Biomedical subjects

Julia F Ridpath

Publications and source records attributed to Julia F Ridpath.

24 records · Page 2Linked to original sources

PubMed2003

Distribution of viral antigen and development of lesions after experimental infection of calves with a BVDV 2 strain of low virulence.

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.

Animals↗

PubMed2002

Clinical and epidemiologic observations of bovine viral diarrhea virus in the northwestern United States.

Retrospective analyses of cases from which bovine viral diarrhea virus (BVDV) was isolated from 1980 to 2000 were conducted. These cases originated from the northwestern US and included both beef and dairy cattle. The results indicated that there was a shift in diseases associated with BVDV infection and in the animal age at onset of disease. Comparative results from the 1980 data indicated a low fetal infection rate (<5%), followed by steady increases of clinical cases and peaking at 6 months (30%). By 2000, the shift of BVDV cases was noticeable and indicated a biphasic occurrence of disease. The first phase was fetal infections, which increased to >25%, followed by a second phase at 6 months (>35%). Phylogenetic analysis was conducted on selected isolates from the time period 1998-2000 (n = 54). There were representative viral isolates from the two genotypes (BVDV1 and BVDV2), as well as subgenotypes, BVDV1a and BVDV1b. The types were further correlated with the clinical manifestation, which were reported as mucosal disease, persistently infected (PI)-poor doer, and abortion-open cows. The results indicated that BVDV were distributed throughout the clinical spectrum of disease, with BVDV2 representing the greatest frequency of isolation, and the greatest association with abortion-open cows. When the BVDV genotypes and subgenotypes were categorized into early (<100 days gestation) versus late (>100 days gestation) fetal infections, there was an inverse relationship noted. It was observed that BVDV1a was associated least with early infection (14%) and most with late infections (86%). BVDV1b was intermediate, followed by BVDV2, which was associated more with early infections (45%) and less with late infections (55%) when compared with BVDV1a and BVDV1b.

5' Untranslated Regions↗

PubMed2002

Phylogenetic analysis of Brazilian bovine viral diarrhea virus type 2 (BVDV-2) isolates: evidence for a subgenotype within BVDV-2.

Phylogenetic analysis divides bovine viral diarrhea viruses (BVDV) into two different genotypes (BVDV1 and BVDV2). BVDV1 strains have been further subdivided into two to 11 subgenotypes. Phylogenetic analysis of BVDV2 isolates, however, has not been able to identify discrete subgenotypes. In this study, we identified six South American BVDV2 strains and one North American BVDV2 strain that cluster to a separate genetic group within BVDV2, thus representing a distinct subgenotype. The 5' untranslated region (UTR) sequence homology between these six strains and other BVDV2 from North America, Europe and Asia (81.7%) is lower than the homology used to segregate BVDV1 into BVDV1a and BVDV1b (83.6%). Most nucleotide differences observed between the two subgroups of BVDV2 were concentrated in two regions, which also harbor most of the differences seen between BVDV1a and BVDV1b. To determine if this segregation was real, an additional analysis was performed comparing NS2/3 sequences. Analysis of a conserved sequence located between nucleotides 6670 and 7186 of the NS2/3 coding region also segregated these isolates to a separate group. The sequence homology between the two subgroups (86.3%) was higher than the homology in the 5'UTR (81.7%), with mean sequence homologies of 91 and 87.2% within the proposed subgroups. In contrast to the 5'UTR, alignment of the NS2/3 sequences revealed nucleotide differences distributed across the region. These results demonstrate that BVDV2 isolates cluster to two genetically distinct subgroups within BVDV2. The differences in both the 5'UTR and NS2/3 are consistent and justify this segregation. We suggest that BVDV2 may thereafter be subgenotyped into BVDV2a and BVDV2b. The existence of subgroups within the BVDV2 genotype with genetic heterogeneity similar to that seen among BVDV1 subgroups argues against BVDV2 isolates arising from BVDV1 in a recent evolutionary event. Unless the evolutionary clocks for BVDV1 and BVDV2 isolates tick along at different rates, these results indicate that BVDV2 have existed as long as BVDV1.

5' Untranslated Regions↗

PubMed2002

Evaluation of the reverse transcription-polymerase chain reaction/probe test of serum samples and immunohistochemistry of skin sections for detection of acute bovine viral diarrhea infections.

