Myxomatosis in Rabbits Symptoms, Vaccine and More

Myxomatosis refers to a highly contagious viral rabbit disease that only affects Oryctolagus cuniculus (European rabbits) caused by the myxoma virus, not the same thing as ‘myxoma’, which is a tumor of primitive connective tissues.

This viral infection together with Viral Hemorrhagic Disease (VHD and VHD2) is the major viral infections that affect Oryctolagus cuniculus.  All breeds including lop-eared and dwarf breeds are susceptible.

Myxoma virus

The myxoma virus ( MV or MYXV) is a poxvirus that belongs to the genus of Chordopoxvirinae while its species is Leporipoxviruses. This brick-shaped virus has a double-stranded DNA and it causes the lethal myxomatosis disease in rabbits, specifically the Oryctolagus cuniculus.

Myxoma virus causes cutaneous fibroma benign (skin tumors) in its natural hosts, S. bachmani (Californian strains) rabbits in the Americas or Sylvilagus brasiliensis (South American strains) which can persist for several weeks.[1]  However, in the European rabbit, the virus is fatal and can cause sudden death. 

The MYXV was first identified in Paraguay, a South American country, introduced deliberately in Australia in 1950 ( to control wild rabbit population), then it went to France in 1952 before spreading to other parts of Europe and the world.

Myxomatosis wild rabbits

Although they can carry this viral disease and it can make them ill, most of them have become resistant to the effects of this causative virus. Therefore, they have a low mortality.

Initially, when the virus was noted in various places including the UK, it killed about 99.8 % [2] of wild rabbit population and when it was introduced to Australia, it wiped over 99% of the infected ones. However, wild rabbits have developed resistance and their death rate has dropped significantly.

The resistance of myxomatosis in wild rabbits is not well understood but is assumed to be related to genetic resistance.

Not all affected ones die. However, the survival rates in the wild are low with less than 10% considering the tough conditions.

Transmission

This virus can spread from an infected rabbit to a healthy one via the following means

• Mainly by biting bugs such as fleas, mites, ticks, mosquitoes, and black flies. The ticks, lice, and mites play a smaller role.
• Direct contact of a healthy and an infected animal
• Contact with infected surfaces i.e., contact of the contaminated surface by a since one.

Myxomatosis in humans – Is it contagious

Is myxomatosis contagious to humans and are there possible symptoms? No, it is not contagious to humans and there are no myxomatosis symptoms in humans. Also, this virus cannot cause illness in humans. It affects only rabbits.

CSIRO chairman Ian Clunies Ross and two other scientists,  Macfarlane Burnet and Frank Fenner injected themselves with the myxoma virus just to prove it did not affect humans. [3]

Are there cases of myxomatosis in dogs or cats?

As in the case of human beings, this viral disease does not affect dogs or cats. There is no evidence of cats or dogs reported with this virus.

Myxomatosis incubation period

The incubation period varies from one rabbit to another, but it ranges from 5-14 days [10] depending on virus dosage, inoculation means, and its strain [11].

A lump on the site where the infection occurred may be noted within 2-4 days, skin lesions after 4-5 days and other generalized signs may appear after 6-14 days.

Myxomatosis symptoms

This viral disease has a rapid onset and death, usually within days or hours. Some of the symptoms associated with it include the following:

• Raised cutaneous lesions found on the body, legs, and ears about 1-2 cm in diameters that begin as skin nodules at the point of infection. Later secondary lesions will develop.
• Loss of appetite
• Fever
• Lethargy
• Swollen nose, lips, ears, eyelids, or genital area and face distortion  [4]
• Sleepy eyes and blindness
•  An ocular nodule that evolves to blepharoconjunctivitis as well mucopurulent ocular discharge from the nose  [5]
• Ano-genital edema

If your rabbit has gram-negative bacteria, to be more specific the Pasteurella multocida and Bordetella bronchiseptica in their conjunctiva and respiratory tract, they will contribute to the severity of the condition.

Diagnosis

Diagnosis is primarily by looking at some of the clinical signs and biopsies.  Also, viral isolation,  immunofluorescence, and agar gel immunodiffusion may also be used.

