Chytridiomycosis - AbsoluteAstronomy.com

Chytridiomycosis is an infectious disease

Infectious disease

Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...

of amphibians, caused by the chytrid Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis is a chytrid fungus that causes the disease chytridiomycosis. In the decade after it was first discovered in amphibians in 1998, the disease devastated amphibian populations around the world, in a global decline towards multiple extinctions, part of the Holocene...

, a non-hyphal zoosporic fungus

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, Central America

Central America

Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

, South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

, eastern Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, and Dominica

Dominica

Dominica , officially the Commonwealth of Dominica, is an island nation in the Lesser Antilles region of the Caribbean Sea, south-southeast of Guadeloupe and northwest of Martinique. Its size is and the highest point in the country is Morne Diablotins, which has an elevation of . The Commonwealth...

and Montserrat

Montserrat

Montserrat is a British overseas territory located in the Leeward Islands, part of the chain of islands called the Lesser Antilles in the West Indies. This island measures approximately long and wide, giving of coastline...

in the Caribbean

Caribbean

The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...

. The fungus is capable of causing sporadic deaths in some amphibian populations and 100% mortality in others. There is no effective measure for control of the disease in wild populations. The disease is contributing to a global decline in amphibian populations

Decline in amphibian populations

Dramatic declines in amphibian populations, including population crashes and mass localized extinctions, have been noted since the 1980s from locations all over the world...

that apparently has affected 30% of the amphibian species of the world.

History

The disease in its epizootic

Epizootic

In epizoology, an epizootic is a disease that appears as new cases in a given animal population, during a given period, at a rate that substantially exceeds what is "expected" based on recent experience . Epidemic is the analogous term applied to human populations...

form was first discovered in 1993 in dead and dying frogs in Queensland

Queensland

Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

, Australia

Australia

. Research since then has shown that it has been present in the country since at least 1978 and is widespread across Australia. It is also found in Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, the Americas

Americas

The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

, Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

and Oceania

Oceania

Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...

. In Australia, Panama

Panama

Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...

, and New Zealand, the fungus seemed to have just suddenly ‘appeared’ and expanded its range at the same time as when frog numbers declined. However, it may simply be that the fungus occurs naturally and was only identified recently because it has become more virulent or more prevalent in the environment, or because host populations have become less resistant to the disease. The fungus has been detected in four areas of Australia — the east coast, Adelaide, south-west Western Australia and the Kimberley — and is probably present elsewhere.

The oldest reports of infection of Batrachochytrium were from African clawed frog

African clawed frog

The African clawed frog is a species of South African aquatic frog of the genus Xenopus. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food...

s of the genus Xenopus
Xenopus
Xenopus is a genus of highly aquatic frogs native to Sub-Saharan Africa. There are 19 species in the Xenopus genus...

. Because Xenopus has been widely transported around the world, it is one potential vector for transmission of B. dendrobatidis. Other studies, however, suggest that B. dendrobatidis has been present in North and Central America for decades. It is still not clear if it is a new emergent pathogen or if it is an old pathogen with recently increased virulence

Virulence

Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...

Disease Progression

Chytridiomycosis is believed to adhere to the following course: zoospore

Zoospore

A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some algae, bacteria and fungi to propagate themselves.-Flagella:...

s first encounter amphibian skin and quickly give rise to sporangia, which produce new zoospores. The disease then progresses as these new zoospores reinfect the host. Morphological changes of amphibians infected with the fungus include a reddening of the ventral skin, convulsions with extension of hind limbs, accumulations of sloughed skin over the body, sloughing of the superficial epidermis

Epidermis (zoology)

The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...

of the feet and other areas, slight roughening of the surface with minute skin tags, and occasional small ulcers or hemorrhage. Behavioral changes can include lethargy, a failure to seek shelter, a failure to flee, a loss of righting reflex

Righting reflex

The righting reflex is a reflex that occurs when the body of an animal becomes inverted. It causes the body to turn around so that the animal is on its feet. The reflex may occur in the cerebral cortex, via visual cues, or in the midbrain via the labyrinthine or proprioception cues. The reflex can...

, and abnormal posture (e.g. sitting with the hind legs away from the body)

Research

Laboratory studies suggest that the fungus performs poorly above 28 °C (82.4 °F), and that exposure of infected frogs to high temperatures will kill the fungus. This may explain why chytridiomycosis-induced amphibian declines occur primarily in cool regions, like mountain chains where the cloud cover

Cloud cover

Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location...

is apparently more abundant than in the warmer jungle regions. However, conflicting research does exist. It has been shown that naturally produced cutaneous peptides can inhibit the growth of B. Dendrobatidis when the infected amphibians are around temperatures near 10 °C (50 °F) - which is like placing them in the Northeastern United States

Northeastern United States

The Northeastern United States is a region of the United States as defined by the United States Census Bureau.-Composition:The region comprises nine states: the New England states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont; and the Mid-Atlantic states of New...

during the autumn months, allowing species like Rana pipiens, or Northern Leopard Frog, to clear the infection in about 15% of cases.

Although many declines have been credited to the fungus B. dendrobatidis, there are species that resist the infection and some reports have found that some populations can survive with a low level of persistence of the disease. In addition, some species that seem to resist the infection may actually harbor a non-pathogenic form of Batrachochytrium dendrobatidis.

Some researchers contend that the focus on chytridiomycosis has made amphibian conservation efforts dangerously myopic. In Guatemala, for example, several thousands of tadpoles perished from an unidentified pathogen distinct from B. dendrobatidis . Such researchers stress the need for a broader understanding of the host-parasite ecology that is contributing to the modern day amphibian declines.

Treatment options

It was reported in the June 8, 2009 issue of New Scientist that Reid Harris of James Madison University has found that coating frogs with Janthinobacterium lividum appears to protect them from chytridiomycosis.

Archey's frog Leiopelma archeyi, a critically endangered species endemic to New Zealand, was successfully cured of chytridiomycosis by applying chloramphenicol

Chloramphenicol

Chloramphenicol is a bacteriostatic antimicrobial that became available in 1949. It is considered a prototypical broad-spectrum antibiotic, alongside the tetracyclines, and as it is both cheap and easy to manufacture it is frequently found as a drug of choice in the third world.Chloramphenicol is...

topically.

Use of Rooibos tea (Aspalathus linearis) in container water was found by Jay Redmond at WWT Slimbridge

WWT Slimbridge

WWT Slimbridge is a wetland reserve managed by the Wildfowl and Wetlands Trust at Slimbridge, Gloucestershire, England. Slimbridge is halfway between Bristol and Gloucester on the estuary of the river Severn. The reserve was the first WWT centre to be opened, on 10 November 1946, thanks to the...

, Gloucestershire, to effectively ward off chytridiomycosis in poison dart frogs.

External links

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