Batrachochytrium dendrobatidis

The generic name is derived from the Greek words batrachos (frog) and chytra (earthen pot), while the specific epithet is derived from the genus of frogs from which the original confirmation of pathogenicity was made (Dendrobates),{{cite journal | doi = 10.2307/3761366 |vauthors=Longcore JE, Pessier AP, Nichols DK | year = 1999 | title = Batrachochytrium Dendrobatidis gen. et sp. nov, a chytrid pathogenic to amphibians | jstor = 3761366| journal = Mycologia | volume = 91 | issue = 2| pages = 219–227 }} dendrobatidis is from the Greek dendron, "tree" and bates, "one who climbs", referring to a genus of poison dart frogs.{{cite journal|date=July 2016 |title=Etymologia: Batrachochytrium salamandrivorans |journal=Emerg Infect Dis |volume=22 |issue=7 |page= 1282|doi=10.3201/eid2207.ET2207 |pmc=4918143 }}

Batrachochytrium dendrobatidis was until recently considered the single species of the genus Batrachochytrium. The initial classification of the pathogen as a chytrid was based on zoospore ultrastructure. DNA analysis of the SSU-rDNA has corroborated the view, with the closest match to Chytridium confervae.{{Citation needed|reason=By what research was this conclusion reached?|date=September 2024}} A second species of Batrachochytrium was discovered in 2013: B. salamandrivorans, which mainly affects salamanders and also causes chytridiomycosis.{{cite journal|last=Martel|first=A. |author2=Spitzen-van der Sluijs, A. |author3=Blooi, M. |author4=Bert, W. |author5=Ducatelle, R. |author6=Fisher, M. C. |author7=Woeltjes, A. |author8=Bosman, W. |author9=Chiers, K. |author10=Bossuyt, F. |author11=Pasmans, F. |title=Batrachochytrium salamandrivorans sp. nov. causes lethal chytridiomycosis in amphibians|journal=Proceedings of the National Academy of Sciences of the United States of America |year=2013|volume=110|issue=38|pages=15325–15329|doi=10.1073/pnas.1307356110|pmid=24003137|pmc=3780879|bibcode=2013PNAS..11015325M |doi-access=free }} B. salamandrivorans differs from B. dendrobatidis primarily in the formation of germ tubes in vitro, the formation of colonial thalli with multiple sporangia in vivo, and a lower thermal preference.

File:CSIRO ScienceImage 1392 Scanning Electron Micrograph of Chytrid Fungus.jpg of a frozen intact zoospore and sporangia of the chytrid fungus (Batrachochytrium dendrobatidis), CSIRO]]

B. dendrobatidis infects the keratinized skin of amphibians. The fungus in the epidermis has a thallus bearing a network of rhizoids and smooth-walled, roughly spherical, inoperculate (without an operculum) sporangia. Each sporangium produces a single tube to discharge spores.

Zoospores of B. dendrobatidis, which are typically 3–5 μm in size, have an elongate–ovoid body with a single, posterior flagellum (19-20 μm long), and possess a core area of ribosomes often with membrane-bound spheres of ribosomes within the main ribosomal mass. A small spur has been observed, located at the posterior of the cell body, adjacent to the flagellum, but this may be an artifact in the formalin-fixed specimens. The core area of ribosomes is surrounded by a single cisterna of endoplasmic reticulum, two to three mitochondria, and an extensive microbody–lipid globule complex. The microbodies closely appose and almost surround four to six lipid globules (three anterior and one to three laterally), some of which appear bound by a cisterna. Some zoospores appear to contain more lipid globules (this may have been a result of a plane-of-sectioning effect, because the globules were often lobed in the zoospores examined). A rumposome has not been observed.

A nonfunctioning centriole lies adjacent to the kinetosome. Nine interconnected props attach the kinetosome to the plasmalemma, and a terminal plate is present in the transitional zone. An inner ring-like structure attached to the tubules of the flagellar doublets within the transitional zone has been observed in transverse section. No roots associated with the kinetosome have been observed. In many zoospores, the nucleus lies partially within the aggregation of ribosomes and was invariably situated laterally. Small vacuoles and a Golgi body with stacked cisternae occurred within the cytoplasm outside the ribosomal area. Mitochondria, which often contain a small number of ribosomes, are densely staining with discoidal cristae.

File:Chytridiomycosis2.jpg. The arrows indicate discharge tubes through which zoospores exit the host cell. Scale bar = 35 μm.]]

