Viremic Animals Research Articles

Induced sero‐conversion in heifers with a field strain of bovine pestivirus–a comparison of methods and doses

Losses from pestivirus infection in a closed herd of cattle occurred over several years. In order to prevent further losses, controlled exposure of non-pregnant heifers to pestivirus from viraemic carrier animals was undertaken. Two initial experiments were conducted using either intra-nasal EDTA blood or field contact. Subsequently, other yearling heifers were inoculated with various dilutions of serum using subcutaneous, conjunctival and intra-nasal routes. Effective doses were determined. Neither inoculation nor contact infection produced any clinical illness. The highest dilutions of serum at which sero-conversion occurred were conjunctival, undiluted; intranasal, 10(-1) and subcutaneous 10(-5). With the subcutaneous route all heifers sero-converted at 10(-3). The results for the subcutaneous inoculations showed that the 50% infectious dose for cattle was not distinguishable from that determined in cell culture. Inoculation with a field strain of pestivirus in freeze-thawed serum has effectively and safely induced sero-conversion in heifers. Inoculation of all cattle at risk is considered necessary because no secondary transmission from inoculated heifers was observed.

Epidemiology of bovine virus diarrhoea virus

A better understanding of the epidemiology and pathogenesis of bovine virus diarrhoea virus (BVDV) has emerged in recent years. Fetal infections and in particular those resulting in birth of persistently infected calves are of central importance for the epidemiology of BVDV. A prevalence of persistently infected, viraemic animals of about 1% is found in Denmark and elsewhere by examination of randomly collected blood samples. A recent field study shows that 53% of randomly selected herds in an area in Denmark where BVDV is endemic had one or more persistently infected animals. Persistently infected cows may breed and will always transmit the infection to the calf. Such familial occurrence of persistent infection seems to be a fairly common phenomenon. Persistently infected cattle are important sources of infection to other cattle. Transiently infected cattle following experimental exposure will usually not transmit the infection by contact but this may not always apply to cattle after natural infection. Knowledge of the occurrence and potential for spread of virus from persistently infected bulls is reviewed. Virus is excreted with semen of both persistently and transiently infected bulls and BVDV may be transmitted by use of infected semen for insemination. The potential for spread of the infection through embryo transfer should be avoided by the use of adequate testing and controls.

Demonstration of bovine virus diarrhoea virus antigen in formalin fixed, paraffin embedded tissue using a streptavidin/biotin technique

The detection of bovine virus diarrhoea virus (BVDV) antigen in sections from formalin fixed, paraffin embedded tissue is described. Pre-digestion of the sections with 0.02 per cent protease XIV for 18 hours at 4 degrees C is necessary to unmask formalin fixed antigen. A hyperimmune antiserum prepared in a pig, using a combination of BVDV and hog cholera virus inoculations, linked to a biotinylated anti-pig/streptavidin peroxidase detection system demonstrated antigen in a wide range of tissues from cases of mucosal disease and persistently viraemic animals. The inclusion of a monoclonal anti-pig immunoglobulin linked to a biotinylated anti-mouse/streptavidin peroxidase detection system greatly reduced non-specific staining.

Tumorigenic potential of a myc-containing strain of feline leukemia virus in vivo in domestic cats

The oncogenic capacity of a myc-containing strain of feline leukemia virus (FeLV), termed LC-FeLV, has been examined after inoculation of the virus into neonatal kittens. Like other myc-containing strains of FeLV, LC-FeLV may induce with relatively short latency, but does not necessarily induce, thymic lymphosarcoma in viremic animals. Naturally occurring and experimentally induced tumors are T-cell lymphomas which contain clonally integrated LC-FeLV proviral DNA and which cannot readily be cultivated in vitro in the presence or absence of exogenously supplied interleukin-2. Acquisition of myc by FeLV decreases the period of latency before the appearance of tumors but does not expand the spectrum of tumors induced by FeLV alone.

Immunotherapy of Murine Leukemia. V. Protection Against Friend Leukemia Virus-Induced Immune Complex Glomerulonephritis by Passive Serum Therapy<xref ref-type="fn" rid="fn2">2</xref><xref ref-type="fn" rid="fn3">3</xref>

The development of immune complex glomerulonephritis in DBA/2 mice infected with Friend murine leukemia virus (F-MuLV) was compared with that in mice protected against virus-induced disease by administration of chimpanzee anti-F-MuLV antiserum (CaF-MuLV). Morphologic analysis of glomeruli from viremic (infected) normal chimpanzee serum-treated animals revealed significant renal disease within 2 weeks following virus inoculation, with glomerular immune complex deposits and C-type viral particles seen by electron microscopy. Localization of F-MuLV envelope and core antigens (gp71 and p30, respectively) was also detected by immunofluorescence, as was murine IgG and C3. However, age-matched DBA/2 mice treated with CaF-MuLV antiserum alone or following F-MuLV inoculation showed no evidence of systemic disease and neither localization of F-MuLV antigens nor detectable virus particles. These data indicate that in addition to erythroleukemia, F-MuLV infection results in severe immune complex glomerulonephritis and that passive immunotherapy can protect susceptible mice from both aspects of viral pathogenesis.

