Limited genetic diversity and purifying selection in Iranian Plasmodium falciparum Generative Cell Specific 1 (PfGCS1), a potential target for transmission-blocking vaccine

Mosquito-borne viral diseases and potential transmission blocking vaccine candidates

Mosquito-borne viral diseases (MBVDs) have a complex biological cycle involving vectors and vertebrate hosts. These viruses are responsible for many deadly diseases worldwide. Although MBVDs threaten mostly developing countries, there is growing evidence indicating that they are also of concern in western countries where local transmission of arboviruses such as West Nile, Zika, Chikungunya and Dengue viruses have been recently reported. The rapid rise in human infections caused by these viruses is attributed to rapid climate change and travel facilities. Usually, the only way to control these diseases relies on the control of vectors in the absence of licensed vaccines and specific treatments. However, the overuse of insecticides has led to the emergence of insecticide resistance in vector populations, posing significant challenges for their control. An alternative method for reducing MBVDs can be the use of Transmission Blocking Vaccines (TBVs) that limits viral infection at the mosquito vector stage. Some successes have been obtained confirming the potential application of TBVs against viruses; however, this approach remains at the developmental stage and still needs improvements. The present review aims to give an update on MBVDs and to discuss the application as well as usage of potential TBVs for the control of mosquito-borne viral infections.

Worldwide population genetic analysis and natural selection in the Plasmodium vivax Generative Cell Specific 1 (PvGCS1) as a transmission-blocking vaccine candidate

GENERATIVE CELL SPECIFIC 1 (GCS1) is one of the Transmission Blocking Vaccine (TBV) candidate antigens, which is expressed on the surface of male gametocytes and gametes of Plasmodium species. Since antigenic diversity could inhibit the successful development of a malaria vaccine, it is crucial to determine the diversity of gcs1 gene in global malaria-endemic areas. Therefore, gene diversity and selection of gcs1 gene were analyzed in Iranian Plasmodium vivax isolates (n=52) and compared with the corresponding sequences from worldwide clinical P. vivax isolates available in PlasmoDB database. Totally 12 SNPs were detected in the pvgcs1 sequences as compared to Sal-1 sequence. Five out of 12 SNPs including three synonymous (T797C, G1559A, and G1667T) and two amino acid replacements (Y133S and Q634P) were detected in Iranian pvgcs1 sequences. According to four amino acid replacements (Y133S, N575S, Q634P and D637N) observed in all world PvGCS1 sequences, totally 5 PvGCS1 haplotypes were detected in the world, that three of them observed in Iranian isolates including the PvGCS-A (133S/634Q, 92.3%), PvGCS-B (133Y/634Q, 5.8%), and PvGCS-C (133S/634P, 1.9%). The overall nucleotide diversity (π) for all 52 sequences of Iranian pvgcs1 gene was 0.00018±0.00006, and the value of dN-dS (-0.00031) were negative, however, it was not statistically significant. In comparison with global isolates, Iranian and PNG pvgcs1 sequences had the lowest nucleotide and haplotype diversity, while the highest nucleotide and haplotype diversity was observed in China population. Moreover, epitope prediction in this antigen showed that all B-cell epitopes were located in conserved regions. However, Q634P (in one Iranian isolate) and D637N (observed in Thailand, China, Vietnam and North Korea) mutations are involved in predicted IURs. The obtained results in this study could be used in development of PvGCS1 based malaria vaccine.