B. dendrobatidis has two primary life stages: a sessile, reproductive zoosporangium and a motile, uniflagellated zoospore released from the zoosporangium. The zoospores are known to be active only for a short period of time, and can travel short distances of one to two centimeters.{{cite journal|vauthors=Garner TW, Perkins MW, Govindarajulu P, Seglie D, Walker S, Cunningham AA, Fisher MC |title=The emerging amphibian pathogen Batrachochytrium dendrobatidis globally infects introduced populations of the North American bullfrog, Lithobates catesbeiana |journal=Biology Letters |volume=2 |issue=3 |pages=455–459 |date=September 2006 |pmid=17148429 |pmc=1686185 |doi=10.1098/rsbl.2006.0494 }} However, the zoospores are capable of chemotaxis, and can move towards a variety of molecules that are present on the amphibian surface, such as sugars, proteins and amino acids.{{cite journal |vauthors=Moss AS, Reddy NS, Dortaj IM, San Francisco MJ |title=Chemotaxis of the amphibian pathogen Batrachochytrium dendrobatidis and its response to a variety of attractants |journal=Mycologia |volume=100 |issue=1 |pages=1–5 |year=2008 |pmid=18488347 |doi= 10.3852/mycologia.100.1.1}} B. dendrobatidis also contains a variety of proteolytic enzymes and esterases that help it digest amphibian cells and use amphibian skin as a nutrient source.{{cite journal | doi = 10.1007/s11046-008-9135-y |vauthors=Symonds EP, Trott DJ, Bird PS, Mills P | year = 2008 | title = Growth characteristics and enzyme activity in Batrachochytrium dendrobatidis isolates | journal = Mycopathologia | volume = 166 | issue = 3| pages = 143–147 | pmid = 18568420 |s2cid=8545084 }} Once the zoospore reaches its host, it forms a cyst underneath the surface of the skin, and initiates the reproductive portion of its life cycle. The encysted zoospores develop into zoosporangia, which may produce more zoospores that can reinfect the host, or be released into the surrounding aquatic environment.{{cite journal |vauthors=Berger L, Hyatt AD, Speare R, Longcore JE |title=Life cycle stages of the amphibian chytrid Batrachochytrium dendrobatidis |journal=Diseases of Aquatic Organisms |volume=68 |issue=1 |pages=51–63 |date=December 2005 |pmid=16465834 |doi= 10.3354/dao068051|doi-access=free }} The amphibians infected with these zoospores are shown to die from cardiac arrest.{{cite journal | journal=Science | volume=326 | issue=5952 | pages=582–585 | vauthors=Voyles J, Young S, Berger L, Campbell C, Voyles WF, Dinudom A, Cook D, Webb R, Alford RA, Skerratt LF, Speare R | s2cid=52850132 | title=Pathogenesis of chytridiomycosis, a cause of catastrophic amphibian declines | doi=10.1126/science.1176765 | pmid=19900897 | year=2009 | bibcode=2009Sci...326..582V }}

Besides amphibians B. dendrobatidis also infects crayfish (Procambarus alleni, P. clarkii, Orconectes virilis, and O. immunis) but not mosquitofish (Gambusia holbrooki).{{ Cite journal | title=McMahon, Taegan A. et al "Chytrid fungus Batrachochytrium dendrobatidis has nonamphibian hosts and releases chemicals that cause pathology in the absence of infection." Proceedings of the National Academy of Sciences 110.1 (2013): 210-215. Web. 01 Nov. 2020. | year=2013 | doi=10.1073/pnas.1200592110 | pmid=23248288 | last1=McMahon | first1=T. A. | last2=Brannelly | first2=L. A. | last3=Chatfield | first3=M. W. | last4=Johnson | first4=P. T. | last5=Joseph | first5=M. B. | last6=McKenzie | first6=V. J. | last7=Richards-Zawacki | first7=C. L. | last8=Venesky | first8=M. D. | last9=Rohr | first9=J. R. | journal=Proceedings of the National Academy of Sciences of the United States of America | volume=110 | issue=1 | pages=210–5 | pmc=3538220 | doi-access=free }}

B. dendrobatidis can grow within a wide temperature range (4-25 °C), with optimal temperatures being between 17 °C and 25 °C.{{cite journal | doi = 10.2307/3761981 |vauthors=Piotrowski JS, Annis S, Longcore JE | year = 2004 | title = Physiology of Batrachochytrium dendrobatidis, a chytrid pathogen of amphibians | jstor = 3761981| journal = Mycologia | volume = 96 | issue = 1| pages = 9–15 | pmid = 21148822 }} The wide temperature range for growth, including the ability to survive at 4 °C gives the fungus the ability to overwinter in its hosts, even where temperatures in the aquatic environments are low. The species does not grow well above temperatures of 25 °C, and growth is halted above 28 °C. Infected red-eyed treefrogs (Litoria chloris) recovered from their infections when incubated at a temperature of 37 °C.{{cite journal |vauthors=Woodhams DC, Alford RA, Marantelli G |title=Emerging disease of amphibians cured by elevated body temperature |journal=Dis. Aquat. Org.|volume=55 |issue=1 |pages=65–7 |date=June 2003 |pmid=12887256 |doi= 10.3354/dao055065|doi-access=free }}

