CARAZ, Peru — Seventeen years ago, Liliana Salvador Ibáñez's year-old son came down with a high fever, then broke out with bleeding lesions on his legs. Four years later, his brother came down with the same illness, and a few years later a young niece died. All had bartonellosis, also known as Carrion's disease, which is caused by a bacterium transmitted by a sand fly.
In this Andean mountain valley in central Peru, mothers observed that there was an outbreak every four years or so. The cycle intrigued Dr. Larry Laughlin, now dean of the school of medicine at the Uniformed Services University of the Health Sciences in Bethesda, Md.
Comparing disease statistics with climate data, he found that the outbreaks roughly coincided with El Niño, the warm Pacific Ocean current that brings higher temperatures and rainfall to this part of Peru. Researchers in Lima found a similar correlation with hospital admissions for diarrheal illnesses, especially among children in the shantytowns ringing the sprawling capital.
In tropical countries like Peru, health experts are keeping a close eye on climate change. Rising temperatures can change the way diseases behave, while collateral effects — from the retreat of glaciers that provide vital drinking and irrigation water to more frequent, intense storms and flooding — increase the burden on developing economies.
As diseases like dengue, bartonellosis and malaria spread, pressures mount on already understaffed, underfunded health services. As crops dry up and farmers migrate to urban shantytowns lacking clean water and basic sanitation, the burden is amplified.
"If the environmental impacts are unavoidable, the health sector needs to be mobilized so that the health impacts become avoidable," said Dr. Carlos Corvalán, Pan American Health Organization senior adviser on sustainable development and environmental health in Brazil.
Carrion's disease, once found in a few valleys, has crept up the mountainsides. The disease, readily cured with antibiotics, must be treated early, as later stages render patients extremely vulnerable to potentially fatal secondary infections. Illnesses like malaria and diarrhea hit children particularly hard and can leave long-term, debilitating effects that extract a high cost from tropical countries.
But while it is tempting to conclude that warmer temperatures have created a more hospitable environment for disease vectors like the sand fly, it may simply be that humans have carried the bacillus to a place where it has found more susceptible hosts.
"It's really complicated to sort out how much is attributable to climate change," said Dr. Mary Wilson, associate professor of global health and population at the Harvard School of Public Health. Nevertheless, "many infections, including dengue, yellow fever, hanta virus, bartonellosis and leishmaniasis, are very sensitive to climate and to temperature, humidity and rainfall."