Efficacy of recombinant fowl poxvirus vaccine in protecting chickens against a highly pathogenic Mexican-origin H5N2 avian influenza virus

Internationally and nationally, governments and the poultry industries have used various strategies to control avian influenza (AI), ranging from a minimum of living with mildly pathogenic AI virus (AIV) infections to the other extreme of implementing a total quarantine-slaughter approach for eradication of highly pathogenic (HP) forms of the disease. However, recent economic considerations in various countries have prompted a broader reevaluation of vaccination as one of several tools to be used in AI control programs, including H5 and H7 HP AI. In the current study, 1-day-old chickens were immunized with a recombinant fowl poxvirus vaccine containing a hemagglutinin gene insert (Vector-HA) from an H5 AIV. Vector-HA- and negative control (vector-control)-vaccinated chicks were challenged with a HP H5N2 AIV isolated from chickens in Mexico. All immunized chickens were antibody negative on the agar gel precipitin test, indicating that vaccination would not interfere with routine AI serologic surveillance programs in the United States. However, in the hemagglutinin-inhibition test, a few immunized chickens (8%) had low serologic titers. Protection against illness (90-100%) and death (90-100%) was provided by the vector-HA vaccine from 3 wk of age to the end of the 20-wk study. The number of chickens shedding the challenge AIV from their enteric tracts was significantly reduced (50-75%) and the quantity of challenge AIV shed from respiratory and enteric tracts was significantly reduced (10(1)-10(2.1) mean embryo lethal dose/ml) in most vector-HA vaccine groups when compared with vector-control groups. Furthermore, vector-HA vaccination reduced in contact transmission of HP AI challenge virus to both vector-HA- and vector-control-vaccinated chickens. These findings indicate the recombinant fowl poxvirus vaccine can be a useful tool in an AI control program by preventing illness and death in chickens and reducing intestinal and respiratory shedding of H5 AIV. However, for an AI control program to be successful, enhanced biosecurity and surveillance must be practiced, and the vaccine's use must be controlled by an industry and/or government task force.

Evolution of H5 subtype avian influenza A viruses in North America

The phylogenetic relationships of the hemagglutinin (HA) and non-structural (NS) genes from avian influenza (AI) H5 subtype viruses of North American origin are presented. Analysis of the HA genes of several previously uncharacterized isolates from waterfowl and turkeys provided clear evidence of significant sequence variation and existence of multiple virus clades or sub-lineages, maintained in migratory waterfowl. Phylogenetic analysis of NS gene sequences further demonstrated multiple sub-lineages and also demonstrated re-assortment of two NS alleles in wild duck populations. Based on currently available HA1 gene sequences, at least four clades exist with waterfowl isolates included in three of the four groups. The most genetically unstable of these sub-lineages is composed of recent poultry isolates from the outbreak of AI in Central Mexico. This group of viruses, which replicated unabated in chickens for at least 16 months, exhibited an increased rate of mutation in both the HA and NS gene. Comparison of the HA1 sequence data for all available North American H5 subtype viruses demonstrated minimal variation both in and around the amino acids predicted to be involved in the HA receptor binding site. The sequences also revealed that migratory waterfowl, live poultry market chicken, and turkey isolates uniformly lack a glycosylation site at amino acid 236 in the HA protein which is present in commercial chicken isolates.

