Sylvatic dengue virus type 4 in <i>Aedes aegypti</i> and <i>Aedes albopictus</i> mosquitoes in an urban setting in Peninsular Malaysia

Dengue fever is endemic in Malaysia, contributing to significant economic and health burden in the country. Aedes aegypti and Ae. albopictus are the main vectors of the dengue virus (DENV), which circulates in sylvatic and human transmission cycles and has been present in Malaysia for decades. The study investigated the presence and distribution of DENV in urban localities in the Klang Valley, Peninsular Malaysia. A total of 364 Ae. aegypti and 1,025 Ae. albopictus larvae, and 10 Ae. aegypti and 42 Ae. albopictus adult mosquitoes were screened for the presence of DENV. In total, 31 (2.2%) samples were positive, of which 2 Ae. albopictus larvae were co-infected with two serotypes, one with DENV-2 and DENV-3 and the other with DENV-3 and DENV-4. Phylogenetic analysis determined that the isolates belonged to DENV-1 genotype I (1 Ae. aegypti adult), DENV-2 (1 Ae. albopictus larva), DENV-3 genotype V (3 Ae. aegypti larvae and 10 Ae. albopictus larvae) and DENV-4 genotype IV (6 Ae. aegypti larvae and 12 Ae. albopictus larvae), a sylvatic strain of DENV-4 which was most closely related with sylvatic strains isolated from arboreal mosquitoes and sentinel monkeys in Peninsular Malaysia in the 1970s. All four DENV serotypes were co-circulating throughout the study period. The detection of a sylvatic strain of DENV-4 in Ae. aegypti and Ae. albopictus mosquitoes in urban areas in Peninsular Malaysia highlights the susceptibility of these vectors to infection with sylvatic DENV. The infectivity and vector competence of these urban mosquitoes to this strain of the virus needs further investigation, as well as the possibility of the emergence of sylvatic virus into the human transmission cycle.登革热在马来西亚呈地方性流行，给该国带来了沉重的经济与健康负担。埃及伊蚊（Aedes aegypti）和白纹伊蚊（Ae. albopictus）是登革病毒（Dengue virus, DENV）的主要传播媒介，该病毒存在丛林传播与人际传播两种循环途径，且已在马来西亚流行数十年。本研究针对马来西亚半岛巴生谷的城区开展调查，旨在明确登革病毒在当地的存在状况与分布特征。研究共收集364只埃及伊蚊幼虫、1025只白纹伊蚊幼虫，以及10只埃及伊蚊成蚊、42只白纹伊蚊成蚊，对所有样本进行登革病毒筛查。结果显示，共计31份样本（占总样本量的2.2%）呈病毒阳性，其中2份白纹伊蚊幼虫样本为双重感染：1份同时携带登革病毒2型（DENV-2）与登革病毒3型（DENV-3），另1份同时携带DENV-3与登革病毒4型（DENV-4）。系统发育分析结果表明，本次分离得到的病毒毒株分别隶属于以下亚型：DENV-1基因型I（1株，分离自埃及伊蚊成蚊）、DENV-2（1株，分离自白纹伊蚊幼虫）、DENV-3基因型V（共13株，其中埃及伊蚊幼虫3株、白纹伊蚊幼虫10株），以及DENV-4基因型IV（共18株，其中埃及伊蚊幼虫6株、白纹伊蚊幼虫12株）。其中DENV-4基因型IV为丛林型毒株，其与1970年代在马来西亚半岛从树栖蚊虫及哨兵猴体内分离得到的丛林毒株亲缘关系最为接近。研究周期内，全部4种登革病毒血清型均在该区域共同循环传播。本次在马来西亚半岛城区的埃及伊蚊与白纹伊蚊体内检出DENV-4丛林毒株，凸显了这类城区媒介蚊虫对丛林型登革病毒的易感性。针对这些城区蚊虫对该毒株的感染性与媒介传播能力，以及丛林型病毒突破物种屏障进入人际传播循环的可能性，仍需开展进一步的深入研究。