34. Myxomatosis.

Question 1

History, Occurrence?

Answer 1

Leporipox genus

Myxomatosis - NOTIFIABLE

• History, occurrence
• First description: South America ʹ in European rabbits
• Subclinical infection in cotton-tailed rabbits ʹ severe disease in domestic rabbits
• Introduction into Australia in the middle of the 20th century as a biological control agent against
• rural rabbits
• reducing virulence (90%-40% mortality),
• development of herd immunity
• Introduction into France in 1952 ʹ spread around Europe
• World-wide distributed

Question 2

Causative agent?

Answer 2

Causative agent:

Myxoma virus (Leporipoxvirus genus)

• Natural hosts: Sylvilagusminensis, S. brasiliensis, S. bachmani
• European rabbit (Oryctolagus cuniculus) ʹ susceptible, sensitive
• European brown hare (Lepus europaeus) ʹ not susceptible
• 2 serotypes, virulence-variants

Question 3

Epizootiology?

Answer 3

Epizootiology

• Arthropod (mosquitoes, fleas, flies) ʹ mechanical vectors, carry for months
• Seasonalityʹ autumn; epizootics in few-year intervals
• Direct and iatrogenic transmission may occur
• Low virulence strains (Australia, England)

Question 4

Pathogenesis?

Answer 4

Pathogenesis

• Day 1 oedema at site of entry (i.e. earskin)
• Day 2: virus in lymph nodes
• Day 3: viraemia, blood vessel damages, virus in spleen, liver
• Day 4: virus other organs and tissues
• Day 5: blepharoconjunctivitis
• Day 6: onset of clinical signs (generalized, skin, mucosa)
• Days 8-9: typical signs ʹ tumour-like lesions
• Day 10-: death (because the capillary endothelia proliferation)
• Virus transmission : Blood -> vector discharges skin lesions
• Recovery: lysis of myxoma cells

Question 5

Clinical signs?

Answer 5

Clinical signs

• Incubation: ~ 1 week, mortalities after ~1 week of illness
• Typical form: gelatinous swellings, lion head, cold-like signs, pneumonia
• Nodular form: firm nodules, benign
• Conjunctival/respiratory/atypical form: cold-like signs, no/mild swellings

Question 6

Diagnosis?

Answer 6

Diagnosis

• Clinical signs ʹ in typical forms, PCR
• Atypical forms: histopathology, virus detection (PCR, isolation ʹ RK cell line, CAM)

Question 7

Prevention and control?

Answer 7

Prevention and control

• Sanitary prophylaxis
• Closed farming, mosquito nets, arthropod control
• Outbreaks control: movement restrictions, slaughter of affected animals, vaccination in protection zone
• Medical prophylaxis - vaccinations
• Shope fibroma virus heterologous vaccine ʹ from 3 weeks of age, protects for 3-6months
• Attenuated myxoma virus ʹ from 5 weeks of age, protects for 1 year
• I.m, (s.c. ʹ local reaction); vaccination in early summer, repeat in bunnies
• Recombinant vaccine: RHDV surface antigens in myxoma virus vector (vaccinate against both
• diseases with one injection)