Amazing stuff!
"Of the hundreds of parasites known to infect humans, more than half depend on water. Some, like Giardia and Cyclospora, spread directly through contaminated drinking water or lurk on the surface of poorly washed lettuce. ...
One might assume that drought, which dries up water sources, would help curb the spread of these diseases. This assumption sometimes holds true:
In the early 2000s, for example, a major drought in Kenya reduced schistosomiasis cases in humans by killing off the snails that transmit it. And chytrid fungus, which spells doom for amphibians around the globe, tends to spread poorly under dry conditions.
In other cases, however, drought actually amplifies infectious pathogens that rely on water.
In the 2020s, when drought-induced water shortages forced people in the Horn of Africa to rely on unsafe water sources, major cholera outbreaks followed.
Two years ago, a particularly dry summer in California helped spark one of the largest outbreaks of avian botulism ever recorded.
And now, scientists suggest drought is to blame for Brazil’s first yellow fever outbreak in almost 80 years, even though the disease is spread by mosquitoes. “Species are adapting,” ...
In a review paper published last week in Trends in Ecology and Evolution, scientists set out to investigate this counterintuitive “drought-disease paradox.” By synthesizing nearly 100 previous studies, the authors identified three main mechanisms that determine how a given pathogen will fare when water dries up. “ ...
The researchers found that, as drought dries up rivers and ponds, animals are forced to congregate around a region’s few remaining [and shrinking] watering holes, creating more opportunities for pathogens to spread. ...
Drought, which does more than just reduce available water, can also influence the health of parasites and hosts alike. As water evaporates from freshwater and marine ecosystems, for example, salinity rises. Increased salt concentrations were good news for oyster-infesting Perkinsus parasites but bad news for invasive copepods, which struggled to infect their tilapia hosts during a drought in South Africa. Stress from high temperatures, dehydration, and other drought-induced risk factors, meanwhile, can weaken hosts and make them more susceptible to infection. ..."
From the highlights and abstract:
"Highlights
Drought is becoming a defining ecological force, yet its consequences for infectious diseases remain difficult to predict across systems.
Emerging evidence shows that water limitation can intensify many water-associated diseases, challenging assumptions that drying suppresses transmission.
Rather than acting solely as a climatic stressor, drought restructures transmission by altering host aggregation, parasite persistence, community composition, and contact networks across space and time.
Divergent disease responses to drought can be explained through three recurring mechanisms: the concentration of interactions, the ecological filtering of communities, and spatial heterogeneity in transmission.
Viewing drought as a multiscale ecological restructuring process provides a general framework for predicting disease outcomes in an increasingly water-limited world.
Abstract
Droughts are intensifying worldwide, reorganizing ecosystems and threatening biodiversity and human health. Yet their effects on infectious diseases are poorly understood and sometimes paradoxical, with water limitation often amplifying water-associated infections.
This complexity arises because drought not only reduces water availability but also restructures the host–pathogen interactions that govern transmission. Synthesizing theory and empirical evidence from water-associated diseases, we identify three ecological mechanisms through which drought modifies infection dynamics:
concentrating organisms into shrinking refugia,
selectively favoring drought-tolerant hosts, vectors, and pathogens, and
amplifying transmission heterogeneity across landscapes.
By linking hydrological change to core epidemiological and ecological processes, this framework highlights parasite traits and strategies likely to be favored during drought while providing a foundation for forecasting infections in a water-limited world."
ScienceAdviser
