EPIDEMIOLOGY OF DENGUE IN MALAYSIA AND THE DYNAMICS OF DENGUE VIRUS-VECTOR-HOST INTERACTIONS

Abstract

Dengue is a mosquito-borne viral infection that has developed into a major public health problem globally, including Malaysia where all four dengue virus (DENV) serotypes co-circulate. The study aimed to identify the spatial and temporal trends of dengue in Malaysia from 2011 to 2017, as well as evaluate the role of intrinsic and extrinsic factors influencing the shift in DENV serotypes. The presence and distribution of native Wolbachia and the infecting DENV strains in the vector and in dengue patients were assessed, along with local weather conditions. In total, 446,976 registered dengue cases were analysed and mapped. During the study period there was an exponential increase in annual dengue cases, peaking in 2015. The majority of cases were from the densely populated Klang Valley, where age-standardised incidence rates were significantly higher than the national rate (227.6/100,000 population). Field collections (May 2016 – April 2017) from Subang Jaya and Bukit Jalil yielded 15,994 Aedes larvae and 98 adult mosquitoes, of which a disproportionate number, 94.8% and 76.5% respectively, were Ae. albopictus. In total, 30 (2.2%) out of 1,389 larvae and 1 (1.9%) out of 52 adult mosquitoes that were screened were DENV-positive with all four serotypes detected. Phylogenetic analysis confirmed the presence of DENV1genotype 1 (n=1), DENV2 Asian II (n=1), DENV3 genotype V (n=13) and sylvatic DENV4 genotype IV (n=18). None of the Ae. aegypti samples were positive for Wolbachia. Of the 1,025 Ae. albopictus larvae screened, 587 (57.3%) were positive, most of which (59.8%) were superinfected with both Wolbachia types wAlbA and wAlbB. All 42 adult Ae. albopictus were Wolbachia-positive. Five out of the 30 DENV-positive Aedes larvae were co-infected with Wolbachia. A majority of the serum samples (n=234) were positive for DENV3 (53.0%), followed by DENV2 (25.6%) and DENV1 (20.9%), with no DENV4 infections and different serotypes dominating within each study area. Only monthly mean relative humidity (RH) displayed a marginally positive correlation with the vector population in Subang Jaya (ρ=0.31, p>0.05), indicating RH may affect the resident vector population. Results showed that native Wolbachia is highly prevalent in Ae. albopictus, which remained susceptible to DENV infections regardless of Wolbachia infection. The high density of Ae. albopictus and the detection of sylvatic DENV4 in Aedes larvae in both urban study areas are crucial findings that warrant further study. The geographic variations in dengue incidence may be attributed to population growth and distribution, urbanisation and land use. Differences in local weather conditions also influence vector population density and consequently, the transmission of dengue.