Prevention

“Mosquito repellent, 5/2016, pic by Mike Mozart of TheToyChannel and JeepersMedia on YouTube #Mosquito #Repellent” by JeepersMedia is licensed with CC BY 2.0.

Preventing dengue virus depends on controlling mosquitoes, reducing human–mosquito contact and vaccination. This page is split into 3 sections: advice for individuals, advice for governments, and advice for organisations on how to prevent dengue infections. In general, the prevention of dengue is split into pharmaceutical and non-pharmaceutical methods. The pharmaceutical method of vaccination is covered in the ‘governments’ section, while everything else on this page would fall into the category of non-pharmaceutical methods.

ADVICE FOR INDIVIDUALS

As a mosquito-borne disease, prevention on an individual level means preventing mosquito bites. Individuals are suggested (but not limited to) the following (Nature, 2021, “Dengue and severe dengue” and WebMD, 2019, “Dengue Fever” and CDC, 2010, Avoid Dengue by Preventing Mosquito Bites):

  • Use mosquito repellents (Centres for Disease Controls recommends repellent containing DEET, picaridin, lemon eucalyptus oil or IR3535)
  • Wear long-sleeve clothes and long trousers when outdoors
  • Install mosquito nets in windows and doors, and/or use mosquito nets while sleeping
  • Try to avoid areas with standing water
  • Avoid outdoor activity around dusk and dawn
  • Frequently clean sources of still water in your household, and replace the water often
  • Keep living areas dry and clean
  • Use larvicide on indoor plants, either in the form of a spray, or a powder which can be applied onto plants with a spoon
  • Consider the use of adulticide in your household, which can be applied with a spray – adulticide is toxic, so use with caution. Spray when no one is in the household, and thoroughly ventilate the building after use.
  • Mosquitofish, goldfish, dragonflies and small turtles kill mosquitoes or their larvae, so consider placing these in water habitats outside your house
  • Use ovitraps in areas of high mosquito concentration. These trap and kill mosquitoes
“Gambusia affinis Mosquitofish” by David A. Hofmann is licensed with CC BY-NC-ND 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-nd/2.0/

WHAT GOVERNMENTS CAN DO

For governments, it is important to have a mixture of central ‘top-down’ initiatives, as well as community based education and guidance for individuals. For guidance that governments could give to their citizens, please see the ‘individuals’ section above.

Policy-lead initiatives can be separated into two types: pharmaceutical and non-pharmaceutical approaches. The pharmaceutical approach involves vaccination schemes, whereas non-pharmaceutical approaches involve mosquito population control to avoid human contact with potential dengue carriers.

Pharmaceutical approaches

At the moment, there is only one available dengue vaccine, called Dengvaxia®, that is authorised for use in many countries. Dengvaxia was created by Sanofi Pasteur, and became the first licensed dengue vaccine in 2015. The vaccine is usually given to people in the age range of 9 – 45, in 3 doses, 6 months apart. Dengvaxia has very different effects on individuals based on whether they are seropositive or seronegative. (Dengue vaccine: WHO position paper, September 2018 – Recommendations, 2019)

Seropositive individuals = people who have been infected by a dengue virus before

Seronegative individuals = people who have never been infected by a dengue virus

Individuals who have already been infected by dengue are much more likely to experience severe illness upon a second infection of the virus. Because the Dengvaxia vaccine is a live attenuated vaccine, it acts like a ‘silent natural infection’. For seropositive individuals, the vaccine provides long-term protection from dengue. However, for seronegative individuals who get vaccinated, this means that if they are then to be infected with dengue again, there is a much higher chance in it resulting in severe dengue. Because of this, the World Health Organisation (WHO) suggests pre-vaccine screening, to make sure that only seropositive people receive a vaccine. If this isn’t possible, they suggest only vaccinating in areas where recent rates of dengue were high (high = seroprevalance rates of at least 80% in 9 year olds). (Dengue vaccine: WHO position paper, September 2018 – Recommendations, 2019)

