Protective immunity against Newcastle disease: the role of cell-mediated immunity

The role of cell-mediated immunity (CMI) in protection of birds from Newcastle disease was investigated by two different strategies in which only Newcastle disease virus (NDV)-specific CMI was conveyed without neutralizing antibodies. In the first strategy, selected 3-wk-old specific-pathogen-free (SPF) birds were vaccinated with either live NDV (LNDV), ultraviolet-inactivated NDV (UVNDV), sodium dodecyl sulfate-treated NDV (SDSNDV), or phosphate-buffered saline (PBS) (negative control) by the subcutaneous route. Birds were booster vaccinated 2 wk later and challenged with the velogenic Texas GB strain of NDV 1 wk after booster. All vaccinated birds had specific CMI responses to NDV as measured by a blastogenesis microassay. NDV neutralizing (VN) and hemagglutination inhibition (HI) antibody responses were detected in birds vaccinated with LNDV and UVNDV. However, birds vaccinated with SDSNDV developed antibodies that were detected by western blot analysis but not by the VN or HI test. Protection from challenge was observed only in those birds that had VN or HI antibody response. That is, birds with demonstrable CMI and VN or HI antibody response were protected, whereas birds with demonstrable CMI but no VN or HI antibody response were not protected. In the second strategy, birds from SPF embryos were treated in ovo with cyclophosphamide (CY) to deplete immune cells. The birds were monitored and, at 2 wk of age, were selected for the presence of T-cell activity and the absence of B-cell activity. Birds that had a significant T-cell response, but not a B-cell response, were vaccinated with either LNDV, UVNDV, or PBS at 3 wk of age along with the corresponding CY-untreated control birds. The birds were booster vaccinated at 5 wk of age and were challenged with Texas GB strain of NDV at 6 wk of age. All birds vaccinated with LNDV or UVNDV had a specific CMI response to NDV, VN or HI NDV antibodies were detected in all CY-nontreated vaccinated birds and some of the CY-treated vaccinated birds that were found to have regenerated their B-cell function at 1 wk postbooster. The challenge results clearly revealed that CY-treated birds that had NDV-specific CMI and VN or HI antibody responses to LNDV or UVNDV were protected, as were the CY-nontreated vaccinated birds. However, birds that had NDV-specific CMI response but did not have VN or HI antibodies were not protected from challenge. The results from both strategies indicate that specific CMI to NDV by itself is not protective against virulent NDV challenge. The presence of VN or HI antibodies is necessary in providing protection from Newcastle disease.     

Effect of in ovo administered reovirus vaccines on immune responses of specific-pathogen-free chickens

We investigated the effect of in ovo administered reovirus vaccines on the immune responses of specific-pathogen-free chickens. T-cell mitogenic responses to concanavalin A were numerically lower at 9 and 12 days of age and significantly lower at 6 days of age in birds vaccinated with a commercial reovirus vaccine compared with unvaccinated birds or birds vaccinated with an experimental reovirus-antibody complex vaccine. There were no significant differences in proportions of subpopulations of helper (CD4+CD8-) or cytotoxic (CD4-CD8+) T cells except at 12 days of age, when the percentages of CD4-CD8+ cells in the two vaccinated groups were statistically higher than in the nonvaccinated group. B-cell populations were not different among vaccine groups except at 9 days of age, when the vaccinated groups had the highest level of B cells. This commercial reovirus vaccine should not be given in ovo to embryos having little or no maternal antibody, otherwise immunosuppression may occur in the chicks. The addition of the antibody complex to the vaccine prevented this T-cell immunosuppression.     

Vaccination of cyclophosphamide-treated chickens against Newcastle disease virus infection

Newly-hatched chickens were treated with 3 mg of cyclophosphamide (CY) per day for 4 consecutive days. At 2 weeks of age, these chickens, together with a group of untreated controls, were vaccinated intranasally or subcutaneously with the La Sota strain of Newcastle disease virus (NDV). All chickens were challenged intranasally with the GB strain of NDV 2 weeks later. CY-treated, intranasally vaccinated chickens were highly resistant to NDV challenge, yet none of the chickens produced any detectable humoral antibodies to NDV; antibodies to NDV were detectable in the tracheal washings, however.     

