BVD-virus infection in peripheral blood mononuclear cells from persistently viraemic calves studied by correlative immunoelectron microscopy

Experimental infection with Babesia divergens in cattle persistently infected with bovine virus diarrhoea virus

Nine Norwegian Red cattle, aged 7-14 months, persistently infected with bovine virus diarrhoea virus (BVDV) were inoculated with a Swedish strain of Babesia divergens. Six persistently infected cattle of the same age and breed were kept as controls. Blood and serum samples were collected regularly during the observation period. Rectal temperatures were recorded every morning for 25 days post infection, and the animals were examined clinically on a daily basis. Sera were examined for antibodies to B. divergens by indirect immunofluorescence antibody test (IFAT). Eight of the infected animals developed fever of 2-5 days duration. Babesia divergens organisms appeared in the erythrocytes of all infected animals on the day after inoculation. The parasitaemia lasted for 4-11 days. One animal had a transient haemoglobinuria. Compared with the control group, there was a 20% decrease in the haematocrit. There was a transient lymphopenia and thrombocytopenia during the period of fever. There were no differences in mean numbers of neutrophils between the two persistently infected groups. Compared with cattle free of BVDV, the persistently infected cattle had consistently lower total leucocyte count that was mainly due to decreased mean numbers of neutrophils and monocytes. All infected animals develop antibodies > or = 1:1280 between day 7 and 10 post infection. The magnitude of the antibody response was considerably lower than that of BVDV-free animals inoculated with the same strain and dosage of B.divergens.

The pathologies of bovine viral diarrhea virus infection. A window on the pathogenesis

Pathologic lesions caused by bovine viral diarrhea virus (BVDV) infections comprise a wide spectrum of type, degree, and, by implication, pathogenesis, including congenital defects, necroticerosive lesions in mucosal epithelia and skin, and reactive as well as degenerative changes in lymphoid tissues. At least some of the pathology may not be solely due to BVDV replication per se, but rather caused by a host response to the virus, particularly the production of pro-inflammatory cytokines.

Pathogenesis of intrauterine infections with bovine viral diarrhea virus

BVDV shares with other Pestiviruses the ability to cross the placenta of pregnant host animals. The effects of fetal infections are complex and depend on a number of factors, e.g., age of the zygote/embryo stage, no infection seems to occur. During the last one third of gestation the infection is terminated by the ontogeny of the fetal immune system. This leaves a window of susceptibility during early stages of fetal development allowing establishment of viral persistence and/or the development of a number of fetopathologic effects. Additionally, fertility problems and abortions are observed. Calves that are born immunotolerant to BVDV and persistently viremic display a wide variety of abnormalities. However, there is an unknown proportion of calves born without any clinical signs indicative of persistent infection. The time of fetal infection during the first stages of pregnancy seems to play a crucial role with respect to the lesions induced. Generally, early infections seem to induce less damage compared with late infections, suggesting an indirect, possibly immune-mediated pathogenesis. Additionally, direct virus-cell interactions may play a role. Few data exist about the influence of differences in viral virulence on fetal pathology. Likewise the role of the viral target cell range is not clear.

The hog cholera virus

Hog cholera virus (HCV) is a spherical enveloped particle of about 40-60 nm dia. The viral genome is a single strand RNA of about 12,000 bases with positive polarity. One single large open reading frame codes for presumably four structural, i.e. three glycoproteins and a core protein, and about three to five nonstructural proteins. The functional role is not yet fully clear for all viral proteins. HCV belongs to the pestivirus group and it is closely related to bovine viral diarrhoea and border disease viruses. The relationship extends to morphology, antigenicity, host spectrum and molecular properties. Pestiviruses hold generic status in the family Flaviviridae.

Detection of cattle infected with bovine viral diarrhea virus using nucleic acid hybridization

A ribonucleic acid (RNA) hybridization assay to identify cattle infected by bovine viral diarrhea virus (BVDV) is described. The RNA probe was derived from the coding region at the 3' end of the genome of the NADL strain of BVDV. Total RNA from infected cell cultures or peripheral blood leukocytes from suspect animals was extracted and applied to nylon membranes with a slot blot apparatus. Peripheral blood leukocytes were tested concurrently for BVDV by virus isolation. The results of hybridization and virus isolation were in agreement for 92% of the cases. When compared with virus isolation, hybridization had a sensitivity of detection of 59.5% and a specificity of 95%. Cross-reactivity to RNA extracts of border disease virus-infected cells was noted. No cross-reactivity was detected to other common bovine viruses (bovine herpesvirus-1, bovine respiratory syncytial virus, parainfluenza-3 virus, and bluetongue virus), to viruses classified in related families (equine arteritis virus and Venezuelan equine encephalitis virus), or to viruses having similar genomic organization (dengue virus type 2 and Japanese encephalitis virus).