Myxomatosis or rabbit plague is a viral disease occurring predominantly in domestic and wild rabbits(Oryctolagus cuniculus). The main hosts of the virus are the European wild rabbit(Oryctolagus cuniculus) and its breeding form, the domestic rabbit(Oryctolagus cuniculus forma domestica). The wild rabbits of South America(Sylvilagus brasiliensis) are much more resistant to the myxomatosis virus (mild or asymptomatic infection!) than their European representatives. Hares are largely insensitive to myxomatosis; even under high infection pressure, a maximum of 1 % of hares become ill. Other animals or humans are not endangered by the myxomatosis virus.
The causative agent of myxomatosis belongs to the poxvirus genus Leporipoxvirus (subfamily: Chordapoxvirinae) and is called myxoma virus. The genus Leporipoxvirus also includes Hare fibroma virus (FIBV, causative agent of fibromatosis in hares), Rabbit fibroma virus (RFV, causative agent of fibromatosis in rabbits) and Squirrel fibroma virus (SQFV, causative agent of fibromatosis in squirrels). Leporipoxvirus is a brick-shaped DNA virus with a genome size of 160 kbp.
The spread of myxomatosis in Europe was triggered in 1952 by the release of diseased, infected rabbits in France. Subsequently, the myxomatosis virus spread in Europe at a rapid pace and - similar to Australia - had an almost population-destroying effect. After the last outbreak of the disease in Austria was reported in 1955, cases of myxomatosis in free-living wild and domestic rabbits became more frequent in Austria in autumn 2009 and autumn 2010. Myxomatosis is widespread in Europe: outbreaks were reported in England (Leeds, Sussex, Essex, Cambridge etc.) in 2004/2005, Switzerland in 2007, Luxembourg in 2008, Russia in 2009 and England (Wales) again in 2009. In Austria, among others, wild rabbits and domestic rabbits were/are affected in the area of Vienna and Lower Austria. More precise information on the geographical spread of myxomatosis in Austria cannot be provided, as the disease is not notifiable.
The virus is mainly transmitted by biting insects such as mosquitoes or fleas in summer; especially the rabbit flea is considered to be the main vector. Transmission of the myxomatosis virus by mites, ticks and lice cannot be excluded either. The virus remains active in the insect for up to 3 months. Increased insect populations during warm, humid summers and in the fall result in a clustered occurrence of the disease. Myxomatosis is known to occur only every 4-5 years, but then highly virulent.
Other transmission routes are direct animal-to-animal contact by sniffing and mucous membrane contact, indirect transmission via the environment, indirect mechanical transmission via flies. Humans can also act as indirect vectors when in contact with diseased animals. Dirty tools, stable clothing and stable accessories are also responsible for spreading the virus when they come into contact with infected animals. Sick animals should not be touched with bare hands (hand washing, hand disinfection, gloves). The virus remains virulent in the environment for up to 7 months.
Depending on the virulence of the pathogen, mortality ranges from 20 to 100 %. After initial mortality of up to 100 % caused by a highly virulent strain, milder and atypical courses increasingly develop as the virus weakens and adapts to its hosts. After an incubation period of 3 to 9 days, the first symptoms appear; after about 10 to 14 days, the disease usually ends in death. The main symptoms are:
- Swelling, lumps and inflammation around the eyelids.
- Eye discharge
- Swelling and lumps in the area of the head (mouth, ears, lips)
- Swelling and lumps in the genital area
- Difficulty swallowing
- High fever
- oedema (oedema of the hind legs in exceptional cases)
Myxomatosis mainly manifests itself in three forms: acute course: Typical are swollen eyelids (conjunctivitis), swellings in the head area (nose, ears, lips, eyes) and purulent eye secretion, later also fever and oedema formation all over the body. As a result of the swellings and knot formation at the ear, the ears bend in standing-eared breeds (high weight load!). Due to the edema formation, the head also becomes misshapen ("hippopotamus head" or "lion head"). Subcutaneous oedema is found more frequently in the area of the genitals, the anal region, the hind legs, the lower abdomen and on the back. At the beginning of the disease, the animals are still lively and eat food; after 1-2 weeks, they stop eating and die. peracute course: disease symptoms less pronounced: Usually recognized by signs of eye swelling, which turns into conjunctivitis. The animals die within a few days. chronic course: increased nodular and subcutaneous edema, especially in the head area and on the hind legs. A cure is possible in individual cases; however, the "cured" animal continues to carry the disease.
There is no special treatment for myxomatosis. It cannot be cured, although antibiotics and other medications can be used as a supportive measure. If an animal survives, it will still transmit the virus months later and will not be immunized. Latently infected rabbits also shed myxomatosis virus, making it possible for the disease to spread within the herd via contact infections. The causative agents of myxomatosis are able to survive for a long time, especially on equipment and in housing. Therefore, all objects or buildings with which diseased animals come into contact must be thoroughly cleaned and disinfected after the animals have died. The virus is relatively insensitive to a majority of chemicals such as potassium permanganate, sublimate, phenol and boric acid. The virus is not sensitive to cold, but it is sensitive to heat.
Rabbits newly introduced into a herd should be quarantined for 14 days and vaccinated. As a preventive measure, a six-monthly vaccination with attenuated live vaccine can provide protection against infection. In contrast to Switzerland, vaccination is permitted in Austria and Germany. Detailed information about vaccinations can be obtained from your veterinarian. There are different vaccines, which are mostly applied sub- or intracutaneously.
All domestic rabbits, no matter if free-living or stabled, should be vaccinated; only 100% healthy animals are worthy of vaccination. Pregnancy, suckling or growth (from the age of 4 weeks) are no obstacle. Prior to vaccination, the veterinarian should perform a general health check. Vaccinate in time before the beginning of the warm season! The vaccination can be combined with other rabbit vaccinations (RHD), however, separated by location. The vaccination remains ineffective in rabbits that are already latently infected or already sick. Vaccination does not achieve 100% immunization; it should be accompanied by other precautionary and hygienic measures. The effectiveness of the vaccination can be negatively affected by unfavourable housing conditions as well as by coccidia and parasite infestations or hidden bacterial infections. It can happen that young animals have such a high level of antibodies transmitted by the dam (through suckling) that the immune system of the young rabbits is not stimulated to produce antibodies - an immunological gap is created. The antibodies transferred from the dam and the viruses released by the vaccine compensate for each other, and the young animal does not develop vaccine protection. However, this risk of infection can be limited by vaccinating all animals in the barn.
Further protective or hygienic measures:
- effective mosquito repellent, recommended for larger flocks
- no green fodder from areas where wild rabbits are present
- control of flies, which can spread virus-containing eye secretions or secretions of ruptured pustules
- avoidance of contact between domestic rabbits and wild rabbits in the outdoor enclosure
- cleaning of hands after touching sick animals
- Transmission can also occur during exhibitions
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Last updated: 08.04.2022