Didnt know if this is of any importance to any travellers...im still going Rio but will be using extra bug spray -
source - http://www.fco.gov.uk/
Dengue Fever is endemic to Latin America and the Caribbean and can occur throughout the year. In 2008, an increase in cases has been reported from several states of Brazil compared to 2007. In the state of Rio de Janeiro there is a serious outbreak of Dengue Fever, with over 32,000 cases reported between in the first three months of 2008. This represents 38% of all cases reported in Brazil in that period (source: Brazilian Ministry of Health). The Brazilian military have set up field hospitals to help treat sufferers in a bid to relieve related overcrowding in public and private hospitals.
There is no vaccine to protect against Dengue Fever and you should therefore use mosquito repellent regularly and cover up with suitable clothing to avoid being bitten. Symptoms of Dengue Fever usually begin 7 to 10 days after being bitten and include high fever with aching joints and bones and a headache. If you develop these symptoms you should consult a doctor. You should bring mosquito repellent with you, as this product is currently in short supply in Rio de Janeiro.