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Biomedical subjects

G F de Boer

Publications and source records attributed to G F de Boer.

At least 19 recordsLinked to original sources
PubMed1993

Chicken anaemia virus influences the pathogenesis of Marek's disease in experimental infections, depending on the dose of Marek's disease virus.

Eight groups of 1-day-old chickens were inoculated with 0, 250, 5000, or 100,000 white blood cells of chickens infected with Marek's disease virus strain K (MDV-WBC). Four of these groups were additionally infected with 10(5) TCID50 chicken anaemia virus (CAV). At day 14 after inoculation, chickens infected with CAV had reduced haematocrit levels, reduced body weights, and depletion of the thymic cortex and bone marrow. Semi-quantitative immunohistochemical examination of nerves and visceral organs was performed at day 28 by immunoperoxidase staining in which a monoclonal antibody specific for leucocytes was used. CAV significantly enhanced the number of lymphoproliferative lesions induced by 5000 MDV-WBC. In contrast, CAV significantly reduced the number of lymphoproliferative lesions induced by 100,000 MDV-WBC. Comparable results were found at day 61 after macroscopic examination of nerves and visceral organs. These findings show that the pathogenesis of MD in experimental infections appears to be enhanced or inhibited by CAV, depending on the dose of MDV.

Analysis of Variance↗
PubMed1993

Inactivation of chicken anaemia virus in chickens by heating and fermentation.

The transmission of pathogenic microorganisms such as viruses by the use of animal products in animal feed constitutes a potential risk to the health of livestock. To reduce the risk, it is necessary to understand the survival of viruses during the processing of animal products to feed-stuffs. Since chicken anaemia virus (CAV) is very resistant to inactivation, we used it as a model for the inactivation of pathogenic viruses during treatment of animal products. It is concluded that fermentation of CAV viraemic tissue did not affect the inactivation of CAV, however, heating at a core temperature of 95 degrees C for 30 min or 100 degrees C for 10 min is sufficient to inactivate CAV. Compared with the conditions for inactivation reported in the literature for other pathogenic viruses, our treatment is more stringent. CAV viraemic chickens are thus suitable as a model to test the heat inactivation of pathogenic viruses.

Animal Feed↗
PubMed1992

[Classical fowl plague and milder influenza infections in birds and mammals].

Wild waterfowl are currently considered the largest reservoir of the various haemagglutinin (H) and neuraminidase (N) subtypes of influenza virus. Until now thirteen different H-types and nine different N-types have been detected in these populations. In the first instance, virus transmission from fowl to other animal species and to man is not causing disease problems. However, small changes at the molecular level of a given HN-subtype recently caused a dramatic increase in virulence for chickens. Genes fragments coding for haemagglutinin or neuraminidase can be exchanged between viruses which propagate in the same individual. This phenomenon-'genetic reassortment'-is of major epidemiological significance when it occurs in pigs. New influenza epidemics in the human population consistently originate in areas where waterfowl, pigs and human beings live close together. At the moment, the virological and serological diagnosis of influenza A infections is based ELISAs for antigen and antibody detection. Both ELISAs employ a monoclonal antibody directed against a conserved antigenic determinant of the influenza A nucleoprotein. The use of these tests can simplify the diagnosis of and screening for influenza A infections, particularly in those species which harbour several H- and N-subtypes.

Animals↗
PubMed1992

Transcription of the chicken anemia virus (CAV) genome and synthesis of its 52-kDa protein.

This paper describes the expression of the chicken anemia virus (CAV) genome, a recently characterized single-stranded circular-DNA virus of a new type [Noteborn et al., J. Virol. 65 (1991) 3131-3139]. The major transcript from the CAV genome is an unspliced mRNA of about 2100 nucleotides (nt). Its transcription start point and poly(A)-addition site are located at nt 354 and 2317 of the CAV sequence, respectively. In vitro translation experiments provide evidence that the major CAV open reading frame encodes a 52-kDa protein by using the fifth AUG as a start codon of the unspliced CAV mRNA.

Blotting, Northern↗
PubMed1992

Interference of maternal antibodies with the immune response of foals after vaccination against equine influenza.

