Monday, October 15, 2012

Science and the Chytrid Epidemic by Lex Miller

  Batrachochytrium dendrobatidis
(Bd), more commonly known as the chytrid fungus is a widespread epidemic amongst amphibians that is pushing many species to extinction. The chytrid fungus causes the disease chytridiomycosis which thickens the skin of those amphibians infected with the disease. How does this kill amphibians? When the skin is thickened it reduces the ability for ion transport across the skin membrane, which in turn leads to cardiac arrest. This disease is ravaging frog populations all over the globe. However, other amphibians such as the salamanders and caecilians are not as heavily affected by the epidemic.

  Chytrid is an aquatic fungus that releases zoospores into water sources. The dumping of infected water into an environment can lead to infection of the amphibians in that ecosystem. A study conducted by leading Zoologist Vredenburg also suggests that the amphibians themselves are natural carriers that spread the fungus from habitat to habitat over land as well. (Vredenburg et al, 2007). Many herpetological societies websites’ have pages dedicated to prevention of anthropogenic-mediated spreading of the disease by educating readers about cleaning equipment used by herpetologists and amphibian enthusiasts. (Amphibiaweb.org, 2012).

SECTION 1: THE SOCIETAL AND GLOBAL ISSUE

  Amphibians have been on Earth for over 250 million years. They have survived four of the six Great Mass Extinctions. Now the amphibians are disappearing at an alarming rate. In some frog species populations it takes as little as three years from the time chytrid is introduced to extinction. Removing any species from an ecosystem disrupts homeostasis and generally leads to a collapse of that ecosystem. Considering that entire species of frogs are disappearing from all types of ecosystems and environments, one can conclude that there is something seriously wrong with our planet. While some scientists blame climate change as a factor in amphibian extinctions, research has shown that chytridiomycosis is the main culprit in amphibians vanishing from certain ecosystems.

  The destruction of ecosystems is an issue that affects humans. The chytrid induced extinctions of many species of frogs lead scientists to believe that "ecosystems are beginning to unravel, and the potential to discover important medical cures may be lost forever." (PBS.org, 2012). One study shows that frogs have played an integral part in investigations that have resulted in ten percent of all the Nobel Prizes in Physiology and Medicine. (SavetheFrogs.com, 2012). One can assume that the reduction in frog biodiversity is directly related to a reduction in scientists’ abilities to produce breakthroughs in the field of medicine. Essentially, humans are dependent on amphibians for health and wellness. The proof is in the frogs themselves, such as the Whites Tree Frog which produces a substance that can block HIV transmission or the Waxy Monkey frog that secretes a chemical that treats antibiotic-resistant strains of Staphylococcus.

  The loss of frog species from environments takes a huge link right out of the middle of the food chain in most ecosystems. The effects of amphibian decline and extinctions on humans are already being documented. "In rural West Africa, Mohneke and Rodel (2009) point out that alteration of freshwater ecosystems resulting in the loss of larval anurans may have significant consequences for both humans and cattle; the loss of tadpoles impacts many aspects of freshwater ecology, with consequences potentially including an increase in malaria and significant decrease in stream health." (Amphibiaweb.org, 2012). At the very least the lack of tadpoles in streams and lakes leads to an increase in algae blooms which in turn increases the nitrogen levels and creates an anoxic environment. In turn this reduces further biodiversity and creates unhealthy water.

  Globally the chytrid fungus is present in amphibian populations on every continent except for Antarctica. However, there is one remaining amphibian refuge in the world: Madagascar. There has been no trace of chytrid on the island, and government agencies are hard at work to prevent the fungus from being introduced. The effort put into prevention in Madagascar is fueled by this fact: chytridiomycosis has been associated with the endangerment and/or extinction of over 200 species of frogs in the past thirty years world-wide. (Amphibiaweb.org, 2012).
 
