Myxomatosis

Myxomatose

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Changed on: 22.01.2019
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Myxomatosis is a viral disease that only affects rabbits (pets and wild animals). The pathogen is a member of the Poxviridae, more specifically Leporipoxvirus, and is called Myxoma virus. Other members of the genus Loporipoxvirus are the hare fibroma virus (fibromatosis in hares), the rabbit fibroma virus (fibromatosis in rabbits) and the squirrel fibroma virus (fibromatosis in squirrels).

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Myxomatosis is a viral disease that only affects rabbits (pets and wild animals). The pathogen is a member of the Poxviridae, more specifically Leporipoxvirus, and is called Myxoma virus. Other members of the genus Loporipoxvirus are the hare fibroma virus (fibromatosis in hares), the rabbit fibroma virus (fibromatosis in rabbits) and the squirrel fibroma virus (fibromatosis in squirrels).

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Transmission

The virus is transmitted predominantly by biting, blood-sucking insects, such as mosquitoes or fleas; the rabbit flea is considered the major vector of the disease. A transmission of the myxoma virus by mites, ticks and lice cannot be excluded. The virus remains active inside the insect for up to three months. An increase in the insect population in humid summers and autumns results in a higher number of infections. Myxomatosis is known only to appear every four to five years, but then in a highly virulent form.


Other transmission methods are:

  • Direct contact between animals through smelling and mucous membrane contact 
  • Indirect transmission via green fodder 
  • Indirect transmission via flies


Even humans can be indirect carriers when in contact with infected animals, although the virus is host-specific. Contaminated tools, work clothes and equipment are also responsible for the spreading of the virus when they have been in contact with infected animals. The virus remains infectious for up to seven months.

Hosts, Risk to Humans

Main hosts of the virus are the European rabbit (Oryctolagus cuniculus) and the domestic rabbit. South American rabbits (Sylvilagus brasiliensis) are far more resistant to the myxomatosis virus (mild or no symptoms) than their European counterparts. Hares are largely immune to myxomatosis: even if the likelihood of an infection is high, only a maximum of 1 % of hares will get the infection.

The myxomatosis virus does not pose a threat to any other animals or humans. A veterinarian should be informed immediately, if the suspicion of myxomatosis (see symptoms) arises. Sick animals should not be touched with bare hands (wash hands, disinfect hands, gloves).

Symptoms

The disease’s mortality rate is at 20 to 100 %, depending on the pathogen’s virulence. The disease will progress in a milder and more atypical form after the virus has weakened and  adapted to the host, following a mortality rate of up to 100 % caused by a highly virulent strain,.
The first symptoms show after an incubation period of 3 to 9 days. The disease will end mostly terminally after about 10 to 14 days.

The most important symptoms are:

  • Swelling and inflammation around the eyelids 
  • Secretion of fluids from the eyes 
  • Swelling on the head (mouth, ears, lips) 
  • Swelling around the genitals 
  • Difficulties swallowing 
  • High fever 
  • Oedemas (hind leg oedemas in rare cases)

Forms

Myxomatosis has three primary forms:

a) acute form: typical symptoms include swollen eyelids (conjunctivitis), swellings on the head (nose, ears, lips, eyes) and purulent fluid secreted from the eyes; later fever and oedemas on the entire body. The swellings and lumps on the ears cause the ears to fold in rabbits with stand-up ears (heavier weight!). The oedemas also lead to head deformations (“big head”). Subcutaneous oedemas are found around the genitals, the anus, the hind legs, the lower abdomen and the back. The animals are still lively and eat right after the infection; they will stop eating after one to two weeks and then die.


b) in the peracute form the symptoms are less obvious: in most cases it can be identified via  swellings around the eyes, which will cause conjunctivitis. The animals die within a few days.

c) the chronic form features multiple lumps and subcutaneous oedemas on the head and the hind legs. A cure is possible in individual cases, but the “cured” animal will continue to carry the virus.

Combating Myxomatosis

There is no specific treatment for myxomatosis. The disease is generally incurable, even though medication and antibiotics can be administered to help alleviate the symptoms. Should an animal survive, it will not become immune and still transmit the virus for months. Latently infected rabbits also discharge the myxoma virus, making it possible to spread the disease within the population via contact.

The myxomatosis pathogens can survive for a long period of time, especially on tools and in hutches and enclosures. Thus, all equipment and buildings that come in contact with infected animals must be cleaned thoroughly and disinfected once the animal has died. The virus is relatively immune to most chemicals, such as potassium permanganate, sublimate, phenol and boric acid. It is immune to cold, but sensitive to heat.

Prevention, Protection and Hygiene Measures

A 14-day quarantine period should be observed if new rabbits are added to an existing population, in addition to a vaccination. A semi-annual vaccination with a weaker live vaccine could also protect against an infection. Unlike Switzerland, vaccination is permitted in Austria and Germany. You will receive more detailed information on vaccinations at your local vet’s.
There are several vaccines that are usually administered subcutaneously or intracutaneously.

Basic immunisation in young animals:

  • Vaccination at the age of 4-6 weeks
  • Follow-up: after 4 weeks 
  • Further follow-ups: every 6 months

Basic immunisation in adult animals:

  • Vaccination beginning of March/April, age irrelevant 
  • Follow-up after 4 weeks 
  • Further follow-ups: every 6 months

Domestic rabbits, whether free range or in a hutch or enclosure, should be inoculated; only 100 % healthy animals should receive an injection. Pregnant, nursing or growing (from 4 weeks on) animals are no impediment. A veterinarian should carry out a general health check before administering the vaccine. Have the rabbit(s) vaccinated just before the warmer seasons of the year! This injection can be combined with other rabbit vaccinations (RHD), but should be applied to a different body area. The vaccine has no effect on rabbits that are already infected or latently infected.

The vaccination does not ensure 100 % immunity. It should be accompanied by other preventative and hygiene measures. The effectiveness of the vaccine could be affected negatively by adverse housing conditions, infestation with coccidia and parasites or hidden bacterial infections. Additionally, young animals might have built up such a high level of antibodies (through nursing) that their immune system is not stimulated enough to produce antibodies and they develop an “immunologic gap”. The antibodies transferred from the mother to the young animal and the viruses spread by the vaccine cancel each other out and the young rabbit does not develop any immunity. However, this infection risk can be limited by inoculating all of the animals in the enclosure.

Additional protective and hygiene measures:

  • Efficient mosquito protection, recommended for larger populations 
  • No green fodder from areas with wild rabbits 
  • Combat flies, which may spread virus-contaminated liquid from the eyes or open pustules 
  • Avoid contact between domestic rabbits and wild rabbits in a free-range enclosure
  • Clean hands properly after contact with infected animals 
  • The disease can also be transmitted during shows

Legal Regulations

It is not required to report myxomatosis to the local authorities. However, the OIE must be notified (Notifiable Disease - OIE).

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