Effects of administration of an in ovo coccidiosis vaccine at different embryonic ages on vaccine cycling and performance of broiler chickens,.

Use of a live coccidiosis vaccine has become an increasingly common method to control coccidiosis, especially in antibiotic-free broiler production. The Inovocox EM1 vaccine (EM1) is recommended for the vaccination of embryonated broiler hatching eggs between 18.0 and 19.0 d of incubation (doi). This allows for earlier acquisition of immunity to wild-type coccidia. However, it is unclear whether the difference in embryo age at the time of in ovo injection can influence the effect of the vaccine during grow-out as well as if the growth performance of broiler chickens is affected. Therefore, the objective of the study was to evaluate the effects of 2 injection ages (18.5 and 19.0 doi) and 3 injection types (noninjected, diluent, and vaccine) in a 3 × 2 factorial design, consisting of 10 replicates per treatment (60 treatment-replicate groups). There was a significant effect of injection age on BW at 0, 14, and 35 d after hatch, with a difference in the BW of birds belonging to the 18.5 and 19.0 doi groups up to day 35 after hatch. There was a significant effect of injection type on BW gain, feed intake, and FCR between 0 and 28 d after hatch. Between 0 and 35 d, FCR was lower in the vaccine-injected group in comparison with the noninjected and diluent control groups. Furthermore, total intestine coccidia and lesion indices were higher in the vaccine-18.5 treatment group in comparison with the diluent-18.5 treatment group at 28 d. In conclusion, hatchling weight was affected by injection age, and this subsequently affected growth performance. Furthermore, intestinal coccidia cycling peaked at 28 d, resulting in a reduction in growth performance through 28 d and subsequent compensatory growth by 35 d. There was no significant difference in coccidiosis cycling between the vaccine-18.5 and vaccine-19.0 doi treatment combination groups.

Effects of stage of broiler embryo development on coccidiosis vaccine injection accuracy, and subsequent oocyst localization and hatchling quality.

Control of coccidiosis in broiler chickens continues to pose challenges to commercial poultry producers, especially in an era of increased consumer demand for antibiotic-free broiler production. As a result, coccidiosis vaccines are now commonly used in rotation programs to achieve effective coccidiosis control. Inovocox EM1 vaccine (EM1) is a coccidiosis vaccine that allows for earlier immune acquisition through oocyst cycling, which reduces the effects of wild-type coccidia. The EM1 vaccine is administered to embryonated broiler hatching eggs between 18 and 19 D of incubation (doi). In the U.S., commercial broiler hatcheries vaccinate embryonated eggs at either 18.5 or 19 doi. However, it is unclear whether a difference in embryo age at the time of in ovo injection can impact the actual site of vaccine delivery. In addition, it is unclear where oocysts eventually become localized within the embryo following the in ovo injection of EM1. Therefore, the objective of this study was to determine the effects of stage of embryonic development on the actual deposition site of the EM1 vaccine oocysts when they are in ovo injected and to subsequently investigate the movement and eventual location of EM1 oocysts after in ovo injection. Because all eggs were injected at the same time, a 12-h difference in set time was a means to derive 18.5 and 19.0 incubation age of injection (IAN) treatments. The experimental design was a 3 injection treatment (noninjected, diluent-injected, and vaccine-injected) × 2 IAN factorial. There was a significant main effect of IAN on site of vaccine oocysts delivery, and subsequent hatching chick quality. Qualitative histological evaluation revealed the oral uptake of vaccine oocysts through the amnion, with their subsequent presence in the gizzard and intestinal lumen by 24 to 36 h postinjection. In conclusion, physiological development influenced the site of injection, and oocysts imbibed along with the amniotic fluid in late stage broiler embryos are subsequently transported to the gastrointestinal tract.

Testosterone and trenbolone enanthate increase mature myostatin protein expression despite increasing skeletal muscle hypertrophy and satellite cell number in rodent muscle.

