Chytridiomycosis is an amphibian infectious disease, caused by the chytrid fungi Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans , the nonhyphal zoospora fungus. Chytridiomycosis has been associated with dramatic population decline or even amphibian species extinction in western North America, Central America, South America, eastern Australia, East Africa (Tanzania) and Dominica and Montserrat in the Caribbean. Many New Worlds are also at risk of coming illnesses in the next few years. This fungus is capable of causing sporadic death in some amphibian populations and 100% death in others. There is no known effective measure for controlling disease in wild populations. Various clinical signs are seen by individuals affected by the disease. A number of options are possible to control the fungi that cause the disease, although none of which have proven to be feasible on a large scale. This disease has been suggested as a contributing factor to the global decline of the amphibian population that appears to have affected about 30% of the world's amphibian species.
Video Chytridiomycosis
Histori
Epizootic disease was first discovered in 1993 in dead and dead frogs in Queensland, Australia. It has been present in this country since at least 1978 and is widespread throughout Australia. It is also found in Africa, America, Europe, New Zealand, and Oceania. In Australia, Panama, and New Zealand, the fungus seems to suddenly 'emerge' and expand its reach at the same time the frog numbers are declining. In America, it came from Venezuela in 1987 where it swept the continent to Central America. It was also found in the lower part of Central America in 1987, where it spread to fill the upward sweep of South America. However, it is possible that the fungus is naturally occurring and only recently identified because it has become more virulent or more common in the environment, or because the host population becomes less resistant to disease. Mushrooms have been detected in four areas of Australia - east coast, Adelaide, southwestern Western Australia and Kimberley - and may be elsewhere.
The oldest documented incident of Batrachochytrium is from Japanese giant salamanders collected in 1902, although this fungal strain belongs to an endemic lineage that has not been implicated in mass death events. The next known example of a Bd-infected amphibian specimen from African frog ( Xenopus laevis) was collected in 1938, and this species also seems to be essentially unaffected by the disease, making it a suitable vector. The well-documented first human pregnancy test method involves this species, and as a result, large-scale international trade in African-originated frog life began more than 60 years ago. If Batrachochytrium originated in Africa, it has been theorized that African-clawed frogs are vectors from the initial spread of the continent. The earliest documented case of chytridiomycosis is the American frog (Rana catesbeiana) collected in 1978. It remains unclear whether this is a newly emerging pathogen or if it is an old pathogen with recent virulence enhancement.. Maps Chytridiomycosis
Range
The geographical range of chytridiomycosis is difficult to ascertain. If that happens, the disease is present only where the fungus B. dendrobatidis is present. However, the disease is not always present where the fungus is located. The reason for the drop in amphibians is often called 'mysterious' because the cause is unknown. Why are some areas affected by fungi while others are not fully understood. Oscillating factors such as climate, habitat suitability, and population density may be factors that cause the fungus to infect amphibians in certain areas. Therefore, when considering the geographic range of chytridiomycosis, the range of B. dendrobatidis events should be considered. The geographical range B. dendrobatidis was recently mapped, and reaches most of the world. B. dendrobatidis has been detected in 56 of 82 countries, and in 516 of the 1.240 (42%) species used a data set of more than 36,000 individuals. It is widespread in America, and is sporadically detected in Africa, Asia, and Europe. Asia, for example, has only 2.35% prevalence.
The matching range for B. dendrobatidis in the New World is vast. Areas with the highest suitability include habitats containing the most diversified amphibian fauna in the world. Areas at risk are the Sierra Madre Fall Forest, the Sonoran rain forest and Sinaloan, Veracruz moist forest, eastern Central America from the Isthmus of Tehuantepec, Caribbean Islands, temperate forests in Chile and southern Argentina 30 Â ° S, the Andes above 1000 m above sea level in Venezuela, Colombia, and Ecuador, the eastern slopes of the Andes in Peru and Bolivia, Brazilian Atlantic forests, Uruguay, Paraguay, and northeastern Argentina, and Amazon southwestern Amazon and Madeira-Tapaj rainforests.
Currently, chytridiomycosis effects are most readily seen in Central America, eastern Australia, South America, and western North America.
Climate change
A new study shows that global temperature changes may be responsible for increased proliferation of chytridiomycosis. Temperature rises have increased evaporation in certain forest environments that have consequently promoted cloud formation. Experts suggest that an increase in cloud cover may actually reduce daytime temperatures by blocking the sun, while at night cover clouds serve as isolation to raise nighttime temperatures from their normal range. The combination of daytime temperature drop and nighttime temperature increase can provide optimal growth and reproduction for Chytrid fungi which has a preferred temperature range between 63 ° and 77 ° F (17 ° and 25 ° C). Mushrooms die at temperatures above and above 30 ° C, which without cloud cover from increased evaporation are more easily achieved by the environment and therefore can more easily keep the mushroom population in check.