Genetic control of antinuclear antibodies in mice inoculated with the moloney leukaemia virus.

The production of antinuclear antibodies (ANA) was studied after inoculation with Moloney leukaemia virus (M-MuLV) in different H-2 congenic strains of mice. Using a new sensitive method for ANA detection, it was demonstrated that M-MuLV-induced ANA were genetically controlled by several different factors. A high viral production was first required for ANA triggering. Among viremic animals both high and low ANA producers were observed. H-2 and non H-2-linked genes were involved in the control of M-MuLV-induced ANA; these genes were different from those involved in the control of viremia. The H2b haplotype was associated with an increased ANA response, the transmission of the responder phenotype being intermediate. Non-H-2-linked genes must also control M-MuLV-induced ANA, as demonstrated in mice having the same H-2 haplotypes, since with equivalent viremias they produced different amounts of ANA. No linkage with X chromosome was found.

T cell-mediated immunity to oncornavirus-induced tumors. III. Specific and nonspecific suppression in tumor-bearing mice.

A strong cell-mediated immune response against Friend, Moloney, Rauscher virus-induced (FMR) cell surface antigens has been demonstrated previously in mice which reject oncornavirus-induced tumors. In order to identify an eventual suppressor mechanism in animals with progressively growing tumors, experiments were initiated in C57BL/6 mice bearing either a murine sarcoma virus (MSV) tumor or Moloney virus-induced lymphoma (MBL2). Progressive tumor growth was induced (a) in viremic animals first infected with Moloney murine leukemia virus (M.Mu LV), then inoculated as adult with MSV; (b) in nonviremic animals injected with MBL2 lymphoma cells. In the absence of tumor cells, viremia induces specific tolerance for which there is no evidence for suppressor cells. In tumor-bearing mice, specific suppressor T cells are detected which are able to inhibit the generation of anti-FMR cytolytic T lymphocytes in vitro and enhance the tumor growth in vivo. In addition to the specific suppressor T cells, a nonspecific suppressive activity mediated by metastatic T lymphoma cells is demonstrated in the spleens of lymphoma-bearing animals. The respective role of the virus and tumor cells in the induction of tolerance to M.MuLV-induced antigens, and their relationship to other components of the specific cell-mediated immune response is discussed.

Retroviruses and embryogenesis: Microinjection of Moloney leukemia virus into midgestation mouse embryos

The interaction of Moloney leukemia virus (M-MuLV) with developing post-implantation mouse embryos was studied. First, the frequency at which embryos in utero are infected by transplacental transmission with maternal virus was explored. To exclude milk transmission from the viremic mother, embryos were delivered by cesarean section prior to birth and given to normal foster mothers. None of 72 mice raised this way developed viremia. This indicates that the placenta is an efficient barrier protecting the developing embryo against infection with exogenous retroviruses. To overcome the placental barrier and to introduce virus into embryos at defined stages of differentiation, Moloney leukemia virus was microinjected directly into embryos in utero at day 8 or 9 of gestation. Between 60 and 70% of the injected embryos survived to birth and were tested for viremia at 4 weeks of age. M-MuLVspecific sequences were quantitated in organs of viremic animals derived from midgestation embryos microinjected with virus. Molecular hybridization experiments with nucleic acids extracted from different organs of these animals indicated that every cell type carried M-MuLV-specific DNA sequences and that high concentrations of M-MuLV-specific RNA sequences were present in every organ. In contrast, M-MuLV infection and expression is restricted to lymphatic tissues when animals are exposed to virus after birth or in BALB/Mo mice. These results indicate that the most important parameter determining the “target tropism” of Moloney leukemia virus infection and expression is the stage of embryogenesis and cellular differentiation at which virus infection takes place. In viremic C57BL animals derived from microinoculated embryos, the hair color changed beginning at age 6 weeks. This was not observed in animals exposed to virus after birth. All animals succumbed to MMuLV-induced leukemia at a later age. The results suggest that expression of M-MuLV may also lead to cellular dysfunctions other than leukemic transformation.

Infectious primate type-C virus shed by healthy gibbons

MANY captive gibbons are naturally exposed to infectious type-C virus based on the prevalence of animals with humoral antibodies reactive to the virus1,2 and isolation of virus from tissue of leukaemic3,4 and normal gibbons5. A closely related infectious type-C virus has also been isolated from a woolly monkey with a spontaneous fibrosarcoma6,7 which implies that a common virus could infect unrelated non-human primates. Several reports recently have identified infectious primate type-C virus8,9, viral components10 and humoral antibody reactive to this virus in leukaemic11 and normal humans12 suggesting that man also may be susceptible to infection by a related virus. In an attempt to identify a possible source for infectious primate type-C virus that might infect primates as well as other animals, we decided to investigate whether healthy captive gibbons were shedding viruss ince this non-human primate is frequently displayed at zoos or kept as pets. This report presents evidence that gibbons can have long term viraemia with type-C virus without detectable immune response. These viraemic animals actively shed infectious virus in urine and faeces.