Pathogenicity and diagnosis of H5N2 Mexican avian influenza viruses in chickens

Chickens were inoculated with one of five H5N2 Mexican-origin avian influenza virus (AIV) isolates to determine their pathogenicity for chickens and to determine the ability of routine virologic and serologic tests to detect infections. In laboratory infections, three AIVs, H5/94, M5/94, and J12/94, produced sporadic illness and death and were categorized as mildly pathogenic. Q1/95 produced illness and death in all inoculated chickens and was categorized as highly lethal and highly pathogenic (HP). P11/94B commonly produced clinical illness, but deaths were infrequent. During the presence of clinical signs, oropharyngeal swabs were superior for isolation of AIV, but cloacal swabs were more successful after disappearance of clinical signs. Agar gel precipitin (AGP) serologic test was superior for detecting AIV infection during the clinical phase, but AGP and hemagglutinin inhibition tests were equally effective in detecting infections after recovery from clinical illness. Passage of P11/94B parent stock and selected 14-day-embryo-passed AIVs in adult hens resulted in emergence of some HP AIV derivatives. The hemagglutinin of Q1/95 and P11/ 94B parent stock and derivative AIVs had an identical proteolytic cleavage site of.... Pro-Gln-Arg-Lys-Arg-Lys-Thr-Arg-Gly, consistent with AIVs of high pathogenicity. However, no consistent differences were identified in the sequence of the hemagglutinin gene to explain the discrepancy in lethality patterns of the P11/94B AIVs. This suggests that genes other than the hemagglutinin impact the full expression of high lethality of Mexican-origin AIV infections in chickens.

Genetic and phenotypic characterization of intestinal spirochetes colonizing chickens and allocation of known pathogenic isolates to three distinct genetic groups

Infection with intestinal spirochetes has recently been recognized as a cause of lost production in the poultry industry. Little is known about these organisms, so a collection of 56 isolates originating from chickens in commercial flocks in Australia, the United States, The Netherlands, and the United Kingdom was examined. Strength of beta-hemolysis on blood agar, indole production, API ZYM enzyme profiles, and cellular morphology were determined, and multilocus enzyme electrophoresis was used to analyze the extent of genetic diversity among the isolates. The results were compared with those previously obtained for well-characterized porcine intestinal spirochetes. The chicken isolates were genetically heterogeneous. They were divided into 40 electrophoretic types distributed among six diverse genetic groups (groups b to g), with a mean genetic diversity of 0.587. Strains in two groups (groups d and e) may represent new species of Serpulina, and the groups contained only strains isolated from chickens. Three genetic groups contained isolates previously shown to be pathogenic for chickens. These corresponded to the proposed species "Serpulina intermedius," to an unnamed group (group e), and to Serpulina pilosicoli. Two of the chicken isolates (one "S. intermedius" and one S. pilosicoli isolate) were strongly beta-hemolytic, two (both "S. intermedius") had an intermediate level of beta-hemolysis, and the rest were weakly beta-hemolytic. Fourteen isolates of "S. intermedius" produced indole, as did one isolate from group d. Isolates identified as S. pilosicoli resembled porcine isolates of this species, having four to six periplasmic flagella inserted subterminally in a single row at each end of the cell, and had tapered cell ends. All other spirochetes were morphologically similar, having seven or more periplasmic flagella and blunt cell ends. The identification of three genetic groups containing pathogenic isolates provides an opportunity for more detailed epidemiologic studies with these pathogens and for the development of improved diagnostic tests.

Cases of spirochete-associated necrotizing typhlitis in captive common rheas (Rhea americana)

Ceca from greater or common rheas (Rhea americana) with gastrointestinal disease were collected from diagnostic labs and avian pathologists across the United States. The ceca were evaluated for the presence of spirochetes and necrosis using hematoxylin and eosin stain or Warthin-Starry silver-stained tissue sections and anaerobic culture. Spirochete-associated necrotizing typhlitis was documented in 11 states. Most cases were reported in the summer and fall and occurred in rheas less than 5 mo of age. Spirochetes isolated from ceca with necrosis were either strongly or weakly beta-hemolytic. All spirochetes isolated from ceca without necrosis were weakly beta-hemolytic. Rheas might be host to both pathogenic and nonpathogenic spirochetes.

Comparative pathology of chickens experimentally inoculated with avian influenza viruses of low and high pathogenicity