The androgen-induced alterations in adult rodent skeletal muscle fibre cross-sectional area (fCSA), satellite cell content and myostatin (Mstn) were examined in 10-month-old Fisher 344 rats (n = 41) assigned to Sham surgery, orchiectomy (ORX), ORX + testosterone (TEST; 7.0 mg week-1 ) or ORX + trenbolone (TREN; 1.0 mg week-1 ). After 29 days, animals were euthanised and the levator ani/bulbocavernosus (LABC) muscle complex was harvested for analyses. LABC muscle fCSA was 102% and 94% higher in ORX + TEST and ORX + TREN compared to ORX (p < .001). ORX + TEST and ORX + TREN increased satellite cell numbers by 181% and 178% compared to ORX, respectively (p < .01), with no differences between conditions for myonuclear number per muscle fibre (p = .948). Mstn protein was increased 159% and 169% in the ORX + TEST and ORX + TREN compared to ORX (p < .01). pan-SMAD2/3 protein was ~30-50% greater in ORX compared to SHAM (p = .006), ORX + TEST (p = .037) and ORX + TREN (p = .043), although there were no between-treatment effects regarding phosphorylated SMAD2/3. Mstn, ActrIIb and Mighty mRNAs were lower in ORX, ORX + TEST and ORX + TREN compared to SHAM (p < .05). Testosterone and trenbolone administration increased muscle fCSA and satellite cell number without increasing myonuclei number, and increased Mstn protein levels. Several genes and signalling proteins related to myostatin signalling were differentially regulated by ORX or androgen therapy.

Effects of challenge with very virulent infectious bursal disease virus reassortants in commercial chickens.

Pathogenicity and immune responses were characterized in commercial broilers and layers challenged with very virulent infectious bursal disease virus (vvIBDV) reassortants (vvIBDV segment A + serotype 2 segment B and vvIBDV segment A + classic virulent segment B) at 7 days of age. In addition, functional immunosuppression was evaluated after challenge with infectious bronchitis virus (IBV) at 15 days of age. Layers showed higher levels and increased persistence of IBDV- and IBV-specific maternal antibodies than broilers at 1, 13, and 28 days of age. Cytokine gene expression was evaluated, after IBDV challenge, as an indicator of the innate immune function. Similar results were detected between the groups inoculated with vvIBDV reassortants. Interleukin-1ß (IL-1ß) in the bursa of layers demonstrated down-regulation at 1 day postinfection (DPI; 8 days of age), and no changes at 4 DPI (11 days of age) compared with controls. In broilers, IL-6 expression in the bursa was down-regulated 1 DPI (8 days of age) and up-regulated at 4 DPI (11 days of age). A significant lymphoid depletion was detected at 21 DPI (28 days of age) in broilers exposed to a reassortant of vvIBDV segment A and classic virulent IBDV segment B. Finally, reduced specific antibodies against IBV measured 13 days after challenge were detected in layer and broiler chickens inoculated with a reassortant serotype 2 IBDV in segment B, suggesting functional immunosuppression. These results provide evidence indicating that current IBDV vaccination of breeders does not completely protect progeny chickens from challenge with reassortant vvIBDV.

Conjunctiva-associated lymphoid tissue in avian mucosal immunity.

Conjunctiva-associated lymphoid tissue's (CALT) role in generating avian mucosal adaptive immunity was measured by analyzing cellular composition, expression of the polymeric immunoglobulin receptor (pIgR), and production of cytokines and antibodies in chickens ocular exposed to a replication-deficient adenovirus of serotype 5 (Ad5). These studies demonstrate that CALT contains B cells, γδ T cells, T helper, and cytotoxic T cells, and a T lymphocyte composition, which more resembles Harderian glands than spleen. CALT-derived lymphocytes contain antigen-specific, IgA-secreting plasma cells and cytokine-producing lymphocytes after ocular Ad5 vaccination. The expression of the pIgR in the CALT's lymphoepithelium emphasizes the importance of mucosal immune protection by paraocular lymphoid tissues. The CALT immune response after ocular Ad5 boosting was influenced by prior high dose in ovo Ad5 priming. Thus, both mucosal and systemic immunization influenced Ad5-induced IFN-γ responses in CALT.

Influence of Salmonella enterica serovar Typhimurium infection on intestinal goblet cells and villous morphology in broiler chicks.

