ICMR - Regional Medical Research Centre, North East Region, Dibrugarh, Assam, 786001, India.
SRL Reference Laboratory, Mumbai, 400060, India.
Malar J. 2022 Feb 22;21(1):62. doi: 10.1186/s12936-022-04081-1.
Malaria continues to be a major public health problem in the Northeastern part of India despite the implementation of vector control measures and changes in drug policies. To develop successful vaccines against malaria, it is important to assess the diversity of vaccine candidate antigens in field isolates. This study was done to assess the diversity of Plasmodium falciparum AMA-1 vaccine candidate antigen in a malaria-endemic region of Tripura in Northeast India and compare it with previously reported global isolates with a view to assess the feasibility of developing a universal vaccine based on this antigen.
Patients with fever and malaria-like illness were screened for malaria and P. falciparum positive cases were recruited for the current study. The diversity of PfAMA-1 vaccine candidate antigen was evaluated by nested PCR and RFLP. A selected number of samples were sequenced using the Sanger technique.
Among 56 P. falciparum positive isolates, Pfama-1 was successfully amplified in 75% (n = 42) isolates. Allele frequencies of PfAMA-1 antigen were 16.6% (n = 7) for 3D7 allele and 33.3% (n = 14) in both K1 and HB3 alleles. DNA sequencing revealed 13 haplotypes in the Pfama-1 gene including three unique haplotypes not reported earlier. No unique amino-acid substitutions were found. Global analysis with 2761 sequences revealed 435 haplotypes with a very complex network composition and few clusters. Nucleotide diversity for Tripura (0.02582 ± 0.00160) showed concordance with South-East Asian isolates while recombination parameter (Rm = 8) was lower than previous reports from India. Population genetic structure showed moderate differentiation.
Besides documenting all previously reported allelic forms of the vaccine candidate PfAMA-1 antigen of P. falciparum, new haplotypes not reported earlier, were found in Tripura. Neutrality tests indicate that the Pfama-1 population in Tripura is under balancing selection. This is consistent with global patterns. However, the high haplotype diversity observed in the global Pfama-1 network analysis indicates that designing a universal vaccine based on this antigen may be difficult. This information adds to the existing database of genetic diversity of field isolates of P. falciparum and may be helpful in the development of more effective vaccines against the parasite.
尽管实施了病媒控制措施和改变了药物政策，印度东北部仍持续面临疟疾这一重大公共卫生问题。为了成功研发疟疾疫苗，评估候选疫苗抗原在现场分离株中的多样性非常重要。本研究旨在评估印度东北部特里普拉邦疟疾流行地区恶性疟原虫 AMA-1 候选疫苗抗原的多样性，并与之前报道的全球分离株进行比较，以评估基于该抗原研发通用疫苗的可行性。
对发热和疟疾样疾病患者进行疟疾筛查，并招募疟原虫阳性病例参与本研究。采用巢式 PCR 和 RFLP 评估 PfAMA-1 候选疫苗抗原的多样性。选择部分样本采用 Sanger 技术进行测序。
在 56 例疟原虫阳性分离株中，成功扩增 PfAMA-1 的比例为 75%（n=42）。PfAMA-1 抗原的等位基因频率为 3D7 等位基因 16.6%（n=7），K1 和 HB3 等位基因各 33.3%（n=14）。Pfama-1 基因的 DNA 测序共发现 13 种单倍型，其中包括 3 种之前未报道过的独特单倍型。未发现独特的氨基酸取代。对全球 2761 个序列的分析显示，存在 435 种单倍型，具有非常复杂的网络组成和少量聚类。与东南亚分离株相比，特里普拉邦的核苷酸多样性（0.02582±0.00160）一致，而重组参数（Rm=8）低于印度之前的报告。种群遗传结构显示中度分化。
除了记录恶性疟原虫候选疫苗 PfAMA-1 抗原的所有先前报道的等位基因形式外，还在特里普拉邦发现了之前未报道的新单倍型。中性检验表明，特里普拉邦 Pfama-1 群体处于平衡选择之下。这与全球模式一致。然而，在全球 Pfama-1 网络分析中观察到的高单倍型多样性表明，基于该抗原设计通用疫苗可能具有挑战性。该信息增加了恶性疟原虫现场分离株遗传多样性的现有数据库，可能有助于研发针对寄生虫的更有效疫苗。