Pathologic changes and distribution of viral antigen as determined by immunohistochemistry were compared among 4-wk-old specific-pathogen-free chickens inoculated intratracheally with avian influenza virus (AIV) isolates of either low or high pathogenicity. Viruses of low pathogenicity, previously characterized as mildly pathogenic (MP), included A/chicken/Pennsylvania/21525/83 (H5N2) (MP-Penn) and A/chicken/Alabama/7395/75 (H4N8) (MP-Alab). Viruses of high pathogenicity included A/chicken/Pennsylvania/1370/83 (H5N2), A/chicken/Victoria/A185/85 (H7N7), and A/turkey/Ontario/7732/66 (H5N9). Extremely variable clinical signs ranging from mild respiratory distress to high mortality were present among chickens inoculated with these viruses. Chickens inoculated with highly pathogenic (HP) virus had histologic lesions of necrosis and inflammation in cloacal bursa, thymus, spleen, heart, pancreas, kidney, brain, trachea, lung, and skeletal muscle, whereas chickens inoculated with MP virus had histologic lesions most frequently in lung and trachea or lacked histologic lesions. Immunospecific staining for avian influenza viral proteins was most common in cells within heart, lung, kidney, brain, and pancreas of chicken inoculated with HP viruses, but immunospecific staining was present only and infrequently in trachea and lung of chickens inoculated with MP-Penn AIV. MP-Alab did not produce lesions nor have viral antigen in inoculated chickens but did produce serologic evidence of infection. The pattern of organ involvement and viral antigen distribution in chickens intratracheally inoculated with HP AIV isolates indicates a common capability to spread beyond the respiratory tract and confirms the pantrophic replicative, pathobiologic, and lethal nature of the viruses. However, variability in severity and lesion distribution exists between different HP AIVs. By contrast, MP viruses had the ability to replicate in respiratory or enteric tracts or both and produce lesions within the respiratory tract. These MP viruses exhibited a restricted ability to replicate or produce lesions or both in nonrespiratory or nonenteric tissues; such effects were associated with only sporadic deaths.

Identification of the swine pathogen Serpulina hyodysenteriae in rheas (Rhea americana)

Recently intestinal spirochetes were isolated from rheas in Ohio and Iowa with a necrotizing typhlocolitis. These intestinal spirochetes, strains R1 and NIV-1, were characterized and compared with other intestinal spirochetes, including strains of S. hyodysenteriae. Both rhea spirochetes were indole positive, strongly beta-hemolytic, grew under a 1% O2:99% N2 atmosphere, and were morphologically similar to spirochetes in the genus Serpulina. Analysis of rRNA gene restriction patterns (ribotypes), and immunoblots of whole cell proteins, indicated both spirochetes were similar to Serpulina hyodysenteriae strains from swine. Comparisons of nearly complete sequences (> 1458 bases) of the 16S rRNA gene of the two rhea spirochetes with S. hyodysenteriae strains confirmed that rhea spirochetes R1 and NIV-1 were strains of S. hyodysenteriae. These results indicate that S. hyodysenteriae has a broader host range than previously recognized.

Renal function and organic anion and cation transport during dehydration and/or food restriction in chickens

The effect of dehydration in the presence or absence of continued food intake on renal function was evaluated in chickens. In addition, renal transport of organic anions and cations under these conditions was assessed in vitro by uptake of 14C-para-aminohippuric acid and 14C-tetraethylammonium bromide by renal slices. Water restriction with continued food intake resulted in increases in serum osmolality and serum concentrations of sodium, uric acid, calcium and total protein. If food was restricted in addition to water, only serum osmolality and sodium concentration were significantly increased after 48 hours. Dehydration with continued access to food resulted in marked decreases in extracellular fluid volume, glomerular filtration rate and effective renal plasma flow. If food was restricted during dehydration, the decrease in effective renal plasma flow was attenuated despite reductions in glomerular filtration rate and extracellular fluid comparable to that seen in dehydrated birds allowed free access to food. Transport of organic anions was significantly increased after 24 and 48 hours of water restriction, regardless of whether food was withheld. Enhanced transport of organic anions in the presence of decreased glomerular filtration rate and effective renal plasma flow during dehydration may promote precipitation of urates and nephrosis in chickens.

