Zika infection decreases Aedes aegypti locomotor activity but does not influence egg production or viability

Abstract

Background: Zika has emerged as a new public health threat after the explosive epidemic in Brazil in 2015. It is an arbovirus transmitted mainly by Aedes aegypti mosquitoes. The knowledge of physiological, behavioural and biological features in virus-infected vectors may help the understanding of arbovirus transmission dynamics and elucidate their influence in vector capacity.

Objectives: We aimed to investigate the effects of Zika virus (ZIKV) infection in the behaviour of Ae. aegypti females by analysing the locomotor activity, egg production and viability.

Methodology: Ae. aegypti females were orally infected with ZIKV through an artificial feeder to access egg production, egg viability and locomotor activity. For egg production and viability assays, females were kept in cages containing an artificial site for oviposition and eggs were counted. Locomotor activity assays were performed in activity monitors and an average of 5th, 6th and 7th days after infective feeding was calculated.

Findings: No significant difference in the number of eggs laid per females neither in their viability were found between ZIKV infected and non-infected females, regardless the tested pair of mosquito population and virus strain and the gonotrophic cycles. Locomotor activity assays were performed regardless of the locomotor activity in ZIKV infected females was observed, in both LD and DD conditions.

Main conclusions: The lower locomotor activity may reduce the mobility of the mosquitoes and may explain case clustering within households reported during Zika outbreaks such as in Rio de Janeiro 2015. Nevertheless, the mosquitoes infected with ZIKV are still able to disseminate and to transmit the disease, especially in places where there are many oviposition sites.

Fig. 1:. effect of Zika virus (ZIKV) infection on the eggs quantity (A) and viability (B) of PAEA Aedes aegypti females infected with ZIKV PE243, according to the second and third gonotrophic cycles. The lack of significance is represented by p values > 0.05 obtained by using the parametric t-Student and non-parametric Mann-Whitney tests, respectively. Error bars represent mean ± s.d of three independent experiments.

Fig. 2:. locomotor activity of Aedes aegypti females infected by Zika virus (ZIKV). Locomotor activity of control (blue line, n = 51) and infected Ae. aegypti females (red line, n = 54). The mosquitoes were observed from the second to the seventh days post infection (DPI) in LD12:12 (A). The first DPI was not included because we considered them to be still adapting to the system. We also show an average profile in LD (the graph referred only to 5th, 6th and 7th DPI) (B). On the 8th DPI the mosquitoes were kept in constant darkness (DD) (C). Bars below the graphics indicate the light regime: white = lights on in LD cycles, grey = lights off in DD (“subjective day”), black = lights off in LD or DD (“subjective night”). ZT: Zeitgeber time within a light/dark cycle experiment; ZT0: time the light turns on; ZT12: time the light turns off; CT: circadian time in DD. Error bars were shown for each 30 min interval. Asterisks represent the significance of the t-Student test, where p < 0.05.