Transmission of Marek's disease with oral washings and feces from infected chickens.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
R L Witter
Publications and source records attributed to R L Witter.
Epidemiological studies relating to the control of Marek's Disease.
Explore the source record for details and available documents.
Animals↗
Efficacy of Marek's disease vaccines in Mhc heterozygous chickens: Mhc congenic x inbred line F1 matings.
The goal of this study is to demonstrate that Mhc (B) heterozygous chickens differ in efficacy of response to several Marek's disease (MD) vaccines. Four types of B2 heterozygotes, in addition to B2B2 homozygotes, were developed by crossing 15.B congenic males to inbred line 7(1) (B2B2) hens. The five types of F1 chicks were intermingled in isolators and vaccinated with one of four types of MD vaccine before inoculation with the very virulent Md5 strain of MD herpesvirus. The F1 chickens differ in development of protective immunity following MD vaccination from two perspectives. First, chickens of a particular Mhc genotype were protected better by some vaccines than others. Second, individual vaccine preparations protected some Mhc genotypes more effectively. We conclude that some MD vaccines are more appropriate than others for certain B-haplotypes when chickens are heterozygous for the Mhc. The value of using Mhc-congenic x inbred line F1 animals for studies concerning the influence of the Mhc on vaccinal immunity is discussed.
Animals↗
Neuropathotyping: a new system to classify Marek's disease virus.
A statistical approach was used to establish a new classification system of Marek's disease virus (MDV) on the basis of neurologic responses. To develop the system, neurologic response data from 15x7 chickens inoculated with 30 strains of serotype 1 MDV were statistically analyzed by a cluster analysis. The goal was to identify a statistical system that would verify if three neurovirulence groups correlated with the three pathotypes previously described. The system was also validated in two additional strains of specific-pathogen-free (SPF) chickens, SPAFAS and line SC (Hy-Vac). The proposed system is based on analysis of three variables: 1) frequency of birds showing transient paralysis between 9 and 11 days postinoculation (dpi), (2) mortality before 15 dpi, and (3) frequency of birds showing persistent neurologic disease between 21 and 23 dpi. By use of this system, a MDV may be classified in one of three groups, designated neuropathotypes A, B, and C, which roughly correspond to the virulent, very virulent, and very virulent plus pathotypes, respectively. However, correlation between neuropathotype and pathotype was not absolute, and neuropathotyping is more a complement to the current pathotyping system than a replacement for it. Our results showed that neuropathotyping studies can be conducted in two types of commercial SPF chickens by the use of the same variables, although the system would first have to be standardized by the use of prototype viruses. Neuropathotypes can also be estimated with our statistical analysis with reasonable accuracy. By use of this analysis, we established that MDV strains within the very virulent pathotype may be subdivided into neuropathotypes B and C, thus establishing a previously unrecognized pathotypic classification. This finding illustrates how neuropathotyping may extend important information not identified by conventional pathotyping.
Animals↗
Induction of strong protection by vaccination with partially attenuated serotype 1 Marek's disease viruses.
