An epidemiological and virological study on mosquito-borne flavivirus transmission : The role of urban livestock keeping and the risk for mosquito-borne zoonotic diseases in humans in Hanoi city, Vietnam

Sammanfattning: Mosquito-borne diseases (MBDs), which are transmitted by the bite of mosquitoes to humans, are causing high morbidity and mortality worldwide and are emerging in many tropical cities. Urban livestock keeping is still growing in cities around the world, which can itself contribute to increasing the mosquito populations. In addition, the animals may also serve as reservoirs for zoonotic MBDs, which increase the risks for humans. In this thesis, knowledge and practices related to MBDs were assessed in 513 households, with and without livestock. The perceptions of the community and health care sector were explored, with a focus on the association of MBDs and livestock keeping in Hanoi city of Vietnam. Generally, the participants had relatively low awareness on MBDs prevention and control. Those who had better knowledge did also use more adequate preventive practices against MBDs (p<0.001). An entomological survey was performed to explore how livestock keeping in and around a large city was associated with the presence of mosquitoes and their risk for spreading flaviviruses. The findings indicated that the distribution of vector populations in Hanoi city was heterogeneous, and that livestock played a role in influencing this. Households with better preventive practices reduced the presence of mosquitoes. Pig keeping particularly lead to more mosquitoes – especially of the Culex genus. 12,861 adult mosquitoes were collected and pooled into 385 pools, whereof one pool of Culex tritaeniorhynchus was found positive for Japanese encephalitis virus (JEV) by a pan-flavivirus qPCR. Phylogenetic analysis indicated that the detected virus belonged to genotype I. A hospital-based study with 98 dengue patients and 99 non-dengue patients was conducted to investigate risk factors of dengue infection and dengue virus (DENV) variants circulating in Hanoi. Age group and living district were the identified risk factors that correlated with dengue status. Serum and blood samples were analysed by a panflavivirus qPCR. The results showed that DENV serotypes 1, 2, and 4 were co-circulating during this outbreak, of which DENV serotype 1 was the predominant genotype.This thesis provides insight into the risk of flavivirus-related diseases such as dengue fever and Japanese encephalitis for those living in Hanoi metropolitan city, Vietnam, and the links between mosquitoes, animals and humans. Expanded and effective vector control measures and vaccination programs need to be taken to prevent the transmission of mosquito-borne flavivirus due to the significant dispersion of Culex and Aedes mosquitoes.