Dengue fever is an unpleasant infection that is on the increase globally and often comes up in travellers’ conversations. When I moved out to Indonesia some years ago, I made an effort to contact medical colleagues as I hoped they might tell me how to get permission to work. I was invited to tea with an older missionary doctor who hadn’t practised for a couple of decades but talked of the diseases she’d hosted in her years in Jakarta.
Top of her list was a recent bout of dengue. She’d had fever and aching joints, and had been unwell for ten days. Lots of the expats had it from time to time – it hit them a bit like flu. Medical textbooks focus on the worst end of the spectrum of symptoms, describing a much nastier illness which is also called break-bone fever because along with the high temperature there are severe bone, joint and muscle aches that victims describe as feeling like broken bones.
Dengue has been a huge public health problem in tropical South-East Asia for a very long time, but it is becoming common in many cities of the developing world. There have been recent disastrous outbreaks in tropical Latin America, including the Caribbean, it is now rife in the Indian subcontinent and it continues to simmer in South-East Asia. It is a viral infection so there is no real treatment for the disease. So far there is no vaccine, although there is a race on to produce one and several are at the field trial stage. Until a vaccine is available, the only means of prevention is to avoid being bitten by the vector.
Aedes mosquitoes spread the disease, and a little knowledge of the habits of these maneaters will help to reduce the risk of being bitten. Aedes are called tiger mosquitoes because of their stripes – they look as if they are wearing black and white football socks. They seem to bite more persistently and aggressively than other mosquitoes and the bites are often very itchy.
Unlike the nocturnal mosquitoes that spread malaria, elephantiasis and encephalitis, Aedes wake at dawn and will bite throughout daylight hours. Female mosquitoes need to fuel-up on blood before their eggs can develop, and they tend to skulk near the places they’ve chosen to lay their eggs. They are fastidious about the water in which they lay, choosing pure sources such as drinking-water tanks or collections of rainwater that have been trapped in big tropical plants, tyres, etc. They are insects that I’ve often met in the gardens of plush hotels in warm places. A hotel garden full of huge tropical plants, freshly washed by a tropical downpour, or with uncovered water tanks close by and a range of scantily clad humans to feed on, must be close to insectopia for an expectant mosquito. In Indonesia the government coordinates national water tank (bak mandi) emptying days, which successfully interrupt the breeding cycle of these mosquitoes.
Whereas dark-loving, malaria-bearing mosquitoes tend to hunt at ankle-level where they will find cats, geckos or human feet to bite, Aedes browse around more and require better anti-bite precautions than the application of a little repellent to the ankles. If you are going to a region where the risk of dengue is present, it would be worth taking clothes treated with a contact insecticide such as permethrin. This you can do yourself with a Bugproof kit, such as the one from Nomad. Or you could try Craghopper’s Nosquito range of clothing, or the new Ex Officio BugAway range. Some very tightly woven materials will also foil the probings of the long mosquito proboscis.
Then, in addition to the protection that these clothes give, you will need to apply a good insect repellent: the best, like Ben’s 30, contain 30-50% DEET; if you cannot tolerate DEET because of sensitive skin, try Jungle Formula (Standard Range) or Mijex Extra which contain Merck 3535, a product that is nearly as effective. All repellents need to be reapplied frequently in sweaty environments.
Dengue fever is caused by one of four strains of an arbovirus related to yellow fever. And the reason that it is becoming an increasing problem – it affects several million people a year – is to do with the immune response people mount on being exposed to the various strains of dengue virus. After experiencing dengue fever the victim will be immune to that particular strain, but can become ill with the other three strains.
The disease process is not well understood but there is a severe form of the disease called dengue haemorrhagic fever. This tends to affect children under 14 years of age who have been brought up in regions where dengue outbreaks are common, and it probably has something to do with the victim’s immune response to the various viral subtypes to which they have been exposed. It seems that if children carry some immunity to one dengue type, and are then exposed to another subtype, the disease process can cause problems with their body’s clotting system and a dangerous level of internal bleeding can then occur. This situation requires hospital treatment with transfusions of blood products.
The more likely scenario for the traveller is that about four to six days after being bitten by an infected tiger mosquito (although the possible range of incubation time is three to 14 days) there will be a sudden onset of high fever, headache, sometimes vomiting, and muscle and bone pain. The fever will fade out between days three and five of the illness. Next there is commonly a non-raised, non-itchy dark-red rash that does not disappear if a glass is applied to it. The rash starts on the trunk and spreads to the limbs and face, and during this second phase of the illness there is often a return of the fever and possibly a little bleeding from the gums.
Most people recover within a week although they often feel a bit washed out for much longer. It is a nasty infection but – in travellers – it’s rarely dangerous. Even so, if you get symptoms you should see a doctor in case of complications, and also since fever with a dark-red rash could be meningitis which needs immediate attention and antibiotic treatment. Meanwhile the immediate first aid treatment is to take paracetamol – called acetaminophen in North America – which will help to reduce the fever and relieve the pain. Taking aspirin is not a good idea since this thins the blood and will contribute to any tendency to bleed.
Dr Jane Wilson-Howarth now works as a GP in England; she lived in ‘buggy’ Asia for 11 years but avoided mosquito-borne infections because of careful bite-prevention precautions. She is author of Bugs, Bites & Bowels (Cadogan), Shitting Pretty (Traveler’s Tales), Your Child’s Health Abroad (Bradt) and Lemurs of the Lost World (Impact Books)
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