Live broiler chickens are important in the transmission of Salmonella to humans. Reducing Salmonella levels in the intestine of broiler chickens, in part, requires understanding of the interactions between Salmonella and the intestinal barriers that represent the first line of defense. Such barriers include the mucus layer (composed of mucins secreted by goblet cells) and the underlying epithelium. Two experiments were conducted to evaluate the effect of Salmonella Typhimurium infection on intestinal goblet cell dynamics (density and size) and villous morphology in broiler chicks. In Experiment 1, broiler chicks were either challenged with sterile media (control treatment) or orally given 7.4 x 10(7) colony-forming units (CFU) at 3 days of age (termed the CST treatment). Treatments were similar in Experiment 2, except that chicks in the CST treatment were challenged with 7.8 x 10(6) CFU at 4 days of age. Duration of each experiment was 14 days. At 7 days postchallenge (PC) in Experiment 1, jejunal tissue sections were collected, formalin-fixed, and routinely processed for histologic measurement of villous morphometric indices. In Experiment 2, at 10 days PC, jejunal tissue sections were collected and processed for histologic determination of goblet cell numbers and size, in addition to villous measurements. Results showed that Salmonella Typhimurium infection increased goblet cell density, reduced villous surface area, increased the incidence of epithelial exfoliation, and increased the incidence of heterophil influx into the lamina propria (P < 0.05). It was concluded that Salmonella Typhimurium infection impacts goblet cell biology and exerts morphopathologic changes in the jejunum of broiler chicks.

Pathogenicity of infectious bursal disease virus variant AL2 in young chickens.

Limited information is available on the effects of the recently emerged infectious bursal disease virus (IBDV) variant AL2. In this study, the effects of inoculation of 4-day-old chickens with increasing doses of IBDV AL2 were characterized. IBDV AL2 induced neither overt clinical signs nor mortality. Infected chickens showed reduced bursa indices (BI) and bursa lymphocytic depletion, as determined by histomorphometry. However, histomorphometry and BI values differed during the early stages of the infection. Because data from bursa histomorphometry were consistent with viral RNA detection, such values seem to be more appropriate for the assessment of AL2 viral infectivity in chickens. Both the histomorphometry and BI data indicated a dose-effect pattern. However, with time, even low doses of the virus ultimately resulted in significant damage to the bursa. Samples of spleen were used to assess B- (IgM+) and T- (CD4+ and CD8+) cell populations by flow cytometry. Infected chickens showed a significant increase of splenic IgM+ cells at 5 and 8 days postinoculation (PI). On day 8 PI, the number of total IgM+ cells in the spleen was inversely related to the virus concentration. Others have shown that cell-mediated immunity is essential for protection against IBDV. Our results indicate a significant increase (P < 0.05) of total spleen CD4+ cell counts on day 8 PI in birds that received higher virus concentrations, indicating a role for these cells in protective immunity, while CD8 cell counts remained unchanged. We speculate that the changes in splenic CD4+ and IgM+ cell populations are associated with protective immune responses against IBDV in the host.

Effects of chicken anemia virus and infectious bursal disease virus in commercial chickens.

The effects of chicken anemia virus (CAV) and infectious bursal disease virus (IBDV) coinfection in commercial layer-type and meat-type (broiler) chickens with specific maternal immunity were evaluated. In addition, the broiler progeny used had been vaccinated in ovo against IBDV. Layer chickens were inoculated intramuscularly on day 3 of age with CAV and orally on day 7 of age with an IBDV standard strain (APHIS). Broiler chickens were exposed to CAV and/or an IBDV variant strain (AL2) via the drinking water on days 3 and 14 of age. Following CAV and IBDV inoculation neither mortality nor overt clinical disease was observed in any layer or broiler group. In spite of maternal immunity against both IBDV and CAV, mean hematocrits of all layer groups inoculated with CAV (CAV, CAV + APHIS) were lower than uninfected chickens. IBDV APHIS alone or in combination with CAV did not affect the layer weight gain. However, on day 30 of age and concomitantly with maternal antibody decay, bursa lymphocyte depletion became evident in CAV + APHIS-infected layer chickens. These birds (CAV + APHIS) also seroconverted to IBDV on day 35 of age. CAV persisted at low levels in the layer chickens throughout the experimental period in CAV- and CAV+APHIS-infected chickens. Similarly, infected broiler chickens did not show changes in weight gain. Compared to CAV-infected or uninfected controls, CAV+AL2- and AL2-infected broiler chickens showed significant lymphocyte depletion in the bursa as assessed both by bursal indices and histomorphometry. Broilers also seroconverted to IBDV after day 30 of age confirming that bursal lymphocyte depletion was due to IBDV resuming replication. Thymus histomorphometry revealed significant lymphocyte depletion in all infected broiler groups at 30 days of age, but only in CAV+AL2-infected broiler chickens at 41 days of age, suggesting that IBDV infection delayed repopulation of the thymus.

