Assessing the threat of Aedes albopictus mosquitoes in Morocco: an Infectious Thoughts interview

In 2015, the mosquito Aedes albopictus was detected in Morocco's capital city, Rabat, threatening the region with the introduction of numerous arboviruses. Recent collaborative research between the Institut Pasteur, Moroccan universities and surveillance centres, has sought to establish the vector competence of these local mosquitoes in a bid to assess the risks of emergence of diseases such as dengue fever, chikungunya, Zika and yellow fever. In this Infectious Thoughts interview, we speak to Anna-Bella Failloux, head of the Unit of Arboviruses and Insect Vectors (AIV) at the Institut Pasteur in Paris about the likelihood of virus transmission by Aedes in the region and what this might means in terms of public health priorities and vector control strategies for North Africa and Europe.

What are some of the main reasons for which you have focused your research on Aedes albopictus in Morocco?

Aedes albopictus was first detected in Europe in 1979 in Albania and again, in 1990 in Italy. The species is now present in 20 European countries. In North Africa, Ae. albopictus was detected in Algeria in 2010, in Morocco in 2015, and Tunisia in 2018.

Once a mosquito vector is introduced in a new region, pathogens transmitted by this species are expected to circulate sooner or later in the region. To measure how competent a mosquito is when infected with a pathogen, we run experimental infections in laboratory. We use field-collected mosquitoes and offer them an infectious blood meal (containing the virus). At different days after infection, we measure different parameters describing the vector competence: infection (mosquitoes with virus detected in mosquito midgut), dissemination (mosquitoes with the virus released beyond the midgut infecting mosquito internal organs), and transmission (mosquitoes with the virus detected in the saliva, ready to be injected in a host).

Based on your work, which arboviruses are most likely to take hold in Morocco?

Aedes albopictus can transmit experimentally more than 25 arboviruses: dengue, chikungunya, zika, yellow fever, Japanese encephalitis, West Nile, Rift Valley fever virus… It means that this species is genetically able to be a vector of these pathogens. If the virus is introduced through a traveller coming back from a region where the pathogen is circulating, a local competent Aedes albopictus can become infectious after taking a blood meal on the viremic traveller. Then the infected mosquito can become the source of contamination for other people initiating an autochthonous transmission, and an outbreak.

What implications could this have for the wider region? How do these results fit in to your wider disease and vector surveillance work across your international network of 33 collaborating institutes?

Our results showed that Aedes albopictus in Morocco can transmit dengue, chikungunya, zika and yellow fever viruses. I guess that Aedes albopictus from North Africa (Tunisia and Algeria) can share the same pattern. So there will be a threat of all these arboviruses for the region.

The Institut Pasteur International Network of 33 institutes covering the 5 continents offers invaluable opportunities to work on the emergence of arboviruses. As Aedes albopictus is an invasive species, we can track the emergence of arboviruses transmitted by this mosquito species all over the world.

What policy recommendations can be drawn from your findings?

Using our experimental infections, we are able to measure the time necessary for the virus to be excreted from the saliva after the ingestion of the infectious blood meal. It is 3 days after the blood-meal with chikungunya virus, 14 days for dengue and yellow fever viruses, and 21 days for zika virus.

In the case of chikungunya: when a human case is detected, it is already too late to spray his house with insecticides to control the viral dissemination. Infected mosquitoes have already escaped from the house to contaminate other people.

With dengue and yellow fever viruses, from the detection of a human case, the vector control team has 14 days ahead to control the dissemination of the virus.