The purpose of the study was twofold. First, using two groups of 22 foals each, we investigated the extent to which maternal antibodies interfere with the humoral response against equine influenza. The foals were born to mares that had been vaccinated twice yearly against influenza since 1982. Foals of group I were vaccinated three times at early ages (12, 16, and 32 weeks of age), and foals of group II were likewise vaccinated but a later ages (24, 28, and 44 weeks of age). After the first and second vaccinations, neither group showed an increase in antibodies that inhibit haemagglutination. Group II foals, however, had a significantly stronger antibody response against nucleoprotein after the second vaccination than the foals of group I. After the third vaccination, group II foals had a significantly stronger and longer lasting antibody response against haemagglutinin than the foals of group I. However, the antibody response to nucleoprotein was comparable in both groups. Second, the foals of group II were studied to determine the persistence of maternal antibodies directed against a common nucleoprotein and the haemagglutinin of two strains of equine influenza A virus. Biological half-lives of 39, 32, and 33 days were calculated for maternal antibodies directed against haemagglutinin of strains H7N7 Prague and H3N8 Miami, and against the nucleoprotein respectively. Maternal antibody titres at the time of vaccination were closely related to the degree of interference with the immune response. Because even small amounts of maternal antibodies interfered with the efficacy of vaccination, we conclude that foals born to mares vaccinated more than once yearly against influenza virus should not be vaccinated before 24 weeks of age.

Age Factors↗
PubMed1992

Detection of proviral DNA and viral RNA in various tissues early after avian leukosis virus infection.

Using molecular biological techniques, a study was made of the tissue tropism of avian leukosis virus (ALV) early after infection. Two strains of chickens, one with and the other without endogenous viral genes, were infected with ALV of subgroup A immediately after hatching; specimens of nine tissues and blood samples were analyzed at various times thereafter. A polymerase chain reaction (PCR), specific to ALV subgroup A, was used to detect proviral DNA and viral RNA. In situ hybridization was used to confirm the presence of proviral DNA in tissue samples and to calibrate the PCR. The pattern of detection of proviral DNA and of ALV-RNA in the various tissues was similar for both chicken strains. At 2 weeks of age, ALV-RNA was demonstrated in all tissues tested: bursa of Fabricius, thymus, bone marrow, proventriculus, liver, spleen, kidney, muscle, gonads, and blood samples, and at 4 weeks of age all tissues contained proviral DNA. No tropism for a specific tissue was observed early after an ALV infection.

Amino Acid Sequence↗
PubMed1991

Characterization of cloned chicken anemia virus DNA that contains all elements for the infectious replication cycle.

Circular double-stranded replication intermediates were identified in low-molecular-weight DNA of cells of the avian leukemia virus-induced lymphoblastoid cell line 1104-X-5 infected with chicken anemia virus (CAV). To characterize the genome of CAV, we cloned linearized CAV DNA into the vector pIC20H. Transfection of the circularized cloned insert into chicken cell lines caused a cytopathogenic effect, which was arrested when a chicken serum with neutralizing antibodies directed against CAV was added. Chickens inoculated at 1 day of age with CAV collected from cell lines transfected with cloned CAV DNA developed clinical signs of CAV. The 2,319-bp cloned CAV DNA contained all the genetic information needed for the complete replication cycle of CAV. The CAV DNA sequence has three partially overlapping major reading frames coding for putative peptides of 51.6, 24.0, and 13.6 kDa. The CAV genome probably contains only one promoter region and only one poly(A) addition signal. Southern blot analysis using oligomers derived from the CAV DNA sequence showed that infected cells contained double- and single-stranded CAV DNAs, whereas purified virus contained only the minus strand. It is the first time that the genome of one of the three known single-stranded circular DNA viruses has been completely analyzed.

Amino Acid Sequence↗
PubMed1990

[Transgenic chickens].

Transgenic mice are produced by retroviral insertion, micro-injection in the early embryo, and recently by transfection of embryonic stem cells. Transgenic chickens were only made by retroviral vectors based on avian leukemia virus (ALV) and reticuloendotheliosis (REV) genomes. A replication-defective retroviral vector is preferentially used because these do not induce infectious virus. Since chickens are lacking endogenous REV sequences, a replication defective REV vector is most useful for practical application. Transgenic disease resistance is most likely obtained by blocking of viral receptors. By this approach recently transgenics with resistance against ALV infection were made at the Regional Poultry Disease Laboratory in East Lansing. Inhibition of virus replication by antisense DNA, which is complementary to viral mRNA, is promising for the future. Considerable research efforts still have to be made, however. Production of biomedical proteins will most likely be the first practical use of transgenic chickens. For the time being, vaccines will be used for the control of infectious diseases. The current live-virus vaccines will be replaced by inactivated (sub-unit) vaccines and thereafter by recombinant DNA vaccines based on viral vectors.

