Disease model suggests cholera has become endemic in Haiti

Disease model suggests cholera has become endemic in Haiti

UF researchers at the Emerging Pathogens Institute (EPI) published a study last October showing that the bacterium that causes cholera has become endemic within parts of Haiti.

Creating a model of cholera transmission in the nation’s “département de l’Ouest,” the study shows evidence of established aquatic reservoirs in the region’s Léogâne flood basin. This finding stands in contrast to previous studies about cholera in Haiti.

“Many mathematical models have been made to simulate or explain the Haitian epidemic,” said Thomas Weppelmann, who analyzed data collected from the flood basin as an Environmental and Global Health graduate student working under the supervision EPI faculty members.

“Our model differs from those, however, because it assumes that the causative pathogen, Vibrio cholerae, can persist and multiply in the surface water in response to environmental factors,” he said.

Weppelmann collaborated with fellow graduate student Alex Kirpich, EPI biostatistician Ira Longini, and others to design a model that could explain data collected from the Léogâne flood basin. Léogâne is located just 15 miles from the capital, Port-au-Prince, and was at the epicenter of the January 2010 earthquake that killed tens of thousands of people in Haiti. By October 2010 Haiti was in the midst of its first cholera outbreak in over a century.

According to Weppelman, most models describing the epidemic assumed that once the bacteria enter into the surface water from human waste, they decay at a constant rate and cannot increase without additional shedding. The researchers questioned this assumption, however, considering that as an aquatic pathogen, V. cholerae is well suited to survival in tropical surface waters such as Haiti’s.

The Caribbean nation is at a similar latitude to the Bay of Bengal, where coastal ecosystems in both India and Bangladesh serve as a reservoir for the disease.

Cholera originated in the Ganges delta region in India, and is prevalent throughout Bangladesh, India, and Nepal. Many scientists believe that UN peacekeepers from Nepal accidentally brought cholera to Haiti during the response to the 2010 earthquake. Improper sewage treatment led to the disease’s dissemination into the drinking water, and people exposed to this water passed the disease to others in the unstable conditions following the natural disaster.

Kirpich, a biostatistician, ran statistical analyses on data collected from surface water samples as well as on the weekly reports of the number of cholera cases spanning from 2010 to 2014. Together, Kirpich and Weppelmann conducted a more comprehensive analysis, concluding that cholera had become endemic in Haiti. The bacteria’s growth rate in the coastal ecosystems of Haiti responded to weather changes in similar ways to its growth rate in South Asia, where it originates.

“The current study suggests that if indeed environmental reservoirs of V. cholerae have been established,” Weppelmann said, “the combination of waning acquired immunity from the initial outbreak and lack of improvements in sanitation and hygiene provide the necessary conditions for future cholera transmission in Haiti.”