Mapping dengue fever in the Middle East

The inquiry reported that the mosquito had propagated by nesting inside traditional Egyptian sunbaked clay water containers that the villagers refer to as “zeirs”. 

The disease is usually transmittable through a female mosquito bite. The Aedes aegypti mosquito thrives among humans, but rarely moves beyond an area of 400 meters. 

One single drop of water inside a discarded soda can or a zeir is able to provide a perfect nesting spot for A. aegypti. 

While this outbreak, in October 2015, is the latest on record for Egypt, the populous country has had multiple dengue flare-ups throughout history. The earliest recorded outbreak dates back to the late 18th century, and others took place in the 19th century up to the 1940s, after which a sharp decline in incidence occurred. 

The drop in vector population was due to intensive spraying of DDT, a potent insecticide, during WWII to control malaria and typhus among civilians and troops.

Despite a significant lack of data on dengue fever epidemics globally, epidemiologists like Ary Hoffmann, a professor at the School of Biosciences at Melbourne University, believe the vector is now present in all five continents, having enlarged its geographical scope in the past few decades. 

Because of its resistance to most pesticides, dengue is the fastest spreading mosquito-borne viral disease in the world. According to WHO, in just 50 years, its incidence has increased 30-fold, and during the last decade, the vector has arrived in cities.

Sudan, Oman, Egypt, Saudi Arabia, Iran and Yemen have all experienced major dengue fever blowups. 

Between 1993 and 2008, three major epidemics were reported in Saudi Arabia, resulting in more than 2,500 cases with dengue hemorrhagic fever and dengue shock syndrome, claiming 10 lives. Again in 2015, 6,000 cases of dengue fever were reported in the kingdom, leading to the death of another six patients. 

The recent civil war in Yemen caused a country-wide humanitarian disaster that resulted in famine and water and energy scarcity, which had also led to outbreaks. 

The lack of municipal services and the piles of garbage littering the streets attracted large populations of A. aegypti, which lay eggs in puddles, transmitting dengue to hundreds of people. 

Prior to the war, 1100 cases and 84 deaths were reported in Yemen as a result of three dengue epidemics episodes in the 1990s.

In the Arab Maghreb, the status of dengue is unclear, as data is not readily available. 

Putting dengue on the map 

In order to put dengue fever on the map of crucial viral diseases, Samia Elfekih, a Canberra-based Tunisian research scientist and engineer at the Commonwealth Scientific and Industrial Research Organization (CSIRO), is launching a project to assess the distribution of the vector across Africa and the Middle East. 

At the forefront of adapting novel genomic techniques to entomological systems, Elfekih will include 15 sub-Saharan countries and 10 countries in the MENA region in her upcoming study.

"Refugees rarely have access to a fixed source of water, and vectors that nest inside portable water containers can transmit the disease."

Elfekih is an expert on mapping and control. She studies the vector’s genetics, dispersal, and distribution. “You can stop the disease from spreading if you control the mosquito,” she explains. The A. aegypti vector is also implicated in Zika, Chikungunya, yellow fever and the West Nile virus; controlling it can reign in all such diseases. 

In the absence of any cheap, efficient dengue vaccine, monitoring outbreaks, and improving pest control strategies of the vector remain the most efficient pathway to dengue control, according to Elfekih.

In spite of its severity, dengue receives very little funding compared with malaria. “Malaria accounts for most of funds allocated to mosquito-borne diseases in sub-Saharan Africa,” she says. 

Through her research, Elfekih plans to map dengue fever’s incidence and prepare for future outbreaks. 

“The first objective of this project is to switch from underreported to clear cut data in each country to assess the severity of the problem, and in a second phase, we plan to implement methods of control that have shown their efficiency in other sites,” she says, referencing a Wolbachia-based technique among these methods.

Invented by Hoffmann, the technique utilizes Wolbachia, a bacterium that blocks the transmission of dengue once injected into the mosquito. Introduced through microinjections, Wolbachia easily finds its way to the gonadal tissue, and is transmitted from the female mosquito to its offspring.

“It is not easy to do,” says Hoffmann, “but if you achieve this part, you create a permanently infected line.” After successful trials in residential areas in Cairns, Australia, the technique is currently used in Malaysia and Indonesia. 

The most efficient actions to combat A. aegypti, however, should take place at the municipal level. 

Since stagnant water near human settlements or construction sites is A. aegypti’s prime nesting site, authorities need to increase the coverage of piped water lines in rural and peri-urban areas, and remove rubbish heaps from the streets. Spraying insecticides in all water containers, and applying a layer of oil on top of stagnant water containers to prevent young mosquitos from breaking free is also effective.

Movement of people and climate change

Population displacements in the region can facilitate the transmission of the disease, says Tran Minh Nhu Nguyen, an epidemiologist at WHO specializing in high threat pathogens. 

“Refugees rarely have access to a fixed source of water, and vectors that nest inside portable water containers can transmit the disease,” he says.

The impact of global warming on the dispersion of the vector is uncertain, according to Hoffmann; it will greatly depend on what type of control measures are put in place to mitigate the effects of climate change, he says. 

Hoffmann, who also investigates how species evolve and adapt to climate change, explains that targeted human responses can be very efficient at controlling the vector. “Dengue used to be quite widespread in Australia until water reservoirs were replaced with centralized water systems,” he says. As a result, breeding sites disappeared and led to a sharp decline in dengue transmission.

“A change in climatic patterns and other parameters will result in unexpected outbreaks in regions where dengue never previously existed,” says Elfekih. “An epidemic preparedness and response strategy is crucial.” 

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