User:Graham Beards/viruses/Infections in other species

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

Vertebrates

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

bluetongue.[3] Jersey and Guernsey breeds of cattle are particularly susceptible to pox viruses, which is 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 12 days.[4] The virus was deliberately released in Australia in 1950, in an attempt to control the exponentially growing rabbit population. Rabbits were brought to the continent in 1859 for sport, and having no natural predators, bred at an extraordinary rate.[5] The infection killed 99.8 percent of rabbits, but by the late 1950s, the rabbits started to become immune to the virus and the population of rabbits increased, but never to the vast numbers seen before 1950.[6]

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

Companion animals such as cats, dogs, and horses, if not vaccinated, can catch serious viral infections. Canine parvovirus 2 is caused by a small DNA virus and infections are often fatal in pups.[7] The emergence of the virus in the 1970s was the most significant in the history of infectious diseases. The disease spread rapidly across the world and thousands of dogs died from the infection.[8] The virus originated in cats but a mutation allowed it to cross the species barrier and dogs, unlike cats, had no resistance to the disease.[9] The mutation changed just two amino acids in the viral capsid protein VP2 of feline panleukopenia virus.[10]

Canine distemper virus is closely-related to measles virus and is the most important viral disease of dogs. The disease (which was first described in 1760, by Edward Jenner of smallpox fame) 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.[11]

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

parvoviruses, circulate in marine mammal populations.[14]

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 increasing the temperature to 15–18°C.[15] Like all vertebrates, fish suffer from herpes viruses. These ancient viruses have co-evolved with their hosts and are highly species-specific.[16] In fish, they cause cancerous tumours and non-cancerous growths called hyperplasia.[17]

Invertebrates

Honey bee infected with deformed wing virus

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

invertebrates, the honey bee (Apis mellifera) is susceptible to many viral infections,[19] and their numbers have dramatically declined around the world.[20] These bees often suffer infestations of varroa mites, which are vectors for deformed wing virus,[21] as a result, this virus has become one of the most widely distributed and contagious insect viruses on the planet.[22] The virus causes stunted wings and as a result, the infected bees are unable to leave the hive and forage for nectar.[23] 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.[24]

Baculoviruses are among the best studied of the invertebrate viruses. They infect and kill several species of agricultural pests, [25] 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.[26] Viruses are an attractive alternative to chemical pesticides because they are safe to other wildlife and leave no residues.[27]

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.[28]

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.[29] Phagocytosis was first observed in invertebrates,[30] 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.[31]

Plants

Peppers infected by mild mottle virus

There are many types of

fungi, nematode worms, and single-celled organisms have been shown to be vectors. When control of plant virus infections is considered economical, for perennial fruits, for example, efforts are concentrated on killing the vectors and removing alternate hosts such as weeds.[32] Plant viruses cannot infect humans and other animals because they can reproduce only in living plant cells,[33] and many plant viruses only infect a single plant species.[34]

Plants have elaborate and effective defence mechanisms against viruses. One of the most effective is the presence of so-called resistance (R) genes. Each R gene confers resistance to a particular virus by triggering localised areas of cell death around the infected cell, which can often be seen with the unaided eye as large spots. This stops the infection from spreading.[35] RNA interference is also an effective defence in plants.[36] When they are infected, plants often produce natural disinfectants that kill viruses, such as salicylic acid, nitric oxide, and reactive oxygen molecules.[37] Plant virus particles or virus-like particles (VLPs) have applications in both biotechnology and nanotechnology. The capsids of most plant viruses are simple and robust structures and can be produced in large quantities either by the infection of plants or by expression in a variety of heterologous systems. Plant virus particles can be modified genetically and chemically to encapsulate foreign material and can be incorporated into supramolecular structures for use in biotechnology.[38] The International Committee on Taxonomy of Viruses now recognises over 900 plant viruses.[39]

Bacteria

An electron micrograph showing a portion of a bacterium covered with viruses
Transmission electron micrograph of multiple bacteriophages attached to a bacterial cell wall

Bacteriophages are a common and diverse group of viruses and are the most abundant form of biological entity in aquatic environments – there are up to ten times more of these viruses in the oceans than there are bacteria,

T4 phage, in just over twenty minutes after injection over three hundred 'phages could be released.[42]

The major way bacteria defend themselves from bacteriophages is by producing enzymes that destroy foreign DNA. These enzymes, called

acquired immunity
to infection.

Archaea

Some viruses replicate within

repetitive DNA sequences within archaean genomes that are related to the genes of the viruses.[48][49]

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  2. ^ Murphy pp. 587–599
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  4. ^ MacLachlan p. 160
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