Immunosuppression in specific-pathogen-free broilers administered infectious bursal disease virus vaccines by in ovo route

The effect of two infectious bursal disease virus (IBDV) vaccines (IBDV-immune complex [Icx] and IBDV-2512), administered in ovo, on the cell-mediated immunity of specific-pathogen-free (SPF) broilers was examined. A decrease (P < 0.05) in the T-cell mitogenic response occurred in birds vaccinated with both vaccines on days 9 and 21 post in ovo vaccination (PIOV), but an increase (P < 0.05) occurred on day 15 PIOV. The T cells from birds given the IBDV-2512 were less responsive. There were no significant differences in proportions of lymphocytes expressing CT4+CT8 and CT8+CT4- except on day 21 PIOV, where an increase (P < 0.05) in IBDV-2512-vaccinated birds and a decrease (P < 0.05) in percentage of CT4+CT8- in IBDV-Icx-vaccinated birds was observed. There was an increase (P < 0.05) in percentage of CT8+CT4- T cells on day 21 PIOV in both vaccinated groups. A decrease (P < 0.05) in B-cell percentage was observed on day 21 PIOV in birds given both vaccines. Results indicated that although humoral immunosuppression is associated with destruction of B cells (bursal atrophy), cell-mediated immunosuppression induced by these two IBDV vaccines in SPF birds was not associated with altered helper (CT4+CT8-) or cytotoxic (CT8+CT4-) subpopulations of T lymphocytes.     

Advancement in vaccination against Newcastle disease: recombinant HVT NDV provides high clinical protection and reduces challenge virus shedding with the absence of vaccine reactions

Newcastle disease (ND) is a highly contagious disease of chickens causing significant economic losses worldwide. Due to the limitation in their efficacy, current vaccination strategies against ND need improvements. This study aimed to evaluate a new-generation ND vaccine for its efficacy in providing clinical protection and reducing virus shedding after challenge. Broiler chickens were vaccinated in ovo or subcutaneously at hatch with a turkey herpesvirus-based recombinant vaccine (rHVT) expressing a key protective antigen (F glycoprotein) of Newcastle disease virus (NDV). Groups of birds were challenged at 20, 27, and 40 days of age with a genotype V viscerotropic velogenic NDV strain. Protection was 57% and 81%, 100% and 95%, and 100% and 100% after the subsequent challenges in the in ovo and subcutaneously vaccinated chickens, respectively. Humoral immune response to vaccination could be detected from 3-4 wk of age. Challenge virus shedding was lower and gradually decreased over time in the vaccinated birds compared to the unvaccinated control chickens. In spite of the phylogenetic distance between the NDV F gene inserted into the vector vaccine and the challenge virus (genotype I and V, respectively), the rHVT NDV vaccine provided good clinical protection and significantly reduced challenge virus shedding.     

Avian adeno-associated virus-based expression of Newcastle disease virus hemagglutinin-neuraminidase protein for poultry vaccination

The avian adeno-associated virus (AAAV) is a replication-defective nonpathogenic virus member of the family Parvoviridae that has been proved to be useful as a viral vector for gene delivery. The use of AAAV for transgenic expression of Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) protein and its ability to induce immunity in chickens were assessed. Proposed advantages of this system include no interference with maternal antibodies, diminished immune response against the vector, and the ability to accommodate large fragments of genetic information. In this work the generation of recombinant AAAV virions expressing the HN protein (rAAAV-HN) was demonstrated by electron microscopy, immunocytochemistry, and western blot analysis. Serological evidence of HN protein expression after in ovo or intramuscular inoculation of the recombinant virus in specific-pathogen-free chickens was obtained. Serum from rAAAV-HN-vaccinated birds showed a systemic immune response evidenced by NDV-specific enzyme-linked immunosorbent assay and hemagglutination inhibition testing. Positive virus neutralization in embryonated chicken eggs and indirect immunofluorescence detection of NDV infected cells by serum from rAAAV-HN vaccinated birds is also reported. A vaccine-challenge experiment in commercial broiler chickens using a Venezuelan virulent viscerotropic strain of NDV was performed. All unvaccinated controls died within 5 days postchallenge. Protection up to 80% was observed in birds vaccinated in ovo and revaccinated at 7 days of age with the rAAAV-HN. The results demonstrate the feasibility of developing and using an AAAV-based gene delivery system for poultry vaccination.     

