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Student research: Micah Hahn seeks environmental clues to deadly virus outbreaks

August 2, 2011

For people in rural Bangladesh, poverty, minimal healthcare and a lack of infrastructure pose enormous challenges to their basic quality of life. A new problem has recently emerged that has proven deadly and daunting. Nipah virus (NiV) has been spreading across South Asia, and it has been fatal in three-quarters of 152 reported cases in Bangladesh.

Micah Hahn
Micah Hahn

Micah Hahn, a Ph.D. candidate in the Nelson Institute Environment and Resources program, is searching for environmental conditions that factor into NiV outbreaks.

Hahn says her research "falls under the field of landscape epidemiology, which basically encompasses the idea that we can think of landscape patterns as potential risk factors." She says understanding the relationship between land use and other environmental factors and the spread of disease may enhance our knowledge of disease ecology and lead to preventative measures.

According to the World Health Organization, Nipah virus was first discovered in Malaysia in 1999. It causes encephalitis, respiratory disease and other severe illnesses. The virus has periodically emerged in several South Asian countries and in Australia, and each outbreak has had a fatality rate of 40 to 75 percent. NiV was first identified in Bangladesh in 2001, and since then there have been eight more known outbreaks.

The International Center for Diarrhoeal Disease Research in Bangladesh (ICDDR-B) has taken a leading role in Nipah virus research. Working in part with the ICDDR-B, Hahn has had the chance to work with leading professionals in the world of epidemiology.

"I'm working with the infectious disease branch," she explains. "The project leader is an epidemiologist; there are anthropologists, veterinarians and wildlife specialists. My part covers the ecology aspect."

Specifically, Hahn is looking at the habitat of fruit bats, which have been identified as the natural host of Nipah virus. Commonly known as Indian flying foxes, the fruit bats are highly attracted to a sweet sap excreted by date palm trees. During the winter months, villagers tap the date trees and collect the sap in small clay jugs for their own consumption. Hahn and other researchers believe that Nipah virus is spread from fruit bats to humans. The bats contaminate the sap in the jars by salivating and excreting in the containers. Local residents drink the sap and become infected.

Clay jugs used to capture date palm sap
Clay jugs are traditionally used
to capture date palm sap.

"The virus is occurring in very specific locations, and that's what we're trying to figure out," Hahn says. "People are collecting sap all over Bangladesh, yet only certain villages are affected by the disease."

Hahn and her colleagues plan to compare villages that have experienced outbreaks with others that have not.

"In January we're starting a project that is going to be a case control study," Hahn explained. "There are many villages with cases, but there have been lots without. To do a case control study, you go to all the case villages and a sample of control villages and you chart the differences. That may tell us why some places are affected by the disease and others aren't."

Hahn's study will include visits to fruit bat roosting sites, and she plans to gather detailed data on trees in the area. "I'll be doing a tree census by counting trees, looking at the species, canopy cover, tree diameter, and whether the trees are old versus young," says Hahn. "Then I'll map them and see if there is something about the roosting sites that changes in case and control villages."

This type of case control study is relatively new, according to Hahn. "What they've [epidemiologists] previously done is individual-level case control studies, where they find all the people that got sick, select controls, interview both groups and try to narrow it down to why one person got sick and another didn't," Hahn explains. "Instead of doing individual controls, we're doing village-level controls, something that is relatively novel in epidemiology."

Hahn plans to look at even larger patterns of landscape and disease occurrence. She's using remote sensing imagery in connection with where outbreaks of Nipah virus have occurred, hoping that understanding the connection between regional geography and the prevalence of the disease will lead to answers.

Fruit bats
Fruit bats have been identified as the natural host
of Nipah virus. Photo credit CC/Sergey Yeliseev.

"We're not only researching on the small scale, but also on the large scale, looking at bigger patterns," Hahn says. "What is the percent of deforestation versus forested areas around the case areas? Is the forest more fragmented? Maybe bats really like dense forest. In order to learn more, we're looking at the habitat for the bats."

Working on the project under her advisor Jonathan Patz, a professor who holds appointments in both the Nelson Institute and the Department of Population Health Sciences, Hahn hopes to return to Bangladesh in January for up to eight weeks. She suspects she will be training a field team to assist in her research of fruit bat habitat.

Meanwhile, researchers at the ICDDR-B will work on social factors to help prevent the spread of Nipah virus. Hahn says that could be as simple as persuading villagers not to consume raw date palm sap, but to cook it first. Sap collectors may also need to place protective barriers over the clay pots that they hang from the palm trees. Hahn says the researchers are engaging local villagers to brainstorm ways to curb the disease while preserving their culture and traditional practices, and her work is but one part of a broad interdisciplinary effort to understand and control this emerging disease.

Jenny Peek is a senior majoring in journalism and environmental studies.