WHO

The Zika Virus (ZIKAV) was first isolated from the African forest and only a few human cases were documented until the first epidemic reported from the Pacific Island of Yap in 2007 (Weaver et al., 2016). ZIKAV transmission by sylvatic mosquitoes is almost unknown since only a few studies have found several species of mosquitoes positive for ZIKAV (Diallo et al., 2011) but the specific detection of the virus in the salivary gland which is a pre-requisite of mosquito transmission was confirmed only in 2 Aedes species (Diagne et al., 2015).

After the rural epidemic on the Yap Island where the suspected vector was Aedes hensilli (Ledermann et al.,2014), the ZIKAV emerge into an urban epidemic for the first time in French Polynesia in 2013 and the main vector was Aedes aegypti with a suspected secondary vector with Aedes polynesiensis (Loos et al., 2014). In 2015, ZIKAV was reported for the first time from Brazil.

While epidemic transmission of ZIKAV is reported to occur mainly in urban settings via the anthropophilic Aedes aegypti mosquito, as evidenced by limited field surveillance (Marchette et al., 1969; Olson et al., 1981) and experimental studies (Boorman and Porterfield, 1956; Cornet et al., 1979a; Li et al., 2012), Ae. hensilli and/or Ae. polynesiensis (Musso et al., 2014) may serve as vectors in Yap island and the pacific islands respectively.

In 2007 in Gabon, urban ZIKAV transmission was associated with A. albopictus (Girard et al., 2014). Further experimental studies (Wong et al., 2013) supported a role for Asian populations of A. albopictus as vectors of ZIKV transmission concomitantly with Aedes aegypti (Li et al., 2012). Given its invasive nature and extensive geographic distribution in tropical as well as temperate settings, there is the potential for A. albopictus to become a ZIKAV vector in Europe.

For the American region, recent laboratory studies on Aedes aegypti and Aedes albopictus have proven their competence in the amplification and transmission of ZIKA virus (ChouinCarneiro et al., 2016) with some geographical differences since tis he study also found Ae. aegypti populations from Guadeloupe and French Guiana exhibited a higher dissemination of ZIKV than the other Ae. aegypti populations examined.

Currently, our knowledge of the vectors of ZIKAV in all reported studies, from Africa, Asia, the Pacific region and the Americas are pointing the Aedes mosquitoes as the main vectors. In urban settings, in particular, the evidence strongly suggests that Aedes aegypti is the main vector because this species is highly anthropophilic (McBride, 2016) and Aedes albopictus may play a secondary role as vectors. It is important, however, to further investigate the role that other species may play in ZIKAV transmission. To further strengthen our knowledge on the vectors of ZIKAV, some institutions such as Fiocruz in Brazil and Pasteur Institute in Paris are currently testing other mosquito species such as Culex for their potential competency for ZIKAV. The results are expected soon.

On 29th March 2016, as part of a panel discussion (webinar) in the NIH sponsored conference on Zika, Scott Weaver (University of Texas Medical Branch) mentioned that his lab has been testing mosquitoes collected in Mexico at a site where human ZIKAV infections have been detected. He said that they have identified only Ae. aegypti infected with ZIKV. Ae. albopictus & Cx. quinquefasciatus have been tested, but none have contained detectable viral RNA (probable PCR assay). The WHO secretariat has contacted the research group for further information.

References:

• Weaver et.al (2016) Zika Virus: History, Emergence, Biology, and Prospects for Control. Antiviral Res. 2016 Mar 17. pii: S0166-3542(16)30120-6. doi:10.1016/j.antiviral.2016.03.010. [Epub ahead of print]
• Diawo Diallo, Amadou A. Sall, Cheikh T. Diagne, Oumar Faye, Ousmane Faye, Yamar Ba, Kathryn A. Hanley, Michaela Buenemann, Scott C. Weaver, Mawlouth Diallo (2011). Research Article | published 13 Oct 2014 | PLOS ONE 10.1371/journal.pone.0109442
• Diagne CT, Diallo D, Faye O, Ba Y, Faye O, Gaye A, Dia I, Faye O, Weaver SC, Sall AA, Diallo M. Potential of selected Senegalese Aedes spp. mosquitoes (Diptera: Culicidae) to transmit Zika virus. BMC Infect Dis. 2015 Nov 2;15:492. doi: 10.1186/s12879-015-1231-2
• Ledermann JP, Guillaumot L, Yug L, Saweyog SC, Tided M, Machieng P, et al. (2014) Aedes hensilli as a Potential Vector of Chikungunya and Zika Viruses. PLoS Negl Trop Dis 8(10): e3188. doi:10.1371/journal.pntd.0003188
• Loos S, Mallet HP, Leparc Goffart I, Gauthier V, Cardoso T, Herida M.(2014) Current Zika virus epidemiology and recent epidemics. Med Mal Infect. Jul;44(7):302-7. doi: 10.1016/j.medmal.2014.04.008. Epub 2014 Jul 4.
• Marchette et al., (1969) Isolation of Zika virus from Aedes aegypti mosquitoes in Malaysia. Am J Trop Med Hyg.18:411–5.
• Olson et al., (1981) Zika virus a cause of fever in central Java, Indonesia. Trans.Roy.Soc. of Trop. Med. Hyg. 75(3);389-393
• Boorman JP, Porterfield JS (1956) A simple technique for infection of mosquitoes with viruses; transmission of Zika virus. Trans R Soc Trop Med Hyg 50: 238–242. doi: 10.1016/0035- 9203(56)90029-3
• Cornet M, Robin Y, Adam C, Valade M, Calvo MA (1979) [Comparison between experimental transmission of yellow fever and zika viruses in Aedes aegypti]. Cah ORSTOM ser Ent med et Parasitol 17: 47–53.
• Musso D, Nilles EJ, Cao-Lormeau VM.(2014) Rapid spread of emerging Zika virus in the Pacific area. Clin Microbiol Infect.;20(10):O595–6. doi: 10.1111/1469-0691.12707. pmid:24909208
• Girard et al., 2014
• Wong P-SJ, Li M-zI, Chong C-S, Ng L-C, Tan C-H (2013) Aedes (Stegomyia) albopictus (Skuse): A Potential Vector of Zika Virus in Singapore. PLoS Negl Trop Dis 7(8): e2348. doi:10.1371/journal.pntd.0002348
• Li MI, Wong PS, Ng LC, Tan CH. (2012) Oral susceptibility of Singapore Aedes (Stegomyia) aegypti (Linnaeus) to Zika virus. PLoS Negl Trop Dis;6(8):e1792. doi: 10.1371/journal.pntd.0001792. Epub 2012 Aug 28.
• Chouin-Carneiro T, Vega-Rua A, Vazeille M, Yebakima A, Girod R, Goindin D, et al. (2016) Differential Susceptibilities of Aedes aegypti and Aedes albopictus from the Americas to Zika Virus. PLoS Negl Trop Dis 10(3): e0004543. doi:10.1371/journal.pntd.0004543
• McBride CS. (2016) Genes and Odors Underlying the Recent Evolution of Mosquito Preference for Humans. Curr Biol. Jan 11;26(1):R41-6. doi: 10.1016/j.cub.2015.11.032.