A comparative analysis of the mitogenic response of intestinal intraepithelial lymphocytes in various age groups of turkeys.

Mitogenic responsiveness of intestinal intraepithelial lymphocytes (i-IEL) to concanavalin A (Con A), phytohemagglutinin P (PHA-P), and lipopolysaccharide (LPS) from Salmonella typhimurium were evaluated in various age groups of turkeys by a colorimetric blastogenic microassay. Comparisons were made between mitogenic responses of turkey i-IEL and peripheral blood lymphocytes (PBL). The results from this study demonstrated that i-IEL and PBL of turkeys responded to T-cell mitogens, Con A and PHA-P, in every age group examined. The LPS induced a significant mitogenic response in PBL but not in i-IEL of turkeys. The mitogenic responses of turkey i-IEL and PBL to the three mitogens examined were similar to mitogenic responses observed in an earlier study performed by using chicken i-IEL and PBL. The results indicated a difference in mitogenic response between different age groups. An increase was found in mitogenic response of i-IEL to both T-cell mitogens from 3 days of age to 1 wk of age, whereas mitogenic response of PBL to all three mitogens declined significantly from 1 day of age to 3 days of age. The highest mitogenic response of i-IEL to T-cell mitogens was observed at 1 wk of age. The highest mitogenic response of PBL to both T-cell mitogens was observed at 1 day of age and the highest PBL response to LPS was observed at 16 wk of age. The mitogenic response induced by PHA-P provided less variability between age groups than the mitogenic response induced by Con A.     

Field trial in commercial broilers with a multivalent in ovo vaccine comprising a mixture of live viral vaccines against Marek's disease,infectious bursal disease,Newcastle disease,and fowl pox

A multivalent in ovo vaccine (MIV) was tested for safety and efficacy in a commercial broiler complex. The MIV comprised five replicating live viruses including serotypes 1, 2, and 3 of Marek's disease virus (MDV), an intermediate infectious bursal disease virus (IBDV) and a recombinant fowl poxvirus (FPV) vector vaccine containing HN and F genes of Newcastle disease virus (NDV). The performance of MIV-vaccinated broilers was compared with that of hatchmates that received turkey herpesvirus (HVT) alone (routinely used in ovo vaccine in the broiler complex). The chickens that hatched from the MIV-injected and HVT-injected eggs were raised under commercial conditions in six barns. Barn 1 housed 17,853 MIV-vaccinated chickens and each of the barns 2-6 housed 18,472-22,798 HVT-vaccinated chickens. The HVT-vaccinated chickens were given infectious bronchitis virus (IBV) and NDV vaccines at hatch and at 2 wk of age. The MIV-vaccinated chickens received IBV vaccine at hatch and IBV + NDV at 2 wk of age. The relative values of hatchability of eggs, livability and weight gain of chickens, and condemnation rates at processing were comparable between the MIV and the HVT groups (P > 0.05). Chickens from the MIV- and the HVT-vaccinated groups were challenged with virulent viruses under laboratory conditions. The resistance of vaccinated chickens against Marek's disease could not be assessed because of high natural resistance of unvaccinated commercial broilers to virulent MDV. The relative resistances of the MIV- and the HVT-vaccinated groups, respectively, against other virulent viruses were as follows: IBDV, 100% for both groups; NDV, 81% vs. 19%; FPV, 86% vs. 0%. The successful use of MIV under field conditions expands the usefulness of the in ovo technology for poultry.     

