Unveiling the world of mosquitoes: A guide

The three culprits: Aedes, Anopheles, and Culex

There are over 3,000 species of mosquitoes and of these, mosquitoes in three genera are particularly important in spreading disease to humans.^3,4

1. Anopheles: Found worldwide (except Antarctica), Anopheles mosquitoes are infamous for transmitting malaria.⁵

2. Culex: The most widespread mosquito species worldwide, Culex mosquitoes can transmit encephalitis, West Nile virus, and lymphatic filariasis.⁶

3. Aedes: Flourishing in warmer climates, Aedes mosquitoes are notorious for spreading diseases like Zika, Chikungunya, and dengue.⁷

Aedes aegypti versus Aedes albopictus

Two species of Aedes mosquito: aegypti (originating from Africa) and albopictus (from Asia) are responsible for spreading dengue.^8-10 Despite being of the same species, they have distinct differences.¹¹ Aedes albopictus, also called Asian tiger mosquito, is a more aggressive biter and prefers to bite during the day.¹¹ Aedes aegypti, while also mainly biting during the day, is stealthier, often targeting the ankles and elbows, and has a strong preference for biting humans over other mammals.¹² Aedes aegypti also prefers to live and breed close to, or in, human households, whereas the habitats for Aedes albopictus are diverse: besides indoor environments, they can also include fields and forests.^13,14

Geographically, the distribution of Aedes aegypti is limited to tropical and subtropical regions but Aedes albopictus also appears in warm and cold temperate regions – it is established in a number of European countries.^9,15

Female mosquitoes and disease transmission

Female mosquitoes do all the lifting when it comes to spreading diseases to humans: it is only the females that feed on animal blood (including human), the males do not bite, they only feed on flower nectar and plant juices.¹⁶ In their quest to reproduce, the female mosquitoes of some species use needle-like proboscis to pierce the skin of various mammals, humans included.^17,18 This act of feeding, accompanied by the injection of saliva, can not only trigger swelling and itching but also transmit diseases, such as dengue.^17-20

When infected with the dengue virus from a mosquito bite, individuals may develop a wide range of symptoms, including some that can lead to serious complications.¹⁹ Approximately 1 in 4 dengue infections are symptomatic, and of these, about 1 in 20 can progress to life-threatening severe dengue.²¹ Read more about the symptoms of dengue here.

Dormant Vectors

After feeding on blood, the female lays her eggs – up to 200 at a time – inside a container just above the water line.^13,22 In fact, an area as small as a coin is all the water she needs for this.²³

The laid eggs stick to the wall containers like glue.¹³ They are resistant to drying, and can survive dormant for months, if needed, until conditions are right (such as contact with water from a sprinkler or rain) for them to hatch.¹³

Aedes mosquitoes grow very quickly, from eggs to adults

The hatched eggs give way to highly active larvae or “wigglers” that feed on particles in the water.^13,24,25 Like a caterpillar turning into a butterfly, the mosquito larvae form a case called a pupa, which transforms into a flying mosquito.²⁵

Mere moments: The entire lifecycle of Aedes mosquitoes takes 8– 10 days¹³

Adapted from Centers for Disease Control and Prevention (CDC)¹³

Climate change is creating the ‘perfect storm’ for disease-carrying mosquitoes

Many mosquito-borne diseases are sensitive to environmental factors such as temperature and humidity.²⁶ Raised temperatures can both accelerate mosquito reproduction and development while higher humidity can extend the mosquito’s lifespan.²⁷ In addition, increased rainfall can provide more potential breeding sites (standing water) for mosquitoes.²⁸ Read more about the impact of climate change on the spread of dengue here.

Urbanization is as important as ever to dengue-carrying mosquitoes

For the past 5,000 years, there has been a close association between settled human societies and Aedes aegypti.⁸ These mosquitoes have adapted to breed in artificial containers and developed a preference for human blood.⁸ Today, urbanization continues to help fuel the spread of dengue.³⁰ Urban environments provide an abundance of man-made containers for the mosquitoes to breed in while dense populations allow for rapid virus transmission.³⁰ Additionally, unplanned urbanization often results in poor infrastructure, such as inadequate water drainage and waste management systems, which mosquitoes readily exploit.³⁰