Infection of British deer and farm animals with epizootic haemorrhagic disease of deer virus

Epizootic haemorrhagic disease of deer virus, an orbivirus related to bluetongue virus, was inoculated intravenously into red, fallow, roe and muntjac deer, and into sheep, goats, pigs and cattle. Low level viraemias were recorded in each species apart from goats and pigs but clinical disease was not observed. Virus was not isolated from swabs taken of the nasal, urogenital or rectal mucosae. Control animals in direct contact with inoculated animals did not develop a detectable viraemia or serum antibody. In viraemic animals the virus was associated with the cell fraction of the blood. Beyond 7 days after inoculation the chance of virus isolation was enhanced if the cells were washed and lysed prior to inoculation of the cell cultures. It is suggested that cattle may play a role in the epizootiology of epizootic haemorrhagic disease of deer in North America.

Germ line integration and Mendelian transmission of the exogenous Moloney leukemia virus.

Mice were infected with the exogenous Moloney leukemia virus (M-MuLV) at two different stages of development. Either newborn mice (which can be considered as essentially fully differentiated animals) or preimplantation mouse embryos (at the 4-8 cell stage) were infected with M-MuLV. In both cases, animals that had developed an M-MuLV-induced leukemia were obtained. Two lines of evidence indicate that infection of preimplantation embryos, in contrast to infection of newborns, can lead to integration of the virus into the germ line. 1. Viremic males of the first backcross generation (N-1 generation) transmitted the virus to 50% of their offspring (N-2 generation) when mated with uninfected females. Likewise, a 50% transmission was observed from viremic N-2 and N-3 males to the next generations. 2. Molecular hybridization experiments revealed that viremic N-1 and N-2 animals carried one copy of M-MuLV per diploid mouse genome equivalent in all "non-target" organs tested. Together, both experiments indicate that the exogenous M-MuLV can be converted to an endogenous virus after infection of preimplantation embryos. The available evidence suggests that M-MuLV integrated into the germ line at one out of two possible integration sites. Thus, viremic backcross animals are heterozygous for a single Mendelian locus carrying the M-MuLV gene. During leukemogenesis an amplification of the M-MuLV from one copy to a maximum of four copies per diploid mouse genome equivalent takes place in the tumor tissues.

Experimental Infection with Western Equine Encephalomyelitis Virus in Wild Rodents Indigenous to Kern County, California

Six species of rodents from Kern County, California, were inoculated subcutaneously with western equine encephalomyelitis (WEE) virus to determine their susceptibility to infection and their potential as natural hosts. Ammospermophilus nelsoni, Citellus beecheyi, Dipodomys heermanni, Dipodomys nitratoides, Peromyscus maniculatus, and Sciurus griseus were readily infected. Infection was usually fatal in Dipodomys species, C. beecheyi, and S. griseus, but was clinically inapparent in other species. Viremic responses varied greatly in magnitude and duration in different species and with different viral strains. Viremic animals that survived developed high titers of hemagglutination-inhibiting antibody. Hemagglutination-inhibiting and neutralizing antibodies persisted at high titers for at least 8 to 58 weeks after infection, except in P. maniculatus. If animals died during or shortly after the viremic phase of infection, the virus usually was recoverable from numerous organs. Long-term survival of virus could not be demonstrated in A. nelsoni and Dipodomys species. It is concluded that A. nelsoni and P. maniculatus are not important natural hosts of WEE virus; they are susceptible to infection and develop antibodies, but serological surveys of the same species rarely reveal evidence of infection. S. griseus, D. heermanni, D. nitratoides, and possibly C. beecheyi are aberrant hosts of WEE virus since most of them died when infected. Two species of ticks that are ectoparasitic on rodents in Kern County were evaluated as vectors of WEE virus. Dermacentor parumapertus failed to become infected after feeding on viremic hosts, and Ornithodorus parkeri became infected but failed to transmit virus.

Factors Influencing Transmission of Japanese B Encephalitis Virus by a Colonized Strain of Culex Tritaeniorhynchus Giles, from Infected Pigs and Chicks to Susceptible Pigs and Birds

Summary C. tritaeniorhynchus, the principal mosquito infected in nature by Japanese encephalitis virus in Japan, was shown, after colonization and propagation for 12 to 17 generations in the laboratory, to transmit JE virus readily from chick to chick and from pig to pig, to Blackcrowned Night Heron, to egrets and to baby chicks. Mosquito infection and transmissions followed ingestion of blood containing as little as three mouse-LD50 of JE virus/0.04 ml blood (0.15 LD50/mosquito). The concentration of virus in blood of the host chick or pig governed the numbers of mosquitoes infected and, consequently, the overall transmission rate, although some infected mosquitoes failed to transmit virus. Virus was recovered from mosquitoes within several days after feeding on a viremic animal, but transmission usually did not occur until more than 2 weeks (range of 9 to 34 days) after ingestion of viremic blood.