Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/30/2002
Publication Date: 5/1/2003
Citation: Liebler-Tenorio, E.M., Ridpath, J.F., Neill, J.D. Distribution of viral antigen and development of lesions after experimental infection of calves with a BVDV 2 strain of low virulence. Journal of Veterinary Diagnostic Investigation. 2003. v. 15. p. 221-232. Interpretive Summary: Bovine viral diarrhea virus (BVDV) is an economically important pathogen of cattle worldwide. There are many different strains of BVDV. Some of the strains cause animals to become very ill. Other stains cause no noticeable illness. As part of a project to determine how these strains differ we infected calves with a virus causes a mild disease. This virus was detected in a wide range of tissues in infected animals initially but was disappeared from the animal within two weeks. While severe disease was not observed the animals did have changes in tissues that could be detected using a microscope. Particularly affected were tissue that participate in the animals immune system. However, the damage to these tissues by the virus did not last long. By 9 days after infection most tissues had returned to normal. Virus strains that do not cause disease are used in vaccines. This study is important in that it shows that even in the absence of disease, tissues are damaged as the result of viral infection. While such tissue damage may not result in illness it may impair the animal's ability to respond to other viruses or bacteria.
Technical Abstract: To examine virus-host interaction in subclinical infections, the spread of an avirulent BVDV 2 strain to different organs and development of lesions were investigated. Eight colostrum-deprived, clinically healthy, 2 to 3 months old calves were intranasally inoculated with 106 TCID of the naturally occurring avirulent BVDV 2 strain 28508-5, and two served as controls. Two calves each were euthanized at days 3, 6, 9 and 13 post inoculation (pi). A wide range of tissues was processed for histology and immunohistology. Signs of overt clinical disease were absent. However, a mild temperature elevation at days 7 and/or 8 pi and a moderate decrease of circulating lymphocytes occurred. BVDV antigen was detected at day 3 pi in several lymphoid tissues. At day 6 pi, BVDV antigen was widespread in lymphoid tissues and multifocally in intestinal epithelial cells, but was associated with no or subtle lesions only. At day 9 pi, much less BVDV antigen was detectable, but there was severe depletion of lymphoid tissues At day 13 pi, BVDV antigen had been cleared from most lymphoid tissues which were at variable phases of depletion and recovery. In conclusion, the avirulent BVDV spread to lymphoid tissues and intestinal epithelial cells, but was rapidly eliminated. Transient depletion of lymphoid tissues was followed by recovery with increased proliferation as indicated by reactivity for Ki-67 antigen.