Studies of turkey herpesvirus viremia in two strains of vaccinated chickens strain difference and effects of vaccine dose

Turkey herpesvirus (HVT) viremia was studied at 3-week intervals through 21 weeks of age in individual chickens of experimental (WSU-VS) and commercial strains (C-WL) of White Leghorns vaccinated with graded doses of HVT. HVT viremia was consistently detectable in all WSU-VS birds through 21 weeks postvaccination (PV) regardless of vaccine dose employed, whereas the viremia could not be detected in some of the C-WL birds 9 to 15 weeks PV and thereafter. C-WL birds that lost detectable viremia remained so up to 21 weeks PV, or returned to low levels of viremia which was followed in some birds again by no detectable viremia. Viremia titers were significantly lower in the C-WL than in the WSU-VS birds despite the same vaccination. Both strains of chickens exhibited significantly lower viremia titers when vaccinated with 240 plaqueforming units (PFU) than with 1,480 or 6,600 PFU of HVT, and other C-WL birds lost detectable viremia earlier and more frequently with smaller vaccine doses. This observation indicated a possible genetic difference between the two strains of chickens in susceptibility and viremic response to HVT as well as dose-dependence of HVT viremia.

Avian cell cultures grown in an open system (dishes) without CO2 incubator, and their use for virus cultivation

An organic buffer, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), in a culture medium made it possible to culture chick embryo fibroblast (CEF), duck embryo fibroblast (DEF), and chick kidney (CK) cells in an open system (dishes) under incubation in a bacteriological incubator, requiring no CO2 incubation. CEF, DEF, and CK cells cultured with this system were suitable for cultivation of avain viruses such as Newcastle disease virus, CELO virus, Marek's disease virus, and turkey herpesvirus.

An adenovirus from a turkey pathogenic to both chicks and turkey poults

An adenovirus, designated T-75 isolant, was isolated from the cloacal swab of a clinically normal turkey, 13 weeks old. The T-75 isolant was identified as an adenovirus on the basis of physicochemical properties, cytopathology, and agar-gel precipitin test. Producing two-way cross-neutralization reactions with CELO virus, the isolant was classified as an avian adenovirus of serotype 1. The T-75 isolant was pathogenic to both chicks and turkey poults, causing hepatitis, respiratory disease, atrophy of the bursa of Fabricius, and/or growth depression of experimentally inoculated birds, varying with the host and route of inoculation.

Horizontal transmission of turkey herpesvirus to chickens. 5. Airborne transmission between chickens

Airborne transmission of turkey herpesvirus (HVT) between chickens was studied in two trials using an experimental line of White Leghorns. HVT either did not spread or spread poorly to chickens that had been exposed for 8 weeks to the exhaust air from a cage containing donor chickens inoculated with HVT at 8 weeks of age. There was no airborne transmission of HVT to chickens that had been exposed for 4 weeks. This study indicated a possible by an infrequent spread of HVT between chickens via airborne route.

Marek's disease vaccine breaks: differences in viremia of vaccinated chickens between those with and without Marek's disease

Viremia with turkey herpesvirus (HVT) and/or Marek's disease (MD) herpesvirus (MDHV) was examined in chickens from three different commercial flocks experiencing "vaccine breaks" following vaccination with HVT vaccine against MD. In all groups of sample chickens from the flocks, the incidence of detectable HVT viremia was significantly less in the MD-affected than in the healthy penmates, and incidence of MD was significantly higher in the birds without detectable HVT viremia than in the viremic penmates. The results suggest an association between HVT viremia and protection against MD development.

