Animal virus

Source: Wikipedia, the free encyclopedia.
See also: Veterinary virology

Animal viruses are viruses that infect animals. Viruses infect all cellular life and although viruses infect every animal, plant, fungus and protist species, each has its own specific range of viruses that often infect only that species.[1]

Vertebrates

The viruses of vertebrates are informally distinguished between those that primarily cause infections of humans and those that infect other animals. The two fields of study are called medical (or clinical) virology and veterinary virology respectively.[2] Although not the first viruses to be discovered and characterised,[3] those that cause infections of humans are the most studied.[4] Different viruses can infect all the organs and tissues of the body and the outcomes range from mild or no symptoms, to life-threatening diseases.[5] Humans cannot be infected by plant or insect viruses, but they are susceptible to infections with viruses from other vertebrates. These are called viral zoonoses or zoonotic infections.[6] Examples include, rabies, yellow fever and pappataci fever.[7]

The viruses that infect other vertebrates are related to those of humans and most families of viruses that cause human diseases are represented.

bluetongue.[9] Jersey and Guernsey breeds of cattle are particularly susceptible to pox viruses, with symptoms characterised by widespread, unsightly skin lesions. And most people have heard of myxomatosis, which is a fatal pox virus infection of rabbits: once infected they die within twelve days.[10] The virus was deliberately released in Australia in 1950, in an attempt to control the exponentially growing rabbit population. Rabbits had been brought to the continent in 1859 for sport, and having no natural predators, bred at an extraordinary rate. The infection killed 99.8 percent of rabbits, but by the late 1950s, Australian rabbits started to become immune to the virus and the population of rabbits increased, but never to the vast numbers seen before 1950.[11]

Rabbits around a waterhole during the myxomatosis trial at the site on Wardang Island, South Australia in 1938

Companion animals such as cats, dogs, and horses, if not vaccinated, can catch serious viral infections.

smallpox vaccination, is highly contagious, but is well controlled by vaccination. In the 1990s, thousands of African lions died from the infection, which they contracted from feral dogs and hyenas.[16]

Marine mammals are susceptible to viral infections. In 1988 and 2002, thousands of

parvoviruses, circulate in marine mammal populations.[19]

Fish too have their viruses. They are particularly prone to infections with rhabdoviruses, which are distinct from, but related to rabies virus. At least nine types of rhabdovirus cause economically important diseases in species including salmon, pike, perch, sea bass, carp and cod. The symptoms include anaemia, bleeding, lethargy and a mortality rate that is affected by the temperature of the water. In hatcheries the diseases are often controlled by increasing the temperature to 15–18 °C.[20] Like all vertebrates, fish suffer from herpes viruses. These ancient viruses have co-evolved with their hosts and are highly species-specific.[21] In fish, they cause cancerous tumours and non-cancerous growths called hyperplasia.[22]

Invertebrates

Honey bee infected with deformed wing virus

Arthropods is the largest group of animals and has shown to be a major reservoir of different viruses, both insect-specific viruses (ISV) and viruses that can infect both vertebrates and invertebrates, more known as arthropod-borne viruses (arboviruses). Insect-specific viruses are, as the name reveals, characterised by their incapacity to infect vertebrates. This can be assessed through, viral inoculation of mammalian, avian, or amphibian cell lines.[23] The first (ISV) was discovered over 40 years ago by Stollar and Thomas.[24] It was isolated from an Aedes aegypti cell culture where a large number of syncytia were observed and the virus was named cell fusing agent virus (CFAV). Further, when inoculated on different vertebrate cell lines no cytopathic effect (CPE) could be observed and the virus could not be re-isolated, suggesting that the virus must be insect-specific.[24]

Invertebrates do not produce antibodies by the lymphocyte-based adaptive immune system that is central to vertebrate immunity, but they are capable of effective immune responses.[25] Phagocytosis was first observed in invertebrates,[26] and this and other innate immune responses are important in immunity to viruses and other pathogens. The hemolymph of invertebrates contains many soluble defence molecules, such as hemocyanins, lectins, and proteins, which protect these animals against invaders.[27]

The health of the honey bee has been important to human societies for centuries.

varroa mites, which are vectors for deformed wing virus,[31] as a result, this virus has become one of the most widely distributed and contagious insect viruses on the planet.[32] The virus causes stunted wings and as a result, the infected bees are unable to leave the hive and forage for nectar.[31] Symptomatic bees have a severely reduced life-span of less than 48 hours and are often expelled from the hive by other bees. Bees are crucial to the survival of humans, along with producing honey, they pollinate plants that contribute up to one third of the food we eat, and their dramatic decline is a grave concern.[33]

Baculoviruses are among the best studied of the invertebrate viruses. They infect and kill several species of agricultural pests,[34] and as natural insecticides, they have been used to control insect populations in Brazil and Paraguay such as the velvet bean caterpillar (Anticarsia gemmatalis), a pest of soy beans.[35] Viruses are an attractive alternative to chemical pesticides because they are safe to other wildlife and leave no residues.[36]

Viruses can also change the behaviour of their insect hosts to their own advantage. A baculovirus of the gypsy moth (Lymantria dispar) makes their caterpillars climb to the tops of trees where they die. In doing so, they release a shower of millions of progeny viruses that go on to infect more caterpillars.[37]

References

  1. ^ Leppard p. 3
  2. ^ Murphy, p.ix
  3. ^ Leppard, pp. 4–6
  4. ISBN 9780443073670
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  5. ^ Leppard, p. 295
  6. ^ Leppard, pp. 268–9
  7. ^ Leppard, p. 269
  8. ^ Murphy pp. 587–599
  9. PMID 18035428
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  10. ^ MacLachlan p. 160
  11. PMID 22333483
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  12. PMID 16316389
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  13. ^ Murphy p. 351
  14. PMID 9129667
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  15. ^ Murphy p. 169
  16. ^ Murphy p.423
  17. ^ Hall, A. J., Jepson, P. D., Goodman, S. J. & Harkonen, T. "Phocine distemper virus in the North and European Seas — data and models, nature and nurture". Biol. Conserv. 131, 221–229 (2006)
  18. ^ Murphy p. 426
  19. S2CID 4658457
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  20. ^ Murphy pp. 442–443
  21. ^ Murphy p. 324
  22. ^ Murphy 325
  23. PMID 30632016
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  24. ^
    PMID 806166
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  25. S2CID 25041997
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  26. ^ "Ilya Mechnikov". The Nobel Foundation. Retrieved November 28, 2008.
  27. PMID 15826490
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  28. PMID 22032828
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  29. PMID 17765703
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  30. PMID 22235317
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  31. ^
    PMID 9878295
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  32. S2CID 21852438
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  33. ISBN 1596916397
  34. ^ Mahy (a) p. 426
  35. ^ Moscardi F. Use of viruses for pest control in brazil: The case of the nuclear polyhedrosis virus of the soybean caterpillar, Anticarsia gemmatalis. Memórias do Instituto Oswaldo Cruz, Rio de Janeiro. 1989;84:51–56.
  36. S2CID 11008585
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  37. S2CID 20400126
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Bibliography
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