Studies were conducted to better understand the relationship among Marcek's disease (MD) vaccine strains between induction of protective immunity and the degree of attenuation (or virulence). To obtain viruses at different stages of attenuation, very virulent plus MD strains 584A and 648A and selected clones of these strains were serially passaged in chicken and duck cells. These viruses were considered fully attenuated after passage for 70-100 times in chicken embryo cell cultures until they no longer induced gross lesions in susceptible, maternal antibody-negative (ab-) chickens. Lower passages of the same strains were considered partially attenuated, provided their virulence was less than that of the parent strain. Four of five partially attenuated preparations derived from MD virus strains 584A and 648A or the previously attenuated Md11 strain induced 28%-62% higher levels of protection in maternal antibody-positive (ab+) chickens against virulent MD challenge than the fully attenuated counterpart viruses. The partially attenuated 584A/d2/3 strain replicated in chickens but was totally nonprotective. Data from two subsequent trials in ab+ chickens confirmed that protection induced by the partly attenuated (passage 80) preparations was 79% and 118% higher, respectively, than that induced by the fully attenuated (passage 100) preparations of strain 648A. However, in one trial with ab- chickens, no difference in protection between partially and fully attenuated virus was observed. Strong protection (up to 85%) against highly virulent challenge also was provided by preparations of 648A at passages 40-60, which were moderately oncogenic when used alone. Partially attenuated strains tended to replicate to higher titers in both ab+ and ab- chickens compared with fully attenuated vaccines. Also, ab+ and ab- chickens vaccinated with partially attenuated strains developed three- to nine fold more extensive microscopic lesions in peripheral nerves at 14 and 22 days after virulent challenge than chickens vaccinated with fully attenuated strains. When measured in ab+ chickens, loss of lesion induction by 648A was achieved 30 passages earlier (at passage 70) than when measured in ab- chickens. Thus, maternal antibodies appeared to abrogate the pathogenicity of some partially attenuated strains. These studies establish for MD the principle that at least some partially attenuated MD viruses may replicate better and induce stronger immunity against virulent challenge than fully attenuated preparations of the same strain, at least when tested in ab+ chickens. Moreover, depending on passage level, partially attenuated vaccine strains may be relatively innocuous for ab+ chickens, causing few or no lesions.
Animals↗
Persistence of chicken herpesvirus and retroviral chimeric molecules upon in vivo passage.
Mareks disease virus (MDV), a herpesvirus, and avian leucosis virus subgroup J (ALV-J), a retrovirus, were used for experimental coinfection of chickens. Chimeric molecules having sequences of both viruses were detected by the hotspot-combined polymerase chain reaction (HS-cPCR) system. The detection of chimeric molecules provided evidence for avian retroviral inserts in the herpesvirus genome. The persistence of chimeric molecules on in vivo passage served to indicate the infectivity of the recombinant virus. The evaluation of formation and persistence of the chimeric molecules was performed in two trials involving three in vivo passages. The chimeric molecules were identified according to the primer sets, their product length, and pattern. The persistence of chimeric molecules on in vivo passages served as an indication of their ability to replicate in and infect chickens. In the first experimental passage, MDV and ALV-J prototype strains, MD11 and HC-1, were intraperitoneally (i.p.) injected into 1-day-old chicks. The second trial included two passages. Passage II chicks were injected i.p. and passage III chickens were in contact with the chickens of passage II. For passage II, enriched white blood cells from blood samples of chickens from the first trial that had chimeric molecules were injected i.p. into 1-day-old chicks. For passage III, uninfected chicks were included together with the infected chicks. Synthesis evidence for the various species of chimeric molecules was assessed in the tissues of birds of the second trial. DNA was extracted from blood and feathers and analyzed by the hotspot-combined PCR and by pulsed field gel electrophoresis. To overcome the limits of detection, three amplification assays followed by hybridization of the products to specific viral probes were conducted. A variety of chimeric molecules were detected in low concentrations. Five species of chimeric molecules were characterized in blood, tumors, and feathers. Chimeric molecules were detected in 18 of 36 dually infected birds from the first trial and in 14 of 21 dually infected birds from the second trial. The findings show that, in four out of seven groups of the second trial, the chimeric molecule species persisted on passage.
Animals↗
Protection and synergism by recombinant fowl pox vaccines expressing multiple genes from Marek's disease virus.
