Caudal Thoracic Air Sac Research Articles

Outcomes and Complications Associated With Caudal Thoracic and Abdominal Air Sac Cannulation in 68 Birds.

Air sac cannulation is used both as an emergency procedure in avian patients with severe upper respiratory compromise, as well as a means of routine ventilation for surgery of the head and neck. The objective of this retrospective study was to describe and quantify the complications associated with air sac cannulation in birds. Medical records were retrieved for all patients that underwent caudal thoracic or abdominal air sac cannulation at a single center between August 2004 and October 2020. Patient signalment, indication for air sac cannulation, location of air sac cannula (ASC) placement, occurrence and category of complications encountered, and survival data were recorded. Eighty-four ASCs were placed in 68 birds across 6 orders; 95.2% (80/84) of cases survived general anesthesia for initial ASC placement. The side and position of ASC placement were known in 33.3% (28/84) and 21.4% (18/84) of cases, respectively. Survival to ASC removal was known in 91.3% (73/80) of cases; 43 (58.9%) of these 73 cases survived to ASC removal. Complications were observed in 32.5% (26/80) of cases, and 11.5% (3/26) of cases died as a direct result of the complication. The most common reported ASC complication was loss of patency in 23.8% (19/80) of cases. Increased likelihoods for complications were seen in cases where exercise intolerance (P = 0.04) or abnormal respiratory sounds (P = 0.04) were reported at presentation. Increased likelihoods for survival to ASC removal were seen with intercostal placements (P = 0.049) and peri-interventional antibiotic therapy (P = 0.005). Decreased likelihood for survival to ASC removal was seen in cases where voice change was reported at presentation (P = 0.02). This study demonstrates a moderate risk of ASC complication, with a guarded overall prognosis for survival to ASC removal.

Pathological and mycological characterization of pulmonary Aspergillus fumigatus infection producing gliotoxin in a captive African grey parrot (Psittacus erithacus)

Aspergillosis, the main causative agent of which is Aspergillus fumigatus, causes mortality in all types of birds. Gliotoxin (GT), one of the multiple virulence factors of A. fumigatus, has a variety of immunosuppressive effects. The corpse of an African grey parrot (Psittacus erithacus) was sent for necropsy and diagnostic rule-out. The lungs were enlarged, firm, and had dark-red coloration, on the parietal faces of both lungs, some semi-circular caseous necrosis areas were observed. The caudal thoracic and abdominal air sacs were thickened and contained a fibrin-heterophilic exudate. Histopathologically, a necrotic and granulomatous bronchopneumonia was observed with intralesional hyphae with characteristics compatible with Aspergillus sp. that were positive with Grocott´s staining. Fibrinous and heterophilic airsacculitis was found in the air sacs. A. fumigatus was isolated from lungs, characterized using serial microcultures, and confirmed using polymerase chain reaction. In addition, GT production was detected in vitro from the culture filtrate in which the isolate was grown; the organic extract was analysed via thin-layer chromatography. This is the first detection of GT in a case of pulmonary aspergillosis in a parrot, which could help to understand the pathogenesis of the disease in psittacines.

Use of an Endoloop Ligature and a 2-Portal Coelioscopic Approach for the Removal of an Arrowhead Foreign Body in a Red-Tailed Hawk (Buteo jamaicensis).

A juvenile red-tailed hawk (Buteo jamaicensis) was presented to the Ontario Veterinary College from a wildlife rehabilitation facility for the assessment of an arrowhead foreign body injury. The hawk was found on the ground with the left wing in a dropped position. Radiographic images revealed an arrowhead foreign body superimposed over the left lung and thoracic air sacs, immediately medial to the ribs on the ventrodorsal view, and ventral to the scapulae on the right latero-lateral view. A coelioscopy was performed using a left lateral approach with a 2.7-mm rigid endoscope into the left caudal thoracic air sac, with an additional instrument port through the left abdominal air sac. The arrowhead was visualized adjacent to the left lung, separated from the cranial thoracic air sac cavity by a membrane of fibrous tissue. The tissue membrane was radiosurgically incised. Forceps were then used to guide an Endoloop around the arrowhead. The arrowhead was secured by tightening the Endoloop, and the body wall incision was extended to facilitate the arrowhead extraction.