B. dendrobatidis has occasionally been found in forms distinct from its traditional zoospore and sporangia stages. For example, before the 2003 European heat wave that decimated populations of the water frog Rana lessonae through chytridiomycosis, the fungus existed on the amphibians as spherical, unicellular organisms, confined to minute patches (80-120 μm across). These organisms, unknown at the time, were subsequently identified as B. dendrobatidis. Characteristics of the organisms were suggestive of encysted zoospores; they may have embodied a resting spore, a saprobe, or a parasitic form of the fungus that is non-pathogenic.{{cite journal | vauthors = Di Rosa I et al | year = 2007 | title = The Proximate Cause of Frog Declines? | journal = Nature | volume = 447 | issue = 7144| pages = E4–E5 | doi=10.1038/nature05941 | pmid=17538572| bibcode = 2007Natur.447....4R | s2cid = 4421285 }}

The fungus grows on amphibian skin and produces aquatic zoospores.{{cite journal | vauthors = Ron SR | year = 2005 | title = Predicting the Distribution of the Amphibian Pathogen B. dendrobatidis in the New World | journal = Biotropica | volume = 37 | issue = 2| pages = 209–221 | doi=10.1111/j.1744-7429.2005.00028.x| s2cid = 84272576 | doi-access = free }} It is widespread and ranges from lowland forests to cold mountain tops. It is sometimes a non-lethal parasite and possibly a saprophyte. The fungus is associated with host mortality in highlands or during winter, and becomes more pathogenic at lower temperatures.{{cite journal | vauthors = Daszak P, Cuningham AA, Hyatt AD | s2cid = 16838374 | year = 2003 | title = Infection disease and amphibian population declines | journal = Divers. Distrib. | volume = 9 | issue = 2| pages = 141–150 | doi=10.1046/j.1472-4642.2003.00016.x| bibcode = 2003DivDi...9..141D }}

{{Main|Chytridiomycosis}}

It has been suggested that B. dendrobatidis originated in Africa or Asia and subsequently spread to other parts of the world by trade in African clawed frogs (Xenopus laevis).{{cite journal |vauthors=Weldon C, du Preez LH, Hyatt AD, Muller R, Spears R |title=Origin of the amphibian chytrid fungus |journal=Emerging Infect. Dis. |volume=10 |issue=12 |pages=2100–5 |date=December 2004 |pmid=15663845 |pmc=3323396 |doi= 10.3201/eid1012.030804}} In this study, 697 archived specimens of three species of Xenopus, previously collected from 1879 to 1999 in southern Africa, were examined. The earliest case of chytridiomycosis was found in a X. laevis specimen from 1938. The study also suggests that chytridiomycosis had been a stable infection in southern Africa from 23 years prior to finding any infected outside of Africa. There is more recent information that the species originated on the Korean peninsula and was spread by the trade in frogs.{{Cite news|url=https://www.nytimes.com/2018/05/10/science/frogs-fungus-korea.html|title=Frog-Killing Fungus Found to Have Origins on Korean Peninsula|date=2018-05-10|work=The New York Times|access-date=2018-05-20|language=en-US|issn=0362-4331}}

