What will be the effects of climate change on disease transmission?

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New research explores the effects of climate change on disease transmission in a shellfish model. Bisual Studio/Stocksy
  • The researchers studied the effects of different temperature regimes on a crustacean model of disease transmission.
  • They found that different temperature regimes affect disease transmission in complex ways.
  • They concluded that further research into how temperature patterns affect host-pathogen dynamics is crucial to predicting the effects of climate change on human and environmental health.

Researchers to predict that climate change will increase the Earth’s average temperature, cause temperature fluctuations, and increase the frequency and intensity of extreme weather events. How these changes will affect infectious diseases and impact Human health, Agricultureand wildlife that remains to be seen.

Research shows that temperature variance can alter host-pathogen dynamics. A study found that daily temperature fluctuations increase malaria transmission, and another one suggested that short-term temperature fluctuations lead to reduced transmission.

Further away research shows that how extreme heat events affect host-pathogen dynamics may also depend on the magnitude, duration, and intensity of the heat wave.

For example, a study study of a parasitoid-insect interaction found that a 5°C increase in heat wave increased parasitoid size while a 10°C increase reduced parasitoid growth.

Knowing how host-pathogen dynamics respond to temperature variations could help researchers and policymakers prepare for the effects of climate change.

In a recent study, researchers led by Dr Pepijn Luijckxassistant professor of parasite biology at Trinity College in Dublin, Ireland, studied the effects of different temperatures on host-pathogen dynamics.

They found that temperature variations alter pathogen-host interactions in complex ways, which can affect disease dynamics in unexpected ways.

“Here we show that the temperature variation with each of the traits we measured […] reacts uniquely to different kinds of temperature variations,” said Dr. Luijckx Medical News Today. “Since our mathematical models of disease spread rely on many variables, and our results show that each of them can react uniquely to changes in mean temperature and variance, predicting how global warming can alter the diseases can be incredibly complex.”

The study appears in eLife.

For the study, the researchers looked at the effects of different temperatures on small crustaceans called Daphnia magna alongside his intestinal parasite, Ordospora colligata.

Researchers frequently use Daphnia in research on ecological model systems, and Ordospora transmission is representative of classic environmental transmission, similar to viral infections such as SARS-CoV-2.

They then subjected the crustaceans alongside their parasites and a placebo infection as a control to three temperature regimes for 27 days:

  • constant temperature regimes ranging from 50°F (10°C) at 82.4°F (28°VS)
  • daily temperature variations ±3°C
  • constant temperature regime with a 3-day heat wave increasing temperatures by 6°C

The team selected temperature regimes to mimic temperature events that occur in the study subjects’ natural environments, such as rock pools and small ponds.

In total, the researchers observed temperature effects in 492 individuals. During the experiment, they assessed the longevity of the host, fecundity – the ability to produce offspring, infection status and the number of Ordospora spores in the host’s intestine.

The researchers found that, regardless of the temperature regime, Ordospora achieves optimum performance at approximately 66.2°F (19°C).

Although there was a reduction in infectivity and spore load in Ordospora-exposed Daphnia in fluctuating temperatures, parasite infectivity following a heat wave was almost the same as that maintained at a constant temperature.

The researchers noted that the effects of temperature variation differ depending on the average background temperature and how close it is to the optimum temperature.

For example, the spore load at 60.8°F (16°C) differed by nearly an order of magnitude between fluctuating temperature regimes – at 86 spore clusters – and heat waves: 737 spore clusters .

“That a heat wave of 6°C above ambient temperature could result in a level of disease burden almost 10 times higher at 16°C compared to fluctuating temperatures was remarkable,” said Dr Lujickx . “Furthermore, the fact that this same heat wave, when applied at different average temperatures, results in no difference with fluctuating temperatures or even an opposite result was unexpected.”

Host physical condition was generally reduced by exposure to Ordospora spores or experience a variable temperature regime. The researchers found that Ordospora-exposed Daphnia experienced an 8% reduction in reproductive success at constant temperatures and a 24% reduction in daily fluctuations compared to controls without Ordospora.

This, they say, means that in some circumstances the parasites may be able to acclimate to new temperatures faster than their hosts.

To explain their findings, the researchers noted that, according to the temperature variability assumption, as the parasites are smaller than their hosts, they in turn have a faster metabolic rate. In unpredictable environments, such as a heat wave, the parasites would therefore have an advantage over their hosts.

They noted that host resistance might also decrease due to a barter between energy demand for acclimatization and immunity against pathogens thriving.

Dr Luijckx said that although this is the most promising explanation, some aspects of their findings remain unclear: “Although this theory may explain the observed increase in the number of spores of the pathogen at 16℃, it cannot, however, explain why we see that the outcome depends on the average temperature.Other theories, however, have suggested that when the disease has a lower temperature tolerance than its host, it may lead to reduced performance of the disease at temperatures that exceed its tolerance.

The researchers concluded that improving their understanding of temperature variation on host-parasite dynamics is key to predicting disease dynamics as the climate changes.

The team noted several limitations to their findings. Dr Luijckx explained that because they only conducted their experiments on one species of water flea and one disease, they don’t know if their findings can apply to other organisms and lead to higher levels. high levels of disease in livestock, agriculture or disease vectors.

He added: “In addition, our study was conducted at the individual level. To fully understand disease outbreaks and dynamics, we would need to test how temperature variations and extreme weather conditions affect disease at the population level. We plan to do such experiments soon.

“We must be careful in extrapolating these results to homeotherms like humans, whales and larger charismatic endangered species,” Dr. Joseph K. Gaydos, VMD, Ph.D.chief scientist at the University of California, Davis School of Veterinary Medicine, said DTM. Dr. Gaydos was not involved in the study.

“Yet, that said, what happens to very small, even microscopic, creatures has a huge effect on much larger species. Imagine what parasitic changes in krill – a small poikilothermic oceanic plankton – could do to krill populations and how it might affect krill-eating whales,” he continued.

When asked how these findings could affect public health policy and research, Dr Luijckx said:

“Our findings, if applicable to other diseases, suggest that ongoing climate change may alter where and when epidemics occur.”

“However, to accurately predict the spread of disease with ongoing global warming and inform health policy, we will first need to explore the generality of our results, identify the mechanism responsible for our observations, and test whether our results are always valid when we do similar experiments with entire populations.

Dr Gaydos added: “We are thinking a lot about how climate change will affect [the] distribution of human, domestic and wild animal parasites like mosquitoes or ticks, but we often forget that even small organisms like freshwater plankton (Daphnia) have parasites and that climate-related changes in host-parasite interaction [are] going to have major implications on the food chain.

“This means that we as scientists have to think a bit further than what we currently think. Human health is linked to animal health and environmental health, and the complexities are enormous.

“For me, the biggest homecoming is this: Kunze, Luijckx and the team reminded us that despite our best efforts to predict how our changing climate will affect disease, parasitism, humans, pets and wild populations, it’s always a crapshoot as to what’s going to happen there.

“Not only do we need to pay more attention, but we need to get our A game in place to better plan for climate resilience. Yes, the world will change in some of the ways we expect, but there will be plenty of curveballs to come. »

– Dr. Gaydos

“This article reminds us that it won’t just be linear – consistent higher temperatures won’t produce the same things, as more extreme fluctuations and heat waves can also have different effects. The only way to prepare ourselves for the Uncertainty is about taking better care of the limited natural resources we currently have and ensuring that we have as much resilience as possible in natural systems, so that the system can compensate. The 30×30 global initiative is a promising opportunity “, he concluded.


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