Conservation biology of parasites
A large proportion of living species on Earth live a parasitic way of life. Parasites have traditionally been seen as targets of eradication efforts, and they have often been overlooked in conservation efforts. In the case of parasites living in the wild – and thus harmless to humans and domesticated animals – this view is changing.
Endangered parasite species
A note published in 1990 pointed out that the captive breeding and reintroduction program to save the black-footed ferret would cause the loss of its specific parasites and demanded "equal rights for parasites!". Then a paper in 1992 has warned that not only the loss of certain host species from the wild, but even host population bottlenecks or the fragmentation of host populations would predictably lead to the extinction of several host specific parasite species. It also noted that parasites are not only components of biodiversity by definition, but they also exert selective pressures upon their host populations that increase host genetic diversity. Firstly, this view met with open scepticism. Soon after, it became clear that the co-extinction of hosts and their specific parasites is likely to increase the current estimates of extinction rates significantly. A decade later, a study focusing on some highly host-specific groups (such as fig wasps, parasites, butterflies, and myrmecophil butterflies) estimated the number of co-endagered species (i.e. endagered by the endagered status of the host) at about 6300. Other authors argued that host specific parasite faunae have an unexpected advantage for conservation scientists. Their genealogies and population genetic patterns may help to illuminate their hosts' evolutionary and demographic history. Recently, scientists suggested that rich parasite faunae are inevitably needed for healthy ecosystem functioning  and also that parasites and mutualists are the most endangered species on Earth. Even vets have started to argue about the conservational values of parasite species.
A recent study on parasites of coral reef fish suggested that extinction of a coral reef fish species would eventually result in the coextinction of at least ten species of parasites. Although this number might seem high, the study included only large parasites such as parasitic worms and crustaceans, but not microparasites such as Myxosporea and Microsporidia.
Example: extinct avian lice
The list below follows that of Mey (2005)
- Acutifrons caracarensis parasite of the extinct Guadalupe Caracara (Caracara lutosa), Guadelupe Island, Mexico;
- Longimenopon dominicanum parasite of the extinct Guadalupe Storm Petrel, Oceanodroma macrodactyla, Guadelupe Island, Mexico;
- Rallicola piageti parasite of the extinct New Caledonian Rail (Gallirallus lafresnayanus), New-Caledonia;
- Coloceras hemiphagae parasite of the extinct Norfolk Island Pigeon (Hemiphaga novaeseelandiae spadicea), Norfolk Island, New-Zealand;
- Coloceras restinctus parasite of the extinct Norfolk Island Pigeon (Hemiphaga novaeseelandiae spadicea), Norfolk Island, New-Zealand;
- Rallicola extinctus parasite of the extinct Huia (Heteralocha acutirostris), New-Zealand;
- Philopteroides xenicus parasite of the extinct Bushwren (Xenicus longipes), New-Zealand;
- Psittacobrosus bechsteini parasite of the extinct Cuban Red Macaw (Ara tricolor), Cuba;
- Colpocephalum californici, parasite of the California Condor (Gymnogyps californianus). The host have been saved by captive breeding and repatriation programs, however, the parasite have been lost, either spontaneously or perhaps exterminated by wildlife vets.
Additionally, Columbicola extinctus is a parasite of the extinct Passenger Pigeon (Ectopistes migratorius). However, recent taxonomic studies show that it is conspecific with the lice living on Band-tailed Pigeon (Columba fasciata), thus it is not extinct.
Extermination by purpose
Naturally, medical (and veterinary) science and practice aim to exterminate parasites and pathogens living in humans (and in domesticated animals). In case of the few highly host-specific pathogens, this equals the extinction of the pathogen species. Throughout human history, however, only a single one species, i.e. smallpox virus, was eradicated from the Globe. The last cases of smallpox occurred 1978. However, secured stocks still exist in the United States and Russia for defensive purposes such as developing new vaccines, antiviral drugs, and diagnostic tests.  It is not known whether or not these superpowers have shared their stocks with some of their allies during the Cold War.
A second candidate for purposeful extermination is the Dracunculus medinensis (Guinea Worm). Once widespread across some 20 nations of Africa and Asia, the parasite nowadays is much withdrawn occurring only in four countries in Sub-Saharan Africa with only a few hundred known cases of infection in 2011. Prevalent civil wars in the region, such as the War in Darfur have ensured the survival of this species up to the present.
Notes and references
- Windsor DA (1998). "Most of the species on Earth are parasites". International Journal for Parasitology 28 (12): 1939–1941. doi:10.1016/S0020-7519(98)00153-2. PMID 9925276.