Gross morphological features of the air sacs of the hooded crow (Corvus cornix).

Air sacs are considered to be one of the controlling factors of bird behaviour and habits in addition to their roles in ventilation, regulating body temperature, swimming and flight. As a scavenger and an omnivorous flight bird, air sacs of the hooded crow were the focus of this study. Eight healthy, adult hooded crows were used to examine the morphological characteristics of the air sacs, which were examined grossly and with latex and cast preparations. In general, the morphological overview of the hooded crow air sacs is similar to other avian species. We observed nine air sacs; four paired sacs (cervical, cranial thoracic, caudal thoracic and abdominal air sacs) and one unpaired sac; the clavicular air sac. The cervical air sac communicated to the lung through the medioventral bronchus and had three diverticula; intermuscular, subscapular and subcutaneous. The clavicular air sac communicated with lung through the medioventral bronchus and had subscapular, axillary, humeral, subpectoral and sternal diverticula. The cranial and caudal thoracic air sacs were communicated with lung through the lateroventral bronchi and the both sacs did not have any diverticula. The abdominal air sacs were posterior to the caudal thoracic air sacs. The left abdominal sac was the largest air sac. The right and left abdominal sacs gave off branches to diverticula that pneumatized synsacrum. The abdominal air sacs gave off femoral diverticula behind the hip joint as well as perirenal diverticula.

RELAÇÕES TOPOGRÁFICAS DOS SACOS AÉREOS DE CODORNAS (Coturnix coturnix)

Resumo A morfologia das aves é pouco relatada, o que dificulta a prática veterinária nestes animais. O seu sistema respiratório é diferenciado pela presença dos sacos aéreos, estrutura de fundamental importância para as aves, porém muito susceptível a doenças. Dessa forma, objetivou-se descrever a anatomia dos sacos aéreos (SA) em codornas em relação às suas relações topográficas. Para tanto, foram dissecadas quinze codornas que tiveram seu trato respiratório injetado com Neoprene látex corado e fixadas em solução de formol a 10%. O SA cervical é ímpar e possui uma porção mediana localizada entre as artérias braquiocefálicas. O SA clavicular também é ímpar e inicia-se próximo às primeiras vértebras torácicas. Os SA torácicos cranial e caudal estão lateralmente ao pulmão e medialmente às costelas. O SA torácico cranial dispõe-se da margem dorso-látero-cranial até a margem ventral do fígado e o SA torácico caudal, do quarto látero-caudal do fígado até o terço cranial do SA abdominal. O SA abdominal vai da base caudal do fígado até a região cloacal. Contudo, os sacos aéreos das codornas estudadas nesta pesquisa seguem um padrão topográfico, formando divertículos entre os órgãos adjacentes.

COMPUTED TOMOGRAPHIC ANATOMY AND CHARACTERISTICS OF RESPIRATORY ASPERGILLOSIS IN JUVENILE WHOOPING CRANES.

Respiratory diseases are a leading cause of morbidity and mortality in captivity reared, endangered whooping cranes (Grus americana). Objectives of this retrospective, case series, cross‐sectional study were to describe computed tomography (CT) respiratory anatomy in a juvenile whooping crane without respiratory disease, compare CT characteristics with gross pathologic characteristics in a group of juvenile whooping cranes with respiratory aspergillosis, and test associations between the number of CT tracheal bends and bird sex and age. A total of 10 juvenile whooping cranes (one control, nine affected) were included. Seven affected cranes had CT characteristics of unilateral extrapulmonary bronchial occlusion or wall thickening, and seven cranes had luminal occlusion of the intrapulmonary primary or secondary bronchi. Air sac membrane thickening was observed in three cranes in the cranial and caudal thoracic air sacs, and air sac diverticulum opacification was observed in four cranes. Necropsy lesions consisted of severe, subacute to chronic, focally extensive granulomatous pathology of the trachea, primary bronchi, lungs, or air sacs. No false positive CT scan results were documented. Seven instances of false negative CT scan results occurred; six of these consisted of subtle, mild air sacculitis including membrane opacification or thickening, or the presence of small plaques found at necropsy. The number of CT tracheal bends was associated with bird age but not sex. Findings supported the use of CT as a diagnostic test for avian species with respiratory disease and tracheal coiling or elongated tracheae where endoscopic evaluation is impractical.

