Читать книгу Canine and Feline Epilepsy - Luisa De Risio - Страница 261

Canine distemper (CD) is a common polysystemic disease of dogs that may infect the CNS. CD is caused by canine distemper virus (CDV), an RNA virus that belongs to the genus Morbillivirus, family Paramyxoviridae (Martella et al., 2008; Greene and Vandevelde, 2012). Although the incidence of CD has decreased since the introduction of the modified-live CDV vaccines in the 1950s, it is still a common CNS disorder worldwide, primarily in unvaccinated dogs but also occasionally in dogs with a vaccinal history as immunity to virulent CDV is not absolute after vaccination. Dogs that are not immunized regularly may lose their protection and become infected following stress, immunosuppression or contact with diseased animals. CDV is quickly inactivated in the environment and transmission mainly occurs by direct animal-to-animal contact or by exposure to infectious aerosol. The virus enters the new host by the nasal or oral route and promptly starts replication in the lymphoid tissues (Martella et al., 2008). Eight to 9 days after infection, CDV spreads by cell-associated viraemia to the epithelial cells in most organs and CNS tissue. Transient fever, loss of appetite, lethargy, ocular and nasal discharge and tonsillitis may be observed. At this stage, the outcome of the infection and the severity of the clinical signs vary markedly depending on strain virulence, environmental conditions and the dog’s age and immune status. If the dog develops a strong immune response, the virus is cleared from most tissues and the animal shows no clinical signs of infection. If the immune response is intermediate by day 9 to 14 post-infection, the virus is able to reach the epithelial tissues (resulting mainly in respiratory and gastrointestinal signs) and the CNS. The respiratory and gastrointestinal signs may resolve as antibody titre increases. However, CDV may persist for extended periods in the uvea, neurons, urothelium and in some cutaneous areas such as the foot pads. The CNS signs are generally delayed and hyperkeratosis is observed in some dogs. Dogs unable to mount an adequate immune response by day 9 to 14 post-infection undergo viral spread to many tissues, develop severe and rapidly progressive clinical signs and die.