The Hole in Disease Modeling

The Hole in Disease Modeling Why don't most studies of climate change include molecular methods? By Jonathan Scheff Vibrio parahaemolyticus, a common scourge in India, recently found in the warming ocean waters of Alaska. Related Articles: 1 "This was probably the most convincing evidence to date of the impact of climate change on pathogen outbreaks in North America," says McLaughlin. Average daily marine temperatures in the sound had been rising steadily, the

Jan 1, 2008
Jonathan Scheff

The Hole in Disease Modeling

Why don't most studies of climate change include molecular methods?

By Jonathan Scheff
Vibrio parahaemolyticus, a common scourge in India, recently found in the warming ocean waters of Alaska.

Related Articles:

1

"This was probably the most convincing evidence to date of the impact of climate change on pathogen outbreaks in North America," says McLaughlin. Average daily marine temperatures in the sound had been rising steadily, the McLaughlin group found. During the summer harvest of 2004, water temperatures exceeded 15° C, the theorized threshold for the risk of illness from the bacterium due to the consumption of raw oysters.

The McLaughlin group also used molecular tools. Andy DePaola, of the FDA Gulf Coast Seafood Laboratory in Alaska, used pulsed-field gel electrophoresis to determine that the strain was V. parahaemolyticus O6:K18, a strain similar to one found 1,000 km south.

The use of molecular analyses such as DePaola's is uncommon in predictive climate change modeling. "There's a little bit of a disconnect in the field," says Katia Koelle, a theoretical biologist at Duke University. "The people doing molecular work don't ask questions on the climate change level, and the people doing theoretical work don't take into account molecular factors." Current modeling techniques are primarily theoretical, basically assuming that pathogens remain constant and placing them in hypothetical greenhouse conditions, without accounting for adaptation, explains Koelle.

Rita Colwell, former director of the National Science Foundation who has spent decades modeling cholera distributions, says this is a problem. "There is very little if any biological data in the climate modeling that is done," says Colwell, now chair of Canon US Life Sciences. "I feel very strongly that there is a void in contributing biological factors."

"There is very little if any biological data in the climate modeling that is done." --Rita Colwell

The field of botany makes some use of molecular techniques. In his work modeling climate and plant diseases such as Sorghum ergot and Fusarium head blight, Sukumar Chakraborty of CSIRO Plant Industry in Australia characterizes both pathogens and plants under various climatic conditions, using controlled growth chambers. In one project, Chakraborty studied several generations of the plant fungus Colletotrichum gloeosporioides under different atmospheric and climatic conditions.2 So far, he's found that the genetic fingerprint and karyotype of isolates changed for some carbon dioxide conditions, but these adaptations were not related to aggressiveness.

Chakraborty says that his research applies mostly to agriculture. "We have to think about adaptation; as the climate changes, we have to breed plants that are resistant," he says. "We try to isolate [genetic] changes that make them more susceptible or less susceptible."

Chakraborty says that even in plant pathogen research, not enough work applies molecular biology to investigate climate change. That's even more of an issue for diseases that affect humans, which is something scientists such as G. Balakrish Nair, the director of the National Institute of Cholera and Enteric Diseases in Calcutta, are trying to change.

Nair would like to determine why a new infectious serotype of cholera emerged in the 1990s. Researchers have observed increases in ocean temperatures and sea level, and Nair hypothesizes that these changes have helped trigger the observed evolution of cholera. Perhaps, he reasons, gene-transfer events take place faster in higher water temperatures. His evidence "is indirect at this point, but these are some reasons that we're working on this at great length."

Nair also studies V. parahaemolyticus, a widespread cause of diarrhea in India. He cites the Alaskan outbreak of 2004 as evidence that pathogens do evolve due to temperature change. "There are many serotypes, but we've witnessed one serotype that causes most of the cases here - 80 or 90 percent. And now, we've found it halfway across the world, in Alaska."

1. J.B. McLaughlin et al., "Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters," N Engl J Med, 353:1463-70, 2004.
2. S. Chakraborty, S. Datta, "How will plant pathogens adapt to host plant resistance at elevated CO2 under a changing climate?" New Phytologist, 159:733-42, 2002.