Assessment of the ability of ratite-origin influenza viruses to infect and produce disease in rheas and chickens

Pathobiologic characteristics were determined for three mildly pathogenic (MP) ratite-origin avian influenza viruses (AIVs). Ratite-origin AIVs produced respiratory disease in rheas, and virus was reisolated from oropharyngeal and cloacal swabs on days 2-6 postinoculation. Inoculation of two ratite-origin AIVs in the upper respiratory tract of chickens resulted in viral infections, but the mean chicken infectious dose (CID50) for A/emu/Texas/39924/93 (H5N2) (Emu/Texas) virus was 500-fold lower than the CID50 for the A/rhea/North Carolina/39482/93 (H7N1) virus. In ovo and in vivo passage of the MP parent Emu/Texas isolate resulted in emergence of a highly pathogenic (HP) variant that had high plaquing efficiency in chicken embryo fibroblast cultures and was highly lethal in chicken pathotyping tests. This variant virus produced gross lesions in chickens similar to those reported for other HP AIVs. These findings demonstrated that ratite-origin AIVs can produce significant clinical disease in rheas and have a realistic potential for interspecies transmission to domestic poultry. Furthermore, HP variants can emerge from MP H5 ratite-origin AIVs if introduced and allowed to circulate in chicken populations.

Immunohistochemistry of transmissible gastroenteritis virus antigens in fixed paraffin-embedded tissues

An immunohistochemistry technique was developed using fixed tissues to study the presence and location of transmissible gastroenteritis virus (TGEV) antigens in situ. Experimentally infected gnotobiotic and conventional pigs as well as pigs with natural TGEV infection were examined. The staining technique was based on detection of the major structural protein of TGEV, the nucleocapsid, by using a pool of 3 monoclonal antibodies. Formalin and periodate-lysine-paraformaldehyde (PLP)-fixed intestinal tissues from a gnotobiotic pig inoculated with virulent TGEV were used to determine optimal antibody concentrations and incubation times. The intestinal tissues remained in their respective fixatives for 6 months, and serial sections were removed at sequential times and embedded in paraffin blocks. PLP and 10% neutral buffered formalin were acceptable fixatives and preserved TGEV nucleocapsid antigenicity for up to 6 months. Formalin, in comparison with PLP as a fixative, was better for preserving original tissue morphology and provided better antigen detection. Conventional crossbred pigs were inoculated with virulent TGEV, and animals were euthanized on various postexposure days. Intestinal tissues were positive for TGEV nucleocapsid antigens on postexposure days 2, 4, and 8. The immunohistochemistry technique detected TGEV antigen in stored paraffin-embedded tissues from 14 naturally infected pigs previously confirmed as positive for TGEV using a direct immunofluorescence assay on intestinal mucosal smears, whereas 9 naturally infected pigs confirmed negative for TGEV antigen by the same immunofluorescence assay showed no staining consistent with the presence of TGEV antigen. Immunohistochemistry provides a method to detect TGEV and possibly other closely related coronaviruses such as porcine respiratory coronavirus in situ. A diagnostic test using the same fixed tissues processed for histopathology provides veterinary practitioners an alternative to delivering live pigs or refrigerated fresh intestinal samples containing infectious virus to a diagnostic laboratory. Investigators can utilize this technique to retrospectively screen fixed tissues for TGEV antigen.

An Arg-Lys insertion at the hemagglutinin cleavage site of an H5N2 avian influenza isolate

Recent isolations of H5N2 subtype avian influenza (AI) viruses in North America have raised questions concerning their origin, transmission to commercial poultry, and potential for virulence. One ratite-origin isolate of low pathogenicity, A/emu/TX/39924/93 (H5N2), was subjected to a procedure that rapidly selects and/or amplifies highly pathogenic (HP) strains. The resulting highly virulent derivative had an altered hemagglutinin (HA) gene containing an additional six nucleotides at position 970-975 in the HA1 coding region. This resulted in an arg-lys insertion near the proteolytic cleavage site of the HA protein. The remainder of the HA sequence differed by an additional seven amino acids from the parent. The HA precursor of the derivative, but not the parent, was readily cleaved during replication in cell culture without addition of trypsin. In experimentally infected chickens, the derivative produced lesions typical of highly pathogenic avian influenza. A reverse transcriptase-polymerase chain reaction (RT-PCR) primer set was designed to amplify exclusively from molecules with the inserted six nucleotides. The set yielded product only from the selected derivative samples and not the parent. Thus, the levels of the HP variants in the parent stock were undetectable, or the insertion occurred rapidly during the selection process.

