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 myxomatosis virus (mild or asymptomatic infection!) than their European representatives. Field hares are largely insensitive to myxomatosis; even under high infection pressure, a maximum of 1% of field 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 Leporipoxviruses also includes Hare fibroma virus (FIBV, causative agent of fibromatosis of hare), Rabbit fibroma virus (RFV, causative agent of fibromatosis of rabbit), and Squirrel fibroma virus (SQFV, causative agent of fibromatosis of squirrel). 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 rapidly in Europe and had an almost population-destroying effect, similar to that in Australia. After 1955, when the last outbreak of the disease in Austria was reported, cases of myxomatosis occurred in Austria in free-living wild and domestic rabbits 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, Greece in 2012, Portugal and Spain in 2018, Finland in 2020. In Austria, wild rabbits and domestic rabbits were/are affected in the Vienna and Lower Austria area, among others.
Myxomatosis is one of the two diseases of Lagomorpha (the mammalian family that includes rabbits, hares, and pikas) listed in the WOAH Terrestrial Animal Health Code. Member countries are required to report outbreaks of the disease in accordance with the WOAH Terrestrial Animal Health Code.
Transmission of the virus occurs primarily via biting bloodsucking insects such as mosquitoes or fleas during the summer; the rabbit flea in particular is considered the primary vector. Transmission of myxomatosis virus by mites, ticks, and lice also cannot be ruled out. 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 modes of transmission are direct animal-to-animal contact by sniffing and mucosal 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 or accessories are also responsible for spreading the virus when in 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, increasingly milder and atypical courses occur due to attenuation and adaptation of the virus to the 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
- edema (hind leg edema in exceptional cases)
Myxomatosis manifests itself mainly 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 edema formation on the whole body. As a result of the swellings and knot formation at the ear, the ears of standing-eared breeds bend in (high weight load!). Due to the edema formation, the head also becomes misshapen ("hippopotamus head", "lion head", "big head disease"). Subcutaneous edema is found increasingly in the area of the genital organs, 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 take food; after 1-2 weeks, they stop feeding and die. peracute course: disease symptoms less pronounced: Usually recognized by eye swelling that 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. Cure is possible in individual cases; however, the "cured" animal continues to carry the disease.
A respiratory form of the disease without skin lesions has also been reported.
There is no specific treatment for myxomatosis. It is not curable, although antibiotics and other medications can be used adjuvantly. If an animal survives, it still transmits the virus months later and is not immunized. Latently infected rabbits also shed myxomatosis virus, allowing disease spread via contact infections within the herd. The pathogens that cause myxomatosis can 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 semi-annual vaccination with live attenuated 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, whether free-ranging or housed, should be vaccinated; only 100% healthy animals are worthy of vaccination. Pregnancy, suckling or growth (from 4 weeks of age) are not an 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, location-separated. 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 unfavorable housing conditions, as well as by coccidia and parasite infestations or hidden bacterial infections. It may happen that young rabbits 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 occurs. 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 hands after touching sick animals
- Transmission can also occur during exhibitions
Last updated: 19.04.2023