SECTION 2: SCIENCE’S INFLUENCE IN SPREADING CHYTRIDIOMYCOSIS

  A study was conducted in 2004 that tested museum samples of African frogs from the years 1879 to 1999 for the chytrid fungus. The first known case of chytrid in amphibians is attributed to a sample taken from a preserved Xenopus laevis in South Africa from 1938. Of the specimen sampled there were not many that were positive for chytrid, but the presence of the fungus suggested further research be done regarding its spread. The reason the researchers pursued the X. laevis as the initial host of chytrid and eventual carrier was due to the prevalence of the small frog being exported globally for scientific research. "Soon after the discovery of the pregnancy assay for humans in 1934, enormous quantities of the species were caught in the wild in southern Africa and exported around the world. The pregnancy assay is based on the principle that ovulation in X. laevis is induced by injection with urine from pregnant women because of high levels of gonadotropic hormones in the urine. X. laevis was selected as the most suitable amphibian for investigating the mechanism of the mating reflex because of the relative ease with which the animal can be maintained in captivity." (Weldon et al, 2004). This made the X. laevis a popular import to many cities across the globe. "After the introduction of nonbiological pregnancy tests, X. laevis became important as a model for the scientific study of immunity and later embryology and molecular biology. In the importing country, escaped frogs, the water they lived in, or both, could have come into contact with local amphibians species, and subsequent transmission of the disease could have followed." (Weldon et al, 2004). It appears that science intended to study these frogs for the greater good of mankind, but in the process contributed to the decimation of amphibian populations on Earth.

  How could this destructive organism be spread so easily globally? The simple answer is that X. laevis is not adversely affected by the chytrid fungus, does not appear sick when infected, and therefore was exported to every inhabited continent without discretion. The X. laevis was the most popular laboratory animal amongst British naturalists, chemists, and biologist in the late nineteenth century and early twentieth century. One was considered a serious scientist if they could obtain a batch of Xenopus from Africa for their research. The benefits of studying these small frogs were that they were easy to care for, required a smaller space than other traditional laboratory animals such as mice and rabbits, and did not produce as many foul odors. The downside was that they were small enough to escape into the wild. Once feral populations of X. laevis were established it can be assumed that native populations of amphibians were easy prey for the chytrid fungus they carried with them. "In support of B. dendrobatidis as a novel pathogen are mass mortalities in susceptible amphibian populations that suggest that the hosts are naive or new, virulent fungal genotype has spread through existing fungal populations." (Vredenburg et al, 2007). It is believed that chytrid in California is due to the escape and contamination from "tank water" from studies on X. laevis conducted by Stanford University. One can see the ease of which this epidemic spread globally if you consider that one of the world’s top universities may be responsible for contaminating an area as large as California.

  Evidence for proving that scientific study is the cause of the chytrid epidemic by transporting the Xenopus species of frogs around the globe may "involve a series of key steps: 1) occurrence of B. dendrobatidis in an amphibian vector in southern Africa that is relatively resistant to disease (X. laevis), 2) sudden rise in 1935 of export trade in this vector because of technological advances (Xenopus pregnancy test), 3) escape of pathogen from the exported Xenopus to establish new foci in other countries (possibly expedited in some countries by establishment of feral populations of X. laevis), 4) transmission into other vector amphibians (food and pet trade), and 5) further transmission to other countries along different trade routes in key amphibian vectors that move in high numbers and become established in commercial populations and closely interact with wild frogs, which likely leads to feral populations (food frogs Rana catesbeiana)." (Weldon et al, 2004).
 
SECTION 3: SCIENCE ADDRESSING THE ISSUE OF THE CHYTRID EPIDEMIC

  Most scientific organizations and herpetological societies concerned for amphibians are focusing on prevention of spreading the pathogen. Since science has yet to prove the mode of naturally occurring travel for chytrid, these agencies focus on anthropogenic-mediated contamination of environments. There are websites dedicated to educating readers about the spread of chytrid. The websites suggest "cleaning boots and field equipment (such as dip nets) with a ten percent Clorox solution in water". (Amphibiaweb.org, 2012). Field researchers studying amphibians now take great care in cleaning equipment when traveling from habitat to another to prevent this mode of chytrid transportation. However, there are two other ways that humans spread chytrid from place to place unintentionally: one is by utilizing amphibians as bait for fishing, and the other is collection and releasing pet frogs or tadpoles. Amphibiaweb.org suggests that "amphibians should not be used as bait or released back into the wild once they have been taken into captivity." (Amphibiaweb.org, 2012).
 
