Chytridiomycosis << kih TRIH dee oh my KOH sihs >> is an infectious disease harming amphibians worldwide. The disease has led to a serious loss of amphibian species (kinds) in some areas. The worst losses have happened in western North America, Central and South America, Europe, and eastern Australia. Chytridiomycosis has even caused some species to become extinct.
Chytridiomycosis is caused by either of two species of chytrid << KIH trihd >> fungi of the genus Batrachochytrium. One species is referred to as the amphibian chytrid fungus. It is known to affect all types of amphibians, including frogs, toads, salamanders, and caecilians. The other species is called the salamander chytrid fungus. So far, it is known only to affect some species of salamanders. Both species of chytrid fungi are microscopic, single-celled organisms. The fungus invades the outer layers of the amphibian’s skin, causing chytridiomycosis if the infection is severe. Symptoms of the disease include excessive shedding of the skin and weakness or lethargy (lack of energy). Some animals show an increased development of keratin on the surface of the skin. Keratin is a tough, insoluble protein found in the outer layer of the skin of many animals.
The salamander chytrid fungus causes heavily infected salamanders to have large open sores on the skin as well as excessive shedding of the skin. An infected salamander may be weak and lethargic. This fungus is native to Asia, but infected salamanders in Asia do not show signs of the disease. The discovery of large numbers of dead, diseased salamanders in western Europe indicates that the fungus has been transported to that area. There, it is causing declines in vulnerable species that have not previously been exposed to it.
Chytridiomycosis is not always fatal. When it is, death results from an imbalance of substances called electrolytes in the amphibian’s body, causing the heart to stop beating. The infection may contribute to such an imbalance by reducing the transport of electrolytes through the amphibian’s skin. The fungus spreads among individuals in the form of a specialized structure called a zoospore, which swims freely through the water. Chytrid fungus can also be passed directly between animals through physical contact.
Scientists are searching for ways to treat or control epidemics of chytridiomycosis in the wild. The best way to protect wild populations is by preventing the spread of infected animals or contaminated water. Some species or individuals are relatively tolerant of infection and can thus act as carriers of the disease. For this reason, it appears to be impossible to completely eliminate the chytrid fungus from entire ecosystems.