Air Sac Nematode Monopetalonema alcedinis in a Belted Kingfisher (Megaceryle alcyon) in Maryland, USA

Sporadic and geographically widespread reports of parasites affecting the Belted Kingfisher (Megaceryle alcyon) have been published but few have described details of the pathology. A female, adult kingfisher was found dead in a heavily wooded area of a zoo in Maryland, USA. At necropsy, numerous sexually dimorphic, 4.4-40.5-cm adult Monopetalonema alcedinis nematodes were found tightly wound within the coelomic cavity between organs and completely filling the caudal thoracic and abdominal air sacs. Abundant, 30-60-µm diameter, larvated, thick-walled ova were found in the bronchi and parabronchi, within the mesentery, and in the serosa of multiple coelomic organs. Monopetalonema alcedinis is a characteristic member of the superfamily Diplotriaenoidea, a group of nematodes occurring in birds and reptiles. Infective larvae within an invertebrate intermediate host are ingested and penetrate the intestine, traveling to the lungs and then into the air sacs, where the adult females release eggs. The ova are coughed up by the avian host and passed in feces. Specimens of M. alcedinis have been found in the Belted Kingfisher, although typically intensity of infection is low and infections remain asymptomatic. In contrast, we report the second documented case of high numbers of M. alcedinis resulting in pathologic changes in which parasitism contributed to host mortality.

Diagnosis and treatment of proventricular nematodiasis in an umbrella cockatoo (Cacatua alba)

A 16-year-old female umbrella cockatoo (Cacatua alba) was referred to the University of Georgia College of Veterinary Medicine for evaluation of a 3-year seasonal history of lethargy and weight fluctuation. Abnormalities detected via clinicopathologic analyses included mild leukocytosis, heterophilia, and lymphopenia consistent with a stress leukogram. Previous fecal examinations failed to diagnose enteric parasite infestation. Results of a fecal flotation test with Sheather sugar solution revealed spirurid eggs (Spiruroidea). Coelomic radiography revealed a widened cardiohepatic waist with increased soft tissue opacity at the level of the hepatic silhouette. The caudal thoracic and abdominal air sacs bilaterally appeared compressed against the coleomic wall. The proventriculus was increased in diameter, with a proventriculus-to-keel ratio of 1.0. Coelomic ultrasonography and positive-contrast upper gastrointestinal radiography revealed severe thickening and irregularity of the proventricular wall. The animal was anesthetized for an endoscopic examination of the upper gastrointestinal tract. Intralesional nematodes were identified on histologic examination of biopsy specimens from the proventriculus. Effective fenbendazole treatment (15 mg/kg [6.8 mg/lb], PO, alternating between 5 days of treatment and 5 days of no treatment, which continued for 4 periods) was confirmed by repeated endoscopy and fecal examinations. The bird remained free of clinical signs 27 months after diagnosis and treatment. Antemortem diagnosis of proventricular nematodiasis has not been reported in psittacines. Spirurid nematode eggs are shed intermittently, which may lead to false-negative results on a single routine fecal examination. In this patient, radiography, endoscopy, and histologic evaluation facilitated antemortem diagnosis. This is the first report of successful treatment of this condition in psittacines.

