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BUENOS AIRES, Feb 18 2011 (IPS) - One of the potential impacts of climate change that arouses most concern is an increase in diseases transmitted by tropical insects, like Chagas’ disease, Argentina’s main endemic illness.
However, while they are aware of shifting climate zones, experts consider the biggest threat of expansion of Chagas’ disease to arise not from global warming, but from inadequate control of its transmission vectors (insect carriers), which have already been eliminated in Brazil, Chile and Uruguay.
“Vectors capable of transmitting the disease are present in 19 of Argentina’s 24 provinces,” epidemiologist Sergio Sosa-Estani, head of the vector-borne disease unit at the Health Ministry, told IPS. “In some areas, the vectors are under control, but if vigilance lapses, they are back within two years.”
His unit has registered close to two million infected persons, 30 percent of whom will go on to develop heart problems.
Chagas’ disease has an early acute phase, during which patients can be treated and cured with antiparasitic medicines. But if it is not detected in time, chronic illness sets in and can lead to life-threatening heart and digestive system disorders. Initial symptoms of the infection are fever, vomiting, shortness of breath and convulsions.
The disease is caused by the protozoan parasite Trypanosoma cruzi, which is transmitted to humans by Triatoma infestans, a blood-sucking insect known in the Southern Cone of South America as the “vinchuca”, which lurks in crevices in the mud walls or thatched roofs in the houses of the rural poor.
When it bites a person to ingest blood, the vinchuca bug defecates on the skin, depositing parasites close to the wound. Scratching the itchy bite introduces the parasites into the bloodstream.
Transmission via the insect vector is the infection route in 90 percent of cases. It can be controlled by spraying insecticide to kill the vinchuca bugs, followed by regular inspections to check for any reappearance of the insects.
Congenital transmission of the infection from mother to foetus through the placenta during pregnancy is also possible, as well as through blood transfusions and organ donations. But all these transmission routes are susceptible to control and cure.
According to Sosa-Estani, vinchuca reproduction is sensitive to the environment, and temperature is a key factor. “That’s why there aren’t any of these insects in Tierra del Fuego, the southernmost province of Argentina, nor in Alaska,” he said.
The vinchuca needs a favourable microclimate, such as exists in rural areas in the northern Argentine provinces, where there are bare mud walls, thatched roofs and chicken runs close to the houses.
The habits of the insect are stable, Sosa-Estani said, but “one cannot rule out a change that might provoke a long-term alteration,” such as longer lasting maximum temperatures that would favour its reproductive cycle.
“Scientists are permanently monitoring the situation. A potential impact on vector dynamics due to climate change cannot be disregarded, but there is no imminent threat of this happening,” he said.
He emphasised that to keep the disease under control, houses must be sprayed, walls must be smoothed or plastered, thatched roofs should be avoided, and hen runs or animal pens should not be located close to bedrooms. Boxes containing clothing or shoes may also be hiding places for vinchucas and should be removed.
“If a house is tidy and has a proper roof and walls, you can see the insects at once and you can spray them,” he said. “The goal of eliminating Chagas’ disease transmission will take at least six months of uninterrupted vector control actions that must be established and maintained over time.”
Sustained action depends not only on the national government, but also on the provinces, which are autonomous in matters like fumigation and vector control.
There were 300 new cases a year of Chagas’ disease in the 1960s, a number that fell to barely six new cases in 2001. However, because of the severe social and economic crisis that broke out that year, control measures were relaxed, and the number of new infections began to rise again.
Biologist Ricardo Gürtler, a researcher on vector-transmitted diseases, told IPS it was “very difficult to predict the true impact of climate change on the vinchuca and in general terms on the transmission of Chagas’ disease.
“If houses are well constructed and sealed, so that the insects can’t get in, or if control measures are taken when the vinchucas try to colonise the home, the impact of climate change will be mitigated,” he said.
Gürtler, a professor at the state University of Buenos Aires who has been working to beat Chagas’ disease for the last 30 years, said that the recent appearance of a vinchuca bug in Chubut province, in the southern region of Patagonia, should not be misinterpreted.
“The insect appeared because of internal migration of people, from areas where vinchucas live to places where they don’t,” he said. “The insects are transported along with luggage, furniture or produce, but climate change plays no part in it.”
Gürtler said some areas of Argentina “still require continuous hard work at the national and provincial levels” to curb transmission of the disease. He stressed the difficulties of implementing national government policies at the local level.
“Implementing the policies and sticking to them strictly until the goals have been achieved is perhaps Argentina’s major historical weakness in regard to controlling Chagas’ disease and other public health problems,” he concluded.
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