Hotter, drier, sicker? How a changing planet breeds disease May 11, 2024

Dengue has become an increasing global health concern © BAY ISMOYO / AFP/File

By AFP - Agence France Presse

Bangkok (AFP) - Humans have made our planet hotter, more polluted, and increasingly less hospitable to many species, and these changes are driving the spread of infectious diseases.

Hotter, drier, sicker? How a changing planet breeds disease

Warmer, wetter climates can expand the range of vector species, such as mosquitoes, while habitat loss can bring disease-carrying animals into closer contact with humans.

New research reveals the complexity of the effects, with our impact on the climate and the planet turbocharging some diseases and altering the transmission patterns of others.

Biodiversity loss appears to play an extraordinary role in the rise of infectious diseases, according to a paper published in the journal Nature this week.

The study analyzed almost 3,000 datasets from existing studies to see how biodiversity loss, climate change, chemical pollution, habitat loss or change, and species introductions affect infectious diseases in humans, animals, and plants.

The study found that biodiversity loss was by far the biggest driver, followed by climate change and the introduction of new species.

Parasites target the most abundant species that offer the most potential hosts, explained senior author Jason Rohr, a professor of biological sciences at the University of Notre Dame.

And species with large populations are more likely to “invest in growth, reproduction, and dispersal, to the detriment of defenses against parasites,” he told AFP.

However, the rarer and more resilient species are vulnerable to biodiversity loss, which leaves us with “more abundant and parasite-competent hosts”.

The warmer climate produced by climate change offers new habitats for disease vectors, as well as longer reproductive seasons.

“If there are more generations of parasites or vectors, there could be more diseases,” said Rohr.

Change in transmission

However, not every human adaptation to the planet increases infectious diseases.

Habitat loss or change has been associated with a drop in infectious diseases, largely due to sanitation improvements resulting from urbanization, such as piped water and sewage systems.

The effects of climate change on disease are also not uniform around the world.

In tropical climates, warmer and wetter weather is causing an explosion in dengue fever.

However, drier conditions in Africa could reduce the areas where malaria is transmitted in the coming decades.

Research published in the journal Science this week has modeled the interaction between climate change, rainfall, and hydrological processes, such as evaporation, and how quickly water infiltrates the soil.

It predicts a greater decline in areas suitable for disease transmission than predictions based on rainfall alone, with the decline starting from 2025.

The study also reveals that the malaria season in parts of Africa could be four months shorter than previously estimated.

The findings are not necessarily good news, warned lead author Mark Smith, associate professor of water research at the University of Leeds.

“The location of areas suitable for malaria will change,” he told AFP, with the Ethiopian highlands among the regions likely to be affected.

People in these regions may be more vulnerable because they have not been exposed.

Populations are predicted to grow rapidly in areas where malaria will remain or become transmissible, so the overall incidence of the disease could increase.

Forecasting and preparation

Smith warned that very adverse conditions for malaria could also be very adverse for us.

“The change in the availability of water for drinking or agriculture could be very serious indeed.”

The links between climate and infectious diseases mean that climate modeling can help predict outbreaks.

Local temperature and rainfall forecasts are already used to predict dengue outbreaks, but they offer a short timeframe and can be unreliable.

An alternative could be the Indian Ocean Basin-wide (IOBW) index, which measures the regional average of sea surface temperature anomalies in the Indian Ocean.

Research also published in Science this week analyzed dengue data from 46 countries over three decades and found a close correlation between IOBW fluctuations and outbreaks in the northern and southern hemispheres.

The study was retrospective, so the predictive power of the IOBW has yet to be tested.

But monitoring could help authorities better prepare for outbreaks of a disease that is a major public health concern.

Ultimately, however, dealing with the rise in infectious diseases means dealing with climate change, said Rohr.

Research suggests “that the increase in disease in response to climate change will be consistent and widespread, further emphasizing the need for reductions in greenhouse gas emissions,” he said.

sah/tym

© 2024 AFP