Morphologic characteristics of oviducts from hens producing eggs of different Haugh units caused by genetics and by feeding vanadium as determined with computer software-integrated digitizing technology

Magnum and isthmus morphologic characteristics (surface epithelium height, fold height and diameter, and periodic acid-Schiff-positive area and surface epithelium cells) of stained 6-micron tissue sections were measured by light microscopy, with data acquisition using a digitizing tablet interfaced to a microscope and to a personal computer with morphometric-dimensional software. Tissues were obtained from Leghorn layers in two separate experiments in which production of eggs with low and high Haugh unit (HU) values was induced by either genetic selection or by feeding V. Eggs produced by these hens had HU differences between the high and low groups of 11 to 14 units (both experiments, P = .0001) and had a greater volume of thick albumen fraction in high-HU groups (both experiments, P = .0001). The computer software-integrated digitizing system enabled rapid measurements of multiple characteristics. In the genetic lines, higher magnum fold height and magnum and isthmus surface epithelium height were detected at moderate significance (all at P < .05) in the tissues of the layers producing high-HU eggs than in tissues from the low-HU line. Other morphologic variables were not different between genetic lines. In response to feeding V, none of the morphological characteristics were affected, although magnum fold height approached difference at P < .07. Based on the observations in these two experiments, magnum fold height may be a further important factor related to egg albumen condition, in addition to surface epithelium height. It appears, however, that layers producing eggs of considerably different HU values, due in these experiments to genetics or V feeding, can have magnum or isthmus morphological characteristics that are indistinguishable, or only moderately different, as detected by integrated digitizing technology.

Tissue tropism and replicative properties of waterfowl-origin influenza viruses in chickens

Waterfowl-origin influenza (WFOI) viruses were evaluated for their tissue tropism and replicative properties in chickens. The 14 WFOI isolates used in this study represented 13 different hemagglutinin-neuraminidase combinations recovered during 1987 and 1988 and included isolates possessing the H5 and H7 hemagglutinin subtypes and one isolate possessing the H5N2 combination. Following intravenous challenge, the frequencies of virus recovery within individual experiments were generally higher for the lower digestive tract and kidney samples. Virus titers ranged up to 10(8.5) mean embryo infective doses per gram of kidney tissue in clinically normal chickens. Differences in frequencies of virus recovery and virus titers in tissues indicated that some of these uniformly nonpathogenic and low-pathogenicity WFOI virus isolates replicated more extensively in chickens than did others. This enhanced ability to replicate in chickens should be further evaluated as a potential factor associated with the threat WFOI viruses present to poultry.

Hypophosphatemic rickets in rheas (Rhea americana)

Rickets was diagnosed in 11 rheas from four flocks in Ohio. At necropsy, had pliable bones with prominent valgus or varus deformation of the femoral bone and/or the tibiotarsal bone, marked thickening of the metaphyseal plates, and frequent fractures. Histopathologically, bones of rachitic birds showed marked retention of cartilage core within the growth plate, mainly because of a significant lengthening of the hypertrophied zone of the growth plate in relationship to the remaining zones. Feed analysis showed that rachitic birds were fed diets having higher calcium/phosphorus (Ca/P) ratios (1.38-4.32) than that of the diet fed to nonrachitic birds from a different flock (0.65 Ca/P ratio). Serum analysis of blood from clinically rachitic birds from the affected flocks revealed a marked hypophosphatemia (3.0-4.7 mg/dl), mild hypocalcemia, and normal 25-(OH)-vitamin D concentrations as compared with values in nonrachitic birds, which had serum phosphorus concentrations of 8.5-8.7 mg/dl. These findings suggest that rickets in growing rheas was associated with marked hypophosphatemia and improper Ca/P ratios.

Identification of a new intestinal spirochete with pathogenicity for chickens

Two intestinal spirochete isolates obtained from chickens with diarrhea were examined by electron microscopy, biochemical tests, rRNA gene restriction pattern analysis, and multilocus enzyme electrophoresis. One isolate (strain 91-1207/C1) was pathogenicity tested in vivo in chickens. The chicken spirochetes were morphologically indistinguishable from Serpulina innocens and Serpulina hyodysenteriae and phenotypically similar to S. innocens. However, the chicken spirochetes could be distinguished from S. innocens, S. hyodysenteriae, and other swine intestinal spirochetes by rRNA gene restriction pattern analysis and multilocus enzyme electrophoresis. In pathogenicity tests in 1-day-old chicks and 14-month-old hens, chicken spirochete 91-1207/C1 produced pale-yellow, watery cecal contents and mild lymphocytic typhlitis. These findings support the conclusion that avian intestinal spirochetes can be pathogenic to commercial poultry and that the microorganisms are different from intestinal spirochetes that infect pigs.