Recombinant fowl poxviruses (rFPVs) were constructed to express genes from serotype 1 Marek's disease virus (MDV) coding for glycoproteins B, E, I, H, and UL32 (gB1, gE, gI, gH, and UL32). An additional rFPV was constructed to contain four MDV genes (gB1, gE, gI, and UL32). These rFPVs were evaluated for their ability to protect maternal antibody-positive chickens against challenge with highly virulent MDV isolates. The protection induced by a single rFPV/gB1 (42%) confirmed our previous finding. The protection induced by rFPV/gI (43%), rFPV/gB1UL32 (46%), rFPV/gB1gEgI (72%), and rFPV/gB1gEgIUL32 (70%) contributed to additional knowledge on MDV genes involved in protective immunity. In contrast, the rFPV containing gE, gH, or UL32 did not induce significant protection compared with turkey herpesvirus (HVT). Levels of protection by rFPV/gB1 and rFPV/gl were comparable with that of HVT. Only gB1 and gI conferred synergism in rFPV containing these two genes. Protection by both rFPV/gB1gEgI (72%) and rFPV/gB1gEgIUL32(70%) against Marek's disease was significantly enhanced compared with a single gB1 or gI gene (40%). This protective synergism between gB1 and gI in rFPVs may be the basis for better protection when bivalent vaccines between serotypes 2 and 3 were used. When rFPV/gB1gIgEUL32 + HVT were used as vaccine against Md5 challenge, the protection was significantly enhanced (94%). This synergism between rFPV/gB1gIgEUL32 and HVT indicates additional genes yet to be discovered in HVT may be responsible for the enhancement.
Animals↗
The efficacy of recombinant fowlpox vaccine protection against Marek's disease: its dependence on chicken line and B haplotype.
Earlier studies have shown that the B haplotype has a significant influence on the protective efficacy of vaccines against Marek's disease (MD) and that the level of protection varies dependent on the serotype of MD virus (MDV) used in the vaccine. To determine if the protective glycoprotein gene gB is a basis for this association, we compared recombinant fowlpox virus (rFPV) containing a single gB gene from three serotypes of MDV. The rFPV were used to vaccinate 15.B congenic lines. Nonvaccinated chickens from all three haplotypes had 84%-97% MD after challenge. The rFPV containing gB1 provides better protection than rFPV containing gB2 or gB3 in all three B genotypes. Moreover, the gB proteins were critical, since the B*21/*21 chickens had better protection than chickens with B*13/*13 or B*5/*5 using rFPV with gB1, gB2, or gB3. A newly described combined rFPV/gB1gEgIUL32 + HVT vaccine was analyzed in chickens of lines 15 x 7 (B*2/*15) and N (B*21/*21) challenged with two vv+ strains of MDV. There were line differences in protection by the vaccines and line N had better protection with the rFPV/gB1gEgIUL32 + HVT vaccines (92%-100%) following either MDV challenge, but protection was significantly lower in 15 X 7 chickens (35%) when compared with the vaccine CVI988/Rispens (94%) and 301B1 + HVT (65%). Another experiment used four lines of chickens receiving the new rFPV + HVT vaccine or CVI988/Rispens and challenge with 648A MDV. The CVI 988/Rispens generally provided better protection in lines P and 15 X 7 and in one replicate with line TK. The combined rFPV/gB1gEgIUL32 + HVT vaccines protected line N chickens (90%) better than did CVI988/Rispens (73%). These data indicate that rFPV + HVT vaccines may provide protection against MD that is equivalent to or superior to CVI988/ Rispens in some chicken strains. It is not clear whether the rFPV/gB1gEgIUL32 + HVT vaccine will offer high levels of protection to commercial strains, but this vaccine, when used in line N chickens, may be a useful model to study interactions between vaccines and chicken genotypes and may thereby improve future MD vaccines.
Animals↗
Protection of turkeys from hemorrhagic enteritis with a recombinant fowl poxvirus expressing the native hexon of hemorrhagic enteritis virus.
Hemorrhagic enteritis (HE) is an economically important disease of turkeys caused by a type II aviadenovirus, hemorrhagic enteritis virus (HEV). The vaccines currently available to the commercial poultry producer are highly effective in preventing disease outbreaks; however, they are immunosuppressive. A recombinant fowl poxvirus (rFPV) expressing the native hexon of HEV has been shown to induce an anti-HEV humoral immune response in turkeys. In this study, the rFPV expressing the native hexon of HEV was compared with a commercial HEV vaccine (vxHEV) for its ability to protect turkeys from virulent HEV challenge. Complete protection from the enteritis of HE was achieved in experimental groups vaccinated with either the rFPV or the vxHEV. Lymphocyte stimulation was measured in turkeys inoculated with rFPV, vxHEV, or a sublethal dose of HEV or not inoculated. No statistically significant immunodepression was observed in turkeys receiving the rFPV.
