Abstract:
The control of Newcastle disease (ND) in South Africa has proved difficult since 2002 following the introduction
of lineage 5d/VIId Newcastle disease virus (NDV) strain (‘‘goose paramyxovirus’’ – GPMV) to
which commercially available ND vaccines appeared less effective. Most of the ND infections, even in
fully vaccinated hens were characterized consistently by a drop in egg production. In this study, commercial
and SPF hens-in-lay were vaccinated with La Sota vaccine and challenged with a GPMV isolate.
Immunohistochemical labeling was used to determine the distribution of viral antigen in the oviduct
of the hens. Following reports that cloacal vaccination offered better protection against egg production
losses than the oro-nasal route, the efficacy of cloacal and ocular routes of vaccination against challenge
were compared. Results showed that La Sota vaccine offered birds 100% protection against the virulent
ND (GPMV) virus challenge from clinical disease and death, but not against infection and replication of
the GPMV, as birds showed varying degrees of macropathology. Histopathology of the oviduct of infected
birds revealed multifocal lymphocytic inflammation in the interstitium as well as mild glandular ectasia
and mild edema. Finely granular NDV-specific immunolabeling was demonstrated in the cytoplasm of
epithelial cells and mononuclear (lymphohistiocytic) cells in the interstitium of the oviduct. Both vaccine
and virulent GPMV showed greatest tropism for the uterus (versus the magnum and isthmus). There was
no clear difference in the protection of the oviduct and in the distribution of oviductal GPMV antigens
between the two routes of vaccination.