Study of Nebulization Delivery of Aerosolized Fluorescent Microspheres to the Avian Respiratory Tract

This study investigated the delivery of an aerosol of monodisperse microspheres to the respiratory tract of birds following aerosol exposure. Adult domestic pigeons (Columbia livia domestica, n = 5 birds per timed treatment) were exposed to an aerosol of fluorescent 1.0 microm diameter carboxylate microspheres for 0.5, 1, 2, or 4 hr. During the aerosolization period, the birds were free-standing in a plexiglass treatment chamber and the aerosol was delivered using a commercial nebulizer. Immediately following aerosol exposure, the birds were euthanatized and the carcasses were intravenously infused with a modified paraformaldehyde/gluteraldehyde fixative. Evaluation of microsphere distribution was performed using a stereoscopic microscope with an epifluorescent module. The results from this study revealed that the amount of aerosolized particles delivered using a commercial nebulizer was proportional to exposure periods. Aerosol exposure periods of 0.5 hr or 1 hr did not result in a readily observable distribution of 1.0 microm fluorescent microspheres to the cranial thoracic, caudal thoracic, or abdominal air sac membranes. This was partly attributed to the relatively low concentration of the individual monodisperse microspheres in the aerosolized suspension. The 2- and 4-hr exposure periods resulted in readily observable deposition of the 1.0 mirom fluorescent microspheres in the cranial thoracic, caudal thoracic, or abdominal air sac membranes, with the 4-hr exposure period resulting in the greatest number of particles on the membrane surfaces. For each of the exposure periods, there was individual animal variation regarding the distribution and relative number of spheres deposited. This study demonstrates the widespread deposition of particles that had an aerodynamic equivalent diameter of approximately 1 microm and provides a better understanding of particle deposition efficiency within the respiratory system following aerosol exposure in birds.

Pulmonary Carcinoma in a Great Horned Owl (Bubo virginianus)

Pulmonary carcinoma was diagnosed in an 18+-year-old captive female great horned owl (Bubo virginianus). The owl presented with a history of progressive weakness and sudden onset of frank blood in the droppings. On physical examination, the owl had multiple white to yellow plaques in the oral cavity, decreased air sac sounds on the right side, dyspnea (during manual restraint), and reduced pectoral musculature. Whole-body radiographs revealed obliteration of the right-sided air sacs, a soft tissue plaque/density in the left caudal thoracic air sac, soft tissue opacity over the coelomic organs, and increased medullary opacity in the distal right humerus. The owl died during anesthetic recovery, and the body was submitted for necropsy. Although the clinical signs, physical examination results, radiographic signs, and gross pathology supported a diagnosis of mycotic infection, such as aspergillosis, histopathology confirmed pulmonary carcinoma with metastases to the air sacs and humerus.

Cardiopulmonary effects of controlled versus spontaneous ventilation in pigeons anesthetized for coelioscopy

To evaluate the cardiorespiratory effects of controlled versus spontaneous ventilation in pigeons anesthetized for coelioscopy. Prospective study. 30 healthy adult pigeons (Columbia livia). During isoflurane anesthesia, 15 pigeons were allowed to breathe spontaneously (SP group) and 15 were mechanically ventilated (MV group) by use of a pressure-limited ventilator. In each group, cardiopulmonary variables (including end-tidal CO2 concentration [ETCO2]) were measured before (baseline), during, and after coelioscopy. An arterial blood sample was collected for blood gas analyses from each pigeon before coelioscopy and after the procedure, when the caudal thoracic air sac was still open. At baseline, hypoventilation was greater in the SP group than the MV group. Compared with the SP group values, ETCO2 overestimated PaCO2 to a greater degree in the MV group. Cardiovascular variables were not different between groups. After coelioscopy (when the air sac was open), PaCO2 had decreased significantly from baseline in the MV group. In the SP group, hypoventilation worsened despite an increase in respiratory rate. After coelioscopy, PaO2 in the SP group had decreased from baseline and was lower than PaO2 in the MV group; arterial blood pressure and heart rate in the MV group had decreased from baseline and were lower than values in the SP group. In adult pigeons, controlled ventilation delivered by a pressure-limited device was not associated with clinically important adverse cardiopulmonary changes but may be associated with respiratory alkalosis and cardiovascular depression when air sac integrity has been disrupted.