American bullfrogs (Lithobates catesbeianus), also widely distributed, are also thought to be carriers of the disease due to their inherent low susceptibility to B. dendrobatidis infection.{{cite journal | doi = 10.1046/j.1472-4642.2003.00013.x |vauthors=Kats LB, Ferrer RP | year = 2003 | title = Alien predators and amphibian declines: review of two decades of science and the transition to conservation | journal = Diversity and Distributions | volume = 9 | issue = 2| pages = 99–110 |s2cid=85969277 | doi-access = free |bibcode=2003DivDi...9...99K }}{{cite journal |vauthors=Daszak P, Strieby A, Cunningham AA, Longcore JE, Brown CC, Porter D | year = 2004 | title = Experimental evidence that the bullfrog (Rana catesbeiana) is a potential carrier of chytridiomycosis, an emerging fungal disease of amphibians | journal = Herpetological Journal | volume = 14 | pages = 201–207 }} The bullfrog often escapes captivity and can establish feral populations where it may introduce the disease to new areas. It has also been shown that B. dendrobatidis can survive and grow in moist soil and on bird feathers, suggesting that B. dendrobatidis may also be spread in the environment by birds and transportation of soils.{{cite journal |vauthors=Johnson ML, Speare R |title=Possible modes of dissemination of the amphibian chytrid Batrachochytrium dendrobatidis in the environment |journal=Dis. Aquat. Org.|volume=65 |issue=3 |pages=181–6 |date=July 2005 |pmid=16119886 |doi= 10.3354/dao065181|url=https://researchonline.jcu.edu.au/6209/1/6209_Johnson___Speare_2005.pdf|doi-access=free }} Infections have been linked to mass mortalities of amphibians in North America, South America, Central America, Europe and Australia.{{cite journal | doi = 10.1046/j.1523-1739.1999.97185.x | author = Lips KR | s2cid = 86205459 | year = 1999 | title = Mass mortality and population declines of anurans at an upland site in western Panama | journal = Conservation Biology | volume = 13 | issue = 1| pages = 117–125 | bibcode = 1999ConBi..13..117L }}{{cite journal |doi=10.1046/j.1472-4642.2003.00016.x |vauthors=Daszak P, Cunningham AA, Hyatt AD |year=2003 |title=Infectious disease and amphibian population declines |url=http://www.conservationmedicine.org/papers/Infect.%20Dis.%20&%20Amphib%20Pop%20Declines%202003.pdf |journal=Diversity and Distributions |volume=9 |issue= 2|pages=141–50 |bibcode=2003DivDi...9..141D |s2cid=16838374 |url-status=dead|archive-url=https://web.archive.org/web/20081226223230/http://www.conservationmedicine.org/papers/Infect.%20Dis.%20%26%20Amphib%20Pop%20Declines%202003.pdf |archive-date=2008-12-26 }}{{cite journal | doi = 10.3354/dao064247 |vauthors=Herrera RA, Steciow MM, Natale GS | year = 2005 | title = Chytrid fungus parasitizing the wild amphibian Leptodactylus ocellatus (Anura: Leptodactylidae) in Argentina | journal = Diseases of Aquatic Organisms | volume = 64 | issue = 3| pages = 247–52 | pmid = 15997823 | doi-access = free }} B. dendrobatidis has been implicated in the extinction of the sharp-snouted day frog (Taudactylus acutirostris) in Australia.{{cite journal | doi = 10.1007/s10393-005-0012-6 |vauthors=Schloegel LM, Hero JM, Berger L, Speare R, McDonald K, Daszak P | year = 2006 | title = The decline of the sharp-snouted day frog (Taudactylus acutiostris): the first documented case of extinction by infection in a free-ranging wildlife species? | journal = EcoHealth | volume = 3 | pages = 35–40 |citeseerx=10.1.1.602.3591 |s2cid=11114174 }}