Adenoviridae Infections↗
An acute form of transient paralysis induced by highly virulent strains of Marek's disease virus.
A novel syndrome was observed after inoculation of 3-wk-old chickens with highly virulent Marek's disease virus (MDV) strains. This syndrome was characterized by the acute onset of neurologic signs including flaccid paralysis of neck and limbs 9-10 days postinoculation, typically resulting in death 1-3 days after the onset of clinical signs. Most affected birds died, and spontaneous recovery was rare. Few if any gross tissue changes were found. Histologic brain lesions included acute vasculitis with vasogenic edema and perivascular cuffing. The syndrome was influenced by the virus strain and dose and by chicken strain and B haplotype and was prevented by vaccination with turkey herpesvirus. Chickens up to 18 wk of age were susceptible. On the basis of clinical signs and histopathology, the syndrome was determined to be an acute form of transient paralysis (TP); its more acute nature and virtual lack of spontaneous recovery differentiated this syndrome from classical TP. Affected birds were viremic, and brains were positive for viral DNA by polymerase chain reaction assays, but these tests were also positive in inoculated chickens without clinical signs and may have limited value for diagnosis. Although acute TP should occur only rarely in Marek's disease-vaccinated commercial flocks, this syndrome may be important in laboratory studies, where it could interfere with pathogenesis trials. Finally, acute TP appears to be one component in the pathogenesis of the early mortality syndrome, a previously described immunodepressive disease induced by inoculation of 1-day-old chicks with highly virulent MDV.
Animals↗
Four distinct neurologic syndromes in Marek's disease: effect of viral strain and pathotype.
A chronological study of central nervous system disorders induced by Marek's disease virus (MDV) has been conducted. Neurologic clinical signs were recorded daily for individual chickens of two genetic lines after inoculation of 13 serotype 1 MDV strains representing all three pathotypes. In addition to classical transient paralysis (TP) previously described by many workers, and acute TP, described in the companion paper, we have identified for the first time two other neurologic syndromes, persistent neurologic disease (PND) and late paralysis (LP). PND designates birds that showed a variety of neurologic signs (ataxia, torticollis, and nervous tics) after recovery from paralysis (12-15 days postin-oculation [DPI]) that either persisted through the observation period or presented a cyclic pattern. LP was a rare syndrome characterized by the late onset of the paralytic stage (about 20 DPI), perhaps indicating occasional failure of the initial intraabdominal inoculation to induce infection. Clinical signs and histopathologic alterations of the brain were also evaluated sequentially in chickens of two genetic lines after inoculation with two MDV strains (virulent MDV and very virulent plus MDV). Although clinical response differed greatly among treatment groups, types of lesions (endotheliosis, mononuclear perivascular cuffing, vasculitis, vacuolization, and increase in cellularity of the neuropil) were similar. However, early onset of lesions (by 6 days) appeared to be associated with a greater severity of clinical signs. We also found that neurologic response was greatly influenced by viral pathotype (virulence). This study thus confirms that the central nervous system is an important target organ for MDV resulting in several distinct clinical manifestations and suggests that neurologic responses in antibody-free chickens might be a useful criterion for virus pathotyping.
Animals↗
MDV glycoprotein D is expressed in the feather follicle epithelium of infected chickens.