In vitro biological differences between the pathogenic and the apathogenic Marek's disease herpesvirus

When three pathogenic and four apathogenic isolants of Marek's disease herpesvirus (MDHV) were compared, the pathogenic isolants differed from the apathogenic isolants in their in vitro growth and sensitivity to plaque inhibition by dextran sulfate. Plaques by the pathogenic MDHV isolants were distinctively different in their morphology from those by the apathogenic isolants, the plaque difference being most pronounced in chick embryo fibroblase (CEF) and duck embryo fibroblast (DEF) cell cultures. The pathogenic isolants formed plaques similarly in both CEF and DEF cultures, whereas the apathogenic isolants did so readily in CEF cultures, but very poorly in DEF cultures. The pathogenic isolants replicated better in DEF than in CEF cultures, whereas the apathogenic isolants replicated better in CEF than in DEF cultures. The sensitivitty to plaque inhibition by dextran sulfate was greater for the apathogenic isolants than for the pathogenic isolants of MDHV.

A possible association between plaque type and pathogenicity of Marek's disease herpesvirus

Eighteen isolants of Marek's disease herpesvirus (MDHV) were examined for their plaque types in chicken embryo fibroblast cell cultures and their pathogenicity to an experimental line of White Leghorns highly susceptible to MD. Seven isolants (Id-1, GA, WSU-GF, and 4 field isolants) induced morphologically similar small-cell plaques (SC plaques) consisting of small round refractile cells, whereas 11 isolants (HN and 10 isolants from zoo birds) all induced large-cell plaques (LC plaques) containing large cells along with small refractile cells. The 7 SC plaque isolants all produced clinical MD with high incidences of gross MD tumors, while all 11 LC plaque isolants produced subclinical infection with only minimal histologic lesions. This observation strongly suggests a possible association between plaque type and pathogenicity of MDHV isolants.

Effects of IgY antibody on the development of Marek's disease

The effects of passive immunization with immunoglobulin Y (IgY) on the pathogenesis of Marek's disease (MD) were examined in an experimental line of White Leghorn chickens highly susceptible to MD. Purified IgY with anti-MDV antibody activity, when injected into chicks, delayed the development of MDV viremia and lesions until 9 days postinoculation (PI) with Marek's disease virus (MDV). The blastogenic response of spleen cells to concanavallin-A was depressed at 6 days PI in the birds without passive immunization, whereas it was not totally depressed until 17 days in birds passively immunized with IgY anti-MDV antibody.

Immunoglobulins and anti-Marek's disease virus antibody synthesis in chickens after passive immunization with immunoglobulin Y anti-Marek's disease virus antibody

The effect of passive immunization with immunoglobulin Y (IgY) antibody against Marek's disease virus (MDV) was examined in MDV-susceptible chickens. The production of IgY, immunoglobulin M, and probably also immunoglobulin A was depressed in passively immunized chickens when compared with that in MDV-exposed chickens which had not been given IgY anti-MDV antibody. In passively immunized chickens, the synthesis of immunoglobulin M and IgY anti-MDV antibodies in response to MDV infection also was delayed as determined by agar gel precipitin and indirect fluorescence antibody tests.

Effect of cyclophosphamide on the response of chickens to a virulent strain of Marek's disease virus

The effect of cyclophosphamide on the pathogenesis of Marek's disease was examined in a line of chickens which is relatively resistant to Marek's disease. The injection of cyclophosphamide into newly hatched chickens delayed and reduced viremia and also reduced the development of Marek's disease lesions until 2 weeks after exposure to Marek's disease virus. The data indicate that a population of T cells susceptible to infection with virus and possibly viral transformation is affected by cyclophosphamide.

Virologic and serologic studies of zoo birds for Marek's disease virus infection

One hundred and eleven zoo birds representing 49 species in 14 orders were examined for Marek's disease (MD) herpesvirus (MDHV) infection. MDHV was isolated from 10 birds, all belonging to genus Gallus. The precipitating antibodies against MDHV were demonstrated only in the Gallus birds, when 51 selected birds including 34 Galliformes and 17 other birds representing 12 species from nine orders were examined. The 10 MDHV isolates all induced morphologically similar plaques in cell cultures closely resembling those of HN strain, a low pathogenic isolate of MDHV. Six of the 10 isolates, when inoculated into an experimental line of chickens highly susceptible to MD, caused only a minimal degree of histologic lesions without causing clinical MD, gross MD lesions, or deaths from MD. Natural hosts of MD are probably Galliformes, primarily affecting Gallus and less often other genera of Galliformes.