A wide variety of amphibian hosts have been identified as being susceptible to infection by B. dendrobatidis, including wood frogs (Lithobates sylvatica),{{cite journal | author = Reeves MK | year = 2008 | title = Batrachochytrium dendrobatidis in wood frogs (Lithobates sylvatica) from Three National Wildlife Refuges in Alaska, USA | journal = Herpetological Review | volume = 39 | issue = 1| pages = 68–70 }} the mountain yellow-legged frog (Lithobates muscosa),{{cite journal |vauthors=Andre SE, Parker J, Briggs CJ | year = 2008 | title = Effect of temperature on host response to Batrachochytrium dendrobatidis infection in the mountain yellow-legged frog (Lithobates muscosa) | journal = Journal of Wildlife Diseases | volume = 44 | issue = 3| pages = 716–720 | pmid = 18689660 | doi=10.7589/0090-3558-44.3.716| doi-access = free }} the southern two-lined salamander (Eurycea cirrigera),{{cite journal | doi = 10.1656/1528-7092-7.3.551 |vauthors=Byrne MW, Davie EP, Gibbons JW | year = 2008 | title = Batrachochytrium dendrobatidis occurrence in Eurycea cirrigera | journal = Southeastern Naturalist | volume = 7 | issue = 3| pages = 551–555 |s2cid=84713825 }} San Marcos Salamander (Eurycea nana), Texas Salamander (Eurycea neotenes), Blanco River Springs Salamander (Eurycea pterophila), Barton Springs Salamander (Eurycea sosorum), Jollyville Plateau Salamander (Eurycea tonkawae),{{cite journal | doi = 10.1007/s10393-009-0229-x |vauthors=Gaertner JP, Forstner MR, O'Donnell L, Hahn D | year = 2009 | title = Detection of Batrachochytrium dendrobatidis in endemic salamander species from Central Texas | journal = EcoHealth | volume = 6 | issue = 1| pages = 20–26 | pmid = 19424755 |s2cid=23997421 }} Ambystoma jeffersonianum,{{cite journal |vauthors=Brodman R, Briggler JT | year = 2008 | title = Batrachochytrium dendrobatidis in Ambystoma jeffersonianum larvae in southern Indiana | journal = Herpetological Review | volume = 39 | issue = 3| pages = 320–321 }} the western chorus frog (Pseudacris triseriata), the southern cricket frog (Acris gryllus), the eastern spadefoot toad (Scaphiopus holbrooki), the southern leopard frog (Lithobates sphenocephala),{{cite journal |vauthors=Lehtinen RM, Kam Y-C Richards CL | year = 2008 | title = Preliminary surveys for Batrachochytrium dendrobatidis in Taiwan | journal = Herpetological Review | volume = 39 | issue = 3| pages = 317–318 }} the Rio Grande Leopard frog (Lithobates berlandieri),{{cite journal |vauthors=Lovich R, Ryan MJ, Pessier AP, CLaypool B | year = 2008 | title = Infection with the fungus Batrachochytrium dendrobatidis in a non-native Lithobates berlandieri below sea level in the Coachella Valley, California, USA | journal = Herpetological Review | volume = 39 | issue = 3| pages = 315–317 }} the Sardinian newt (Euproctus platycephalus),{{cite journal |vauthors=Bovero S, Sotgiu G, Angelini C, Doglio S, Gazzaniga E, Cunningham AA, Garner TW | year = 2008 | title = Detection of chytridiomycosis caused by Batrachochytrium dendrobatidis in the endangered sardinian newt (Euproctus platycephalus), in Southern Sardinia, Italy | journal = Journal of Wildlife Diseases | volume = 44 | issue = 3| pages = 712–715 | pmid = 18689659 | doi=10.7589/0090-3558-44.3.712| doi-access = free }} and endemic frog species, the Beysehir frog in Turkey (Pelophylax caralitanus).{{cite journal |vauthors=Erismis UC, Konuk M, Yoldas T, Agyar P, Yumuk D, Korcan SE | year = 2014 | title = Survey of Turkey's endemic amphibians for chytrid fungus Batrachochytrium dendrobatidis, in Turkey | journal = Journal of Wildlife Diseases | volume = 111 | issue = 2| pages = 153–157 | pmid = 25266902 | url = https://www.int-res.com/articles/dao2014/111/d111p153.pdf | doi = 10.3354/dao02742| doi-access = free }}

While most studies concerning B. dendrobatidis have been performed in various locations across the world, the presence of the fungus in Southeast Asia remains a relatively recent development. The exact process through which the fungus was introduced to Asia is not known, however, as mentioned above, it has been suggested transportation of asymptomatic carrier species (e.g. Lithobates catesbeianus, the American Bullfrog) may be a key component in the dissemination of the fungus, at least in China.{{cite journal | author = Bai, C. |author2=T. W. Garner |author3=Y. Li |name-list-style=amp | year = 2010 | title = First evidence of Batrachochytrium dendrobatidis in China: discovery of chytridiomycosis in introduced American bullfrogs and native amphibians in the Yunnan Province, China | journal = Dis Aquat Org | volume = 92 |issue=1 | pages = 241–244 |doi=10.1007/s10393-010-0307-0 |pmid=20372969 |s2cid=24321977 }} Initial studies demonstrated the presence of the fungus on island states/countries such as Hong Kong,{{cite journal |vauthors=Rowley J, Chan SK, Tang WS, Speare R, Skerratt LF, Alford RA, Cheung KS, Ho CY, Campbell R | year = 2007 | title = Survey for the amphibianchytrid Batrachochytrium dendrobatidis in Hong Kong in native amphibians and in the international amphibian trade | journal = Diseases of Aquatic Organisms | volume = 78 | issue = 2 | pages = 87–95 | doi=10.3354/dao01861| pmid = 18286805 | doi-access = free }} Indonesia,{{cite journal | vauthors = Kusrini MD, Skerratt LF, Garland S, Berger L, Endarwin W | year = 2008 | title = Chytridiomycosis in frogs of Mount Gede Pangrango, Indonesia | url = https://researchonline.jcu.edu.au/6196/1/6196_Kusrini_et_al_2008.pdf| journal = Diseases of Aquatic Organisms | volume = 82 | issue = 3 | pages = 187–194 | doi=10.3354/dao01981 | pmid=19244970| doi-access = free }} Taiwan, and Japan.{{cite journal |vauthors=Fisher MC, Garner TW, Walker SF | year = 2009 | title = Global emergence of Batrachochytrium dendrobatidis and amphibian chytridiomycosis inspace, time, and host | journal = Annual Review of Microbiology | volume = 63 | pages = 291–310 | doi = 10.1146/annurev.micro.091208.073435 | pmid=19575560 }} Soon thereafter, mainland Asian countries such as Thailand,{{cite journal | vauthors = McLeod DS, Sheridan JA, Jiraungkoorskul W, Khonsue W | year = 2008 | title = A survey for chytrid fungus in Thai amphibians | journal = Raffles Bulletin of Zoology | volume = 56 | pages = 199–204 }} South Korea,{{cite journal | author = Yang H | author2 = H. Baek | author3 = R. Speare | author4 = R. Webb | author5 = S. Park | author6 = T. Kim | author7 = K.C. Lasat er | author8 = S. Shin | author9 = S. Son | author10 = J. Park | author11 = M. Min | author12 = Y. Kim | author13 = K. Na | author14 = H. Lee | author15 = S. Park | name-list-style = amp | year = 2008 | title = First detection of the amphibian chytrid fungus Batrachochytrium dendrobatidis in free-ranging populations of amphibians on mainland Asia: survey in South Korea | journal = Dis Aquat Org | volume = 86 | issue = 1 | pages = 9–13 | doi=10.3354/dao02098| pmid = 19899344 | doi-access = free }} and China{{cite journal | author = Wei, Y. | author2 = K. Xu | author3 = D.-Z. Zhu | author4 = X.-F. Chen | author5 = X.-L. Wang | name-list-style = amp | year = 2010 | title = First Early-spring survey for Batrachochytrium dendrobatidis in wild Rana dybowskii in Heilongjiang Province, China | journal = Dis Aquat Org | volume = 92 | issue = 3 | pages = 241–244 | doi=10.3354/dao02172| pmid = 21268987 | doi-access = free }} reported incidents of B. dendrobatidis among their amphibian populations. Much effort has been put into classifying herpetofauna in countries like Cambodia, Vietnam, and Laos where new species of frogs, toads, and other amphibians and reptiles are being discovered on a frequent basis.{{Citation needed|reason=I'm sure evidence of "much work" would be appreciated by researchers here.|date=September 2024}} Scientists simultaneously are swabbing herpetofauna in order to determine if these newly discovered animals possess traces of the fungus.{{Citation needed|reason=Which scientists?|date=September 2024}}