Avian influenza in ovo vaccination with replication defective recombinant adenovirus in chickens: vaccine potency, antibody persistence, and maternal antibody transfer

Protective immunity against avian influenza (AI) can be elicited in chickens in a single-dose regimen by in ovo vaccination with a replication-competent adenovirus (RCA)-free human adenovirus serotype 5 (Ad)-vector encoding the AI virus (AIV) hemagglutinin (HA). We evaluated vaccine potency, antibody persistence, transfer of maternal antibodies (MtAb), and interference between MtAb and active in ovo or mucosal immunization with RCA-free recombinant Ad expressing a codon-optimized AIV H5 HA gene from A/turkey/WI/68 (AdTW68.H5(ck)). Vaccine coverage and intrapotency test repeatability were based on anti-H5 hemagglutination inhibition (HI) antibody levels detected in in ovo vaccinated chickens. Even though egg inoculation of each replicate was performed by individuals with varying expertise and with different vaccine batches, the average vaccine coverage of three replicates was 85%. The intrapotency test repeatability, which considers both positive as well as negative values, varied between 0.69 and 0.71, indicating effective vaccination. Highly pathogenic (HP) AIV challenge of chicken groups vaccinated with increasing vaccine doses showed 90% protection in chickens receiving > or = 10(8) ifu (infectious units)/bird. The protective dose 50% (PD50) was determined to be 10(6.5) ifu. Even vaccinated chickens that did not develop detectable antibody levels were effectively protected against HP AIV challenge. This result is consistent with previous findings ofAd-vector eliciting T lymphocyte responses. Higher vaccine doses significantly reduced viral shedding as determined by AIV RNA concentration in oropharyngeal swabs. Assessment of antibody persistence showed that antibody levels of in ovo immunized chickens continued to increase until 12 wk and started to decline after 18 wk of age. Intramuscular (IM) booster vaccination with the same vaccine at 16 wk of age significantly increased the antibody responses in breeder hens, and these responses were maintained at high levels throughout the experimental period (34 wk of age). AdTW68.H5(ch)-immunized breeder hens effectively transferred MtAb to progeny chickens. The level of MtAb in the progenies was consistent with the levels detected in the breeders, i.e., intramuscularly boosted breeders transferred higher concentrations of antibodies to the offspring. Maternal antibodies declined with time in the progenies and achieved marginal levels by 34 days of age. Chickens with high maternal antibody levels that were vaccinated either in ovo or via mucosal routes (ocular or spray) did not seroconvert. In contrast, chickens without MtAb successfully developed specific antibody levels after either in ovo or mucosal vaccination. These results indicate that high levels of MtAb interfered with active Ad-vectored vaccination.     

Effect of genetic selection and MHC haplotypes on lymphocyte proliferation and interleukin-2 like activity in chicken lines selected for high and low antibody production against sheep red blood cells

