Summary
Contagious
ecthyma is caused by the orf virus, a member of the family Poxviridae,
genus Parapoxvirus. Morbidity in affected sheep flocks is
approximately 100%, while mortality varies between 1% and 10%. A
live attenuated vaccine was produced by the Istituto Zooprofilattico
Sperimentale dellAbruzzo
e del Molise G.
Caporale.
Quality control was performed in accordance with the European Pharmacopoeia.
A wild virus strain was attenuated through serial passages on primary
chicken embryo fibroblast tissue cultures. The virus suspension
was treated according to standard procedures and freeze dried. The
immunising dose was 1 ml containing 104,5TCID50,
administered intramuscularly. The safety of the vaccine was successfully
tested by intramuscular inoculation of 20 susceptible sheep and
20 lambs with the routine dose, 10 times the immunising dose and
two normal doses administered at seven-day intervals. The efficacy
of the vaccine was tested using three groups of susceptible animals.
The first group included 10 lambs and the second 10 adult sheep;
the animals were immunised intramuscularly with 1 ml of the reconstituted
vaccine. The third group, used as controls, included five sheep
and five lambs. Serological reactivity was monitored by indirect
enzyme-linked immunosorbent assay (ELISA). The animals were challenged
30 days later with a pathogenic strain administered intradermally
along the labial area. Vaccinated animals did not show any clinical
signs of disease, whereas all the controls developed typical signs
of contagious ecthyma. To confirm the efficacy of the vaccine, a
field trial was conducted in four flocks affected by the disease.
The trial showed that the vaccine was able to block the normal course
of the disease and induce rapid recovery.
Keywords
Contagious
ovine ecthyma, Orf, Parapoxvirus, Poxviridae, Sheep, Vaccine,
Virus. |