RIO DE JANEIRO (Thomson Reuters Foundation) - Malaria has resurfaced in Rio de Janeiro as a historic drought in Brazil's southeastern region is driving mosquitoes in the Atlantic Forest to seek water in areas frequented by people, such as waterfalls.
"The mosquitoes in this area habitually lay their eggs in water collected in bromeliads (plants), deep in the forest," said infectologist Alberto Chebabo.
"So the drought probably forced them to look for water in more humid places, such as rivers and waterfalls, where people often go at this time of year," Chebabo, of the Federal University of Rio de Janeiro, said in a recent interview.
"This may have increased contamination."
Rio de Janeiro and most regions in southeastern Brazil have been considered malaria-free zones for the past 40 years, with just a few cases reported each year. Malaria is only endemic in the northern region, particularly in the Amazon basin.
In the past three weeks, 14 cases have been reported in Rio de Janeiro state, compared with eight in all of 2014, according to the Health Ministry.
The people who were infected had travelled to dense Atlantic Forest areas in the interior of Rio state. The cases are not considered severe, as the mosquitoes in the area transmit the Plasmodium vivax parasites, which are less virulent than the Plasmodium falciparum, the deadliest species.
Southeast Brazil, home to the country's wealthiest cities, is grappling with the worst drought in at least 80 years as unusually low rainfall since 2013 has resulted in rivers and reservoirs drying up.
Scientists have cited the continuing deforestation of the Amazon as a contributing factor, as it reduces the amount of humidity that rises from the forest and travels south in the form of rain.
Malaria is caused by parasites that are transmitted through the bites of infected female mosquitoes. The parasites travel to the liver, invade liver cells and then attack red blood cells, which carry oxygen through the body. Symptoms include fever, headache, chills and vomiting.
The disease killed an estimated 584,000 people in 2013, mostly among children in Africa, out of about 198 million cases globally, according to the World Health Organization.
Mortality rates have dropped 47 percent globally and 54 percent in Africa since 2000, WHO data show.
Health authorities in Rio say the recent cases do not represent an epidemic, and researchers are investigating how victims became infected.
"There is no reason to panic, this is not the worst kind of malaria and the numbers are still low," said Alexandre Chieppe, epidemiology chief at Rio state's Health Secretariat.
The 14 cases occurred in areas where malaria had already been registered in the past, and there are no new areas of contamination, he said.
(Editing by Tim Pearce)
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