Air Sac Functional Anatomy of the Sulphur-crested Cockatoo (Cacatua galerita) During Isoflurane Anesthesia

The air sac functional anatomy of sulphur-crested cockatoos (Cacatua galerita) during isoflurane anesthesia was studied by evaluation of respiratory casts of sulphur-crested cockatoos, blood gas analysis, and air sac gas analyses. The air sac anatomy of the sulphur-crested cockatoo was different from that described previously in nonpsittacine bird species, with more extensive cranial and caudal thoracic air sacs and smaller abdominal air sacs. Blood gas analysis results indicated arterial and venous hyperoxia as a result of using 100% O2 as the anesthetic carrier gas, the significance of which in birds is currently unclear. Cranial and caudal thoracic air sac oxygen and carbon dioxide partial pressures (Po2 and Pco2, respectively) were similar to those previously described in birds ventilated with 100% O2. Clavicular air sac Po2 and Pco2 were significantly lower than the cranial thoracic air sac, indicating significantly less ventilation of the clavicular air sac than of either the cranial or caudal air sacs.

Comparison of Endotracheal, Caudal Thoracic Air Sac, and Clavicular Air Sac Administration of Isoflurane in Sulphur-Crested Cockatoos (Cacatua galerita)

Ten sulphur-crested cockatoos (Cacatua galerita) were anesthetized twice, 2 weeks apart, to evaluate the effects on respiratory function of endotracheal (ET), caudal thoracic (CT) air sac, and clavicular air sac administration of isoflurane anesthesia. Four administration methods were evaluated by administering anesthetic gases through either the ET tube or the air sac as an open or closed system. Respiratory function was monitored by arterial and venous blood gas determination, gas-in-gas determination of both ET tube and air sac gases, and spirometry. Both ET tube and CT air sac administration provided a reliable method of maintaining anesthesia and resulted in minimal alteration in respiratory function. Blood pH, partial pressure of carbon dioxide (Pco2), bicarbonate, total carbon dioxide, and base excess were not significantly altered by CT air sac administration. Increased partial pressure of oxygen and oxygen saturation were evidence of hyperoxia. CT air sac Pco2 decreased to 12.7 ± 7.9 mm Hg with CT administration, and this was sufficient to maintain spontaneous respiratory movements. Spirometry demonstrated maintenance of tidal and minute volumes with each administration method despite apparent reduction in visible respiratory movements. Clavicular air sac administration was not successful in providing ventilation or maintaining anesthesia. Despite the demonstrated ability to flush a bolus of gas through this air sac and out the ET tube, no spontaneous ventilation was detected in this air sac in either an open or closed system, preventing delivery of sufficient isoflurane to maintain anesthesia.

Increased Tracheal Colonization in Chickens without Impairing Pathogenic Properties of Avian Pathogenic Escherichia coli MT78 with a fimH Deletion

Several studies suggest that the expression of F1 fimbriae could be involved in the virulence of Escherichia coli for chickens. F1 fimbriae display multivalent properties such as adhesion to epithelia or interaction with the immune system that imply specific interactions between the adhesin FimH and different cell receptors. We constructed a delta fimH mutant of the avian pathogenic E. coli MT78 and evaluated its in vivo colonization and pathogenicity, as compared to that of the parent strain. The generated mutant PA68 was unable to adhere in vitro to chicken epithelial pharyngeal or tracheal cells; mutant bacteria were mostly afimbriated although a minority of them displayed altered piliation phenotypes. Two inoculation routes were used to compare the ability of MT78 and PA68 to colonize the respiratory tract and to induce colibacillosis in chickens. In the first model, 2-wk-old axenic chickens were inoculated intratracheally with one or both E. coli strains, after primary infection with infectious bronchitis virus. In the second model, 3-wk-old specific-pathogen-free chickens were inoculated via the caudal thoracic air sac. After intratracheal inoculation, the delta fimH mutant was found to be a better colonizer than MT78 in the trachea of inoculated chickens. Furthermore, when both strains were inoculated simultaneously, the delta fimH mutant constituted 98% of the bacterial population in the trachea at day 7 postinoculation. Irrespective to the inoculation route, MT78 and PA68 showed similar abilities to induce macroscopic lesions in chickens, to provoke bacteremia, and to colonize the internal organs. However, 4 days after intra-air sac inoculation, bacterial counts of the mutant were lower in the spleen and liver than those of MT78. Our results show that FimH is not required for colonization of the trachea of axenic chickens by E. coli and that it is not a major determinant of bacterial pathogenicity. On the contrary, the lack of expression of FimH seems to favor the in vivo colonization of the trachea of chickens by E. coli.