Due to insufficient data, the WHO also advised against pregnant / breastfeeding women and immunocompromised individuals being vaccinated. (Dengue vaccine: WHO position paper, September 2018 – Recommendations, 2019)

More, accessible information on the WHO recommendations can be found here: ‘Revised SAGE recommendations on use of dengue vaccine’

Non-Pharmaceutical Approaches

As mosquitoes lay eggs in still water, governments can reduce human contact with mosquitoes by ensuring that all communities have access to a reliable piped water source, and by encouraging communities to remove unnecessary sources of still water (WHO, 2021, “Dengue and severe dengue”). Necessary sources of still water can either be covered with a fine mesh, or treated using Bti bricks. Bacillus thuringiensis israelensis (Bti) is a naturally occurring soil bacteria that kills mosquito larvae in water. Bti is available in small bricks that float on water and treat deep water (Nature, 2021, “Controlling Dengue Outbreaks”). 

Targeted use of larvicide and adulticide can also be used to reduce human contact with mosquitoes: 

  • For larvicide treatment of drinking-water, temephos and methoprene can be applied with a dosage of up to 1 mg of active ingredient per litre (1 ppm); pyriproxyfen can be applied at dosages up to 0.01 mg per litre (0.01 ppm) and Bti at1–5mg per litre (WHO, 2009, “Dengue Guidelines for Diagnosis, Treatment, Prevention and Control”). Two or three applications per year should be optimal in controlling larva propagation, but the species of mosquito, measure of local rainfall, and local larvae habitats should also be considered (WHO, 2006, “Pesticides and their Application”). 
  • Adulticide can be used as residual surface treatments or space treatments. Mosquito populations are considerably reduced in areas that have been treated with adulticide (WHO, 2006, “Pesticides and their Application”).

Considering the insufficient coverage, insecticide is not a 100% prevention, so it is suggested that other methods are used alongside the scheduled cycle of insecticide use.

Governments may also want to consider the methods in the ‘organisations’ section below.

WHAT ORGANISATIONS ARE DOING

Several organisations across the globe have been working on genetically modifying mosquitoes in different ways to reduce dengue. Below are some examples:

“Lançamento da Ação do Método Wolbachia. Niterói – RJ, 02/12/2019. Foto: Erasmo Salomão/MS” by Ministério da Saúde is licensed under CC BY-NC-SA 2.0
  • Oxford University = a team of researchers genetically modified female mosquitoes to be flightless. To court males, female mosquitoes perform a flying ‘dance’, so without being able to fly, the researchers hoped that female mosquitoes wouldn’t be able to successfully breed. As well as this, lacking the ability of flight would leave female mosquitoes more vulnerable to predators. (Fu, G., et al., 2010) The effect of introducing these females would be to reduce the mosquito population size.
  • Oxford University = the same team of researchers also genetically modified male mosquitoes, leaving them sterile. This would also reduce the mosquito population size. These sterile mosquitoes were released in a trial in Grand Cayman to see how well it could reduce dengue. (Nature, 2021, “Controlling Dengue Outbreaks”)
  • World Mosquito Program (WMP) = Wolbachia is a bacteria that is carried by 60% of insect species, but does not naturally infect Mosquitoes (Nature, 2021, “Controlling Dengue Outbreaks”). First discovered by Dr Scott O’Neill, when injected into mosquitoes, wolbachia appears to kill the dengue virus within the mosquitoes (Callaway, E., 2021). WMP conducted a large-scale trial, releasing wolbachia-infected mosquitoes in Yogyakarta, Indonesia. The full results have not yet been published, but the preliminary results are very promising; rates of dengue were 77% lower in areas with wolbachia mosquitoes, for several years after their initial release. WMP hopes to release wolbachia mosquitoes into areas covering 75 million at-risk inhabitants (Callaway, E., 2021). Find out more here: https://www.worldmosquitoprogram.org/en/randomised-control-trial-rct