Pathogenesis of infectious bronchitis virus in vaccinated chickens of two different major histocompatibility B complex genotypes.

Infectious bronchitis (IB) disease progression in vaccinated chickens after challenge was evaluated in a single commercial line of layer chickens presenting two different major histocompatibility complex (MHC) B complex genotypes. MHC B genotypes were determined by DNA sequence-based typing of BF2 alleles. In total, 33 B2/B15 and 47 B2/B21 chickens were vaccinated with an Ark-type IB virus (IBV) attenuated vaccine and challenged with Ark-type IBV field isolate AL/4614/98 14 days later. Additional chickens of both genotypes served as unvaccinated/challenged and unvaccinated/nonchallenged controls. Clinical signs, histopathologic analysis, detection of IBV genomes in tears, and IBV-specific immunoglobulin A (IgA) in tears were used to evaluate disease progression and immune response. The incidence of IBV respiratory signs was significantly higher in B2/21 than in B2/B15 MHC genotype birds. However, neither the severity and duration of respiratory signs nor the severity and incidence of histologic lesions differed significantly with MHC genotype. The levels of IBV-specific IgA in tears of vaccinated and challenged chickens did not differ significantly between MHC genotypes. IBV genomes were present in the tears of vaccinated and challenged birds, and the incidence of detectable IBV genomes did not vary significantly with MHC B genotype. From an applied perspective, these results indicate that vaccinated commercial outbred chickens with these MHC genotypes are equally resistant to IBV.

Transmissible proventriculitis in broilers.

This article reviews transmissible proventriculitis in poultry from 1971 to 2006. The disease is important in commercial broilers worldwide, resulting in reduced profits. The aetiology of this disease is unknown and different clinical presentations often result in a confused or complicated diagnosis. The lesion of enlarged proventriculus is often referred to as proventriculitis. However, the term proventriculitis can only be used correctly when there is microscopic evidence of inflammation of the proventriculus glands. Infectious and non-infectious causes of proventriculitis, with major emphasis on the infectious or transmissible causes, are reviewed.

Espondilolistese em frango de corte no Brasil / Spondylolisthesis (\"Kinky Back\") in broiler chickens in Brazil

Eight 28-day-old broiler chickens of both sexes were examined. Clinical signs, gross findings, radiological, and histopathological changes were described. Spondylolisthesis was characterized by dorsal displacement of the sixth and seventh thoracic vertebrae, resulting in compression of the spinal cord. The major clinical manifestation was paraplegia. Risk factors such as genetics, nutrition, stress, rate of growth, and age were discussed.

Epidemiological and experimental evidence for immunodeficiency affecting avian infectious bronchitis.

We evaluated the effects of viral immunodeficiency on the outcome of infectious bronchitis virus (IBV) infection in chickens as a hypothetical cause for failure of adequate protection in vaccinated chickens. Initially, we investigated IBV isolations from cases of respiratory disease in association with the presence of thymic and/or bursal atrophy in 322 submissions during 1997 to 2002. Arkansas (Ark)-type IBV was most frequently isolated in spite of extensive ArkDPI vaccination in the broiler industry. The number of IBV isolations was consistently higher in broilers aged 27 to 43 days, coinciding with lymphocytic depletion of the bursa and/or thymus, providing circumstantial evidence that immunodeficiency and IBV incidence may be linked. S1 gene sequence analyses, antigenic characterizations, and challenge of susceptible chickens demonstrated that the field IBV isolates tested were closely related to vaccine strains and had low pathogenicity for chickens. We experimentally evaluated the effects of immunodeficiency caused by co-infection with chicken anaemia virus and infectious bursal disease virus on the outcome of IBV infection. Clinical signs and histological lesions were more persistent in immunodeficient chickens. Local specific IgA production was delayed and lower levels were achieved in immunodeficient chickens. At the same time, IBV RNA concentrations in tracheas and lachrymal fluids were higher and more persistent in immunodeficient chickens. Collectively, these results indicate that viral immunodeficiency most probably plays a relevant role in the epidemiology and outcome of IBV infection.