Chickens from third generation matings of lines of chickens selected for high (HA) and low (LA) antibody production to sheep red blood cells (SRBC) and typed for MHC genotypes B13/13, B13/21, and B21/21 were used in this study. Chickens from both lines carried all the three genotypes B13/13, B13/21, and B21/21. To study T- and B-lymphocytes mitogenic activity, 12-week-old female chickens were injected intravenously with 0.2 ml of 9% SRBC and spleens were collected at 0, 6 h, and 6 day post-antigen injection (pAg). Isolated lymphocytes were incubated with either Concanavalin-A (Con-A) for T-cell activity, or Pokeweed mitogen (PWM) for B-cell activity and thymidine 3H uptakes were measured. To study the Interleukin-2 (IL-2)-like activity in the same lines and genotypes, splenic lymphocytes from 12-week-old chickens were passed through nylon wool columns to enrich the T-cell population. After a 24 h incubation with Con-A, the conditioned media (CM) were collected. The CM were tested for IL-2 like activity by determining whether they altered the proliferation of Con-A stimulated T cells. This proliferation effect was then compared to that of a reference conditioned media (RCM) prepared from K-strain birds and that were used as the standard for the assay. There was no significant difference (p > 0.05) in IL-2 like activity between HA and LA lines, however, the LA was significantly higher than HA (p < 0.05) in T- and B-cell mitogenic activity. The genotype B13/13 had significantly higher (p < 0.05) IL-2 like activity than the B21/21. The genotype B13/13 was also significantly higher (p < 0.05) in T- and B-cell mitogenic activity than the B21/21. At 0 h, pAg T- and B-mitogenic activity was significantly higher (p < 0.05) than 6 h. In summary, our results indicate that although the birds were selected for high antibody production to SRBC, their lymphocyte mitogenic activity was lower than those selected for low antibody production. Hence, humoral and cell-mediated immune responses appear to be under different genetic controls, and that selection for greater humoral response may be at the expense of cellular responses. Our results also suggest differences in IL-2 like activity production between chickens carrying different MHC B-haplotypes, and that genetic control of such activity is possibly linked to the MHC genes.     

Effects of Polyether Ionophores on the Protective Immune Responses of Broiler Chickens against Angara Disease and Newcastle Disease Viruses

Immunization against Angara disease virus (ADV), a serotype 4 avian adenovirus, and Newcastle disease virus (NDV), an avian paramyxovirus serotype 1, is the mainstay of a broiler vaccination programme, while polyether ionophores usually form an essential component of a broiler medication programme in most parts of India and Pakistan. The role of polyether ionophores in the protective immune responses of broiler chickens vaccinated and challenged with ADV and NDV was investigated. A total of 1600 birds were divided into eight groups of 200 birds each. First four groups were vaccinated against NDV and ADV, while the remaining four served as unvaccinated controls. The first 3 groups of birds were administered salinomycin, monensin and cyclophosphamide (CYP), respectively. The last group served as an untreated control. The same treatment schedule was also followed for the next four unvaccinated groups. The post-vaccination and post-challenge serological responses to NDV and ADV, body and lymphoid organ weight gains, post-challenge survival rate and detection of NDV and ADV in the tissues of infected birds were evaluated. Birds administered salinomycin showed a significant stimulation of protective immune responses against both NDV and ADV as compared to the untreated and CYP-treated birds. Monensin also enhanced the protective immune responses against both viruses but the effect was not statistically significant. Thus, it is concluded that monensin and salinomycin augment the anti-NDV and anti-ADV immune responses in broiler chickens, which supports their use in poultry flocks.     

Immunosuppression and histopathological changes in the bursa of fabricius associated with infectious bursal disease vaccination in chicken

The effect of the infectious bursal disease (IBD) live virus vaccine on the immune response of chicken was evaluated by the assessment of antibody response following vaccination as well as resistance to challenge with virulent virus. Birds were vaccinated at various ages and later challenged with a heterologous vaccine (NDV) or wild-type IBD virus. The BF was examined for histological changes at regular intervals. Antibody levels to NDV were monitored.

Significantly higher mortality rates were observed in birds vaccinated with IBD vaccine than unvaccinated birds (P < 0.01) following challenge, BF from vaccinated birds showed marked lymphocyte depletion and cellular infiltration with mononuclear cells.

Intraocular NDV (NDV-i/o) vaccine given at day old largely prevented the immunodepressive effect of IBD vaccination on NDV vaccine. Groups that received IBD vaccine on day 14 but no NDV i/o suffered higher mortality (41.2%) and showed lower antibody response than those vaccinated on day 1 (0%) or controls which did not receive IBDV (11.8%).     

