Healthy Biodiversity: Taking Care of the Environment and Our Health

Biodiversity is an important element in the natural world: it maintains ecosystem function by preserving species dominance and protects species health by ensuring genetic diversity. Biodiversity also acts as a buffer to many diseases—a genetically diverse population is much more likely to withstand outbreaks, while weak genetic diversity within wildlife can lead to an increase of epidemics and poor public health.1 Other services biodiversity provides include the filtering of toxic substances from the air, water, and soil, the breaking down of wastes, the recycling of nutrients, and the production of medicines that are derived from plants, animals, and microbes.2 Although many have expressed concern about the continuing loss of biodiversity, little attention has been given to its effects on human health.

Our health is directly related to the health of the environment we live in. The loss of biodiversity leads to ecosystems that are less resilient, more vulnerable to shocks and disturbances, and less able to supply humans with needed environmental services. Ecosystems play a vital role in controlling the emergence and spread of infectious diseases by maintaining equilibrium among different parasites, hosts and vectors.3 An organism that acts as a good host to the parasite is called a competent reservoir host, and it becomes dominant when there is a decline in biodiversity. Incompetent reservoir hosts are found in areas with higher biodiversity, and they produce a dilution effect by deflecting parasites from more competent hosts.4 In other words, preservation of biodiversity can decrease disease transmission worldwide. To demonstrate the importance of species richness to public health, this article will discuss the various ways ecological change has exacerbated the spread of prominent diseases such as Lyme, the West Nile Virus and malaria.

Lyme disease is the most common tick-borne illness in North America and Europe, and one the fastest growing infectious diseases in the United States thanks to suburban expansion and forest fragmentation. These factors increase the prevalence of vectors that carry Lyme disease, such as Ixodidae ticks. The ticks feed on white-footed mice and deer that carry the spirochete bacterium that causes them to become infected with Lyme.1 The disease is then transmitted to humans when an infected tick feeds on a person. Forest fragmentation has likely caused a decline in the number of predators that prey on these mice and deer, such as long-tailed weasels, red foxes, gray foxes, coyotes, and barred owls. This reduction in predators increases the prevalence of mice and the number of ticks feeding on them since the lack of host diversity decreases the dilution effect of the disease.5 Computer modeling can help us determine how rapidly the disease risk will increase when studying patterns of species loss with habitat fragmentation. It has demonstrated that Lyme disease patterns show that lower species richness tends to coincide with higher rates of disease transmission to humans.6 That gives strong evidence that biodiversity is necessary to maintain ecosystem and human health.

Research on the dilution effect has also helped our understanding on the relationship between biodiversity and West Nile Virus (WNV). This virus is untreatable and is transmitted from birds to humans through Culex mosquitoes. One study found that there was a negative correlation between the diversity of non-passerine (non-songbirds) birds and the number of mosquitoes found with WNV. 7 Some anthropogenic factors contributing to the loss of non-passerine biodiversity include deforestation, agricultural expansion, and urbanization. Certain urbanized areas of the United States are inhabited by populations of introduced bird species that are capable of producing high levels of WNV in their bloodstream.8 This clearly suggests that the increased prevalence of WNV among humans may be a result of the change in avian biodiversity, especially the decrease in non-passerine birds, which tend to be poorer hosts to the virus than passerine birds.1, 7

Third, there is also a documented connection between ecosystem alteration and species loss with the risk of contracting malaria. These ecosystem alterations are due to number of factors, such as urban rice cultivation, poorly designed irrigation systems, deforestation of tropical forests, increased travel, and the increase in human population.2, 9 Chivian states that certain species of mosquitoes, like the Anopheles darlingi in the Amazon, “benefit more from these changes than others, and tend to out-compete rival species that are less effective vectors for malaria.”2 Carlson, Byrd and Omlin found that there is a negative correlation between mosquito density and the diversity of its predators; they also found that manmade areas were more likely to contain a higher density of mosquitoes than natural habitats.10 This strongly supports the argument that the destruction of natural habitats has caused a decrease in species diversity and has allowed for the dominance of malaria carrying mosquitoes.

Although biodiversity does not act as a buffer for all diseases, it plays a significant role in mitigating numerous diseases from spreading. It also protects our immune system by providing nutrition and medicine that can help protect us from emerging diseases. Essentially, public health is intrinsically linked to environmental health, and measures to deal with one problem such as disease control must also take into account related issues, such as biological conservation. To aid conservation of biodiversity and respect for the environment, we must stress how vital the environment and species richness is to humans. Discussing the relationship biodiversity has with human health will make it more relevant to a wider range of people and will help increase efforts to protect biodiversity. This connection will also allow a more holistic approach to conserving biodiversity because it allows us to see the larger picture: that humans are not separate from nature and we are all victims of environmental disruption.

References

  1. Keesing, Felicia, Lisa K. Belden, Peter Daszak, Andrew Dobson, C. Drew Harvell, Robert Holt, Peter Hudson, Anna Jolles, Kate Jones, Charles Mitchell, Samuel Myers, Tiffany Bogich and Richard Ostfeld. “Impacts of biodiversity on the emergence and transmission of infectious diseases” Nature 468 (2010): 647–652. http://www.nature.com/nature/journal/v468/n7324/full/nature09575.html (accessed December 16, 2011).
  2. Chivian, Eric. ed. 2002. Biodiversity: Its Importance to Human Health. Boston, MA: Center for Health and the Global Environment, Harvard Medical School.
  3. Alves, Romulo, and Ierece Rosa. “Biodiversity, traditional medicine and public health: where do they meet?” Journal of Ethnobiology and Ethnomedicine 3(2007):14 http://www.ethnobiomed.com/content/3/1/14 (accessed November 21, 2011)
  4. Schmidt, Kenneth, and Richard Ostfeld. 2001. Biodiversity and the Dilution Effect in Disease Ecology. Ecology 82, no. 3 (March): 609–19. http://www.esajournals.org/doi/abs/10.1890/0012-9658(2001)082[0609:BATDEI]2.0.CO;2 (accessed November 21, 2011).
  5. Otsfeld, Richard. Habitat Fragmentation. Cary Institute of Ecosystem Studies. http://www.ecostudies.org/people_sci_ostfeld_habitat_fragmentation.html (accessed December 16, 2011).
  6. Ostfeld, Richard, and Kathleen LoGiudice. 2003. Community disassembly, biodiversity loss, and the erosion of an ecosystem service. The Ecological Society of America 84, no. 6 (June): 1421-1427. http://www.ecostudies.org/reprints/Ostfeld_and_LoGiudice_2003_Ecology_84_1421-1427.pdf (accessed December 16, 2011).
  7. Meadows, R. Biodiversity May Curb West Nile Virus. Conservation in Practice. 7, no. 1 (2006): 9.
  8. First Conservation Medicine. West Nile Virus. Consortium for Conservation Medicine. http://conservationmedicine.org/wnv.htm (accessed November 21, 2011)
  9. Van Hoose, Natalie. Global Warming and Malaria. http://plaza.ufl.edu/inkling/mosquito-borne_diseases.html (accessed November 21, 2011)
  10. Carlson, John, Brian Byrd, and Francois Omlim. Field assessments in western Kenya link malaria vectors to environmentally disturbed habitats during the dry season. BMC Public Health 4, no.33 (2004). http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=512294 (accessed November 21, 2011).
  11. Dom Dada. Biodiversity. flickr. http://www.flickr.com/photos/ogil/2540634421/ (accessed December 28, 2011)

Samah Rizvi is a first-year graduate student studying social service administration at the University of Chicago. Follow The Triple Helix Online on Twitter and join us on Facebook.

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