Bovine viral diarrhea viruses (BVDV) cause both acute and persistent infections. While diagnostic tests have been designed to detect animals persistently infected (PI) with BVDV, the reliability of these tests in detecting acute BVDV infections is not known. It is also possible that acute BVDV infections may be confused with persistent infections in surveys for PI animals. In this study, 2 tests presently in use in diagnostic laboratories to test for PI animals, polymerase chain reaction amplification followed by probe hybridization (RT-PCR/probe) of serum samples and immunohistochemical detection of viral antigen in skin biopsies (IHC), were evaluated for their ability to detect acute BVDV infections. Sixteen colostrum-deprived, BVDV-free, and BVDV-antibody-free calves were infected with 6 different BVDV strains. Clinical signs, seroconversion, and virus isolation indicated that inoculated animals did replicate virus. Virus could be detected in 19% (3/16) of acutely infected animals by the RT-PCR/probe technique. No acutely infected animals were positive by IHC.

Acute Disease↗

PubMed2002

Isolation of bovine viral diarrhea virus from an alpaca.

A frozen, stillborn alpaca (Lama pacos) was submitted to the Minnesota Veterinary Diagnostic Laboratory for diagnostic purposes. No gross or histopathologic changes of any significance were seen. A pool of lung, liver, and brain tissues was positive for bovine viral diarrhea virus (BVDV) by reverse transcription-polymerase chain reaction. On inoculation in cell cultures, a noncytopathic BVDV (type 1b) was isolated. No evidence of BVDV was seen on immunohistochemical examination of tissues. This indicates the importance of using multiple tests for arriving at a diagnosis and appears to be the first report of BVDV isolation from alpaca.

Animals↗

PubMed2002

Bovine viral diarrhea virus (BVDV) 1b: predominant BVDV subtype in calves with respiratory disease.

The prevalence of bovine viral diarrhea virus (BVDV) infections was determined in 2 groups of stocker calves with acute respiratory disease. Both studies used calves assembled after purchase from auction markets by an order buyer and transported to feedyards, where they were held for approximately 30 d. In 1 study, the calves were mixed with fresh ranch calves from a single ranch. During the studies, at day 0 and at weekly intervals, blood was collected for viral antibody testing and virus isolation from peripheral blood leukocytes (PBLs), and nasal swabs were taken for virus isolation. Samples from sick calves were also collected. Serum was tested for antibodies to bovine herpesvirus-1 (BHV-1), BVDV1a, 1b, and 2, parainfluenza 3 virus (PI3V), and bovine respiratory syncytial virus (BRSV). The lungs from the calves that died during the studies were examined histopathologically, and viral and bacterial isolation was performed on lung homogenates. BVDV was isolated from calves in both studies; the predominant biotype was noncytopathic (NCP). Differential polymerase chain reaction (PCR) and nucleic acid sequencing showed the predominant subtype to be BVDV1b in both studies. In 1999, NCP BVDV1b was detected in numerous samples over time from 1 persistently infected calf; the calf did not seroconvert to BVDV1a or BVDV2. In both studies, BVDV was isolated from the serum, PBLs, and nasal swabs of the calves, and in the 1999 study, it was isolated from lung tissue at necropsy. BVDV was demonstrated serologically and by virus isolation to be a contributing factor in respiratory disease. It was isolated more frequently from sick calves than healthy calves, by both pen and total number of calves. BVDV1a and BVDV2 seroconversions were related to sickness in selected pens and total number of calves. In the 1999 study, BVDV-infected calves were treated longer than noninfected calves (5.643 vs 4.639 d; P = 0.0902). There was a limited number of BVDV1a isolates and, with BVDV1b used in the virus neutralization test for antibodies in seroconverting calves' serum, BVDV1b titers were higher than BVDV1a titers. This study indicates that BVDV1 strains are involved in acute respiratory disease of calves with pneumonic Mannheimia haemolytica and Pasteurella multocida disease. The BVDV2 antibodies may be due to cross-reactions, as typing of the BVDV strains revealed BVDV1b or la but not BVDV2. The BVDV1b subtype has considerable implications, as, with 1 exception, all vaccines licensed in the United States contain BVDV1a, a strain with different antigenic properties. BVDV1b potentially could infect BVDV1a-vaccinated calves.

Animals↗