In Cambodia, a study showed B. dendrobatidis to be prevalent throughout the country in areas near Phnom Penh (in a village <5 km), Sihanoukville (frogs collected from the local market), Kratie (frogs collected from streets around the town), and Siem Reap (frogs collected from a national preserve: Angkor Centre for Conservation of Biodiversity).{{cite journal |vauthors=Gaertner JP, Mendoza JA, Forstner MR, Neang T, Hahn D | year = 2011 | title = Detection of Batrachochytrium dendrobatidis in frogs from different locations in Cambodia | journal = Herpetological Review | volume = 42 | pages = 546–548 }} Another study in Cambodia questioned the potential anthropological impact in the dissemination of B. dendrobatidis on local amphibian populations in three different areas in relation to human interaction: low (an isolated forest atop a mountain people rarely visit), medium (a forest road ~15 km from a village that is used at least once a week), and high (a small village where humans interact with their environment on a daily basis). Using quantitative PCR, evidence of B. dendrobatidis was found in all three sites with the highest percentage of amphibians positive for the fungus from the forest road (medium impact; 50%), followed by the mountain forest (low impact; 44%) and village (high impact; 36%).{{cite journal |vauthors=Mendoza JA, Gaertner JP, Holden J, Forstner MR, Hahn D | year = 2011 | title = Detection of Batrachochytrium dendrobatidis on amphibians in Pursat Province, Cambodia | journal = Herpetological Review | volume = 42 | pages = 542–545 }} Human influence most likely explains detection of the fungus in the medium and high areas, however it does not provide an adequate explanation why even isolated amphibians were positive for B. dendrobatidis. This may go unanswered until more research is performed on transmission of the fungus across landscapes. However, recent evidence suggests mosquitoes may be a possible vector which may help spread B. dendrobatidis.{{Citation needed|reason=What "recent evidence"?|date=September 2024}} Another study in French Guiana reports widespread infection, with 8 of 11 sites sampled being positive for B. dendrobatidis infection for at least one species.{{cite journal |vauthors=Courtois EA, Gaucher P, Chave J, Schmeller DS | year = 2015 | title = Widespread Occurrence of Bd in French Guiana, South America | doi = 10.1371/journal.pone.0125128 | pmid = 25902035 | pmc = 4406614 | journal = PLOS ONE | volume = 10 | issue = 4 | pages = e0125128 | bibcode = 2015PLoSO..1025128C | doi-access = free }} This study suggests that Bd (Batrachochytrium dendrobatidis) is more widespread than previously thought.

