Malaria remains a major cause of health concern in the world. According to the World Health Organization, the mosquito-borne disease infected more than 229 million people and claimed more than 400,000 lives in 2019. Children under five accounted for more than 67% of all malaria deaths worldwide. Especially in tropical and subtropical regions, such as South Asia, sub-Saharan Africa, and Central America, malaria continues to disrupt lives and livelihoods.

It is thus vital to understand how to contain it, for which it is crucial to understand the ways in which it spreads. A new study, published this week in the journal Environmental Research Letters, offers some clues. In some parts of Central America — Costa Rica and Panama — researchers found a link between the death of amphibians like frogs, and a surge in malaria infections. That is, there was a correlation observed between the frogs’ vanishing and the severity of the malaria outbreak.

“The results in our paper suggest that some policies, such as amphibian conservation policies or the regulation of wildlife trade, could have benefits for human health which are not currently accounted for,” study author Joakim Weill said earlier.

For their research, the scientists analyzed medical and ecological data from the 1980s to 1990s in Costa Rica, and from the 2000s to mid-2010s in Panama. During these periods, a virulent fungal pathogen — the Batrachochytrium dendrobatidis (Bd) — caused mass deaths of frogs and salamanders in the two nations respectively. The study collates data from public health records, satellite images, and ecological surveys.

The researchers observed a higher occurrence of malaria cases during those years in which mass amphibian deaths due to Bd were reported. In both Costa Rica and Panama, the usual rate of malaria ranges around 1.1-1.5 cases per 1,000 population. In years of Bd-induced mass amphibian deaths, however, both nations reported almost 1 extra case per 1000 population, implying a 70-90% increase in the total number of cases.

The research highlights the role healthy ecosystems play in human welfare, pointing out how the deterioration of the former can significantly alter the health of the latter. The ongoing Covid19 pandemic is a telling case study, highlighting the necessity of adapting the maintenance and restoration of ecosystem balance as a policy approach for better human healthcare.

“This previously unidentified impact of biodiversity loss illustrates the often hidden human welfare costs of conservation failures,” the authors write in their research.

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Amphibians serve an important role in ecosystems — they are both predator and prey in the food web. As predators, their diets comprise mosquitoes and other insects, which helps to regulate the latter’s populations and consequently reduces the risk of insect-borne diseases.

Bd is known to infect the amphibians’ skins, disrupting essential functions like osmotic regulation — maintaining the balance between water and vital minerals in the body, that occurs in amphibians through their skin — that results in their death. So far, Bd is estimated to have dwindled populations in more than 400 species, and for causing extinction in another 90.

Despite this well-known utility, people have largely overlooked the causal links between dwindling amphibian populations and the rise in insect-borne diseases such as malaria. The current study attempts to bridge that gap to better highlight the integrated manner in which ecosystems function.

Scientists, however, observed one anomaly in their data. In the years following 2016, data in the study suggests that the effect of Bd on human malaria cases has reduced. Scientists speculate that one reason for this could be the greater use of insecticides and pesticides to kill mosquitoes, more public health measures, or just a rise in other mosquito-borne diseases that would result in a reduction of malaria cases. Another limitation of the study is the absence of extensive data on dengue or other mosquito-borne diseases on the scale on which data on malaria was available. Hence, there is a need for more conclusive research on dengue and other diseases and their relations with amphibian deaths.

But arguably, the link is telling of the many ways in which human healthcare cannot be addressed without paying heed to the health of the entire ecosystem. “If scientists and decision-makers fail to reckon with the ramifications of such past events,” the study noted, “they also risk failing to fully motivate protection against new calamities.”