Serological evidence of chicken infectious anemia virus in the United States at least since 1959.

A retrospective, serological survey was performed to determine an approximate time frame for when chickens were first exposed to chicken anemia virus (CAV) in the southeastern United States. A serum collection covering most of the period between 1959 and 2005 was available for the present study. These sera were obtained from adult chicken flocks that were maintained in experimental chicken farms at Auburn University's Department of Poultry Science. Sera were tested for the presence of CAV-specific antibodies using a commercially available competitive enzyme-linked immunosorbent assay (ELISA) kit. Values <0.6 were considered positive. Fresh sera obtained from hens in 2005 showed 45.5% negative and 54.5% positive for CAV antibodies. The assessment of serum samples covering the time period of 1959 through 1979 resulted in most sera being positive for CAV antibodies. The percentage of positive samples between years varied from 43% to 100%. These serological results support assumptions based on circumstantial evidence that CAV must have been present in the United States long before its first isolation in 1989.

Pharmacokinetics of levamisole in broiler breeder chickens.

The pharmacokinetics of levamisole was studied in 20 broiler breeder chickens (chickens that give eggs to breed broilers). A single dose of levamisole (40 mg/kg) was administered orally or intravenously to chickens before the onset of egg production, prelay (age = 22 weeks), and repeated at the peak of egg production (age = 32 weeks). A high-pressure liquid chromatographic with ultraviolet detection method (HPLC-UV) was used for quantification of levamisole in plasma. Using compartmental analysis, levamisole followed a three-compartmental open model with mean values of alpha = 0.1224 and 0.4968, beta = 0.01663 and 0.01813, gamma = 0.002 and 0.002/min at the prelay and at the peak of egg production periods, respectively. The mean values for volume of distribution at steady state (V(ss)), determined by compartmental analysis, were significantly different for prelay and peak of egg production (8.358 and 13.581 mL/kg), respectively.

The avian major histocompatibility complex influences bacterial skeletal disease in broiler breeder chickens.

This study evaluated bacterial skeletal disease in conjunction with the major histocompatibility complex (MHC) in a genetically pure line of broiler breeder chickens. Chickens from six broiler breeder flocks were examined for skeletal lesions, bacterial pathogens, and MHC genotype. During a 10-week period, eighty-eight, 9- to 21-week-old lame chickens and 34 normal, age-matched controls were selected. Tenosynovitis, arthritis, and femoral or tibiotarsal (or both) osteomyelitis occurred in 86 of 88 (97.7%) lame chickens. Ninety-five bacterial isolates were obtained from 83 of 88 (94.3%) lame birds and 4 of 34 (11.8%) controls. Staphylococcus spp. was isolated from 72.6% of the skeletal lesions, predominantly Staphylococcus aureus (38.9%). MHC B complex genotypes were determined by hemagglutination for 88 lame birds, 34 controls, and 200 randomly selected birds from each of the six flocks (1,200 total). Combined chi-square analysis revealed that the homozygous MHC genotypes B(A4/A4) (chi(2) = 14.54, P = 0.0063) and B(A12/A12) (chi(2) = 42.77, P = 0.0001) were overrepresented in the sample of symptomatic birds compared with random samples from the same flocks. The homozygous A4 and A12 MHC genotypes influenced flock chi-square values more than the corresponding heterozygotes. An MHC B complex influence on bacterial skeletal disease was apparent in this line of broiler breeders.

Pigeon paramyxovirus: association with common avian pathogens in chickens and serologic survey in wild birds.