Causes agent
Chytridiomycosis caused by the fungus B. dendrobatidis primarily affects the outermost layer of skin containing keratin. When most species reach the 10,000 zoospores threshold, they can not breathe, hydrate, osmoregulate, or thermoregulate properly. This is evidenced by blood samples showing a certain lack of electrolytes, such as sodium, magnesium, and potassium. B. dendrobatidis is currently known to have two stages of life. The first is the asexual zoosporangial stage. When the first host suffers from the disease, the spores penetrate the skin and attach themselves to the microtubule roots. The second stage occurs when early asexual zoosporangia produces motile zoospores. To disperse and infect epidermal cells, a moist surface is required. The second species of Batrachochytrium , B. salamandrivorans , was discovered in 2013 and is known to cause chytridiomycosis in salamanders.
Transmission and disease progression
B. dendrobatidis , a water-borne pathogen, spreading the zoospores into the environment. Zoospores use flagella to move through the water system until they reach a new host and enter cutaneously. The B. dendrobatidis 'life cycle continues until a new zoospora is generated from zoosporangium and out into the environment or infects the same host. Once the host is infected with B. dendrobatidis , it is potentially developing chytridiomycosis, but not all infected hosts develop it. Other forms of transmission are currently unknown; however, chytridiomycosis is postulated to be transmitted by direct contact of the host or through an intermediary host.
Many ways B. dendrobatidis successfully sent from one host to the next are mostly unknown. Once released into the aquatic environment, zoospores run less than 2 cm in 24 hours before they enter. The limited range of B. dendrobatidis zoospores suggests some unknown mechanism by transmitting from one parent to the next, which may involve the pet trade, and especially the American Bullfrog. Abiotic factors such as temperature, pH levels, and nutritional levels affect the success of dendrobatidis zoospores. Zoospora fungi can survive in the temperature range 4-25Ã, Â ° C and pH range 6-7.
Chytridiomycosis is believed to follow this course: the zoospores first encounter the amphibian skin and quickly generate sporangia, which produces a new zoospora. The disease then develops because the new zoospora is re-infecting the host. Morphological changes in the fungi-infected amphibians include flushing of the ventral skin, spasms with rear leg extension, accumulation of peeled skin, superficial epidermal decay of the foot and other areas, less rough surface with minute skin tag, and occasionally small ulcers or bleeding. Behavioral changes may include lethargy, failure to seek refuge, failure to escape, loss of reflex straightening, and abnormal posture (eg sitting with hind legs away from the body).
Clinical signs
Amphibians infected with B. dendrobatidis have been shown to show many different clinical signs. Perhaps the initial sign of infection is anorexia, occurring as soon as 8 days after exposure. Infected individuals are also often found in sluggish state, characterized by slow motion, and refuse to move when stimulated. Excessive skin shedding is seen in most frog species affected by B. dendrobatidis . These pieces of leather shed are described as blurry, gray-white, and brown. Some of these skin patches are also found attached to the amphibian skin. The signs of this infection are often seen 12-15 days after exposure. The most characteristic symptom of chytridiomycosis is skin thickening, which immediately leads to the death of an infected individual because people can not take proper nutrition, release toxins, or, in some cases, breathe. Other common signs are skin redness, seizures, and loss of reflex straightening. In tadpoles B. dendrobatidis affects the mouth, where keratin is present, leading to abnormal eating behavior or oral discoloration.
Research
Amphibian chytrid fungi seem to grow best between 17 and 25 Â ° C, and exposure of infected frogs to high temperatures can cure frogs. In nature, the more time individual frogs are found at temperatures above 25 Â ° C, the less likely they are to be infected by amphibian chytrid. This may explain why the decrease in amphibians induced by chytridiomycosis occurs mainly at higher elevations and during the cold months. The naturally occurring cutaneous peptide can inhibit the growth of dendrobatidis when the infected amphibians are at approximately 10 ° C (50 ° F), allowing species such as the northern leopard frog ( Rana pipiens ) to clear the infection in about 15% of cases.
Although much of the decline has been credited to the fungus dendrobatidis , some species fight infections and some populations may survive with low levels of disease persistence. In addition, some species that seem to fight infection may actually have a non-pathogenic B. dendrobatidis form.
Some researchers believe the focus on chytridiomycosis has made conservation efforts of harmless amphibians nearsighted. A review of data on the IUCN Red List found that the threat of the disease is assumed in many cases, but no evidence suggests, in fact, it is a threat. Conservation efforts in New Zealand continue to focus on healing the highly endangered Archey's native frog, Leiopelma archeyi , from chytridiomycosis, although studies have shown clearly that they are immune from infection by B. dendrobatidis and is dying in the wild from other diseases still to be identified. In Guatemala, several thousand tadpoles die from unknown pathogens different from B. dendrobatidis .