Comparative evaluation of cell culture-adapted and chicken embryo-adapted fowl pox vaccine strains

Two types of vaccines, chicken embryo adapted (VacCE) and cell culture adapted (VacCC), were tested for their efficacy to elicite the immune response in birds vaccinated at 2 and 8 wk of age. The cell-mediated immune response studied by blastogenesis assay showed that birds vaccinated at the second week of age by both VacCE and VacCC vaccines had significant increase in T-lymphocyte count at 21 days postvaccination (PV) and 7 days postchallenge (PC), whereas in birds vaccinated at 8 wk of age, a significant increase was seen at 21 days PV and 7 days PC with the VacCC vaccine. The rise in passive hemagglutination titers was observed up to 21 days PV and 7 days PC in birds vaccinated at 2 wk of age. However, only the birds vaccinated with VacCC at 8 wk of age showed rise in titers at days 21 PV and 7 PC. Birds were challenged 90 days PV by scarification on the thigh region, and the birds vaccinated with VacCC showed 90% and 70% protection when vaccinated at 2 and 8 wk, respectively. The birds vaccinated with VacCE showed only 60% and 20% protection at the corresponding levels, respectively.     

Duration of immunity engendered by a single dose of a cold-adapted strain of Avian pneumovirus

The duration of immunity after a single dose of a cold-adapted strain of Avian pneumovirus (APV) was studied. Turkeys were vaccinated at 1 wk of age and challenged with virulent virus 3, 7, 10, and 14 wk later. Nonvaccinated groups were also challenged at the same times. No clinical signs were observed in the vaccinated birds after vaccination or after any challenge. No viral RNA was shed by the vaccinated birds after any challenge. The nonvaccinated birds shed viral RNA after all challenges. Avian pneumovirus-specific humoral antibodies were detected in the vaccinated birds until 14 wk after vaccination. The results of this preliminary study indicate that inoculation with a single dose of a cold-adapted strain of APV at 1 wk of age provides protection until 15 wk of age.     

Reproduction of hydropericardium syndrome in three-week-old cyclophosphamide-treated specific-pathogen-free chickens by adenoviruses from inclusion body hepatitis

The pathogenicity of serotype 8 group I avian adenovirus (GIAAV) strains (TR630 and Saga97 strains) from inclusion body hepatitis (IBH) against cyclophosphamide (CY)-treated 3-wk-old specific-pathogen-free (SPF) chickens was examined. SPF chickens were inoculated intramuscularly with 10(7) plaque-forming units of viruses. Both strains from IBH could produce hydropericardium and mortality in CY-treated chickens as hydropericardium syndrome (HPS) that serotype 4 GIAAV strains cause, although they could not induce either hydropericardium or mortality in nontreated chickens. Histologically, hepatocytic necrosis with intranuclear inclusions, pancreatic acinar necrosis with intranuclear inclusions, and epicardial edema were seen in CY-treated chickens inoculated with GIAAV from IBH. Immunohistochemically, these inclusions were positive against GIAAV antigen. There were neither histologic lesions nor positive reactions against GIAAV antigen in nontreated chickens inoculated with GIAAV from IBH. From the present findings, pathogenic characteristics of IBH strains and HPS strains in the chickens were essentially the same.     

Floor pen study to evaluate the serological response of broiler breeders after vaccination with ts-11 strain Mycoplasma gallisepticum vaccine