Animals↗
PubMed1990

An ELISA for detection of antibodies against influenza A nucleoprotein in humans and various animal species.

A double antibody sandwich blocking ELISA, using a monoclonal antibody (MAb) against influenza A nucleoprotein (NP) was developed to detect antibodies against influenza. Collections of serum samples were obtained from human and various animal species. All influenza A subtypes induced antibodies against hemagglutinins and NP. A close correlation between titers of the hemagglutination inhibition (HI) test and the NP-ELISA was seen. Antibodies against influenza NP were demonstrated in serum samples from humans, ferrets, swine, horses, chickens, ducks, guinea pigs, mice, and seals. The serum samples were collected at intervals during prospective epidemiological studies, from experimental and natural infections, and vaccination studies. The decline of maternal antibodies was studied in swine and horses. The NP-ELISA enables rapid serological diagnosis and is suited for influenza A antibody screening, especially in species which harbor several influenza subtypes. The HI and neuraminidase inhibition tests, however, must still be used for subtyping.

Animals↗
PubMed1990

Expression of avian leukaemia virus env-gp85 in Spodoptera frugiperda cells by use of a baculovirus expression vector.

We studied the genetic expression of gp85 of avian leukaemia virus (ALV) subgroup A in a baculovirus/insect cell system. 5'terminal sequences of the gag gene were added to precede the ALV gp85 sequence and a stop codon was introduced at the boundary of gp85 and gp37. The resulting construct was then cloned into the baculovirus transfer vector pAcYM1, which contains the polyhedrin promoter of Autographa californica nuclear polyhedrosis virus (AcNPV). Cells of the insect Spodoptera frugiperda (Sf9) were cotransfected with the resulting recombinant transfer vector pAc85 and infectious AcNPV/E2 DNA. After cotransfection, recombinant baculovirus that lacked the polyhedrin gene and expressed gp85 was selected from the supernatant and used to infect Sf9 cells. The expression of the gp85 gene peaked 3 days after infection, but expression products were not released into the culture medium even though the signal peptide had been cleaved. Owing to incomplete N-glycosylation in the insect cells the largest gp85 product had an Mr of only 65,000. In immunofluorescence tests and immunoblots the recombinant gp85 products reacted with polyclonal and monoclonal antibodies directed against ALV gp85 of subgroup A. Chickens inoculated with crude lysates of Sf9 cells infected with gp85-expressing recombinant baculovirus developed antibodies directed against ALV gp85. These antibodies were not capable of neutralizing ALV.

Animals↗
PubMed1989

Transient depletion of cortical thymocytes induced by chicken anaemia agent.

Chicken anaemia agent (CAA) causes severe anaemia, loss of body weight, and hypoplasia of thymus at day 14 after inoculation of one-day-old chickens. Several reports have described an enhancement of concurrent infections with f.e. Marek's disease virus, Infectious Bursal Disease virus, and Reovirus. Immunohistochemical methods were used to describe the immunopathological lesions of the thymus that probably form the basis of the immunodeficiency caused by CAA. Monoclonal antibodies and antisera against leucocytes, T lymphocytes, CD4, B lymphocytes, mononuclear phagocytes, MHC class II, and keratin were used. At day 14 after inoculation, the thymic cortex was completely depleted of thymocytes, whereas the medulla was not. T-cell areas in the spleen also lacked T lymphocytes. In contrast the cortex still contained stromal cells with MHC class II molecules and keratin. At day 21, the cortex had completely regenerated and all clinical signs of CAA infection had disappeared. Labelling experiments with BrdU in 4-week-old control chickens demonstrated that 25% of the divided cells was detected in the medulla and 75% in the cortex. The tissue tropism of CAA may, apart from the preference for rapidly dividing cells, be directed by specific cell determinants.

Anemia↗
PubMed1988

Influenza A viral nucleoprotein detection in isolates from human and various animal species.

A double antibody sandwich, enzyme-linked immunosorbent assay (DAS-ELISA) was developed to detect influenza A viral antigen, employing a monoclonal antibody directed against type-specific influenza A nucleoprotein (McAb anti-NP). McAb anti-NP was used to coat ELISA plates as well as to prepare the peroxidase conjugate. Influenza A viruses of avian, equine, swine, and human origin were detected in allantoic fluids of inoculated eggs with higher sensitivity by the DAS-ELISA than by hemagglutination (HA) assays. Minimal concentrations of 8 ng/ml influenza virus protein were detected in Nonidet P40-treated virus preparations. Viral antigen detection in tissues of experimentally infected chickens and pigs was successful, but in pigs yielded a lower positive score than the conventional method of virus isolation in eggs. The test is sensitive, rapid, and easy to perform, but does not permit influenza A subtyping. In avian species, the McAb anti-NP DAS-ELISA differentiates between influenza and Newcastle disease viruses. In pigs, the test distinguishes between influenza and Aujeszky's disease.

