This deadly fungal disease could use climate change to mobilize

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Popular science

The vast majority of the 10,000 cases of Valley Fever diagnosed each year in the United States occur in Arizona and California. In these two states, the environment and weather conditions – a dry desert with rainy seasons – create the conditions that Coccidioides the fungus, which causes the disease, needs to survive and thrive.

But as the climate changes, temperatures rise and rain patterns change. At the same time, by 2100, the mushroom range will expand, resulting in a 50% increase in the number of valley fever cases, according to a new published model. in the GeoHealth log. At the present time, rain and temperature limit the fungus to its current territory, but climate change is lifting some of these environmental barriers.

"We know that valley fever and the fungus that causes it are limited to hot, dry places, namely desert climates," said lead author Morgan Gorris, Researcher at the Department of Earth System Sciences at the University of California at Irvine. . "In response to climate change, we thought that there could be more areas that this mushroom could live in the future."

the Coccidioides Fungi grow in the soil in low rainfall areas, then dry out during periods of drought and create spores that can be blown into the air by wind or other disturbances. The spores are then inhaled into the lungs, causing fever in the valley. The disease is usually mild and causes coughing, fever and chills. However, it causes about 200 deaths each year in the United States, particularly among the elderly or with weakened immune systems. In comparison, an average of about 120 people die each year from West Nile virus.

The study compared rainfall, heat and other environmental data to valley fever rates to identify environmental conditions correlated with the incidence of the disease. Then he used the information on this relationship to predict where the disease would be regularly found under the climatic conditions expected in future climate models. The model estimated that areas regularly affected by valley fever would extend into most western states and to the north.

"This will cross Oklahoma, Colorado and Wyoming, drier areas," says study author James Randerson, a professor in the Department of Earth System Sciences at the University of California at Irvine. "He will move to the area where the Dust Bowl was present. This is worrisome because we know that past conditions have led to dust production "and that dusty conditions can interact with and increase fever levels in the valley. However, in northern California and parts of Oregon, climate change is expected to result in increased precipitation, which would protect against fungi even if temperatures rise.

The study also showed that if the level of climate change was more moderate (if fossil fuel consumption decreased and if steps were taken to stop warming), Valley fever would not have a expansion as important. "This has really highlighted the importance of the positive impact of mitigation measures on climate change on public health," Randerson said.

At present, only some states report cases of Valley fever to the Centers for Disease Control (CDC). "Our maps and projections suggest that it would be really beneficial for peripheral states to report more cases to see if the disease is evolving," Randerson said. It would also help educate public health officials and physicians who do not usually meet the disease.

"As a doctor, it's very difficult to adapt to diseases that you do not have a habit of seeing," says Sarah Coates, a dermatologist at the University of California at San Francisco. "It's a fundamental question we have to answer as part of medical training: talk about climate change and the diseases that are sensitive to it." San Francisco usually does not see many cases of valley fever – about one a year. But in 2016, the region recorded more than normal cases of illness, which could be linked to heavy rainfall that year. Coates has consulted on cases where the fungus has affected the skin, which is a sign that the disease is severe. "For me, it showed that it was important to add that to the list of things that could be well," she says. "All these diseases, if it's not something you're trained to recognize, you might not have the tools to properly diagnose them."

Models can help doctors recognize the types of diseases they may encounter in the near future, as well as the climate in which they live. "It's helpful to use the best data we have, okay, especially in those states, I'm going to train people to add it to their list of sickness cases. As an educator, it makes a difference, "says Coates.

Gorris hopes that public health officials will be able to use this study to develop disease surveillance programs. "It would be beneficial to help the community understand the risk of disease and provide data for future research."

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