Endoscopic Gross Anatomy Findings of the Thoracic Air Sac of the Turkey

The gross anatomy of the cranial thoracic air sacs was studied in the live turkey with a fiber-optic endoscope fitted with a video system. Thirty-five out of 39 (89.7%) of the turkeys had paired single thoracic air sacs with two ostia. The other 10.3% of the turkeys had paired cranial and caudal thoracic air sacs, each with a single ostium. The air flow pattern through the common thoracic air sac with two ostia is unknown. Furthermore, 42.3% of the turkeys with a single thoracic air sac had an invagination arising from the floor of the air sac that partially divided the single thoracic air sac creating a blind-ended sac. The blind sac formed by the invagination may trap small inhaled particulate matter.

Virulence mechanisms of avian fimbriated Escherichia coli in experimentally inoculated chickens

Virulence mechanisms of avian pathogenic Escherichia coli were investigated by inoculating commercial broiler chickens via the left caudal thoracic air sac with three highly pathogenic and three less pathogenic E. coli isolates. At 6 h postinoculation, all isolates had colonized the respiratory tract (trachea, lungs, and air sacs) and internal organs (liver, spleen, and kidney) of inoculated birds, but bacteria were recovered from pericardial fluid and blood only of birds inoculated with the more pathogenic isolates. F1 fimbriae were expressed on a high proportion of bacteria colonizing the trachea and to a lesser extent on bacteria in the lungs of birds inoculated with each of the isolates. F1 fimbriae were also expressed on bacteria in air sacs only for the less pathogenic isolates. P(F11) fimbriae were expressed on bacteria present in air sacs, lungs, kidney, blood, and pericardial fluid of birds inoculated with one of the more virulent isolates. On electron microscopy, bacteria of the more pathogenic isolates but not of the less pathogenic isolates were observed often associated with or within macrophages, which appeared to be viable, in the air sacs and lungs. In in vitro assays, the more pathogenic but not the less pathogenic isolates, were resistant to opsonization and phagocytosis in the absence of F1 fimbriae, whereas bacteria of all isolates were rapidly killed by avian macrophages when they expressed F1 fimbriae. These results suggest that resistance to phagocytosis may be an important mechanism in avian colisepticemia. They also suggest that F1 fimbrial phase variation to the nonfimbriated phase is favored in the avian lower respiratory tract, is more marked for the more pathogenic isolates, and may be a virulence mechanism.

Localization of the in vivoexpression of P and F1 fimbriae in chickens experimentally inoculated with pathogenic Escherichia coli