Horizontal transmission of turkey herpesvirus to chickens. IV. Viral maturation in the feather follicle epithelium

An experimental line of White Leghorns (WSU-VS) and a commerical line inoculated with turkey herpesvirus (HVT) at 1 or 8 weeks old did not differ in the occurrence of infectious cell-free HVT in their feather-tip preparations (FT-HVT). The birds examined at 2 weeks postinoculation (PI) were always positive for FT-HVT regardless of age at virus inoculation, dose of HVT inoculated, or genetic line of chickens, whereas only a few were positive at 4 weeks and none at 6 weeks PI.

Viremic responses of genetically susceptible and resistant chickens to experimental infection with acute, mild, or both strains of Marek's disease herpesvirus

The development and persistence of viremia were followed in two lines of Single-Comb White Leghorns: one experimental line (WSU-VS) highly susceptible, and one commercial line (C-WL) relatively resistant to Marek's disease(MD). In the resistant C-WL chicken, viremia with a mild strain of MD herpesvirus (MDHV) persisted in all viremic birds through 8 weeks postinoculation (PI), while viremia with an acute strain of MDHV did not, resulting in a decrease in number of viremic birds after 2 weeks PI. In the susceptible WSU-VS chicken, viremia with acute MDHV persisted in all viremic birds whereas viremia with mild MDHV was detected in a decreasing number of birds after 6 weeks PI. The pattern of viremia observed in the dually infected groups simulated a combination of the responses of the two groups respectively inoculated with mild and acute MDHV. Whether inoculation was with acute MDHV alone, or together with mild MDHV, levels of viremia with acute MDHV were appreciably higher in the WSU-VS than in the C-WL chicken. In both lines, levels of viremia were higher with acute MDHV than with mild MDHV but viremia with acute MDHV could not be demonstrated in the C-WL bird at 6-8 weeks PI. Levels of viremia with mild MDHV were consistently and similarly low in both WSU-VS and C-WL chickens.

Horizontal transmission of turkey herpesvirus to chickens. 3. Transmission in three different lines of chickens

Horizontal transmission of turkey herpesvirus (HVT) was studied in three separate trials using three different lines of chickens in each trial. There was no horizontal spread of HVT to contact cagemates through 8 weeks regardless of the line of donor chickens, when inoculated subcutaneously with 9.2 times 10-3 plaque-forming units (PFU) of HVT at 1 week of age. The virus spread poorly to a few cagemates from an experimental line of White Leghorns (W.S.U.-V.S.), but not from a commercial line of White Leghorns (C.-W.L.) or meat-type (C.-M.T.) chickens, when inoculated with 9.4 times 10-4 PFU of HVT at 1 week of age. The virus spread readily to contact cagemates from W.S.U.-V.S. but not at all from C.-W.L. or C.-M.T. chickens when inoculated with 2 times 10-4 PFU of HVT at 8 weeks of age. The incidence among cagemates of contact infection by HVT appeared similar regardless of genetic lines. This observation indicated a difference among different genetic lines of chickens in the development and/or shedding of infectious HVT following virus inoculation.

Isolation and characterization of an isolate (HN) of Marek's disease virus with low pathogenicity

A cytopathic agent was isolated and characterized as an isolate of Marek's disease herpesvirus (MDHV) with low pathogenicity, and referred to as the HN isolate. This isolate of MDHV did not cause clinical Marek's disease (MD) or death in a highly susceptible line of chickens within 5 weeks after exposure. Gross lesions of limited extent were noted in a few of the inoculated birds. Microscopic nerve lesions in the inoculated and contact-infected birds were invariably minimal, closely resembling C-type MD lesions.