Allantois↗
PubMed1988

The monoclonal antibody CVI-ChNL-68.1 recognizes cells of the monocyte-macrophage lineage in chickens.

The characteristics of monoclonal antibody CVI-ChNL-68.1, which specifically reacts with a group of chicken non-lymphoid cells, are described. Both tissue distribution shown on cryostat sections using immuno-enzyme histochemistry, and quantitative data obtained on cell suspensions are presented. Functional characteristics of CVI-ChNL-68.1-positive cells, such as antigen uptake and glass adherence, are determined. Results show that CVI-ChNL-68.1 reacts with monocytes, macrophages, and interdigitating cells. Possible relationships between the various non-lymphoid cells are discussed.

Acid Phosphatase↗
PubMed1987

Biological characteristics of Marek's disease vaccine CVI-988 clone C1.

Biological characteristics of Marek's disease virus (MDV) CVI-988 clone C, of importance for vaccine application, are described. CVI-988 clone C was shown to be nonpathogenic for highly MD-susceptible chickens and slightly more effective than prototype CVI-988 vaccine. During plaque purification and serial cell-culture passages, reductions were observed in the release of 'A' antigen from infected cell cultures, in spreading properties and in virus replication in vivo. Pre-licensing batches of CVI-988 clone C vaccine afforded excellent protection against challenge infection with virulent MDV and highly virulent MDV strains. Groups of chickens with bivalent (HVT/SB-1) vaccine-induced maternal antibodies were equally protected by a double dose of CVI-988 clone C vaccine. Field trials performed in the Netherlands and in the United States confirmed the safety and protective efficacy of monovalent CVI-988 clone C vaccine.

Animals↗
PubMed1984

Maedi-visna control in sheep II. Half-yearly serological testing with culling of positive ewes and progeny.

In 1979 a field trial was started to study the feasibility of maedi-visna control in sheep by half-yearly serological testing (by ELISA) with culling of sero-positive ewes and their progeny. In 13 commercial flocks, with a mean initial incidence of serological reactors of 17%, the sero-positive ewes and all their progeny, those of preceding years included, were culled after each half-yearly test. The percentage of sero-positive sheep decreased gradually and at the end of the second year, at the 5th test, all flocks were sero-negative. Also the 6th and 7th test did not yield sero-positive sheep. At the 8th test, however, 3 sero-positive ewes were detected in one of the flocks. A definite conclusion as to the source of infection could not be drawn. The following flock test was negative. In 2 other commercial flocks, which had a mean initial incidence of sero-positive sheep of 53%, those sero-positive and only their suckling lambs were culled. Here too, a gradual decrease in the incidence of sero-positive sheep was observed at the 2nd and 3rd test, but at the 4th test a sharp increase occurred. The programme was continued and a decrease followed until 0% was reached at the 7th test (end of third year). Age analysis of the sero-positive sheep which caused this peak revealed that the majority had been born before the start of the trial. This suggests that a 'second wave' of sero-positive sheep may be prevented and a quicker result obtained if progeny of preceding years are culled as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

[2 field trials for the study of the possible effects of avian leukosis control measures on production characteristics].

Two field trials were performed to study possible effects of the lymphoid leukosis (LL) control programme as carried out in the Netherlands, on production characteristics. Progeny groups of selected ALV-negative, congenitally non-shedding, hens and progeny of conventional flocks were divided into flocks either to be reared in conventional conditions or in isolation for a period of eight weeks followed by controlled exposure (vaccination) with ALV. Detrimental effects on production characteristics attributable to the LL control programme were not observed in the two trials. The LL control procedure was successful in the prevention of lymphomas and elimination of congenital ALV shedding. Differences in egg production between LL control groups and conventional flocks were not observed. This was presumably due to the absence or too small a number of ALV-infected hens in the conventional flocks. Relatively low immunoglobulin class IgA levels were observed in serum samples of chickens which were reared in isolation for a period of eight weeks. Quantitative differences in immunoglobulin classes IgG and IgM were not perceptible between samples from chickens which were reared in isolation and those reared in conventional conditions.

Animals↗