Tropical nasty arrives at holiday resort
MEDICAL MATTERS:Why has dengue fever broken out in Madeira, asks MUIRIS HOUSTON
YOU PROBABLY don’t think twice about really nasty infections such as malaria when planning a holiday in Europe. Well it’s time to think again: one of the tropical “nasties” has arrived in Europe via the Portuguese island of Madeira.
Dengue fever has hit the Atlantic holiday destination for the first time with a total of 18 confirmed cases and some 191 probable cases reported by authorities as of October 10th.
Dengue fever (also known as break bone fever) is a severe, flu-like viral illness that affects young children and adults. It is transmitted by the bite of an infected mosquito with Aedes mosquitoes being the type most commonly associated with the virus. This type of mosquito tends to bite more during the daytime as well as at dawn and dusk. Aedes mosquitoes travel well, particularly in cargo ships and the four subtypes of dengue virus have spread to most tropical and subtropical countries in their wake.
Dengue originated in Africa and was introduced to Asia some 600 years ago. The first recognised dengue epidemics occurred almost simultaneously in Asia, Africa, and North America in the 1780s. During the last 200 years the disease has continued to spread, reaching epidemic proportions in the last 30 years.
It is now the most important mosquito-borne disease affecting humans after malaria, with about 40 million cases of dengue fever and several hundred thousand cases of the more serious dengue haemorrhagic fever (DHF) each year. The main endemic areas are Latin America, the Caribbean, Africa, south and southeast Asia, and parts of the Pacific.
Until the outbreak in Madeira, dengue remained an imported disease in Europe – it had only been identified in travellers returning from the tropics and sub-tropics.
So what has happened to allow the dengue virus get its first foothold on the Continent? Investigations are ongoing but it is likely due to a number of climate and environmental factors. An increased harvesting of food in woodlands with a high concentration of ticks means more humans are exposed to the disease-carrying mosquito. And our own changing recreational habits probably play a part.
Research by the Public Health Agency in Latvia showed no direct correlation between high tick numbers and high numbers of reported
tick bites in a forested area near the capital Riga. Rather tick bites peaked on rain-free weekends when average temperatures rose above 15 degrees following heavy rainfall during the previous week.
These conditions are associated with an abundant growth of edible mushrooms; the good weekend weather encouraged people to go out and forage for mushrooms thereby increasing their exposure to tick bites.
Research such as this suggests it may be changes in human habits that are leading to a general increase in tick-borne disease rather than a change in behaviour by mosquitoes and other ticks. It is likely a similar behavioural change in human activity will emerge as a contributing factor for the Madeira outbreak of dengue. But with four separate elements – the virus, mosquito, wildlife such as deer and humans – in play, it may take some time to figure out exactly what is going on.
If you have been in Madeira recently and you develop flu-like symptoms within 10 days of your return you should contact your doctor. Dengue fever is quite an unpleasant illness with a high fever, headache, backache and extreme exhaustion lasting up to 10 days the classic picture. A full recovery is the usual outcome; occasionally the illness progresses to dengue haemorrhagic fever which can be fatal. But this complication is more common in people who live in endemic areas and who have had a series of infections with the virus in the past.
It is likely the increase in dengue fever seen in Europeans returning from the tropics will continue. To what extent visitors to Madeira are affected remains to be seen.
According to the Health Protection Surveillance Centre, the only way to reduce the risk of being infected is to avoid mosquito bites.
You will also find some useful protection information on hpsc.ie