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SOUTH AMERICA: Climate Change Fuels Spread of Dengue Fever

Marcela Valente*

BUENOS AIRES, Mar 19 2007 (IPS) - Climate change, which has resulted, for example, in heavier and more persistent rains in South America, is forcing countries to take more proactive measures to prevent the spread of diseases like dengue fever.

Paraguay has been struck by an epidemic of the more dangerous variant, dengue haemorrhagic fever.

"Global warming increases the risk of future epidemics," entomologist Anthony Erico Guimaraes, a researcher at the Oswaldo Cruz Institute, Brazil's leading centre for the study of tropical diseases and the development of medicines to combat them, told IPS.

The rise in global temperatures "indirectly influences the spread of dengue by modifying rainfall frequency," he explained.

The head of Bolivia's Latin American Scientific Research Centre (CELIN), Dr. Franklin Alcaraz del Castillo, told IPS that the immense lagoons created by torrential rainfall in the last three months in the Bolivian Amazon "fuel the reproduction of the mosquito" that transmits the disease.

Dengue fever is a viral disease transmitted by the Aedes aegypti mosquito, which picks up the virus when it feeds on the blood of an infected person, and infects other people when it bites them. The symptoms are fever, headache and muscle pain. But haemorrhagic dengue causes intense abdominal pain, nausea and bleeding under the skin and into mucous linings.


Global warming also speeds up the development of the virus in the mosquito vector, extends the habitat of the mosquitoes and increases their capacity to adapt to colder temperatures, Argentine scientist Osvaldo Canziani, a member of the United Nations Intergovernmental Panel on Climate Change, told IPS.

That is why it is important to continue taking preventive measures, even when the outside temperature gets as low as 15 degrees, he added.

There is a consensus among scientists that global warming is largely due to human activities that emit greenhouse gases, such as the burning of gas, coal and oil.

In Bolivia, about 40,000 families have been evacuated from their homes due to flooding in the eastern and northern departments (provinces) of Santa Cruz and Beni, which are also the most affected by dengue fever. "Overcrowding, poverty, and lack of knowledge of how to defend themselves against the mosquito have aggravated the spread of the disease," Alcaraz said.

At present, 2,800 cases of dengue fever have been registered in Bolivia, according to a report late last week by the National Epidemiological Unit, but Alcaraz said that it would be necessary to thoroughly fumigate the most vulnerable areas and to be prepared for other diseases associated with the flooding, such as malaria, yellow fever and tetanus.

Brazil reported 85,000 cases of dengue fever in January and February 2007, nearly 30 percent more than for the same period in 2006. Half the cases were in the western state of Mato Grosso do Sul, which borders on Bolivia and Paraguay.

Fifty-five people came down with haemorrhagic fever, six of whom died. "In Brazil, the populace isn't mobilised to eliminate breeding sites," that is, containers with clean, still water where the mosquitoes reproduce, said Guimaraes.

In Paraguay, the epicentre of the South American outbreak, the authorities have registered some 20,000 cases, including 12 deaths. However, doctors there suspect that underreporting is huge. In the Central department alone, in the west of the country, press reports say 300,000 people are infected, and the government has not denied the claim.

As dengue fever symptoms can be flu-like, many patients self-medicate and their cases are not registered, say doctors in Paraguay. Every infected patient who is not under strict supervision and care may infect other people if mosquitoes bite him or her again.

And now haemorrhagic fever cases are appearing, which are more virulent, although not necessarily deadly.

There are four types of dengue virus. When a person contracts the disease, he or she develops immunity against the strain responsible for the infection, but becomes more vulnerable to the other serotypes. If that person is subsequently infected by another serotype of the virus, he or she may contract dengue haemorrhagic fever.

"The 1999-2000 regional epidemic of dengue fever was bad, but it was all classical dengue. Now we are also seeing cases of haemorrhagic fever," the head of the dengue unit in Hospital Muñiz in Buenos Aires, specialist in infectious diseases Dr. Alfredo Seijo, told IPS.

Cases of classical dengue have been recorded in Argentina since 1988, with peaks occurring in 1999 and 2004, when there were more dengue fever patients than this year. "Now we have seen 90 patients in Hospital Muñiz, and none of them were infected in Argentina," he said.

Before showing symptoms, these people had been in Paraguay, Bolivia or Brazil, where there are many more infected people. Aedes aegypti mosquitoes can be found in nearly all the northern and central provinces of Argentina, but only three out of a total of 172 patients acquired the infection from a local mosquito, the authorities said.

All three cases arose in the northeastern province of Formosa, which borders on Paraguay. "People travelling from a country where there is a major epidemic can unleash an outbreak here, or in other cities where they go," said Seijo, although he said the risk of contagion by mosquito bites in Buenos Aires was minimal.

In Uruguay, although Aedes aegypti mosquitoes have been found in six of its 19 departments, there had only been four dengue cases this year, all of whom had been infected abroad, director general of health at the Health Ministry, Jorge Basso, told IPS. He did not rule out a role for climate change in the spread of the disease.

However, on Sunday Uruguay's health authorities confirmed the country's first case of domestically caught dengue fever in a 30-year-old construction worker living in Salto, a city 500 kilometres from the capital, Montevideo. This is Uruguay's first domestic case of dengue fever in 90 years.

Uruguay has activated Phase One of its dengue control plan. The patient has been isolated in a clinic, houses and parks in Salto are being fumigated to kill the mosquitoes, renewed efforts are being made to get rid of breeding sites, and health personnel are on the look-out for other potentially infected persons in Salto and elsewhere in the country.

This leaves Canada as the only country in the Americas with no domestic dengue infections.

Mosquitoes, with their potential for transmitting diseases, are "extremely sensitive to climate change," Argentine Health Minister Ginés González García said in early March on a visit to the Paraguayan border. "Winds, temperature and rainfall patterns are decisive factors in their distribution and abundance."

Seijo emphasised that outbreaks of dengue fever tend to coincide with El Niño, a periodic climate phenomenon associated with fluctuations of atmospheric pressure and surface temperature in the Pacific Ocean, which has hit Bolivia particularly hard this year.

Since the 1970s, as global temperatures have risen as a consequence of climate change, the storms, torrential rains and other extreme phenomena associated with El Niño have become more frequent, intense and persistent, experts say.

There is a risk that climate change may enlarge the geographical distribution of diseases like dengue fever, malaria, leishmaniasis or Chagas' disease, and that the breeding season of the vectors that transmit them may be prolonged.

* With additional reporting from Franz Chávez (La Paz), Mario Osava (Río de Janeiro) and Raúl Pierri (Montevideo).

 
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