Mauritius currently being in the rainy season, which favours the proliferation of mosquitoes in several regions around the island, the Vector Biology and Control Division is presently implementing a Sterile Insect Technique (SIT) project which forms part of the integrated vector management strategy to tackle mosquito-borne illnesses such as dengue and chikungunya. This Division operates under the aegis of the Ministry of Health and Wellness.
The Vector Biology and Control Division, through the sterile release programme, thus aims at mitigating the proliferation of the vector population of Aedes albopictus, commonly known as Tiger mosquitoes. As such, the Division has already released some 500,000 sterile male Tiger mosquitoes in the region of Champ de Mars from November 2022 to 30 January 2023, which has so far resulted in a 10% decrease in the fertility of Aedes albopictus eggs in the area.
According to the Head of the Vector Biology and Control Division, Dr Diana Pillay Iyaloo, the districts most affected by mosquito proliferation for the month of January 2023 are Rivière du Rempart, Plaines Wilhems and Savanne. These have been determined through surveys carried out by staffs of the Vector Biology and Control Division during which potential mosquito breeding sites were inspected.
Dr Iyaloo emphasised that the Division is now equipped with a recently developed tool, AlboMaurice, which uses meteorological data (rainfall and temperature) from 30 stations around the island to predict the density of mosquito population for the coming months. Based on this prediction model, regions most at risk for the month of February 2023 include Roche Bois, Ste Croix, Coromandel, St Paul, Rose Hill, Castel and Mahebourg.
As far as the sterile release programme is concerned, Dr Iyaloo recalled that it kickstarted on 27 October 2022 with the release of sterile male Tiger mosquitoes. With an initial production of 10 000 sterile males per week, this number was gradually increased to a current production and release of 60,000 sterile males each week at 20 pre-selected locations within the region of Champ de Mars.
Male mosquitoes do not bite and therefore represent no harm to humans, animals and the environment. Instead, sterile males will mate with female mosquitoes in the released area which will lay eggs that will not hatch. With time, there will be an increase in the number of sterile eggs in these regions, which will eventually decrease the population of Tiger mosquitoes thereat.
Dr Iyaloo highlighted that the SIT is targeting one out of fifteen species of mosquitoes present on the island in a target area (Champ de Mars region). She therefore informed that it is very important for the public to take all necessary precautions against mosquitoes, especially during the forthcoming weeks, as their proliferation will be favoured due to the prevailing weather around the island.
Sensitisation campaigns are regularly carried out by staff of the Vector Biology and Control Division. It is to be noted that other vector control methods are also being implemented by the Ministry of Health and Wellness. These include the spraying of larvicides in mosquito breeding sites; fogging of localities following confirmed or suspected cases of vector-borne diseases; port and airport surveillance; and awareness campaign on the necessity to keep the environment clean so as to eliminate any breeding ground of mosquitoes.
Precautionary measures to avoid mosquito bites include, among others:
using electric diffusers;
using mosquito repellent sandals, sprays or crème;
wearing long sleeves and trousers;
using fans; and
using a mosquito net.
Furthermore, in a bid to prevent mosquito proliferation, it is advised to:
prevent accumulation of stagnant water;
change the water in vases once a week;
avoid using saucers underneath flower pots;
cover water containers tightly;
clean up waste lands;
put all used cans and bottles into covered dustbins; and
avoid littering;
Tiger mosquito
The Tiger mosquito is a mosquito native to the tropical and subtropical areas of Southeast Asia. In the past few centuries, however, this species has spread to many countries through the transport of goods and international travel. It is characterised by the white bands on its legs and body. This mosquito has become a significant pest in many communities because it closely associates with humans, and typically flies and feeds in the daytime in addition to at dusk and dawn. In Mauritius, it mainly bites between 05 00 hrs to 07 00 hrs, and 15 30 hrs to 19 30 hrs.
The insect is called a tiger mosquito for its striped appearance, which resembles that of the tiger. Aedes albopictus is an epidemiologically important vector for the transmission of many viral pathogens, including the yellow fever virus, dengue fever, and Chikungunya fever. It can also host the Zika virus and is considered a potential vector for Zika transmission among humans.
The sterile release programme
The sterile release programme is part of a national project being implemented with the collaboration of the International Atomic Energy Agency (IAEA) entitled, 'Enhancing National Capabilities on the Suppression of Aedes albopictus in an Urban Locality Using the Sterile Insect Technique as Part of an Integrated Vector Management Strategy'. It consists, among others, of the rearing and releases of sterile male mosquitoes to induce sterility in the female mosquito population as they are the ones that bite and transmit diseases.
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The IAEA is not only financing the project to the tune of € 200,000, but is also providing technical expertise to the personnel of the Vector Biology and Control Division through expert missions, local and overseas training, technical meetings, scientific visits and the procurement of the required technology.
AlboMaurice prediction tool
The AlboMaurice software runs a mosquito population dynamics model to predict the temporal and spatial abundance of Aedes albopictus, the Dengue disease vector in Mauritius. For each geographical unit, it solves a system of ordinary differential equations describing different stages of the mosquito life cycle.
The tool uses daily rainfall and temperature input data to produce abundance maps used operationally by health services for targeting areas where to apply vector surveillance and control measures. The model simulations were validated against entomological data acquired weekly for one year at nine sites on the island, corresponding to different climates. Different control options (destruction of breeding sites, insecticide spraying) can also be simulated and their effects compared.
