Distribution of Viral Antigen and Development of Lesions after Experimental Infection of Calves with a BVDV 2 Strain of Low Virulence

Abstract

Abstract. To examine the virus-host interaction in subclinical bovine viral diarrhea virus (BVDV) infections, the spread of a BVDV 2 strain of low virulence to different organs and the development of lesions were investigated. Eight colostrum-deprived, clinically healthy, 2-3-month-old calves were intranasally inoculated with 10 6 tissue culture infective dose of the naturally occurring BVDV 2 strain 28508-5 of low virulence, and 2 served as controls. Two calves each were euthanized at days 3, 6, 9, and 13 postinoculation (pi). Representative tissues were processed for histology and immunohistology. Signs of overt clinical disease were absent. However, a mild temperature elevation at days 7 or 8 pi and a moderate decrease of circulating lymphocytes occurred in all inoculated calves. The BVDV antigen was detected at day 3 pi in several lymphoid tissues. At day 6 pi, BVDV antigen was found 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 that were at variable phases of depletion and recovery. In conclusion, the BVDV strain of low virulence spread to lymphoid tissues and intestinal epithelial cells but was rapidly eliminated. Transient depletion of lymphoid tissues was followed by recovery. Bovine viral diarrhea virus (BVDV) is a Pestivirusin the family Flaviviridae. 17 Infections with BVDV are widespread in cattle herds and cause severe economical losses in North America and Europe despite intense efforts to control or eradicate them. 19 On the basis of genomic differences in the 5ЈNTR region of BVDV, 2 species, BVDV 1 and BVDV 2, are currently differentiated. 4,17,33 The BVDV strains can grow in epithelial cell cultures with or without inducing a cytopathic (cp) effect, thus allowing further grouping in cp and noncytopathic (ncp) biotypes. 13,32 Infections with BVDV of both genotypes have been associated with a wide variety of clinical conditions including subclinical infection, reproductive failure, severe acute disease with or without hemorrhagic diathesis, and mucosal disease. 3 During the last decade, an increased number of field cases of severe acute BVD in all age groups of cattle has been reported. 8,10,18,30 The BVDV isolates from these outbreaks in North America predominantly belong to BVDV 2. 8 Besides the highly virulent strains of BVDV 2, there also exist strains causing subclinical infections only. 35 These strains might be even more important for the spread of BVDV because they may circulate undetected in a herd for an extended time period and may predispose to secondary infections or disease.Highly virulent isolates from field cases of severe acute BVD have been used to investigate the pathogenesis and pathology of acute BVD, 1,5,9,12,16,25,28,37 but there exists only 1 study using a BVDV 2 strain of low virulence. 27 It is still unclear how virus...

Effects of Preinfection With Bovine Viral Diarrhea Virus on Immune Cells From the Lungs of Calves Inoculated With Bovine Herpesvirus 1.1

“…56 On the other hand, the increase in B-lymphocyte numbers was more marked and occurred earlier in infection in those calves inoculated with BHV-1 alone. The attenuated Blymphocyte response observed in the BVDV/BHV-1 group may be linked to a severe lymphocyte depletion in BVDV target lymphoid organs, a lesion that has already been described in calves 46 and in other in vivo infections with BVDV, 31,32,37,38,43 in which the depletion has been correlated to the action of apoptotic mechanisms developed during BVD. A difference between groups was observed in the behavior of CD8þ, CD4þ, and Foxp3þ regulatory T cells, as well as in the different cytokines studied in response to the secondary infectious agent.…”

Bovine Viral Diarrhea Virus Infections

“…29, 90 A type 1b isolate, New York 1, has been shown to be virulent and can cause leukopenia, severe lymphoid depletion of thymus, mesenteric lymph nodes, and Peyer patches as well erosions and ulcers in the gastrointestinal tract.…”

“…19,79,89,117,119 BVDV infects a wide variety of cell types but has a predilection for cells of the immune system such as monocytes/macrophages, dendritic cells (DCs), and lymphocytes. 19,61,90 The consequences of infection include the death of these cell populations as an extreme event or more subtle effects on cytokine expression and synthesis of costimulatory molecules. 18,26,61,119 The changes in cytokine production by immune or nonimmune cells affect both innate and adaptive immunity.…”

Virus Distribution and Role of Thymic Macrophages During Experimental Infection With Noncytopathogenic Bovine Viral Diarrhea Virus Type 1

“…24 Thymic depletion has also been described during BVDV1 and BVDV2 infection. 4,11,14,15,26 However, the role of macrophages in the pathogenesis of this thymic depletion remain unclear, although monocyte-macrophages have been identified as one of the target cells for this virus. 3,11,17 The purpose of this study was to investigate, in experimental animals, the relationship among thymic depletion, presence of viral antigen, and changes in distribution and cytokine production by thymic macrophages from colostrum-deprived calves experimentally infected with the low-virulence noncytopathogenic BVDV1 strain 7443.…”