- Windsor DA (1990). "Heavenly hosts". Nature 348 (6297): 104. doi:10.1038/348104c0. PMID 2234071.
- Rózsa L (1992). "Endangered parasite species". International Journal for Parasitology 22 (3): 265–266. doi:10.1016/S0020-7519(05)80002-5. PMID 1639560.
- Bush AO, Kennedy CR (1994). "Host fragmentation and helminth parasites: Hedging your bets against extinction". International Journal for Parasitology 24 (8): 1333–1343. doi:10.1016/0020-7519(94)90199-6. PMID 7729985.
- Stork NE, Lyal CHC (1993). "Extinction or 'co-extinction' rates?". Nature 366 (6453): 307–8. doi:10.1038/366307a0. PMID 8247122.
- Koh LP, Dunn RR, Sodhi NS, Colwell RK, Proctor HC, Smith VS (2004). "Species Coextinctions and the Biodiversity Crisis". Science 305 (5690): 1632–1634. doi:10.1126/science.1101101. PMID 15361627.
- Whiteman NK, Parker PG (2005). "Using parasites to infer host population history: a new rationale for parasite conservation". Animal Conservation 8 (2): 175–181. doi:10.1017/S1367943005001915.
- Hudson PJ, Dobson AP, Lafferty KD (2006). "Is a healthy ecosystem one that is rich in parasites?". Trends in Ecology & Evolution 21 (7): 381–385. doi:10.1016/j.tree.2006.04.007. CiteSeerX: 10.1.1.79.9080.
- Dunn RR, Harris NC, Colwell RK, Koh LP, Sodhi NS (2009). "The sixth mass coextinction: are most endangered species parasites and mutualists?". Proceedings of the Royal Society B 276 (1670): 3037–3045. doi:10.1098/rspb.2009.0413. PMC 2817118. PMID 19474041.
- Pizzi R (2009). "Veterinarians and Taxonomic Chauvinism: The Dilemma of Parasite Conservation". Journal of Exotic Pet Medicine 18 (4): 279–282. doi:10.1053/j.jepm.2009.09.005.
- Justine, J.-L., Beveridge, I., Boxshall, G. A., Bray, R. A., Miller, T. L., Moravec, F., Trilles, J.-P. & Whittington, I. D. 2012: An annotated list of fish parasites (Isopoda, Copepoda, Monogenea, Digenea, Cestoda, Nematoda) collected from Snappers and Bream (Lutjanidae, Nemipteridae, Caesionidae) in New Caledonia confirms high parasite biodiversity on coral reef fish. Aquatic Biosystems, 8, 22. doi:10.1186/2046-9063-8-22
- Mey E (2005). "Psittacobrosus bechsteini: a new extinct chewing louse (Insecta, Phthiraptera, Amblycera) off the Cuban Macaw Ara tricolor (Psittaciiformes), with an annotated review of fossil and recently extinct animal lice". Anzeiger des Vereins Thüringer Ornithologen 5: 201–217.
- Mey E (1992). "Eine neue ausgestorbene Vogel-Ischnozere von Neuseeland, Huiacola extinctus (Insecta, Phthiraptera)". Zoologischer Anzeiger 224: 49–73.
- Clayton, Dale H.; Roger D. Price (1999). "Taxonomy of New World Columbicola (Phthiraptera: Philopteridae) from the Columbiformes (Aves), with Descriptions of Five New Species". Annals of the Entomological Society of America (Entomological Society of America) 92 (5): 675–85.
- Connor, Steve (2002-01-03). "How terrorism prevented smallpox being wiped off the face of the planet for ever". The Independent. Retrieved 2009-12-13.
- Hammond, Edward (2007). "Should the US and Russia destroy their stocks of smallpox virus?". BMJ 334 (7597): 774. doi:10.1136/bmj.39155.695255.94. PMC 1851992. PMID 17431261.
- Agwunobi, John O. (2007). "Should the US and Russia destroy their stocks of smallpox virus?". BMJ 334 (7597): 775. doi:10.1136/bmj.39156.490799.BE. PMC 1851995. PMID 17431262.
- Rózsa L, Nixdorff K 2006. Biological weapons in non-Soviet Warsaw Pact countries. In: Wheelis M et al. (eds.) Deadly cultures: biological weapons since 1945. Cambridge, US: Harvard University Press.
- "The Carter Center Guinea Worm Disease Eradication".