Durgical
EN
Open the app

Culex and Mansonia

  • Parasite
  • Exam priority: medium

Brown night-biting mosquitoes. Culex breeds in dirty standing water and carries West Nile virus and filariasis; Mansonia breeds among water plants.

Updated

Also called: house mosquito (Culex quinquefasciatus), southern house mosquito, zancudo

Quick facts

Type
Parasite · Arthropod vectors
Gram / shape
Plain brown mosquito that rests
Spread
Only the female bites · West Nile and similar viruses
Causes
Lymphatic filariasis · West Nile virus disease
Treatment
Does not apply to the insect

At a glance

Shape
Plain brown mosquito that rests with its body parallel to the surface; Mansonia has speckled wing scales and banded legs
Family
Culicidae, subfamily Culicinae
Type
Blood-feeding dipteran insects (biological vectors)
Size
Adult a few millimetres long

Morphology

  • Culex eggs are stuck together in floating rafts; Mansonia eggs are laid in clusters under floating leaves.
  • Culex larvae hang from the surface by a long breathing siphon.
  • Mansonia larvae and pupae pierce the roots and stems of water plants with a saw-like siphon to take air, so they rarely surface.

Transmission

  • Only the female bites; Culex is most active from dusk to dawn, inside and outside houses.
  • West Nile and similar viruses: the mosquito is infected by biting birds, then bites people and horses (dead-end hosts).
  • Filariasis: microfilariae taken in a blood meal become infective L3 larvae in the mosquito and enter the skin at a later bite.
  • Mansonia bites aggressively at dusk near swamps and lakes with floating vegetation.

Reservoir: Birds (West Nile and related encephalitis viruses); Humans with circulating microfilariae (Wuchereria bancrofti); Wild rodents and other animals for some encephalitis viruses

Vector: Culex quinquefasciatus is the main urban vector of Wuchereria bancrofti worldwide and, with other Culex, of West Nile and Japanese encephalitis viruses; Mansonia carries Brugia filariasis in Asia and also W. bancrofti.

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Culex females lay rafts of 100–300 eggs on still water; Mansonia lays egg clusters under floating plants.
  2. Culex breeds in ponds, drains, septic tanks, latrines, unused pools and containers, including polluted water.
  3. Larvae (wigglers) feed in the water and moult four times.
  4. The non-feeding pupa lives just below the surface (or attached to plants in Mansonia); the adult emerges from it.
  5. Egg to adult takes about one to two weeks in warm weather.
  6. Adults rest by day in cool, dark, humid places and usually fly short distances.

Virulence factors

  • Breeding in polluted water makes Culex thrive in poor urban sanitation.
  • Culex feeds on both birds and mammals, bridging bird viruses to people and horses.
  • Night biting overlaps with sleep, so nets and screens help.
  • Resistance to insecticides is common in Culex quinquefasciatus.

Diseases it causes

Clinical picture

  • Itchy night-time bites; in children, papular urticaria.
  • West Nile: most infections cause no symptoms; a few cause fever and a small number meningitis or encephalitis.
  • Lymphatic filariasis: lymphoedema, hydrocele and elephantiasis years after infection.

Diagnosis

  • Entomology: larvae by siphon and body hairs, adults by wing scales and resting posture.
  • Testing mosquito pools for West Nile virus as an early warning of human cases.
  • Patient: filarial antigen tests or night blood smears for W. bancrofti; IgM antibodies in serum or cerebrospinal fluid for West Nile.

Treatment

Does not apply to the insect. West Nile has no specific antiviral (supportive care); filariasis is treated and prevented with albendazole, diethylcarbamazine and ivermectin in mass drug administration.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Drain, fill or treat standing water: blocked drains, septic tanks, latrines and unused pools.
  • Bed nets, window screens and repellents from dusk to dawn.
  • Removing floating water plants from ponds and channels to control Mansonia.
  • Mosquito and bird surveillance for West Nile; mass drug administration against filariasis.

Test yourself

Think of the answer, then tap the question to see it.

Where does Culex quinquefasciatus prefer to breed?

In still, often polluted water: drains, septic tanks, latrines, ponds and neglected pools.

Why are humans called dead-end hosts of West Nile virus?

Because the virus does not reach high enough levels in human blood to infect new mosquitoes; birds maintain the cycle.

How do Mansonia larvae breathe?

They insert their siphon into the roots or stems of water plants and take air from them, so they rarely come to the surface.

Which filarial worm does Culex quinquefasciatus transmit in cities?

Wuchereria bancrofti, the main cause of lymphatic filariasis.

Add to my cards (4)

Connections

← Back to the group: Arthropod vectors

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: About Culex Mosquitoes | Mosquitoes | CDC (CDC, 2024); About West Nile | West Nile Virus | CDC (CDC, 2025); CDC - DPDx - Lymphatic Filariasis (CDC, 2024); Lymphatic filariasis (WHO, 2025).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.