  A more scientific approach is being studied in laboratories all over the globe for preventing and curing chytridiomycosis. The studies that show the most promise are those that are investigating natural remedies to the epidemic. Studies have shown that amphibians with naturally occurring cultures of the bacteria Janthinobacterium lividum on their skin are resistant to death from chytrid fungal infections. It has been proven that J. lividum can also prevent the effects when added to species of amphibians that do not have the bacteria naturally. (Wikipedia.org, 2012). This is caused by the metabolite violacein, which has antifungal properties and also give J. lividum its violet color. Another promising study has shown that the water flea (Daphnia magna) will eat the spores of chytrid and are another credible candidate for preventing the spread of chytrid in the wild. While science has not come up a plan for a wide scale attack on the epidemic, one can see that the implementation of these cures and prevention plans are on the horizon.

  Current research and experimentation with drugs have proven effective for curing chytridiomycosis in captive colonies of amphibians. One study tested an antibiotic that is used to treat pink eye to rid their subjects of chytridiomycosis and the results were conclusive that in a very short time (eighteen days) chytridiomycosis could be cured. The scientists rubbed the ointment on the frog’s skin and soaked their paper towel substrate for the study. This particular antibiotic had no adverse side effects on the frogs, unlike another antifungal cream itraconazole that caused some kidney damage in frogs. This study conducted by the San Diego Zoological Society continued the experiment by attempting to re-infect the frogs treated with the ointment. While the frogs re-contracted chytridiomycosis the disease went away after only a few days. However, this is not a logical treatment for amphibians in the wild, as it can be hard to keep the concentrations of the antibiotic high enough to be effective in water systems without destroying some of the ecosystem. (Roach, 2007).

  Immunization studies were conducted at the University of California, Berkeley’s Biology department by Stice and Briggs. Immunization has many scientific implications that could lead to a cure and prevention in wild populations. For their study Stice and Briggs obtained three groups of Rana muscosa eggs that were free of chytrid. The study ended after 108 days and the results of the experiment concluded that chytridiomycosis could not be prevented in R. muscosa from immunization. (Stice & Briggs, 2010). While this particular species was not able to be immunized, there is still hope for other amphibians that need to be given the same treatment in laboratory experiments that could unlock the secret to destroying Bd.
 
SECTION 4: SCIENTIFICALLY INFORMED SOCIETAL AND GLOBAL DECISIONS

  Humans must decide that frogs and other amphibians are important to our planet. Science must be responsible for proving to society that amphibians are essential aspects of ecosystem health. In doing so the scientific community must also provide ways for humans to contribute to the solution of the amphibian extinction that is currently happening. Therefore it falls to the governing powers to persuade society.
Amphibians are traded and transported globally as pets, food items, and research mediums. Now that chytrid has been proven to be the major cause of amphibian extinction there must be regulations put in place to ensure that even more wild populations are not infected. A mandatory testing period for all amphibians being transported across borders could possibly derail more accidental infections of native species. However, this would be extremely hard to regulate as some countries value frogs as food more than an important biological factor in ecosystems. Black market amphibian trade is already rampant in all countries. Ambystomids are illegal to own in California, yet one can often find them in non-chain pet stores throughout the state. It would take a conscientious decision by humanity to decide that these acts must be regulated and that chytrid is a real danger to ecosystems that society can ultimately prevent.

  Law makers at the state level have given the Department of Fish and Game more power to restrict movement of chytrid in the past decade. It is illegal to own some types of endangered frogs and salamanders in California and is illegal to even import any Xenopus at all. While the DFG remains diligent against invasive species, an epidemic like chytridiomycosis is harder to look for than someone releasing a python into a local park. Laws against dumping amphibian tank water and releasing amphibians back into the wild should be strict, and research facilities should be scrutinized more so than they have in the past for their disposal procedures. In California one can "field herp" and collect amphibians with a fishing license, but the regulations should be stricter on who may own this type of license and create one specifically for the collection of amphibians for research purposes. Again, this may be hard to convince society about the necessity of such laws and restrictions, but it is imperative that scientific data be available to all people so that they masses can make a choice to care about the epidemic plaguing our ecosystems.

