Le moustique Culex pipiens, vecteur potentiel des virus ... - Toubkal

Abstract
West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two emerging
arboviruses causing epidemics outside their natural range of distribution.
WNV (Flaviviridae, Flavivirus) is one of the most broadly distributed arboviruses in
the world, being found on all continents. Recent outbreaks of WNV were recorded all
over the Mediterranean region. WNV has been isolated from horses and birds in
Algeria, Morocco and Tunisia, indicating an active circulation of the virus in this
region. Emergences may occur when adequate vector and susceptible vertebrate
host populations intersect under permissive climatic conditions. Moreover, RVFV
(Bunyaviridae, Phlebovirus) is endemic to countries bordering the Maghreb region.
Illegal importations of viremic livestocks along trade routes have been suspected to
introduce the virus and initiate local viral transmission.
Culex pipiens is widely found in North Africa. This species has been incriminated in
the transmission of different arboviruses including WNV and RVFV. In this context,
we define the importance of Cx. pipiens as vector of both viruses in the Maghreb
region. For such, we experimentally infected field collected populations of Cx. pipiens
from North Africa with WNV and RVFV at titers of 10 7,8 and 10 8,5 plaque forming
units/mL. Disseminated infection and transmission rates were estimated 14-21 days
following the exposure to the infectious blood-meal. We show that 14 days after
exposure to WNV, all mosquito strains developed a high disseminated infection and
were able to excrete infectious saliva. However, only 69.2% of mosquito strains
developed a disseminated infection with RVFV Clone 13 strain, and among them,
77.8% were able to deliver virus through saliva. We showed that Cx. pipiens from the
Maghreb are efficient experimental vectors to transmit WNV and to a lesser extent,
RVFV.
Cx pipiens has two recognized forms ‘‘pipiens’’ and ‘‘molestus’’ which are
morphologically indistinguishable with distinct behaviors and physiologies that may
influence their vectorial status. In this study, we prospected for these forms in
Morocco by using diagnostic primers designed for the flanking region of microsatellite
CQ11. We established the presence of both forms of Cx. pipiens and their hybrids in
Morocco.
Our findings should be confronted to parameters describing mosquito ecology and
biology. Thus, North Africa should be considered as a bridge region between the
Sub-Saharan region where both viruses are endemic circulating within a selvatic
cycle and the northern latitudes such as Europe for emergence of vector borne
pathogens. Unintentional introductions of birds or animals may have set the stage for
the emergence of WNV and RVFV in Europe.
Key words: Culex pipiens, West Nile virus, Rift valley fever virus, vector
competence, molecular identification, Maghreb region.