Glycoprotein D (gD) and its homologues are essential for many alphaherpesvirus life cycles. A gene encoding a homologue of gD was recently found in the Marek's disease virus (MDV) genome. Interestingly, gD-negative MDV mutants apparently replicate unimpaired in both cell culture and chickens. In this study, we show the expression of the gD homologue of MDV in feather follicle epithelium in infected birds. The gD homologue was detected in a few feather follicles even when most of the follicles were expressing pp38 or gB, other MDV-specific proteins. These observations indicate that the MDV gD homologue is expressed in a very limited set of cells and may be differently regulated. Since feather follicle epithelium of infected birds are the only place where the infectious cell-free MDV virions can be recovered, analysis of the transcriptional regulation of gD may lead to the understanding of the cell-associated nature of MDV.
Animals↗
Development of a quantitative-competitive polymerase chain reaction assay for serotype 1 Marek's disease virus.
We have developed a quantitative-competitive (QC) polymerase chain reaction (PCR) for the detection of Marek's disease virus (MDV) DNA. The assay utilizes a competitor DNA that differs from the viral DNA of interest by having a small insertion. The competitor DNA acts as an internal standard for the estimation of viral DNA in an unknown sample. The amount of viral DNA in a sample is quantitated by coamplification in the presence of a known amount of competitor DNA. The same PCR primers that amplify the viral DNA also amplify the competitor DNA. When the amount of competitor is equal to the amount of viral DNA in a sample, there is equal amplification of the competitor and the virus. Thus, we are able to quantitate the viral DNA in an unknown sample. To establish the utility of this assay, in vivo correlations between virulence and virus replication were studied. Our data demonstrated that a more virulent strain of MDV (648A) replicated better in thymus during cytolytic infection than did a less virulent strain (GA). However, no differences in virus titer were observed when these two viruses were propagated in tissue culture. Our data are consistent with the generally held idea that "hot" strains of MDV replicate earlier and better in birds. Thus, QC-PCR is extremely specific and sensitive to measure MDV DNA over a wide range and can be applied to in vivo studies of viral pathogenesis.
Animals↗
Avian leukosis virus subgroup J infection profiles in broiler breeder chickens: association with virus transmission to progeny.
Profiles of infection with avian leukosis virus subgroup J (ALV-J) and factors that predict virus transmission to progeny were studied. Eggs from an infected broiler breeder flock were hatched at the laboratory. The flock was reared in a floor pen, transferred to laying cages at 22 wk, and inseminated to produce fertile eggs. A cohort of 139 chickens was tested at frequent intervals over a 62-wk period for virus, viral antigens, or antibodies in plasma, cloacal swabs, egg albumen, and embryos. Virus was detected in 7% of chicks at hatch but spread rapidly so that virtually all chicks became infected between 2 and 8 wk of age. Mortality due to myeloid leukosis and related tumors was 22%. Over 40% of the chicks developed persistent infections, whereas the remainder experienced transient infections. Five types of infection profiles were recognized. Novel responses included hens that were positive for virus intermittently or started late in life to shed viral antigens into the cloaca. ALV-J was isolated from 6% of 1036 embryos evaluated between 26 and 62 wk. However, over 90% of the virus-positive embryos were produced between 29 and 34 wk of age. Of 80 hens that produced embryos, 21 produced at least one infected embryo and were identified as transmitters. All but one transmitter hen would have been detected by a combination of viremia, cloacal swab, and albumen tests conducted between 18 and 26 wk. However, virus was transmitted to embryos from hens that were not persistently viremic or that rarely shed viral group-specific antigen into the albumen of their eggs. Intermittent patterns of both antigen shedding and virus transmission to embryos were observed in some hens. These results validate current screening procedures to identify potential transmitter hens and provide some suggestions for improvement but also show that identification of all transmitter hens by such procedures is unlikely. Thus, eradication programs based solely on dam testing may be less effective than those where dam testing is combined with procedures to mitigate early horizontal transmission in progeny chicks.
Animals↗
Influence of turkey herpesvirus vaccination on the B-haplotype effect on Marek's disease resistance in 15.B-congenic chickens.