Treatments and recovery

Owing to the similarity of some of its symptoms to those of Pasteurellosis (a bacterial disease), it is possible for it to be misdiagnosed and antibiotics are prescribed. However, antibiotics will not be of much help in dealing with this viral disease.

There is no cure for myxomatosis besides palliative care to easy the various symptoms your pet may be having as well as treating other possible opportunistic and secondary infections (including snuffles, pneumonia and so on) with the hope that this pet will beat this illness.

Not all rabbits affected by myxomatosis die. Intense nursing (palliative care) that includes proper feeding, IV fluids among others can increase recovery chances. However, full recovery may take a long time – weeks to months [6].

Topical ointments for lesions, analgesic medications for pain, and a warm environment are often recommended during recovery.

Prognosis is often poor with a death rate of over 96% of house rabbits without any resistance. In cases where there is much suffering, euthanasia may be recommended. Death is normally expected after between 10 -14 days, but some can take several weeks before dying.

Myxomatosis vaccine

Vaccines are a requirement and are available in countries in which this viral infection is an epidemic [7]. They are currently not available for people who live in the US or Canada.  Vaccines can be homologous or heterologous.

Similarly, Australia does not have the vaccine for the fear it might spread to wild rabbits making them resistant to this virus and their populations will explode.

In the UK, there are two vaccines designed to help your rabbit fight against Myxomatosis and Rabbit Haemorrhagic Disease RHD (also known as Rabbit Viral Hemorrhagic Disease (RVHD) with RHD1 and VHD other acronyms) and the other ones is for  Rabbit Haemorrhagic Disease 2 (RHD2). Both are through subcutaneous injections.

Usually, the first vaccination is a combination of Myxomatosis-RHD vaccine ( such as myxoma vectored RHD virus strain) which is given to kits when they are as from 5 weeks of age. After the jab, your kit will take about three weeks to develop immunity.

Afterward, your rabbit needs an annual booster vaccine of RHD2 every 6-12 months to protect your rabbit from the RHD2 strain of the virus.

These two vaccines should be given at least after a duration of two weeks, i.e., after the first vaccination, you must wait for at least two weeks to give the second one.

Side effects – The side effects of the vaccines are minimal. Some adverse reactions include a slight rise in temperature, a small swelling on the injection site that resolves completely after three weeks

Similarly, it is advisable to avoid it during the first 14 days of pregnancy as well as avoid it inbreeding bucks. [8]

Vaccine cost – The annual cost of the vaccination can be about around £30-£40 (in the UK). This can vary from one vet to another as well as location [9].

VHD prevention, control, and protection

Since it is a very contagious illness, you need measures to avoid infection and spread of this virus. Here are some ways you can protect these animals from this deadly viral infection. 

• Use safe repellants on various bugs and insects that might bite your pet such as fleas, ticks, and other small biting flies.
• Fur mites and fleas can be treated with Advantage (Imidacloprid), an OTC, or your vet may prescribe Revolution (Selamectin).
• It is advisable to keep your bunnies indoors. If they must stay outside, use netting, screens, and repellents to keep these parasites away. Seek the best advice from your vet on the safe repellents to use.
• Control mosquito breeding by getting rid of any stagnant water in flowerpots, gutters, drainage systems, etc. There are many ways to control mosquitoes from your property which your vet will advise you on. Also, keep rabbit bedding and hutch dry as mosquitoes like damp places.
• Since the virus spreads through direct contact or contact with a contaminated surface, quarantine new rabbits as well as separating the various utilities such as feeding and water bottles and bowls, feeding tray or bowls, toys, etc., unless you have thoroughly disinfected them with household bleach.
• Contact a rabbit savvy vet the moment you notice some of the symptoms we have discussed.

Can you eat rabbits with myxomatosis?

If you are wondering whether you can eat a rabbit with myxomatosis or not, the answer is that the virus will not affect you. [12].

However, since it is not possible to conclusively know whether myxomatosis is the only disease that a sick bunny had, any skin animal should not be eaten by a human being, cats, dogs or other pets.