FACTBOX-Mosquitoes spread deadly dengue fever across globe

(Reuters) - Rapid urbanization has helped to fuel the spread of dengue fever to more than 100 countries, as the mosquitoes which carry the disease find fertile breeding grounds in cities.

Here are some facts about dengue, which poses a threat to 2.5 billion people, or two-fifths of the world's population, according to the World Health Organisation (WHO).

WHAT:

-- A severe, flu-like illness, caused by four distinct, but closely related, viruses known as Dengue 1, 2, 3 and 4.

-- Known colloquially as bone-break fever for the severe muscle and joint pains it induces, the disease only causes death when it develops into a more severe form, dengue hemorrhagic fever (DHF).

HOW:

-- Virus-carrying female Aedes mosquitoes infect humans with the disease when they bite. It takes 4 to 7 days before a person shows symptoms of the disease.

-- After incubating the virus for 8 to 10 days, the black and white striped mosquitoes can transmit it to susceptible individuals for the rest of their two-week life span.

WHEN:

-- Dawn and dusk are peak biting times for the silent, aggressive Aedes, whose name comes from the Greek for "unpleasant". Dengue can peak during rainy seasons when mosquito eggs hatch in stagnant water.

WHERE:

-- Tropical and subtropical regions. It is more common in urban areas where Aedes like to live.

-- Southeast Asia and the Western Pacific are most seriously affected but dengue is now endemic in more than 100 countries around the world, including many in Africa, the Americas and the eastern Mediterranean.

GLOBAL SPREAD:

-- Urbanization provides conducive breeding and feeding conditions for dengue-carrying mosquitoes.

-- The most important dengue mosquito is the predominantly urban species Aedes aegypti, which bites indoors in daytime and does not like to fly very far to find victims.