Sequence analysis of Ancylostoma secreted protein 2 of Necator americanus from Thai isolates

Abstract

Problem/background : Hookworm infection is one of the major neglected tropical infectious diseases causing both overt and cryptic morbidity among ~600 million people living in tropical areas. As conventional hookworm control measures by improving sanitation and mass anthelminthic drug administration are not sustainable, development of hookworm vaccines is mandatory. One of the major vaccine candidates is Ancylostoma secreted protein-2 of Necator americanus (Na-ASP-2). To date, only one Na-ASP-2 sequence is available; therefore, it remains unknown whether the effectiveness of a vaccine derived from this molecule may be compromised by antigenic diversity in hookworm population.

Objectives : To determine the Na-ASP-2 sequences of filariform larvae isolated from infected Thais; and, to test whether the Na-ASP-2 is expressed in the adult stage of N. americanus.

Design : Descriptive study

Setting : Department of Parasitology, Faculty of Medicine, Chulalongkorn University

Materials and Methods : The method deployed reverse transcription-polymerase chain reaction (RT-PCR) to amplify the Na-ASP-2 coding region using a randomly isolated single filariform larva from each of the 3 subjects and an adult female worm as the source of mRNA. The amplified products were used as templates for DNA sequencing.

Results : The Na-ASP-2 amplified products were obtained from all 3 filariform larvae but none from the adult worm. Of 699 nucleotides in the Na-ASP-2 gene, all were conserved among samples and identical with that in the GenBank,^TM database accession number AY28808. Sequence analysis revealed no evidence of codon usage bias whereas a number of putative T cell epitopes were identified.

Conclusion : Sequence conservation in the Na-ASP-2 coding region suggests that efficacy of the vaccine would not be compromised by genetic diversity in hookworm population.