In Europe, they say the first swallow to appear in the skies heralds summer. Here in Hong Kong, it's the first dengue fever mosquito found in traps that tell us summer's here. Every year for the past few years, we've had a warning from the mosquito inspectors, who lay traps where mosquitoes love to breed. And sure enough, the first dengue mosquitoes turned up last week. When the inspectors analysed the eggs collected in their traps, they found that 11 per cent of the eggs laid in a Fanling site belonged to the Aedes albopictus mosquito, the ones that carry dengue fever. They've also been found in Tai Po North (9.8 per cent), Sheung Shui, (5.6 per cent), Cheung Sha Wan (3.8 per cent) and Diamond Hill (2.2 per cent). Panic time? Not at all. It's merely a timely warning. Until the egg count reaches 20 per cent, the mosquito inspectors aren't worried. But what it means is that, if there are some in the traps, the mosquitoes might be breeding in the flower pots on your balcony. Not that this means you'll catch dengue fever. It's more complicated than that. The Aedes albopictus mosquitoes - also known as Asian tigers because they have white stripes on their bodies and legs - are capable of carrying dengue fever. But it doesn't mean they're all infected. They've got to get it from someone before they can pass it on. In other words, one of your neighbours has to have been bitten while on holiday in a dengue fever region, such as Thailand, the Philippines, Malaysia or Indonesia. People are usually infectious for two to seven days - generally while they're running a fever. For this reason, anyone suspected of having dengue needs to be isolated in hospital and away from mosquitoes, even if they're not seriously ill. The virus isn't immediately infectious once it gets into the Aedes albopictus mosquito. It needs to incubate and mature for a further eight to 10 days before it's capable of infecting humans. This breed of mosquito doesn't travel far. According to experts, it's a poor flyer, so there's usually a geographical cluster of cases around the first outbreak. If you know someone who has dengue fever, you need to be obsessive about keeping mosquitoes out of your home. You also should speak with building management about clearing away rubbish in the grounds. Styrofoam lunchboxes and even plastic bags can hold enough water to make a nice nursery for Aedes albopictus. The mother mosquito doesn't like deep water for her eggs, so shopping bags and other bits of rubbish are perfect breeding sites. Lastly, how do you know when you have dengue? The most common symptom is a high fever. It may get up to 42 degrees and last for seven days. Sufferers also get a terrible headache, a flushed face and excruciating pain in their bones and muscles. A common name for dengue is 'break bone disease' because it feels as if you've broken all your bones. If you've been travelling and have any of these symptoms, get checked right away and mention where you've been. At present, Hong Kong isn't a high risk place for dengue. The reason for making a fuss about mosquito control is to keep the city that way. The advice from the Department of Food and Environmental Hygiene is worth following, not just to avoid dengue, but to keep your home free of all breeds of mosquitoes: Remove stagnant water; Properly dispose of refuse, particularly lunchboxes and soft drink cans that can retain water; Cover all water containers, wells and water tanks tightly; Fill all defective ground surfaces with sand, mud or cement; Clear refuse and fallen leaves from drains and surface channels to prevent blockages; Scrub and lime-wash drains and surface sewers with alkaline detergent compound at least once a week; Properly wrap disused tyres or puncture them to prevent water being trapped; Change or remove water in flower vases or saucers under potted plants at least once a week; Ensure no stagnant water is accumulating in traps under air-conditioning units.