolates (n=7) from Assam, Madhya Pradesh and Goa were collected. Members of the stevor multigene family were amplified using degenerate PCR primers. Amplified PCR products were cloned and a total of 35 clones per cloning experiment were sequenced. A maximum likelihood phylogeny was constructed in order to understand the genetic repertoire of members of the stevor multigene family in severe and non-severe isolates and extent of stevor repertoire in Indian isolates.
A range of 21-31 unique sequences was obtained out of 35 clones sequenced for each of the 15 isolates. Nucleotide diversity analysis shows extensive genetic polymorphism that supports the hyper-variability nature of stevor multigene family in field isolates. The repertoire and diversity of the stevor multigene family varied between all four geographical regions of the Indian subcontinent. Phylogenetic tree analysis showed clustering of sequences from complicated isolates, and suggests that the stevor genetic repertoire is less diverse in comparison to uncomplicated isolates.
This study suggests an extensive genetic diversity of stevor in Indian P. falciparum isolates, however the genetic repertoire from complicated cases was less diverse. The high degree of stevor diversity has important implications for the design of effective anti-malaria control measures.
This work was supported by the ICMR-Centenary Postdoctoral Fellowship program of the Indian Council of Medical Research, New Delhi, India and in part by grant number D43TW007884 from the Fogarty International Center (FIC), US National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not necessarily represent the views of the FIC or NIH.