No larvae, no mosquitoes, no dengue fever

This year, dengue serotypes 1 and 2 are the most common cause of dengue infections, with nearly 18,000 people in Laos contracting the virus, of whom 17 have died.
The dengue outbreak is the fourth year round on record in Laos. The last significant outbreak occurred in 2019 when almost 40,000 people fell ill and 76 people died.

A man checks for larvae inside an old tyre, as this is one of many breeding sources of dengue mosquitoes.

Deputy Director of the Centre of Malariology, Parasitology and Entomology, Dr Boualom Khamlome, says dengue fever has four serotypes, which can all be life-threatening if patients do not get the right advice and treatment.
According to the World Health Organisation, although less common, some people develop severe dengue, which can be associated with any number of complications, such as bleeding, organ impairment and/or plasma leakage. Severe dengue has a higher risk of death when not managed appropriately.
Dengue is caused by a virus of the Flaviviridae family and there are four distinct, but closely related, serotypes of the virus that cause dengue (DENV-1, DENV-2, DENV-3 and DENV-4).
Recovery from infection is believed to provide lifelong immunity against that serotype. However, cross-immunity to the other serotypes after recovery is only partial, and temporary. Subsequent infections (secondary infection) by other serotypes increase the risk of developing severe dengue.
The risk of developing severe dengue fever actually increases if people are infected a second, third or fourth time. Dengue fever can cause severe bleeding, shock (sudden drop in blood pressure) and death.
At any one time, all four strains of the dengue virus can be active, although one is usually dominant. There is currently no vaccine against dengue fever due to there being many subtypes of the four serotypes, making it difficult for scientists to produce a vaccine that is effective against all types.
In the absence of a vaccine, Dr Boualom advises members of the public to strictly follow the standard measures on dengue prevention and control.
“If you know you have dengue, avoid getting further mosquito bites during the first week of illness. Viruses may be circulating in the blood during this time, and you may transmit the virus to new uninfected mosquitoes, which may in turn infect other people. As a patient, you are advised to sleep under a mosquito net at all times,” he said.
The proximity of mosquito vector breeding sites to human habitation is a significant risk factor for dengue.  At present, the main method to control or prevent the transmission of dengue is to combat the mosquito vectors. This is achieved through:
Prevention of mosquito breeding:
o   Preventing mosquitoes from accessing egg-laying habitats through environmental management and modification;
o   Disposing of solid waste properly and removing artificial man-made habitats that can hold water;
o   Covering, emptying and cleaning of domestic water storage containers on a weekly basis;
o   Applying appropriate insecticides to outdoor water storage containers.
Personal protection from mosquito bites:
o   Use of personal household protection measures, such as window screens, repellents, coils and vaporisers. This must be done during the day both inside and outside of the home, because the primary mosquito vectors bite throughout the day;
o   Wear clothing that minimises skin exposure to mosquitoes.
Community engagement:
o   Educate communities on the risks of mosquito-borne diseases; 
o   Engage with communities to improve participation and mobilisation for sustained vector control.
Active mosquito and virus surveillance:
o  Active monitoring and surveillance of vector abundance and species composition should be carried out to determine effectiveness of control interventions;
o  Prospectively monitor prevalence of the virus in the mosquito population, with active screening of sentinel mosquito collections;
o  Vector surveillance can be combined with clinical and environmental surveillance.
Dr Boualom says public participation is very important for effectively preventing and controlling the spread of dengue, especially through the removal of mosquito breeding grounds.
“If there are no larvae, there are no mosquitoes. If there are no mosquitoes, there is no dengue,” he said astutely.

By Xayxana Leukai
(Latest Update August 18, 2022)