Dengue fever infections have been spreading rapidly in South America. More than 700 deaths have been confirmed in Brazil this year, prompting local authorities to declare a state of emergency.

The mosquito-borne disease causes high fever and severe headaches, as well as pain in muscles and joints. In severe cases, it can be fatal.

Brazil has reported more than 2 million cases and at least 715 deaths since January.

The country's health ministry says the number of infections so far this year is already the highest of any year since records began in 2000.

Cases have been especially surging in populous regions, such as the states of Sao Paulo and Rio de Janeiro, as well as the capital Brasilia.

Continuing high temperatures and humid conditions due to climate change and the El Nino weather phenomenon are said to be behind the rapid spread of the outbreak.