By Michael Amdi Madsen, IAEA Office of Public Information and Communication

In Cuba, like in most tropical countries, dengue is a growing problem. Transmitted by mosquitoes, this viral infection causes high fever, muscle and joint pains, skin rashes, and, in the most severe cases, death. Globally, the number of dengue cases reported to the World Health Organization has increased eight-fold over the last two decades. The Cuban government is therefore aiming to tackle the spread of dengue by piloting a nuclear technique which can decrease mosquito populations.

The technique in question is the sterile insect technique (SIT): an approach to insect population control relying on the release of sterilised male mosquitos. Supported through the IAEA’s technical cooperation programme and in cooperation with the Food and Agriculture Organization of the United Nations (FAO), a pilot trial of a SIT campaign in a Havana neighbourhood has reduced mosquito (Aedes aegypti) numbers  by up to 90 percent last year  and early reports indicate that cases of mosquito-borne diseases were completely eliminated in the last two months of the trial.

 Using the SIT for mosquitoes is relatively new anywhere in the world, and pilot trials like this one show how promising they can be. For Cuba’s pilot trial, almost 1.3 million sterile male mosquitoes were released in 21 weeks, and the goal in the near future is to scale up the trial with a larger area and consequently many more sterile mosquitoes.

 “In Cuba, controlling Aedes aegypti is a national priority,” said an entomologist and head of the SIT group at Cuba’s Pedro Kourí Tropical Medicine Institute, René Gato Armas. “After a major dengue epidemic in 1981, the government deployed an intensive national programme based on conventional methods which almost eradicated the mosquito in the late 1980s. Since then, however, epidemic outbreaks from imported cases have been frequent. Currently, dengue is considered an endemic disease in Cuba.”

The SIT is among the most environment-friendly insect pest control methods ever developed. Irradiation, such as with gamma rays and X-rays, is used to sterilize mass-reared insects so that, while they remain sexually competitive, they cannot produce offspring. For the last five years Gato Armas has been working closely with experts at the IAEA and the FAO to collect baseline data and develop the pilot SIT trial as an alternative to mosquito control efforts that are declining in their efficacy and are damaging to the environment.

“Dissatisfaction with other mosquito population control techniques, such as sanitary inspection, larvae control and insecticides, has drawn the government to the SIT and lets sterilised mosquitoes do most of the work,” said Gato Armas. He said that the indiscriminate use of insecticides has also triggered resistance to insecticides in Aedes aegypti, and the pilot SIT trial is the start to a more effective and environmental-friendly mosquito control programme. Conducted between April and August 2020, the pilot trial covered an area of 50 hectares in an isolated neighbourhood of southwest Havana, El Cano, which was selected as SIT intervention site. Arroyo Arenas, another neighbourhood of similar size, was used as an untreated control site.

Community for mosquito control

Community acceptance is essential for the success of vector control methods, including SIT. A communication campaign about the pilot trial was supported by family doctors and community leaders, who highlighted that the release of sterile male mosquitoes was safe as male mosquitos do not carry dengue, bite, nor feed on blood, said Gato Armas.

The support from the IAEA and the FAO has been critical to the SIT trials. “While staff and space for breeding mosquitoes was provided by the Cuban government, SIT requires specialised equipment and expertise, and this is where the IAEA could help,” said the IAEA’s Programme Management Officer for Cuba, Raquel Scamilla Andreo Aledo.

The IAEA supported Cuba in attaining equipment to separate male and female mosquitoes ahead of irradiation and release and helped equip mosquito rearing facilities. Prior to the trial, Cuba had little capacity in insect rearing and the IAEA supported Cuban fellows to be sent for training on the technique in Brazil, Colombia, Mexico and at the IAEA laboratories in Austria.

“National institutions can now effectively implement the SIT and will soon be able to support other countries in this technique,” said Scamilla Aledo.

Challenging but effective

Implementing a SIT programme relies on specialised tools and knowledge, said Head of the Insect Pest Control Section at the Joint FAO/IAEA Centre of Nuclear Techniques for Food and Agriculture, Rui Cardoso Pereira.

“Using the SIT for mosquitoes is relatively new anywhere in the world, and pilot trials like this one show how promising they can be. For Cuba’s pilot trial, almost 1.3 million sterile male mosquitoes were released in 21 weeks, and the goal in the near future is to scale up the trial with a larger area and consequently many more sterile mosquitoes,” said Cardoso Pereira, who is working with Gato Armas and others in Cuba to build expertise and scale-up the project.

Gato Armas said that it was possible that by the end of 2022 the project study area will increase, but it will require upgrades to equipment, including an automated ‘sex-sorter’, to reduce time intensive labour and bring down costs. “The IAEA and FAO will continue to offer its support to Cuba and other countries in the region pursuing pest control using the SIT,” Cardoso Pereira said.