Eight recently developed 15.B congenic lines of chickens were tested for Marek's disease (MD) resistance by intra-abdominal injection of cell-associated preparations of MD virus of a virulent strain (JM), a very virulent strain (Md5), or Md5 after vaccination with turkey herpesvirus (HVT) strain FC126. Chickens of the 15.N congenic line (B15B21 or B21B21) were very resistant to JM-induced MD, in contrast to chickens homozygous for the B-haplotypes 2, 5, 12, 13, 15, or 19. After Md5 infection, more than 88% of the chickens in all of the congenic lines developed MD. However, when chickens were vaccinated with HVT before being inoculated with Md5, the B5 and B12 homozygotes were more resistant to MD than were the B2, B13, or B19 homozygotes, and B15 and B21 homozygotes had intermediate resistance. B5B5 and B2B5 F2 chicks inoculated with HVT and Md5 had a lower prevalence of MD than B2B2 sibs. These results demonstrate that a protocol involving HVT vaccination of chicks followed by infection with very virulent MD virus will allow the detection of B-haplotypes determining MD resistance, some of which are not detectable in unvaccinated chicks challenged with virulent MD.
Animals↗
Humoral immune responses to inactivated oil-emulsified Marek's disease vaccine.
When inactivated Md11/75C vaccine was inoculated into 1-day-old chickens, it stimulated antibodies detectable by enzyme-linked immunosorbent assay (at a titer of 6400) and indirect fluorescent antibody test (at a titer of 640), but lacking virus-neutralizing activity. Chickens passively inoculated with these antibodies were protected against bursal atrophy, weight loss, and early mortality when challenged with the virulent Md5 strain of Marek's disease virus (MDV). That led to the conclusion that virus-neutralizing activity is not a prerequisite for protection. In another experiment, antibody titers of adult chickens previously primed by exposure to live turkey herpesvirus and MDV did not increase after immunization with inactivated oil-emulsion MDV vaccines. This result provides little hope that Marek's disease can be controlled in progeny chickens by maternal immunity derived from hyperimmunized parents.
Animals↗
Attenuated revertant serotype 1 Marek's disease viruses: safety and protective efficacy.
In earlier studies, a revertant serotype 1 Marek's disease virus (MDV), clone Md11/75C/R2, was found to be a highly protective vaccine virus but was mildly pathogenic for susceptible chickens. The term "revertant" indicates that the virus, after attenuation, gained virulence following backpassage in chickens. The present study is an attempt to develop a more attenuated but still protective vaccine virus from Md11/75C/R2. Forty-two derivative viruses or clones from Md11/75C/R2 were evaluated. Two of these, designated clones R2/23 and R2/29, induced viremia but little or no pathology in preliminary trials and were selected for further study. In a series of nine trials, both clones provided protection against challenge with very virulent MDV strains that was superior to that induced by turkey herpesvirus (HVT) and was not significantly different (P greater than 0.05) from that induced by a bivalent (HVT + SB-1) vaccine. Both clones appeared fully attenuated based on pathogenicity tests in susceptible antibody-negative chickens. Both clones gained virulence on backpassage in chickens, but this seemed of little concern because neither virus spread by contact to other chickens. Although the two clones were very similar, clone R2/23 appeared to have a slightly lower pathogenic potential following backpassage and thus best meets the combined criteria of safety and efficacy.
Animals↗
A lymphoproliferative disease in Japanese Quail.
A naturally occurring lymphoproliferative disease was found in 3 flocks of Japanese quail in Mexico. The tumorlike lesions were detected mainly in livers and spleens. Histopathology revealed a pleomorphic lymphoproliferative infiltration with dark-staining large cells, lymphocytes of different sizes, and reticulumlike cells. Marek's disease (MD) herpesvirus was not isolated from 74 quail tested, nor were antibodies to MD detected in 84 sera. Antibodies to reticuloendotheliosis (3/24) and avain leukosis virus subgroup A (2/24) were present. The possible etiology of this disease is discussed.
Animals↗