Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2004
Publication Date: 3/1/2005
Citation: Confer, A.W., Fulton, R.W., Step, D.L., Johnson, B.J., Ridpath, J.F. 2005. Viral antigen distribution in the respiratory tract of cattle persistently infected with bovine viral diarrhea virus subtype 2a. Veterinary Pathology. 42:192-199. Interpretive Summary: Bovine viral diarrhea virus (BVDV) is a viral pathogen of cattle. Animals may be infected acutely. In these acute infections the virus is usually cleared from the animal in two to three weeks. However, if an animals is infected as a fetus, it may develop a persistent infection. These persistently infected animals do not clear the virus and as a consequence serve as a source of BVDV infection to other animals for the duration of their life. In addition to constantly shedding virus, animals persistently infected with BVDV have a high incidence of respiratory infections. Treatment of persistently infected animals for respiratory disease can be costly for producers. In this study 10 the respiratory tracts of ten animals persistently infected with BVDV was examined to determine if BVDV could be found in lung and nasal tissue. In cases of bacterial pneumonia, certain cells lining the lung are attacked by bacteria. Bacteria bind to these cells and form colonies. In this study it was found that, in persistently infected animals, these cells contain BVDV. The authors think that the presence of BVDV in these cells makes bacteria more likely to bind to them. This may be the reason persistently infected animals have a higher incidence of respiratory disease than normal animals. It was also found that, in persistently infected animals, cells that produce mucus were infected with BVDV. The authors think that BVDV is excreted in the mucus and this BVDV contaminated mucus may be a major source for infection of other animals with the virus. These findings are important to understanding the health problems of persistently infected animals and how they spread virus to other animals. This information will be used to develop better management and control programs for BVDV.
Technical Abstract: Tissues were obtained at necropsy from the nasal vestibule, turbinates, nasopharynx, trachea, tracheobronchial bifurcation and lung from each of ten clinically healthy calves persistently infected (PI) with bovine viral diarrhea virus (BVDV) serotype 2a. Tissues from the nasal vestibule were obtained by biopsy from five additional PI calves. Formalin-fixed tissues were processed for immunohistochemistry to localize the distribution of BVDV throughout the respiratory tract. Antigen distribution and intensity were subjectively evaluated. Throughout the respiratory tract, mononuclear leukocytes, vascular smooth muscle, and endoneural and perineural cells had BVDV immunoreactivity (BVDV-IR). Multifocally, squamous and ciliated columnar epithelium throughout the respiratory tract contained weak to moderate BVDV antigen . Viral antigen was not seen in goblet cells. BVDV-IR in mixed tubuloalveolar glands of the nasal cavity was weak to strong in serous secretory cells and ductular epithelium. Chondrocytes of the concha often diffusely contained BVDV antigen. Nasal mucus secreting and tracheobronchial glands multifocally contained weak viral signal. In all cases, alveolar macrophages had moderate to strong BVDV-IR, whereas BVDV-IR in alveolar epithelial cells was weak to moderate. BVDV was present in interalveolar leukocytes and mesenchymal cells. Results indicate that serous secretions of the nasal cavity, productive viral infection of epithelium, and infected leukocytes in respiratory secretions are likely major sources of infectious BVDV from PI calves. The presence of BVDV antigen in respiratory epithelium is, at least, indirect support for the notion that this virus predisposes PI cattle to secondary microbial infections.