Viruses as Pest Control: the coevolution of the Myxoma virus and its long-eared hosts: Difference between revisions

From MicrobeWiki, the student-edited microbiology resource
Line 2: Line 2:


==Background==
==Background==
European colonists introduced rabbits to Australia at the end of the 1700s <ref>[https://www.environment.nsw.gov.au/topics/animals-and-plants/pest-animals-and-weeds/pest-animals/rabbits]</ref>. European rabbits (Otyctolagus cuniculus) are native to southern Europe and northern Africa, but is considered an invasive pest species around the world. The rabbit population in Australia grew exponentially due to the lack of natural predators and warm climate that enabled year-round breeding. Australia was home to an estimated 10 billion rabbits by the 1920s <ref>[www.abc.net.au/science/articles/2009/04/08/2538860.htm]</ref>. The Australian rabbit population caused widespread vegetation depletion, leading to soil erosion <ref>[https://web.archive.org/web/20121218144317/http://www.pir.sa.gov.au/__data/assets/pdf_file/0006/173733/Rtn08a.pdf]</ref>. The rabbits caused massive destruction of crops and pastures for livestock, resulting in a significant loss of agricultural productivity and harming the economy. Rabbits competed for resources with native herbivores, and themselves became food for the increasing population of native predators. These factors heavily contributed to the decline of native Australian biodiversity decline <ref>[https://www.publish.csiro.au/wr/WR11166]</ref>. Australian farmers attempted to use various chemical pesticides, but those also proved detrimental to the ecosystem. In the 1950s, scientists proposed using the recently-discovered Myxoma virus to curb the rabbit population. This experiment in biological warfare ultimately failed to eliminate the rabbit infestation, but became an important experiment on the coevolution of a pathogen and its host.
European colonists introduced rabbits to Australia at the end of the 1700s <ref>["Rabbits – fact sheet". www.environment.nsw.gov.au. Retrieved 2020-04-21.]</ref>. European rabbits (Otyctolagus cuniculus) are native to southern Europe and northern Africa, but is considered an invasive pest species around the world. The rabbit population in Australia grew exponentially due to the lack of natural predators and warm climate that enabled year-round breeding. Australia was home to an estimated 10 billion rabbits by the 1920s <ref>[Zukerman, Wendy. “Australia's Battle with the Bunny.” ABC Science, ABC, 8 Apr. 2009, www.abc.net.au/science/articles/2009/04/08/2538860.htm.]</ref>. The Australian rabbit population caused widespread vegetation depletion, leading to soil erosion <ref>["Environmental Damage caused by Rabbits" (PDF). Archived from the original (PDF) on 18 December 2012. ]</ref>. The rabbits caused massive destruction of crops and pastures for livestock, resulting in a significant loss of agricultural productivity and harming the economy. Rabbits competed for resources with native herbivores, and themselves became food for the increasing population of native predators. These factors heavily contributed to the decline of native Australian biodiversity decline <ref>[Cooke, Brain D. 2012. "Rabbits: manageable environmental pests or participants in new Australian ecosystems?". Wildlife Research. 39 (4): 280. doi:10.1071/WR11166]</ref>. Australian farmers attempted to use various chemical pesticides, but those also proved detrimental to the ecosystem. In the 1950s, scientists proposed using the recently-discovered Myxoma virus to curb the rabbit population. This experiment in biological warfare ultimately failed to eliminate the rabbit infestation, but became an important experiment on the coevolution of a pathogen and its host.


==Myxoma virus==
==Myxoma virus==

Revision as of 06:04, 26 April 2020

By Ilana Richter

Background

European colonists introduced rabbits to Australia at the end of the 1700s [1]. European rabbits (Otyctolagus cuniculus) are native to southern Europe and northern Africa, but is considered an invasive pest species around the world. The rabbit population in Australia grew exponentially due to the lack of natural predators and warm climate that enabled year-round breeding. Australia was home to an estimated 10 billion rabbits by the 1920s [2]. The Australian rabbit population caused widespread vegetation depletion, leading to soil erosion [3]. The rabbits caused massive destruction of crops and pastures for livestock, resulting in a significant loss of agricultural productivity and harming the economy. Rabbits competed for resources with native herbivores, and themselves became food for the increasing population of native predators. These factors heavily contributed to the decline of native Australian biodiversity decline [4]. Australian farmers attempted to use various chemical pesticides, but those also proved detrimental to the ecosystem. In the 1950s, scientists proposed using the recently-discovered Myxoma virus to curb the rabbit population. This experiment in biological warfare ultimately failed to eliminate the rabbit infestation, but became an important experiment on the coevolution of a pathogen and its host.