Comparative pathology of intravenously inoculated wild duck- and turkey-origin type A influenza viruses in chickens

Five-week-old specific-pathogen-free chickens were inoculated intravenously with one of 16 low-pathogenicity type A influenza virus isolates; 14 were of wild duck origin, and two were of turkey origin. Tubulointerstitial nephritis was the most frequent specific histopathologic change. The frequency and severity of kidney lesions were independent of the virus hemagglutinin-neuraminidase subtype or titer of the challenge virus. Influenza nucleoprotein was most frequently demonstrated in the kidney and was consistently localized to necrotic proximal and/or distal renal tubule epithelium. Common nonspecific histopathologic changes were lymphoid hyperplasia of the spleen and cecal tonsils, as well as lymphocyte depletion in the cloacal bursa. Uncommon histopathologic changes, in decreasing order of frequency, were interstitial pneumonia, lymphoid follicular hyperplasia in the myocardium, and lymphocytic tracheitis. Histopathologic changes were rare or absent in the jejunum, duodenum, pancreas, and brain. The low-pathogenicity avian-origin type A influenza virus isolates were epitheliotropic in chickens, primarily nephrotropic. Such findings were dissimilar from findings with highly pathogenic avian-origin type A influenza virus isolates both in severity and in tissue distribution of histopathologic changes and influenza viral antigen.

Comparative pathology of a chicken-origin and two duck-origin influenza virus isolates in chickens: the effect of route of inoculation

Forty-nine 5-week-old chickens were inoculated by the intravenous (i.v.), intratracheal (IT), or intranasal (IN) routes with either a chicken-origin or one of two duck-origin type A influenza virus isolates. Twelve control chickens were inoculated with sterile chorioallantoic fluid. For all viruses, i.v. inoculation produced predominate lesions of renal tubule necrosis (nephrosis) and nephritis, and influenza virus nucleoprotein was localized in nuclei and cytoplasm of necrotic renal tubule epithelium. Chickens inoculated by the IT route, and to a lesser extent the IN route, had mild to severe tracheitis, bronchitis, and ventromedial pneumonia associated with secondary bronchi but lacked renal tubule necrosis and nephritis. These data indicate low-virulence avian-origin influenza viruses were nephrotropic during simulated systemic infection (i.v. inoculation) and pneumotropic during simulated local infection (IT and IN inoculation). Gross and histologic kidney lesions produced by i.v. inoculation of the chicken-origin influenza virus were similar to changes reported in outbreaks of low-virulence influenza virus in laying chickens.

Pathological studies of A/chicken/Alabama/7395/75 (H4N8) influenza virus in specific-pathogen-free laying hens

Specific-pathogen-free laying hens were inoculated with avian influenza virus (AIV) A/chicken/Alabama/7395/75 (H4N8) either intratracheally (IT) or intravenously (IV). IT inoculation produced a localized infection of the upper and lower respiratory tracts with lesions of tracheitis, bronchitis, airsacculitis, and pneumonia around the secondary bronchi. IV inoculation produced a systemic infection with major lesions of nephritis, interstitial pneumonia, salpingitis, and splenic and hepatic necrosis. In IV-inoculated hens, AIV nucleo-protein was demonstrated within renal tubule epithelium, in luminal surface and glandular oviduct epithelium, and in mononuclear cells within pulmonary blood capillaries. However, no virus was recovered from internal contents of eggs laid between days 1.5 and 5 postinfection. These data indicate that A/chicken/Alabama/7395/75 has tissue tropism and pathogenicity for the respiratory and urogenital systems of reproductively active laying hens. Site and severity of lesion development are determined by the localized or systemic nature of AIV infection.