Worldwide amphibian populations have been on a steady decline due to an increase in the disease chytridiomycosis, caused by the Bd fungus.{{Citation needed|reason=Unsubstantiated; cite source.|date=September 2024}} Bd can be introduced to an amphibian primarily through water exposure, colonizing the digits and ventral surfaces of the animal's body most heavily and spreading throughout the body as the animal matures. Potential effects of this pathogen are hyperkeratosis, epidermal hyperplasia, ulcers, and most prominently the change in osmotic regulation often leading to cardiac arrest.{{Cite web |title=Chytridiomycosis |url=http://www.amphibiaweb.org/chytrid/chytridiomycosis.html |archive-url=https://web.archive.org/web/20160526003756/http://www.amphibiaweb.org/chytrid/chytridiomycosis.html |archive-date=2016-05-26 |access-date=2016-05-27 |website=www.amphibiaweb.org}} The death toll on amphibians is dependent on a variety of factors but most crucially on the intensity of infection.{{Cite journal |last=Wu |first=Nicholas C. |date=April 2023 |title=Pathogen load predicts host functional disruption: A meta-analysis of an amphibian fungal panzootic |url=https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.14245 |journal=Functional Ecology |language=en |volume=37 |issue=4 |pages=900–914 |doi=10.1111/1365-2435.14245 |bibcode=2023FuEco..37..900W |issn=0269-8463|url-access=subscription }} Certain frogs adopt skin sloughing as a defense mechanism for B. dendrobatidis; however, this is not always effective, as mortality fluctuates between species.{{Cite journal |last1=Wu |first1=Nicholas C. |last2=Cramp |first2=Rebecca L. |last3=Ohmer |first3=Michel E. B. |last4=Franklin |first4=Craig E. |date=2019-01-27 |title=Epidermal epidemic: unravelling the pathogenesis of chytridiomycosis |journal=Journal of Experimental Biology |volume=222 |issue=Pt 2 |doi=10.1242/jeb.191817 |pmid=30559300 |issn=1477-9145|doi-access=free }}{{Cite journal |last1=Wu |first1=Nicholas C. |last2=Cramp |first2=Rebecca L. |last3=Franklin |first3=Craig E. |date=2018-02-27 |title=Body size influences energetic and osmoregulatory costs in frogs infected with Batrachochytrium dendrobatidis |journal=Scientific Reports |language=en |volume=8 |issue=1 |pages=3739 |doi=10.1038/s41598-018-22002-8 |issn=2045-2322 |pmc=5829222 |pmid=29487313|bibcode=2018NatSR...8.3739W }} For example, the Fletcher frog, despite practising skin sloughing, suffers from a particularly high mortality rate when infected with the disease compared to similar species like Lim. peronii and Lim. tasmaniensis. Some amphibian species have been found to adapt to infection after an initial die-off with survival rates of infected and non-infected individuals being equal.{{cite journal |last1=DiRenzo |first1=Graziella |last2=Zipkin |first2=Elise |last3=Grant |first3=Evan Campbell |last4=Royle |first4=J. Andrew |last5=Longo |first5=Ana |last6=Zamudio |first6=Kelly |last7=Lips |first7=Karen |title=Eco-evolutionary rescue promotes host–pathogen coexistence |journal=Ecological Applications |volume=28 |issue=8 |pages=1948–1962 |date=3 October 2018 |doi=10.1002/eap.1792|pmid=30368999 |doi-access=free |bibcode=2018EcoAp..28.1948D }}

According to a study by the Australian National University, the Bd fungus has caused the decline of 501 amphibian species—about 6.5 percent of the world's known total. Of these, 90 species have been entirely wiped out and another 124 species have declined by more than 90 percent, and the odds of the affected species recovering to a healthy population are doubtful.{{cite news |last=Yong |first=Ed |url=https://www.theatlantic.com/science/archive/2019/03/bd-frogs-apocalypse-disease/585862/ |title=The Worst Disease Ever Recorded |work=The Atlantic |date=2019-03-28 |access-date=2019-03-28 }} However, these conclusions were criticized by later studies, which proposed that Bd was not the primary driver of amphibian declines as suggested by the previous study.{{Cite journal|last1=Lambert|first1=Max R.|last2=Womack|first2=Molly C.|last3=Byrne|first3=Allison Q.|last4=Hernández-Gómez|first4=Obed|last5=Noss|first5=Clay F.|last6=Rothstein|first6=Andrew P.|last7=Blackburn|first7=David C.|last8=Collins|first8=James P.|last9=Crump|first9=Martha L.|last10=Koo|first10=Michelle S.|last11=Nanjappa|first11=Priya|date=2020-03-20|title=Comment on "Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity"|journal=Science|language=en|volume=367|issue=6484|pages=eaay1838|doi=10.1126/science.aay1838|issn=0036-8075|pmid=32193293|doi-access=free}}