To determine the Mycoplasma gallisepticum (MG) rapid serum plate agglutination (RSPA) test response of broiler breeders after ts-11 strain vaccination, 55 Cobb pullets derived from a nonvaccinated, MG-negative, commercial, broiler breeder grandparent flock were monitored from 8 to 20 wk of age (over a 12-wk trial period). To evaluate the effect of lateral spread of the ts-11 vaccine strain on RSPA test results from commingled and adjacently penned birds, treatment groups included (A) birds vaccinated with ts-11strain MG at 8 wk of age, (B) commingled nonvaccinates in the same pen as the vaccinated birds, (C) nonvaccinates in a second pen separated from the first pen by a distance of 2 m, and (D) birds vaccinated with ts-11 strain MG at 8 wk of age and kept in a separate room. Rapid serum plate agglutination tests were performed once a week for 6 wk and then every 2 wk for 6 more wk, postvaccination. A polymerase chain reaction (PCR) assay specific fbr ts-11 strain MG was used to confirm vaccination, and a second PCR specific for non-ts-11 strain MG was used to confirm the absence of field infection. Seroconversion was first detected by the RSPA test 2 wk postvaccination and attained maximum positive rates of 58% at 12 wk postvaccination in treatment A and 60% at 8 wk postvaccination in treatment D. Seroconversion rates in nonvaccinated, commingled pullets was 10% at 5 wk and 30% at 12 wk after the vaccination of pen mates. The ts-11-specific PCR detected the vaccine strain in 80%-100% of the vaccinated birds 2 wk after vaccination. One of 15 nonvaccinated birds penned 2 m from vaccinated birds yielded ts-11 by PCR assay 12 wk after vaccination, which indicates that the spread of ts-11 over short distances may be possible in situations in which there is a common caretaker. PCR on tracheal swabs taken 12 wk postvaccination detected ts-l1 in 50% and 60% of the vaccinated birds in treatments A and D, respectively; in 30% of the commingled nonvaccinates; and in 6.6% of the separately penned nonvaccinates. In contrast, choanal swabs collected from vaccinated birds at 12 wk were 21% and 40% PCR positive for ts-11 strain MG, while those from nonvaccinates were negative. All samples were PCR negative for field strain MG. The pattern of seroconversion as measured by RSPA test in small groups of broiler breeders was different from that previously reported for leghorns. Lateral spread of the ts-11 strain to commingled pen mates occurred rapidly, causing RSPA seroconversion patterns that mimicked those of the vaccinated pen mates.     

Short-term exposure to subacute doses of aflatoxin-induced depressed mitogen responses in young mallard ducks

Mallard ducklings were fed diets containing corn naturally contaminated with mixed aflatoxins, purified T-2 toxin, or no detectable mycotoxin in two trials. The aflatoxin level used was 12 ppb in the first trial and 33 ppb in the second. T-2 was added at 2 ppm in both trials. No pathology was associated with the aflatoxin used in this study, and T-2--induced lesions were described in a previous publication. The weights of primary (thymus and bursa of Fabricius) and secondary (spleen) lymphoid organs were significantly reduced in the T-2--treated birds. The total number of viable cells recovered from the thymus was significantly reduced in aflatoxin-treated birds. The numbers of viable cells recovered from thymus, bursa of Fabricius, and spleen were all significantly reduced after treatment with T-2. In each trial, significantly lower mitogenic responses were seen to pokeweed mitogen and concanavalin A in birds fed aflatoxin or T-2, representing reduction in both B-cell and T-cell mitogenesis. Birds fed aflatoxin also had significantly reduced Escherichia coli O55 lipopolysaccharide-induced mitogenic responses. These studies indicate that subacute oral exposure to aflatoxin caused a loss of normal lymphocyte reactivity in mallard ducklings. This finding supports the hypothesis that waterfowl that ingest even small quantities of mycotoxin-contaminated waste grain are likely to be more susceptible to bacterial or viral infections.     

Pathogenicity of fowl adenovirus isolated from gizzard erosions to immuno-suppressed chickens

Pathogenicity of a fowl adenovirus (FAV), JM1/1 strain of serotype 1 derived from gizzard erosions of a broiler chicken, was examined to specific pathogen-free (SPF) chickens pre-treated with infectious bursal disease viruses (IBDVs) or cyclophosphamide (CY). Virulent IBDVs, classical type, were inoculated orally at 3 days of age of SPF chickens. CY was treated subcutaneously for 3 days after hatch. FAV was given orally at 30 days of age. At 40 days of age, all chickens were bled and autopsied for serology and gross observation. Gizzard lesions were ranked by the scores depending on their severities. IBDV- or CY-treated chickens showed significantly higher gizzard lesion scores than non treated birds. There were no gross lesions in any other organs except for bursal atrophy. Serologically, antibody production against FAV was highly suppressed by IBDV infection or CY treatment.