Catching the bug

A serious attack involves fever, sweating, vomiting, muscle spasms, driving thirst, thumping pain behind the eyes and in the joints. Weeks pass, tossing and turning in hellish delirium. And right now, a deadly wave of dengue fever is sweeping across Asia, killing hundreds and leaving tens of thousands sick, over­whelming health services and creating panic among politicians.

The Philippines has seen more than 146,000 confirmed cases of dengue so far this year, and at least 622 Filipinos have died from it. More than 49,000 cases have been report­ed in Thailand, with 64 deaths, and some 24,000 have been treated in Bangladesh, with at least 18 confirmed deaths.

Often known as break-bone fever, dengue is carried by the Aedes aegyptimosquito, which can also transmit other potentially lethal viruses: yellow fever, an acute viral haemorrhagic disease; chikungunya, a dengue-like disease characterised by fever and joint pain; and, more recently, Zika, the virus that has been linked to microcephaly: babies born with abnormally small heads and malformed brains, neurological complications, eye and ear problems, or even still born.

The Aedes aegypti is a prolific breeder, but only the female mosquitoes feed on blood. They need the protein to produce eggs. Biting during the day, the Aedes aegypti rests out of sight in shady places, rarely travelling more than 100 metres from home base, preferring to live indoors, which means it is easily missed by insecticide fogging.

A boy plays underneath a mosquito net in Manila, the Philippines. Photo: AFP
A boy plays underneath a mosquito net in Manila, the Philippines. Photo: AFP

It can breed in the water left in an upturned bottle-cap, and it prefers to live in towns and cities, where food is abundant, whether in Asia, Australia, Africa, the lower parallels of the United States, or Central and South America. Think humid, think hot, chances are those places have it. (A sister species, Aedes albopictus, also carries dengue. It is dominant in Hong Kong and Guangzhou, and can survive at cooler temper­atures than aegypti.)

The current Asian outbreak – Malaysia’s dengue numbers are now at an all-time high – is symptomatic of a larger plague spreading around the world, driven by rapid urbanisation in the “global south” combined with global warming. Current estimates put 40 per cent of the world’s population now at risk.