A global plague, the chytrid fungus, afflicts amphibians and has even driven some species to extinction in the wild, such as the Kihansi spray toad in Tanzania. However, a recent study found that the disease has not yet ravaged West Africa. No one knows how long this safe haven will remain, as conditions are ripe in the region for the fungus to spread.
Nearly 800 West African amphibians were tested for the fungus and all of them were found to be free of the disease in a study published in PLOS ONE. Most of the species were frogs from a variety of habitats in seven nations, Bénin, Burkina Faso, Côte d’Ivoire, Ghana, Guinea, Liberia, Sierra Leone. Conditions in the rainforests of the regions are perfect for the fungus, but it seems that geography may have kept the fungus at bay.
The researchers suggested that a geographic barrier, the Dahomey Gap, may have protected West African frogs. The Dahomey Gap is strip of arid land that splits the Congo forest from the western African rainforest. The dry savannah of the Dahomey Gap may be blocking the fungus, which depends on moist conditions.
Unfortunately for frogs, the Dahomey Gap is no barrier to humans. Highways link the chytrid-infected regions to the east and south with the disease-free west. Some frogs that are regularly eaten can harbor the disease, and human commerce in these animals could spread the disease across the gap.
The disease doesn’t depend on live animals for transport. For example, the study’s authors called for researchers and tourists to avoid moving equipment across the Dahomey Gap. They also recommended mining tools be purchased anew, instead of transported from the east to the west in Africa. However, it seems unlikely that mining companies will spend millions of dollars to avoid infecting frogs.
The chytrid fungus causes amphibians’ skin to grow thicker. This makes it impossible for them to absorb important dietary salts and difficult to breathe, since amphibians absorb nutrients and oxygen through their skin. The lack of salts can lead to heart failure. The disease can also cause some amphibians’ toes to wither and rot off, such as in the American hellbender.
IMAGE: A juvenile crocodile eats a small frog. (Jonathan Blair, Corbis)