It was not the sort of welcome a visiting royal expects. During his recent visit to Rio de Janeiro's Cantagalo shantytown, Prince Charles was preceded by the strange spectacle of a truck spraying insecticide. One in 10 of Brazil's workforce has been struck down in the worst outbreak of dengue fever - a mosquito-borne disease - in the country's history. According to the BBC 44,000 cases have been reported, but the estimated total number of victims could be as high as 430,000. Twenty-four people have died and victims are facing long queues as hospitals in Rio de Janeiro, where a third of the cases has occurred, are struggling to cope.
Dengue fever causes flu-like symptoms such as a high fever, rash, severe headache, muscle and joint pains, but is only rarely fatal. Four closely related viruses cause dengue fever. Recovery from infection by one provides lifelong immunity against that strain, but not against the others. Evidence also suggests that repeated infection causes a higher incidence of the much more dangerous dengue haemorrhagic fever (DHF), a strain which causes internal bleeding and can be fatal. This latest Brazilian outbreak has had a particularly high incidence of DHF and hospitals are running out of blood needed for transfusions.
The mosquitoes which spread dengue fever are found in tropical and sub-tropical regions. They breed in stagnant water, and prefer manmade storage containers, so urban areas where household water storage is common - and especially where waste disposal is inadequate - are at unusually high risk of the disease. Since there is no vaccine available at the moment, the only way to combat the disease is to target the means of transmission. The dramatic increase in the prevalence and duration of epidemics during recent decades has been partly blamed on the erosion of the mosquito eradication programme. Before 1970 only nine countries had experienced an outbreak; today dengue fever is endemic in over 100 countries.
Other factors influencing the rapid spread of the disease has been increased air travel, as well as the international trade in used tyres (a favourite breeding ground of mosquitoes). Environmentalists warn that mosquito-borne diseases such as dengue fever, West Nile virus, yellow fever and malaria will increase dramatically due to global warming. The expected rise in rainfall and mean temperature will greatly enlarge the mosquito's potential habitat, since mosquitoes prefer regions where the temperature does not fall below 50 degrees Fahrenheit (10 degrees Celsius).
Health officials in Brazil fear the end is not in sight. "March and April will be worse," Alexandre Adler, a biologist at Rio's Federal University, told Associated Press. "With the recent rains and the concentration of infected people, we will see a big increase."
