Avoiding mosquito bites protects against dengue fever

By Christiane Loell Sep 27, 2010, 4:06 GMT

Munich - For several months the islands of the French Caribbean, a popular tourist destination, have been in the grip of a dengue fever epidemic. By mid-August, according to media reports, some 60,000 people there had been infected by the mosquito-borne viral disease. Seventeen died.

Dengue fever is most common in the tropics but also occurs in subtropical areas of Latin America and South-east Asia. It has influenza-like symptoms but can lead to life-threatening bleeding and shock.

Doctors advise travellers to affected regions to guard themselves carefully against mosquito bites by wearing clothing with long sleeves, applying a mosquito-repellent to their skin and using a mosquito net. A vaccine is still under development.

'In some regions an infection is always possible, but epidemics also break out regularly in countries normally not seriously affected,' said Gerhard Dobler, a doctor who works at the German armed forces' Institute for Microbiology in Munich.

Dobler said dengue fever occurred periodically in Brazil and that infections were increasing in northern Argentina and Paraguay. A number of cases have also been reported in the countries of East and West Africa, and the Philippines has seen many this year.

'Sporadic cases are also known to occur in Egypt and Jordan,' noted Tomas Jelinek, chief scientist at the Dusseldorf-based Travel Medicine Centre.

Every year more than 50 million people worldwide get dengue fever, making it the most prevalent mosquito-borne viral infection.

Jelinek said it was unclear how many Germans returned from trips abroad with dengue fever, a disease that must be reported to health authorities. 'Symptoms like fever and fatigue can be so mild that infected people don't see a doctor,' he remarked. Other symptoms include joint and muscle pain and a headache.

Dengue fever can be confused with malaria or other diseases accompanied by fever. A blood test can detect the culprit.

'The disease is treated with medications for fever and pain, and also infusions,' Jelinek said. But he warned against the painkiller acetylsalicylic acid (ASA, or aspirin), which interferes with the blood's clotting action. Paracetamol should be taken instead.

'The dengue viruses, like those causing West Nile fever, Japanese encephalitis and yellow fever, belong to the flavivirus family,' explained Matthias Niedrig, a professor at the Berlin-based Robert Koch Institute, the federal institution responsible for disease control and prevention.

The four dengue virus serotypes, whose regional distributions vary, are becoming mixed due to tourism and global freight transport, Niedrig said. 'Infection with one type won't give you immunity to the other three,' he pointed out, adding that a subsequent infection with another serotype could have more serious effects.

This presents a challenge to developers of a vaccine, Dobler said, because 'a vaccine must be effective against all types.' Otherwise people who have been vaccinated could die if infected with another dengue virus serotype.

Experts say the reason a second infection can be fatal is unclear. According to one theory, antibodies produced by the first infection wreak havoc with the immune system during the second infection. Doctors hope to have a vaccine in a few years.

Dengue fever is transmitted by Aedes mosquitoes. Pesticides virtually eliminated Aedes aegypti, also known as the yellow fever mosquito, 50 years ago in Europe. Aedes albopictus, or Asian tiger mosquito, is meanwhile said to be spreading in Europe, among other places, but is not considered to be a primary transmitter of dengue fever.

Dobler said yellow fever mosquitoes preferred habitats near human settlements. 'They lay their eggs in puddles of water in scattered car tyres, flower vases and rainwater tanks,' he noted. Dengue fever is an urban disease, he said, occurring mostly in areas with poor sanitary conditions.