(NaturalNews) A recent discovery has scientists talking about the possibility of vaccinating frogs against a killer fungus and touting vaccination as a possible way to stem the ongoing, catastrophic decline of amphibian populations wide. Yet media reports about this breakthrough are mostly ignoring the fact that widespread environmental contamination may be a more significant factor in amphibian population decline, and may even be responsible for increased susceptibility to fungal infection.
A vaccine for frogs?
For decades, scientists have warned that amphibians worldwide are going extinct at a catastrophic rate. More than one-third of the 6,000 amphibian species known to exist 30 years ago are now considered threatened or extinct.
While the amphibian decline seems to stem from a variety of environmental stressors including habitat destruction, urbanization, pollution and climate change, one of the greatest immediate threats has been identified as a chytrid fungus known as Batrachochytrium dendrobatidis (Bd). This immune-hampering fungus has been devastating populations already struggling for survival due to other environmental threats.
In a study published in the journal Nature, researchers from the University of South Florida have shown that oak toads can actually acquire immunity to Bd following repeated exposure to either the living or the dead fungus. The researchers found that, given enough exposure, toads even learned to avoid Bd in the environment.
Up until now, conservations scientists have responded to the Bd epidemic primarily by capturing wild amphibians in the hopes of preserving their genetic material for a hypothetical time when the epidemic has passed. The new findings have raised the possibility that, instead, whole populations could actually be inoculated against a fungus, boosting their immunity enough to keep Bd from wiping out already fragile populations.
Lead author Jason Rohr warned, however, that many more tests would need to be conducted to determine if such a course of action would be safe or effective. Research would also be needed to learn how long such immunity would last, and whether a "vaccine" could work on tadpoles, or only on adults.
"We are planning on testing whether simply dumping dead Bd into waterbodies will induce acquired immunity and reduce chytrid growth on frogs," Rohr said. "If it does, then it might be worth isolating the antigen on chytrid and synthesizing it. Theoretically, this antigen could then be released at locations where amphibian species are at risk."
Pesticide connection overlooked?
Although many ecologists have raised concerns that pesticides may be poisoning frogs, the chemicals' potential role in the Bd epidemic has been largely overlooked.
According to a study published in the journal Environmental Toxicology and Chemistry in 2003, pesticide exposure may actually increase amphibians' susceptibility to infection. Researchers exposed juvenile leopard frogs to a low-levels mix of pesticides, equivalent to what might realistically be found in their environment, then exposed the frogs to parasitic nematodes. They found that, after three weeks of exposure, the frogs had reduced levels of white blood cells and were more likely to become infected. Three weeks of a pesticide-free environment allowed their immune systems to recover.
Another study, published in the same journal in 2013, found pesticide metabolites even in the bodies of amphibians living far from agricultural areas.
"We found that even frogs living in the most remote mountain locations were contaminated by agricultural pesticides, transported long distances in dust and by rain," said researcher Kelly Smalling, of the U.S. Geological Survey.
Ecologists widely regarded amphibians as global indicator species, or "canaries in a coal mine." Because amphibians are so sensitive to environmental stresses such as climate change or low levels of toxins, they often show population declines or other signs of distress before larger animals do.