Myxoma virus

The Myxoma virus is a poxvirus that lives commensally inside lagomorphs in South America and California (silvers). The virus is vectored by mosquitoes and fleas, but it can also be spread through direct contact with an infected animal (fenner 1952). Myxoma virions are enveloped and rectangular. Like many poxviruses, they contain a bioconcave core (padgett). Myxoma has a non-segemented genome consisting of a single molecule of linear double-stranded DNA (cameron, C). Virons replicate within the cytoplasm of the host cell and reproduce by budding out of the host cell's membrane. The Myxoma virus infects fibroblasts, lymphocytes, and mucosal cells (Kerr, 2013).

Myxoma virus, TEM, colorized blue. Credit: David Gregory & Debbie Marshall.

Pathology

The Myxoma virus produces extracellular proteins that specifically suppress or evade a rabbit’s immune response (stanford). Most lagomorphs are susceptible to the virus, but the virus is easily targeted by the immune systems of other species. The reservoir hosts of the virus (American rabbits) do not usually exhibit symptoms, except for occasional benign skin tumors. However, infected European rabbits contract the deadly disease myxomatosis. An effect of this severe immunosuppression is opportunistic infection by gram-negative bacteria. This disease manifests as development of lesions and tumors, fever, swelling, hemorrhage, respiratory malfunction, blindness, and death (kerr 2013).

Myxomatosis presentation in European rabbit. Credit: Richard Harvey.

Experimental use in Australia

Conventional methods of rabbit elimination had failed to solve the problem. Poisoning rabbits and burning their warrens were expensive and laborious options, and ultimately incapable of destroying rabbits at a higher rate than they could reproduce (ABC). The desperate government of New South Wales offered a £25,000 reward for “any method of success not previously known in the Colony for the effectual extermination of rabbits.” Over one thousand proposals were submitted (Vintage news). The idea of using a biological control agent was unconventional yet promising, and Myxoma was a perfect candidate. The Myxoma virus only affects rabbits, but it had an incredibly high mortality rate.
Preliminary safety tests were performed in 1933, and myxomatosis positive rabbits were successfully released in Australia in 1950 (CSIRO). The experiment immediately saw dramatic results. The Myxoma virus eliminated over 80% of the rabbit population over two years. (Vintage news). Myxomatosis has a mortality rate of 99.8% upon release. Australia’s agricultural industry rapidly recovered. Mosquitoes do not live in arid deserts, so the virus could not spread across the entire country (ABC). Nevertheless, the program was initially hailed as a resounding success.
However, the rabbit population soon began to recover. The rabbit population rebounded to almost 300 million by 1991. (Vintage news) What had changed?

Myxomatosis trials, Wardang Island, South Australia, 1938. Credit: National Archives of Australia A1200, L44186.

On coevolution

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.


[5]




Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2018, Kenyon College.

  1. ["Rabbits – fact sheet". www.environment.nsw.gov.au. Retrieved 2020-04-21.]
  2. [Zukerman, Wendy. “Australia's Battle with the Bunny.” ABC Science, ABC, 8 Apr. 2009, www.abc.net.au/science/articles/2009/04/08/2538860.htm.]
  3. ["Environmental Damage caused by Rabbits" (PDF). Archived from the original (PDF) on 18 December 2012. ]
  4. [Cooke, Brain D. 2012. "Rabbits: manageable environmental pests or participants in new Australian ecosystems?". Wildlife Research. 39 (4): 280. doi:10.1071/WR11166]
  5. Riordan T.. Human infection with Fusobacterium necrophorum (Necrobacillosis), with a focus on Lemierre’s syndrome. Clin Microbiol Rev. 2007;20(4):622-59.