Nuclear technique cuts mosquito numbers in Cuban trial

Friday, 14 January 2022

In Cuba, like in most tropical countries, dengue is a growing problem. Transmitted by the mosquito species Aedes aegypti, 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 Organisation has increased eight-fold over the last two decades.

"In Cuba, controlling Aedes aegypti is a national priority," said René Gato Armas, an entomologist and head of the sterile insect technique (SIT) group at Cuba's Pedro Kourí Tropical Medicine Institute.

"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." He noted the indiscriminate use of insecticides has also triggered resistance to insecticides in Aedes aegypti.

SIT is an approach to insect population control relying on the release of sterilised male mosquitos. Irradiation, such as with gamma rays and X-rays, is used to sterilise 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 International Atomic Energy Agency (IAEA) and the Food and Agriculture Organisation of the United Nations (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.

A pilot trial of a SIT campaign was conducted between April and August 2020 in an area of 50 hectares in El Cano, an isolated neighbourhood of southwest Havana. Arroyo Arenas, another neighbourhood of similar size, was used as an untreated control site. In the pilot trial, almost 1.3 million sterile male mosquitoes were released. Male mosquitos do not carry dengue, bite, nor feed on blood.

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.

"Using the SIT for mosquitoes is relatively new anywhere in the world, and pilot trials like this one show how promising they can be," said Rui Cardoso Pereira, Head of the Insect Pest Control Section at the Joint FAO/IAEA Centre of Nuclear Techniques for Food and Agriculture.

"National institutions can now effectively implement the SIT and will soon be able to support other countries in this technique," said Raquel Scamilla Andreo Aledo, the IAEA's Programme Management Officer for Cuba.

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.