Pigeon paramyxovirus-1 (PPMV-1) was isolated from pigeons from east-central Alabama and used in association with chicken anemia virus (CAV), infectious bursal disease virus (IBDV), or finch Mycoplasma gallisepticum (MG) in specific-pathogen-free chickens to assess dinical disease and pathology. PPMV-1 infection in all groups was conducted at day 10 of age via the ocular route. The low passage PPMV-1 isolate was inoculated into chickens in different groups at 10 days post-CAV infection, 6 days post-IBDV infection, and 6 days post-finch MG infection, respectively. Additionally, to obtain information on the status of paramyxovirus infection in the wild bird population of the region, we used a multispecies competitive enzyme-linked immunosorbent assay kit to assess serum samples from 180 wild birds representing 24 species obtained throughout 2001. Mild respiratory signs characterized by sneezing were observed in PPMV-1-infected chicks. In the brain, PPMV-1 caused disseminated vasculitis in the neuropile and meninges, sometimes with small foci of gliosis. Most brains had only mild lesions. In the upper respiratory tract, lesions were confined to the larynx and proximal trachea as hyperplasia of laryngeal mucosa-associated lymphoid tissue. In the lung, PPMV-1 caused minimal to moderate multifocal interstitial pneumonia. Lymphocytic expansion occurred in the interstitium of the Harderian gland. PPMV-1 in the spleen caused expansion of the white pulp as a result of hypertrophy of the macrophages in the periarteriolar sheaths accompanied by lymphocytic hyperplasia at the periphery. No severe aggravation of either signs or lesions could be attributed to any of the avian pathogens used in association with PPMV-1. The serologic survey in wild birds showed antibody levels that were considered negative or doubtful. Interestingly, significantly (P < 0.05) higher mean titers were observed during the months of October and November 2001, following closely multiple PPMV-1 episodes of mortality in wild collard doves in northwestern Florida.

Use of bacteriophages in combination with competitive exclusion to reduce Salmonella from infected chickens.

Salmonella-spedfic bacteriophages (BP) and competitive exclusion (CE) were used to reduce Salmonella colonization in experimentally infected chickens. A "cocktail" of distinct phage (i.e., phage showing different host ranges and inducing different types of plaques on Salmonella Typhimurium [ST] cultures) was developed. The killing activity of the selected BPs on ST cultures differed significantly, as determined in in vitro killing assays. BPs were administered orally to the chickens several days prior and after ST challenge but not simultaneously. BPs were readily isolated from the feces of the BP-treated chickens approximately 48 hr after administration. A CE product consisting of a defined culture of seven different microbial species was used either alone or in combination with BP treatment. CE was administered orally at hatch. Salmonella counts in intestine, ceca, and a pool of liver/spleen were evaluated in Salmonella-challenged chickens treated with BP or with BP and CE. In both trials 1 and 2, a beneficial effect of the phage treatment on weight gain performance was evident. A reduction in Salmonella counts was detected in cecum and ileum of BP-, CE-, and BP+CE-treated chickens as compared with nontreated birds. In trial 1, BP treatment reduced ST counts to marginal levels in the ileum and reduced counts sixfold in the ceca. A reduction of Salmonella counts with BP, CE, and BP+CE treatments was evident in chickens from trial 2. Both CE and BP treatments showed differences in the reduction of Salmonella counts after challenge between spedmens obtained at days 4 and 14 postchallenge in ceca, liver/spleen, and ileum. The preliminary data presented in this report show that isolation and characterization of Salmonella-specific BP is uncomplicated and feasible on a larger scale. Results indicate a protective effect of both Salmonella-specific BPs and a defined competitive exclusion product against Salmonella colonization of experimentally infected chickens. These results are encouraging for further work on the use of BP as an effective alternative to antibiotics to reduce Salmonella infections in poultry.

Oral infection with chicken anemia virus in 4-wk broiler breeders: lack of effect of major histocompatibility B complex genotype.