One amphibian particular affected by Bd is Lithobates clamitans. Bd kills this frog by interfering with external water exchange, causing an imbalance in ion exchange that leads to heart failure.{{cn|date=September 2024}}

Some amphibian species are immune to Bd or possess biological protections against the fungus.{{Cite journal |last1=Pereira |first1=K. E. |last2=Woodley |first2=S. K. |date=2021-01-11 |title=Skin defenses of North American salamanders against a deadly salamander fungus |url=http://dx.doi.org/10.1111/acv.12666 |journal=Animal Conservation |volume=24 |issue=4 |pages=552–567 |doi=10.1111/acv.12666 |bibcode=2021AnCon..24..552P |s2cid=232030040 |issn=1367-9430|url-access=subscription }} One such species is the alpine salamander (Salamandra atra), which includes several subspecies that share a common trait: toxicity. A 2012 study demonstrated that none of the alpine salamanders in the area were infected with Bd, despite the fungus' prevalence.{{Cite book |last=R |first=Lötters, S Kielgast, J Sztatecsny, M Wagner, N Schulte, U Werner, P Rödder, D Dambach, J Reissner, T Hochkirch, A Schmidt, B |url=http://worldcat.org/oclc/1030045649 |title=Absence of infection with the amphibian chytrid fungus in the terrestrial Alpine salamander, Salamandra atra |date=2012-04-30 |publisher=Deutsche Gesellschaft für Herpetologie und Terrarienkunde (DGHT) |oclc=1030045649}} Alpine salamanders produce alkaloid compounds{{Cite journal |last1=DE MEESTER |first1=Gilles |last2=ŠUNJE |first2=Emina |last3=PRINSEN |first3=Els |last4=VERBRUGGEN |first4=Erik |last5=VAN DAMME |first5=Raoul |date=2020-10-13 |title=Toxin variation among salamander populations: discussing potential causes and future directions |url=http://dx.doi.org/10.1111/1749-4877.12492 |journal=Integrative Zoology |volume=16 |issue=3 |pages=336–353 |doi=10.1111/1749-4877.12492 |pmid=32965720 |hdl=10067/1718680151162165141 |s2cid=221862886 |issn=1749-4877|hdl-access=free }} or toxic peptides that may protect them against microbial infections.{{Cite journal |last1=Lüddecke |first1=Tim |last2=Schulz |first2=Stefan |last3=Steinfartz |first3=Sebastian |last4=Vences |first4=Miguel |date=2018-09-04 |title=A salamander's toxic arsenal: review of skin poison diversity and function in true salamanders, genus Salamandra |url=http://dx.doi.org/10.1007/s00114-018-1579-4 |journal=The Science of Nature |volume=105 |issue=9–10 |page=56 |doi=10.1007/s00114-018-1579-4 |pmid=30291447 |bibcode=2018SciNa.105...56L |s2cid=253637272 |issn=0028-1042|url-access=subscription }}

• Pathogenic fungi
• Decline in amphibian populations
• Ranavirus

==References==

{{Reflist|3}}

• {{cite journal|last=Daszak|first=Peter|author2=Berger L|author3=Cunningham AA|author4=Hyatt AD|author5=Green DE|author6=Speare R.|title=Emerging Infectious Diseases and Amphibian Population Declines|journal=Emerging Infectious Diseases|year=1999|volume=5|issue=6|pages=735–748|doi=10.3201/eid0506.990601|pmid=10603206|pmc=2640803}}
• {{cite journal|last=Johnson|first=Megan L.|author2=Speare, Richard|title=Survival of Batrachochytrium dendrobatidis in Water: Quarantine and Disease Control Implications|journal=Emerging Infectious Diseases|date=August 2003|volume=9|issue=8|pages=915–921|doi=10.3201/eid0908.030145|pmid=12967488|pmc=3020615}}

{{Commons category|Batrachochytrium dendrobatidis}}

{{Wikispecies|Batrachochytrium}}

• [https://web.archive.org/web/20090123174320/http://bama.ua.edu/~nsfpeet/ Chytrid Fungi Online] at University of Alabama
• {{MycoBank|450228}}
• {{IndexFungorum|450228}}

{{Taxonbar|from=Q1543914}}

{{Authority control}}

Category:Aquatic fungi

Category:Chytridiomycota

Category:Fungi described in 1999

Category:Parasitic fungi

Category:Fungus species