Symptoms and Prevention and Control Methods of Rabbit Myxomatosis
Rabbit myxomatosis is a highly contagious and highly lethal infectious disease caused by the myxoma virus. It is characterized by myxomatous swelling under the skin throughout the body, especially on the face and around the natural orifices. The OIE lists it as a Category B disease.
1 Etiology
The myxoma virus is a member of the genus Leporipoxvirus in the family Poxviridae.
This virus has strong resistance to drying, can survive for 2 weeks in dried myxoma nodules, can survive for more than 3 months at 8-10°C in a moist environment, and can survive for 1-2 weeks at 26-30°C. It is sensitive to heat and is inactivated at 55°C within 10 minutes and at 60°C within a few minutes. It has strong resistance to potassium permanganate, mercuric chloride and carbolic acid, and a 0.5%-2% formaldehyde solution requires 1 hour to inactivate the virus.
2 Epidemiology
Sick rabbits are the source of infection, with the highest virus content in the eye discharge and exudate from lesioned skin of sick rabbits. It is mainly transmitted through the bites of arthropods (most commonly mosquitoes and fleas). It can also be transmitted through direct contact with sick rabbits or contact with feed, drinking water and equipment contaminated with the virus.
This disease occurs only in rabbits and hares, and other animals are not susceptible. It mostly occurs in summer and autumn during the season when insects breed and multiply.
3 Clinical Symptoms
The incubation period is generally 3-7 days, with a maximum of up to 14 days.
It is characterized by systemic mucous edema and subcutaneous gelatinous tumors. Primary tumor nodules appear at the sites bitten by virus-carrying insects, followed by swelling of the eyelids, lacrimation, and sticky or purulent eye discharge, with severe cases involving adhesion of the upper and lower eyelids to each other. The swelling can spread throughout the entire head and the subcutaneous tissue of the ears, causing the skin folds on the head to present a lion-head appearance. Edema occurs around the anus, genitals, mouth and nostrils. Subcutaneous gelatinous tumors appear in the edematous areas, especially at the junctions between mucous membranes and skin.
4 Pathological Changes
The prominent lesions are skin tumors, skin and subcutaneous edema, especially obvious in the skin of the face and around the natural orifices. Some virus strains can cause skin hemorrhage, congestion of the serosa of the stomach and intestines, hemorrhage of the endocardium and epicardium, and congestion of the liver, spleen, kidney and lungs.
5 Diagnosis
5.1 A preliminary diagnosis can be made based on typical clinical symptoms and pathological changes, and confirmation requires further laboratory diagnosis.
5.2 Laboratory Diagnosis
In international trade, there is still no designated diagnostic method. Alternative diagnostic methods include agar gel immunodiffusion test (AGID), complement fixation test (CF), and indirect fluorescent antibody test (IFA).
Pathogen isolation and identification: immunodiffusion test (for dead rabbits when visible skin lesions are present), immunofluorescence test, or inoculation of rabbit kidney cells with lesioned material and observation of cytopathic effects can also be used for identification.
Serological tests: complement fixation test, virus neutralization test, agar immunodiffusion test.
Sample collection: collect lesioned tissue, separate the epidermis from the dermis, wash with phosphate-buffered saline, and set aside for use.
6 Prevention and Control
Adopt general comprehensive epidemic prevention methods. When this disease occurs, cull sick rabbits and rabbits in the same group, and carry out harmless disposal. Thoroughly disinfect the contaminated environment, equipment, and so on.