Identify Aedes albopictus as vector for an indigenous dengue outbreak by sympatric saliva cross-adsorbed western blot

Dengue fever is the most prominent arboviral infection in Taiwan. Although the two vector mosquitoes, Aedes aegypti and Ae. albopictus, distribute distinctly, frequent traffic and climate change could result in vector dispersal. Since mosquitoes inject their saliva into the hosts during feeding, the consequential host antibodies elicited by mosquito salivary proteins (MSP) were therefore used as indicators for vector exposure. In 2013, an indigenous dengue outbreak involving a total of 8 cases occurred in Taipei, where only Ae. albopictus thrives. Higher titer of antibody against Ae. albopictus was found in 5 patients by immunofluorescence assay. However, the index case exhibited stronger response against Ae. aegypti. To reduce cross-reactions observed by western blot, a modified method involving pre-absorption was introduced. After treating sera with salivary gland extract (SGE) of Ae. albopictus, 64% of samples still reacted to Ae. aegypti SGE with band at 290-kD. The absorption procedure partially or completely removed the bands at 69- (42.86%), 37- (50%), and 30-kD (42.86%), which might be prone to cross-reactivity. Pre-absorbing non-specific antibodies by Ae. aegypti SGE showed that 79%, 71%, and 50% of samples remained to interact with salivary proteins with molecular weight of 290-, 68-, and 37-kD in Ae. albopictus. For the index case, the pre-absorbed western blot revealed that the patient was bitten by both Aedes mosquitoes. The study applying antibodies against MSP demonstrated Ae. albopictus was responsible for the outbreak in Taipei in 2013. Evidence of exposure to Ae. aegypti of the index case was determined.