The pathologic consequences of chicken anemia virus (CAV) oral inoculation in 4-wk-old broiler breeders of different major histocompatibility B complex (MHC) genotypes were evaluated. MHC B complex was determined by hemagglutination and sequence-based typing. Clinical signs, serology, gross lesions, histopathologic analysis, and CAV genome quantification were used to evaluate disease progression. Clinical disease was not apparent in the inoculated broilers throughout the experimental period. At 14 days postinoculation, antibodies against CAV were detected in 26.4% (29/110) of the inoculated birds. The distribution of percent positive was 34.6% (9/26) and 32.3% (10/31) of the chickens with B A9/A9 and B A9/A4 MHC genotypes, respectively, and seroconversion in six other genotypes was 19% (10/53). These differences among MHC genotypes for specific seroconversion rate were not statistically significant. CAV genomes were detected in the thymus of 87.7% (93/110) of the inoculated birds with no statistically significant differences between MHC genotypes. Mild thymic lymphocytolysis, lymphedema, and medullary hemorrhage were observed in the inoculated chickens. Histomorphometric analysis showed that cortical lymphocyte-to-parenchyma ratios did not differ between inoculated and uninoculated groups or among MHC genotypes. Similar findings have been reported previously in white-leghorn chickens of similar age, suggesting that broilers show a similar resistance to the effects of CAV infection at this age. The absence of significant clinical and pathological changes in the orally inoculated broilers at this age contrasts with CAV-associated thymus damage seen frequently in condemned commercial broilers at harvest.

Pathogenesis of chicken anemia virus: comparison of the oral and the intramuscular routes of infection.

The events during the pathogenesis of chicken anemia virus (CAV) infection following intramuscular (IM) and oral inoculation were further elucidated and compared by sequential clinical, pathologic, and morphometric histopathologic evaluations, and by sequential determination of CAV genome concentrations in different organs. Specific-pathogen-free chickens were inoculated by IM or oral routes with the same dose (2 x 10(6) mean tissue culture infective dose [TCID50]) of CAV isolate 03-4876 at 1 day of age. Weights and hematocrits were obtained at 7, 10, 14, 18, 21, 25, and 28 days postinoculation (DPI). Seven birds from each group were necropsied at 7, 10, 14, and 28 DPI, and samples of thymus, Harderian gland, and cecal tonsils (CT) were obtained for histopathologic examination and CAV genome quantification by real-time polymerase chain reaction. Peak CAV genome concentrations were detected in the thymus at 10 and 14 DPI in the IM and orally infected chickens, respectively. High CAV DNA concentrations were maintained throughout the experimental period until 28 DPI, despite specific seroconversion occurring by 14 DPI in the IM-inoculated chickens. CAV was isolated from both orally and IM-infected chickens 28 DPI. Peak CAV genomes in the thymuses of IM and orally infected chickens coincided with peak lymphocyte depletion in these organs. Lymphocyte repopulation of the thymus occurred by 28 DPI in spite of the presence of the virus in the organs of both infected chicken groups. CAV genomes were detected in the CT, but histopathologic changes were not observed. Compared with the IM route of infection, orally infected chickens did not show apparent signs of illness. Clinical parameters, including reduction of weight gains and hematocrits, and gross and histopathologic changes were delayed and less severe in the orally inoculated chickens. This was concurrent with a delay in accumulation of CAV genomes in the thymus of these chickens.

Genetic characterization of chicken anemia virus from commercial broiler chickens in Alabama.

Chicken anemia virus (CAV) isolates show extremely limited genetic variability worldwide. We determined the nucleotide sequence of an 823-nucleotide portion of the 2.3-kb CAV genome found in 10 liver and/or spleen specimens of Alabama 29-to-49-day-old commercial broiler chickens exhibiting lymphocyte depletion of the thymus submitted to the state diagnostic laboratory because of problems unrelated to anemia. We determined the nucleotide sequence directly from DNA isolated from tissues, without isolation of virus in culture. This procedure enabled us to characterize CAV that might not have replicated in culture and avoided the potential for changes during passage. Results confirmed the limited genetic variability of CAV. All sequences were identical in 93% of nucleotide positions. The sequences encoded only two distinct VP1 hypervariable regions, and both had been found previously in other CAV isolates. A novel amino acid, glutamine, was found at VP1 position 22 in half the sequences, replacing the histidine residue encoded by most previously characterized CAV genomes. We were able to distinguish among CAV genomes with different codons at VP1 amino acid 22 and different hypervariable regions by restriction endonuclease analysis of polymerase chain reaction products.