  While people may not care about the disappearance of frogs from ecosystems, they do care about what is put in their water. With the recent discoveries of how antibiotics can fight off infection from chytrid the reality is that people do not want scientists dumping antibiotics in water systems. Introducing antibiotics into an ecosystem is difficult and it is hard to maintain concentrations high enough to be effective without destroying the ecosystem itself. There may be more feasible solutions in the future, but will society allow science to tamper with the environment for a cause they may not see the value of? That is why it is important of science to prove that this epidemic is real and has consequences beyond the scope of losing a few frogs.
 
SECTION 5: SCIENCE AND THE FUTURE OF THE CHYTRID EPIDEMIC
There are two plausible futures for our planet as far as the chytridiomycosis epidemic is concerned:
1. The science community dedicated to the conservation of amphibians fails at finding a globally useable cure for chytridiomycosis. As a result the only remaining amphibians are those who had an original immunity to the disease and the biodiversity of our ecosystems crashes. We lose valuable resources for medicine and other scientific applications without amphibians and their remarkable secretions and functions. Future generations of curious humans will have to see museum exhibits and captive colonies of frogs and other organisms in the food chains affected by the loss of frogs. Diseases such as malaria rise to epidemic proportions in countries that were under developed before the extinction of their native species of amphibians. Crops devastated by insects that would normally be consumed by amphibians cause a food shortage that creates global panic and strife.

2. Scientists discover an antifungal solution to chytrid. Antifungals "may prove more acceptable to spraying in the wild" than antibiotics and would be easier to administer globally. (Roach, 2007). Once the antifungal dispersal removes chytrid from the remaining amphibian populations, those species that were captured to preserve their genome can be reintroduced into their natural habitats. One study suggests that it would take approximately fifteen years for an amphibian population to re-establish itself and thrive. (Amphibiaweb.org, 2012). Once the amphibians are restored the ecosystems of the Earth would self-regulate and return to homeostasis.
  Science created this issue of epidemic proportions. The need for humans to advance their scientific understanding of themselves helped spread the chytrid fungus world-wide. While one hopes for a future where frogs a chirping and croaking in all habitats once again, there are no solutions that will lead us to that utopian realization as of yet. With the help of science and an awakening of society the chytridiomycosis caused extinction of amphibians can be stopped. This age of discovery that we as humans are currently in is an age when possibilities are endless, and this is the perfect time to find a cure that is globally conducive to restoring amphibians to their past ecological populations.
 
 
  
References
Amphibiaweb (2012). Chytridiomycosis. Retrieved from: http://www.amphibiaweb.org

Public Broadcasting Service (PBS) (2012). Frogs: The Thin Green Line.
Retrieved from: http://www.pbs.org

Roach, J. (2007). Eye Ointment Can Cure Frog Fungus. National Geographic News.

Save the Frogs (2012). Frogs: Bioindicators. Retrieved from: http://www.savethefrogs.com

Stice M., Briggs C. (2010). Immunization is Ineffective at Preventing Infection and
Mortality Due to the Amphibian Chytrid Fungus Batrachochytrium dendrobatidis.
Journal of Wildlife Diseases. 46(1) pp. 70-77. Wildlife Diseases Association.

Vredenburg V., Morgan J., Rachowicz L., Knapp R., Stice M., Tunstall T., Bingham R.,
Parker J., Longcore J., Moritz C., Briggs C., and Taylor J. (2007).
Population Genetics of the Frog-killing Fungus Batrachochytrium dendrobatidis.
Retrieved from: http://www.pnas.org

Weldon C., du Preez L., Hyatt A., Muller R., Speare R. (2004). Origin of the Amphibian
Chytrid Fungus.
Emerging Infectious Disease Journal. Retrieved from:

Wikipedia (2012). Batrachochytrium dendrobatidis. Retrieved from: http://www.wikipedia.org
 
 
 
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