Immunity
Due to the large influence of fungi on amphibian populations, considerable research has been undertaken to devise methods to combat the proliferation in the wild. Among the most promising is the revelation that amphibians in colonies surviving through chytrid epidemics tend to carry higher levels of bacteria Janthinobacterium lividum . These bacteria produce antifungal compounds, such as indole-3-carboxaldehyde and violacein, which inhibit the growth of dendrobatidis even at low concentrations. Similarly, Lysobacter gummosus bacteria was found in red-backed salamanders ( Plethodon cinereus ), producing a 2,4-diacetylphloroglucinol compound that inhibited the growth of dendrobatidis .
Understanding the interactions of microbial communities present in amphibian skin with fungi species in the environment may reveal why certain amphibians, such as the frog Rana muscosa, are susceptible to the fatal effects of dendrobatidis and why Others, such as the Hemidactylium scutatum salamander , can co-exist with mushrooms. As mentioned earlier, the species of the antifungal bacterium Janthinobacterium lividum , found in some amphibian species, has been shown to prevent pathogenic effects even when added to other amphibians without bacteria ( B. dendrobatidis - easily captured amphibian species). The interactions between skin microbiota and B. dendrobatidis may be altered to support disease resistance, as seen in previous studies on the addition of violacein-producing bacteria J. lividum to amphibians that do not have violacein enough, allowing them to inhibit the infection. Although the exact concentration of violacein (an antifungal metabolite produced by J. Lividum ) required to inhibit the effects of
One study has postulated that water flea Daphnia magna consumes fungal spores.
Interactions with pesticides
The hypothesis that the use of pesticides has caused a decrease in amphibian populations has been suggested several times in the literature. The interaction between pesticides and chytridiomycosis was examined in 2007, and subletal exposure to carbaryl pesticides (cholinesterase inhibitors) was shown to increase the susceptibility of white toe legs ( Rana boylii ) in chytridiomycosis. In particular, peptide skin defenses are significantly reduced after exposure to carbaryl, suggesting pesticides may inhibit these innate immune defenses, and increase susceptibility to disease.
Evolution
The guidance of evolutionary resistance that emerged in the rebounding population of the affected frog species was reported from an ecological study of the threatened breeding frog threatened epizootically Mixophyes fleayi from subtropical Australia. Rebound of frog species in Panama after the decline is not associated with pathogen attenuation, but the host factor - whether genetic resistance evolved to fungal infections, or acquired traits (such as proton hyponetogenic micro- colonization) has not been identified..
Maintenance options
Use of heat-induced antifungals and therapies has been suggested as a treatment for B. dendrobatidis. However, some of these antifungal agents can cause adverse skin effects on certain frog species, and although they are used to treat species infected with chytridiomycosis, the infection is never completely eradicated. A study conducted by Rollins-Smith and colleagues showed that itraconazole was the antifungal choice when it came to the treatment of Bd. This is preferred compared with amphotericin B and chloramphenicol due to its toxicity, particularly chloramphenicol because it correlates with leukemia in frogs. This becomes a difficult situation because without treatment, frogs will suffer from deformities and even death, but may also suffer from skin disorders with treatment. "Treatment does not always work 100% and not all amphibians tolerate treatment very well, therefore chytridiomycosis should always be treated with veterinary advice."
Individuals infected with B. dendrobatidis were bathed in intraconazole solution, and within weeks, individuals previously infected with a negative test for B. dendrobatidis using PCR assays. Heat therapy is also used to neutralize B. dendrobatidis in infected individuals. Temperature controlled laboratory experiments are used to increase the individual temperature over the optimal temperature range of B. dendrobatidis . Experiments, in which the temperature rises beyond the upper limit of the optimum range of 25 to 30 ° C, indicating its presence will be lost within a few weeks and the infected individual returns to normal. Formalin/malachite green has also been used to treat individuals infected with chytridiomycosis. An Archey frog has recovered from chytridiomycosis by applying chloramphenicol topically. However, the potential risks of using antifungal drugs on individuals are high.
See also
- An infectious disease appears
- White nose syndrome
- a grueling stomach frog
- Golden Frog
- Guajira stubfoot toad
- Rabb's Fringe-limbed Treefrog
- Holocene Extinction
References
External links
- Article at National Geographic Magazine, April 2009
- Wildlife Trafficking and Emerging Global Diseases
- The main prevention management strategy for Chytrid fungus
- Chytridiomycosis amphibians at Amphibian Diseases Home Page
- 'Amphibian Ark' aims to save frogs from mushrooms
Source of the article : Wikipedia
0 Comments