Mosquitoes are the major arthropod vectors. The US Centers for Disease Control and Prevention have identified mosquitoes as the deadliest animal in the world, despite their size. 700 million people get a mosquito-borne illness each year. It leads to over 725,000 deaths. Mosquitoes cause at least 2.7 million deaths. Even catastrophic population crashes are possible. Then why the celebration?
20 August is the commemoration of British doctor Sir Ronald Ross’s groundbreaking discovery in 1897 that female anopheline mosquitoes transmit malaria between humans. Sharing knowledge about mosquitoes and prevention is the purpose of the celebration of World Mosquito Day.
Mosquitoes are flying insects that belong to the family Culicidae. There are approximately 3,500 species of mosquitoes spread around the world. Only about 200 of these harass humans. An adult mosquito has three main body regions: the head, the thorax, and the abdomen. The mosquito head is the sensory centre. It is nearly spherical and contains a pair of compound eyes, whose surface is divided into small units called facets. A pair of hairier antennas arises between the eyes. These antennas serve as chemosensors and mechanosensors for sound detection.
Below the antennae is the clypeus, which covers the forward projecting portion of the head that gives rise to the paired maxillary palps and the proboscis. In most mosquitoes, the palps are shorter in the females than in the males. The proboscis is the conspicuous, elongated, projecting mouthparts of the adult mosquito. It is composed of a ventral sheath, which holds the styliform (needlelike) elements that pierce flesh, inject mosquito saliva and transport blood. At the tip of the proboscis are the labella, two sensory lobes that mosquitoes use to locate host blood vessels. They have six legs and a pair of wings for locomotion.
The life cycle of a mosquito comprises four stages: egg, larva, pupa, and adult. Eggs are laid on the surface of stagnant or slow-moving water sources, such as clogged gutters. Flowerpots, empty tins and cups, birdbaths, etc. These eggs withstand harsh conditions. Female mosquitoes lay hundreds of eggs during their lifespan. The eggs are hatched and turn into aquatic larvae, which can swim with a jerk. They feed on algae and organic debris, but few of them are predatory.
Unlike other insects, mosquitoes in the pupal stage, are free-swimming and active. Most adult mosquitoes range in size from one-quarter to one-half of an inch. Male mosquitoes are relatively smaller and have hairier antennas than females. The males, and some females, feed on plant fluid like nectar. The females require the proteins obtained from blood in order to mature their eggs. The rapid reproduction rate of mosquitoes contributes to large populations. Their reputation breaks as pests when it comes to ecological roles. Mosquitoes are food sources for several aquatic organisms, including amphibians and birds. As well as contributing to pollination.
Over 90% of mosquito species have no link to human disease. However, mosquitoes are well-known vectors for deadly diseases as they carry a range of pathogens. Some of the diseases carried by mosquitoes include malaria, dengue fever, zika virus, West Nile virus, yellow fever, and chikungunya. Diseases spread through mosquitoes are known as mosquito-borne diseases. As they consume blood, viruses and parasites enter their body with saliva and transmit to another person when they bite.
The Aedes, Anopheles, and Culex genuses each can transmit multiple viruses or parasites. And we may not need them in our ecosystems.
Anopheles
This mosquito is recognized from its resting position. Wings are spotted and live for 18 days to several weeks. As we know, malaria is a life-threatening disease spread to humans by mosquitoes. It is mostly found in tropical countries. Infants, children under 5 years, pregnant women, travellers, and people with HIV or AIDS are at higher risk of severe infection. Malaria mostly spreads to people through the bites of some infected female Anopheles mosquitoes. The first symptoms may be mild, similar to many febrile illnesses, and difficult to recognize as malaria. Left untreated, P. falciparum malaria can progress to severe illness and death within 24 hours.
Culex
The genus Culex is a carrier of viral encephalitis. Egg laying may occur in almost any source of fresh water, including standing polluted water. The life cycle is usually 10 to 14 days, maybe longer in cold weather.
Aedes
Aedes aegypti and Aedes albopictus are invasive species in many parts of the world. These mosquitoes cause yellow fever, dengue, zika, fever, and encephalitis. Wings are uniformly coloured. Aedes is distinguished by a silver thorax with white markings and posterior spiracular bristles. The eggs are capable of withstanding long periods of dryness. Aedes aegypti is a domestic species that accounts for yellow fever. It has white bands on its legs and spots on its abdomen and thorax.
Dengue is one of the most crucial arboviral diseases. Annually, there are 100–400 million infections, as estimated by the WHO. There is no specific treatment for dengue or severe dengue, and early detection and access to proper medical care greatly lower the fatality rates of severe dengue. At first, Aedes aegypti was responsible for dengue. However, in 2023, local transmission of dengue by Aedes albopictus (the tiger mosquito) will be identified in Europe.
Most people with dengue have mild or no symptoms and will get better in 1–2 weeks. Rarely, dengue can be severe and lead to death. If symptoms occur, they usually begin 4–10 days after the infection and last for 2–7 days. High fever (40°C/104°F), severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, swollen glands and rashes are the symptoms.
Individuals who are infected for the second time are at greater risk of severe dengue. Severe dengue symptoms often come after the fever has gone away: severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums or nose, fatigue, restlessness, blood in vomit or stool, being very thirsty, pale and cold skin and feeling weak.
Mosquitoes are most active during dawn and dusk. Female mosquitoes have receptors to detect carbon dioxide, which is exhaled by every human. Also, they have the ability to detect bare skin. They are attracted to the smell of sweat as it contains lactic acid. These complex sensors help them fulfil their hunger with blood. Some people are more attracted to mosquitoes depending on their blood type, metabolic rate, and certain chemicals generated by bacteria on the skin.
Prevention is better than a cure, as always. Necessary steps should be taken to avoid bites from these bloodsucking creatures. The elimination of mosquito breeding sites is important when it comes to prevention. Waste must be disposed properly to avoid man-made habitats. Birdbaths, empty tyres, and flower pots should be avoided, or regular cleaning is needed. Gutters should be cleaned. All stagnant water resources must be checked regularly. Keeping grass short by mowing could reduce the possibility of mosquito breeding. We can use mosquito-repellent plants like citronella, lavender, and marigold in the garden. Numerous tools can be used as an ecological approach to prevent mosquito breeding. Dytiscidae beetles are predators of mosquito larvae. Travel smart and avoid bites. Wear protective clothing and avoid peak times. Use mosquito repellents (containing DEET, IR3535 or Icaridin) after dusk. Use coils and vaporizers. Use window screens as a physical barrier to avoid mosquito bites. Many areas have mosquito control programs that treat public areas and water sources. Nowadays, a variety of methods are being used in the development of biotechnology.
Everyone must be cautious in their own environment. We never know who will be a victim of buzzing blood suckers.
Written by:
Maleesha Bandara
1st Year Undergraduate
Molecular Biology Stream
Faculty of Science
University of Colombo
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