Dengue fever is a viral disease transmitted by Aedes aegypti mosquitoes and has remained one of the major public health challenges in many parts of the world. Due to the absence of specific antiviral treatment for the disease, prevention remains an important approach to controlling its spread. Among the preventive measures, the use of mosquito repellent products against the vector for dengue virus is the most popular and easily available way to minimize human contact with mosquitoes and, consequently, to avoid the transmission of the dengue virus.
Here we provide information about the effectiveness of various everyday repellents that could be used to prevent the incidence of dengue fever, along with their respective merits and demerits.
Understanding dengue and its transmission
Dengue is a viral infection arising due to the dengue virus and transmitted through the infective bite of the Aedes mosquito. As these mosquitoes are most active in the early morning and late afternoon, one will find it of utmost significance that people living in endemic regions guard themselves against the disease throughout the day. This virus causes a range of symptoms, from mild fever to severe dengue, which may lead to complications such as hemorrhagic fever and shock syndrome. Given the absence of a vaccine that offers complete protection, the role of mosquito repellents are pivotal in disrupting this transmission cycle.
Types of mosquito repellents
Mosquito repellents can also be broadly categorized into chemical-based and natural-based formulations. The former includes active ingredients typically hailing from a host of well-known chemicals: DEET(N,N-Diethyl-meta-toluamide), picaridin or IR3535. These mosquito repellent products have been studied at length and are greatly recommended by health authorities due to their paramount efficacy. Plant-based oils and extracts, such as those derived from citronella, lemon eucalyptus and neem oil, comprise the natural repellents and offer a non-toxic and environmentally friendly option to consumers.
Chemical-based repellents
DEET interferes with the ability of a mosquito to detect human skin by masking the chemical signals emitted by humans that attract mosquitoes. It has been considered the gold standard for mosquito repellents and used for many years. Studies have shown that DEET-based mosquito repellent products may protect against mosquito bites for 8-12 hours, depending on the concentration.
The other chemical repellent in widespread use is picaridin, which provides a protective effect similar to DEET without the unpleasant smell and greasy or sweaty feel on the skin. It had also been found to be effective against Aedes aegypti mosquitoes, making it one of the best candidates for dengue prevention. IR3535 is less common but also offers adequate protection. It is manufactured in combination with ingredients like DEET or picaridin to enhance its duration of action.
Natural repellents
Natural repellents contain citronella or lemon eucalyptus oil, are less toxic and have a pleasant smell. However, these types of mosquito repellent products usually are not as long-lasting as chemical products. Citronella, for example, was shown to be effective for no more than about 2 hours and needs subsequent reapplication. Lemon eucalyptus oil, on the other hand, tends to provide longer protection, even up to 6 hours in some cases, yet still does not last as long as DEET or picaridin does.
Neem oil is one of the traditional natural insect repellents, which over time has been part of various cultural practices. Neem oil provides a range of protection. However, most preparations are not as effective as synthetic repellents. In addition, frequent reapplication is often necessary. Furthermore, the strong odor and possible skin irritation hinder its general application.
Evaluating the effectiveness of repellents
Duration of protection
The most important factor in mosquito repellent products’ efficacy is the duration of protection.
- Due to their chemical stability, DEET and picaridin could provide prolonged protection, which is vital in the dengue-endemic areas where Aedes mosquitoes remain very active.
- Natural repellents, on the other hand, being safer for long-term application, often require frequent reapplication, thus lowering their practicality in real-life situations.
Safety and side effects
Another important aspect is the safety profile of mosquito repellent products:
- DEET is highly effective, there have been concerns related to skin irritation and, in rare cases, neurotoxicity at higher concentrations and with extended use.
- Picaridin is new but has an excellent safety record with fewer reports of adverse events.
- Natural repellents are generally safer. However, in sensitive individuals, there can be allergic reactions or skin irritation upon repeated use.
Environmental impact
The environmental impact of mosquito repellent products is a growing concern t due to chemical pollution and resistance. It is efficient, but DEET is a synthetic chemical that tends to persist in the environment and perhaps affects non-target species. Natural repellents are biodegradable and tend to have a low environmental impact, thus probably being more sustainable if one considers long-term use.
Comparing repellents in field studies
Several field studies have also been conducted in an attempt to evaluate various mosquito repellents to manage dengue virus transmission. They often involve counting the number of landings or bites by mosquitoes on treated and untreated skin over some defined period.
A study published that chemical repellent leads to a reduction in the number of bites from the mosquito species, Aedes aegypti, compared with natural repellents. The study underlined chemical repellents for having very high efficacy and longer duration of protection, particularly in high-transmission areas for dengue virus.
Another study on mosquito repellent products, that also involved picaridin, has also shown similar efficacy to DEET, though the number of adverse effects reported by the users was lower. It was further noted that picaridin was well-tolerated even in children, thereby making it a preferred choice for family use.
In contrast, the plant-based repellents, citronella and lemon eucalyptus, which had reasonable efficacy in the short term, remarkably lost their protection after only a few hours. In regions that require sustainable protection, it was observed that the frequency of use of these products is a huge drawback.
Microbe Investigations Switzerland (MIS) offers comprehensive testing services to ensure the efficacy of mosquito repellents and other vector control products.
