K12,13-Culicine Mosquitoes as Disease Vectors

Culicine Mosquitoes

• Culicine mosquitoes belong to the Order Diptera, Family Culicidae, and Subfamily Culicinae.
• The subfamily Culicinae consists of 30 genera of mosquitoes, with medically important ones including Culex, Aedes, Mansonia, Sabethes, Haemagogus, and Psorophora.
• Culicine mosquitoes are found in every continent except Antarctica, with high concentrations in tropical areas.

Biology of Culex spp.

• Culex spp. are holometabolous insects that lay their eggs in stagnant water, which benefits their aquatic larval stage.

Biology of Aedes spp.

• Aedes spp. lay eggs on moist substrates near water lines, such as cans, tree holes, and water reservoirs on stumps.
• Adults of Aedes aegypti and Aedes albopictus are active in the morning and at dusk.
• Aedes aegypti rest in the dark in houses, while Aedes albopictus bites outside the house and sometimes indoors.
• Aedes albopictus rests on plants such as shrubs and grasses.
• Average flight range of Aedes spp. is up to 200m, but can be up to 800m.

Disease Vectors

• Aedes spp. are vectors of:
  • Dengue and dengue hemorrhagic fever
  • Yellow fever
  • Chikungunya
  • Zika
  • Encephalitis
  • Filariasis

Yellow Fever

• Yellow fever is transmitted in Africa and Latin America.
• It is a zoonotic disease, transmitted from monkeys in forests to humans by Aedes africanus.
• Infected monkeys searching for food in farms/orchards are bitten by Ae. simpsoni, which breeds in banana trees, maize, and pineapple.
• Rural people get infected and then spread the disease to urban populations by Ae. aegypti.

Chikungunya

• Chikungunya is a virus from the family Togaviridae.
• Symptoms include febrile fever, joint pain, and maculopular rash.
• Pain in joints can last for weeks or months.

Zika

• Zika is a mosquito-borne virus that is also sexually transmitted.
• Most people infected with Zika have no symptoms.
• Symptoms include fever, rash, joint pain, and red eyes.
• Symptoms usually begin a few days after being bitten by an infected mosquito or having unprotected sex with someone who is infected.
• The illness is usually mild, with symptoms lasting about a week.
• The greatest risk of Zika is to a pregnant woman's developing baby.

Viral Encephalitis

• Eastern equine encephalitis is found in the USA and is transmitted by a few Aedes species.
• California encephalitis virus is transmitted by Aedes melanimon.

Filariasis

• Aedes togoi in Japan and China breeds on stumps by the seaside and is a vector of Wuchereria bancrofti.
• Aedes poecilus in the Philippines breeds on banana tree trunks, shoots, and spreads nocturnal periodic Wuchereria bancrofti.
• Aedes polynesiensis in Polynesia is a vector of Wuchereria bancrofti.

Mansonia Mosquito

• Mansonia mosquitoes lay eggs on the undersides of leaves of aquatic plants.
• Larvae have a siphon that pierces the roots of plants.
• Adult mosquitoes are nocturnal, but can also bite during the day in the shade.
• Adult mosquitoes bite humans, but are more attracted to animals.
• Mansonia mosquitoes prefer to bite on the lower limbs of humans.
• Life cycle:
  • Eggs are laid in masses glued to the lower sides of plants.
  • Larvae and pupae attach themselves to aquatic plants for breathing.
  • They can be found in water bodies with permanent vegetation, such as swamps, ponds, and irrigation canals.

Behaviour of Mansonia Mosquito

• Mansonia species usually bite at night, mostly outdoors, but some species enter houses.
• Resting after a blood-meal normally takes place outdoors.

Importance of Mansonia

• Mansonia species are the most important vector of Brugia malayi.
• Microfilaria in the blood is sucked by Mansonia spp.
• Microfilaria penetrates the midgut into the hemocele and undergoes growth changes.

Prevention and Control

• Personal protection methods:
  • Repellents
  • Protective clothing
  • Insecticide vaporizers
  • Mosquito nets
• Insecticides:
  • Selected for effectiveness against target mosquito species.
  • Insecticidal aerosols are used for immediate results.
  • Space sprays are applied in and around houses and outdoor resting places.
• Prevention of breeding:
  • Source reduction (covering or screening water containers, draining ponds and marshes, etc.)
  • Larvicides (killing immature mosquitoes)
  • Insect growth regulators (IGRs)
  • Microbial larvicides (Bti)
  • Surface oils and films
  • Habitats in and around houses
  • Habitats in the field
• Biological control:
  • Introducing natural enemies, such as parasites, disease organisms, and predatory animals.
  • Fish that eat mosquito larvae
  • Predatory mosquitoes of the genus Toxorhynchites
  • Dragonflies
  • Cyclopoid copepods
  • Nematode worms
  • Fungi that grow in the bodies of mosquito larvae