Escherichia colicausing septicemia in poultry often possess F1 (type 1) and/or P fimbriae which may be involved in bacterial colonization and infection. To investigate the expression of these fimbriae in vivo, two pathogenic E. colistrains with different fimbrial profiles, TK3 ( fim + / pap + ) and MT78 ( fim + / pap − ), were administered to 2-week-old chickens by either the intratracheal or caudal thoracic air sac inoculation route. Antibodies specific for native F1 fimbriae were detected by ELISA and immunodot in the serum of chickens inoculated with either strain MT78 or strain TK3, irrespective of the route of inoculation. Antibodies specific for P fimbriae of serotype F11 were detected by ELISA and immunoblotting in the serum of chickens inoculated by either route with strain TK3. F1, but not P fimbriae, were expressed by bacteria colonizing the trachea of chickens inoculated by the air sac route with strain MT78 or TK3, as demonstrated by examination of frozen tissue sections using immunofluorescence. F1 fimbriae were also expressed by bacteria colonizing the air sacs and lungs, but not by bacteria in the blood or other internal organs, of chickens inoculated with either strain. P fimbriae were expressed by bacteria colonizing the air sacs, lungs, kidney, blood, and pericardial fluid, but not by bacteria colonizing the trachea, of chickens inoculated with strain TK3. Fimbriae-like structures were observed by electron microscopy on bacteria adhering to the epithelial cells of the air sacs of chickens inoculated with strain TK3. These results demonstrate that both strains MT78 and TK3 undergo in vivophase variation with respect to their fimbrial profiles and site of bacterial colonization in different organs of infected chickens and suggest that F1 fimbriae are important for initial bacterial colonization of the upper respiratory tract whereas P fimbriae are important for later stages of the infection.

Dynamics of Escherichia coli Infection in Experimentally Inoculated Chickens

In order to study the dynamics of avian colibacillosis, commercial broiler chickens were inoculated with a pathogenic Escherichia coli strain (01:K1:H7) into the left caudal thoracic air sac. Chickens were euthanatized at different times from 3 to 48 hr postinoculation and examined for bacterial counts and macroscopic and microscopic lesions. The E. coli strain colonized the air sacs, lungs, and trachea and was recovered from blood and all tested extrarespiratory organs of inoculated birds. A gradual increase in bacterial counts in the trachea, lungs, air sacs, and liver was observed from 3 to 12 hr. Clinical signs and macroscopic lesions of colibacillosis were observed in all inoculated birds. Moderate to severe lesions of airsacculitis, pericarditis, perihepatitis, and splenic hypertrophy were observed. Microscopically, inflammatory cell infiltration, serious to fibrinous exudate, and cellular debris on serosal surfaces were present in the liver, spleen, and air sacs. In air sacs, heterophils were present in low numbers perivascularly 3 hr after inoculation and became more numerous by 24 hr postinoculation. Ultrastructurally, epithelial cells in the air sacs and in air capillary regions of the lung were swollen and vacuolated beginning at 3 hr postinoculation. Bacteria were adherent to and present within the epithelial cells at 3 hr postinoculation and were also seen in phagocytic cells and, rarely, in the connective tissue of these organs at 24 hr postinoculation. These results indicate that both air sacs and lungs can be the portal of entry for E. coli into the systemic circulation, probably via damaged epithelium.

Pathogenesis of pancreatic atrophy by avian influenza a virus infection

Specific-pathogen-free (SPF), 2-day-old chicks were inoculated with type A influenza virus (A/whistling swan/Shimane/499/83/(H5N3)) into their caudal thoracic air sac. The original isolate of the virus was of low virulence (ICPI 0. 20 to 0.40), and was passaged 10 times through the respiratory organs of SPF chicks. Most of the chicks inoculated with the passaged virus (strain 499) showed respiratory and alimentary signs. Three of 30 chicks died on days 2, 6 and 7 post-inoculation (p.i.). Almost half of the infected chicks showed poor growth, and the variation of body size in the flock became prominent from day 10 p.i. Infected chicks consistently had pathological changes in the pancreas, liver, kidneys and respiratory tracts, and occasionally in the brain, duodenum and bone marrow. Positive immunoreaction to avian influenza virus (AIV) antigen and recovery of the virus persisted for longer period in the pancreas than in other organs. The pancreatic lesions were caused by a direct, lytic virus infection of the acinar cells and contributed to poor growth of the chicks.

The Avian Lung: Is There an Aerodynamic Expiratory Valve?

The unidirectional gas-flow pattern through the avian lung is thought to result from 'aerodynamic valves'; support for this hypothesis lies mainly in the failure to find any evidence for anatomical valves. During expiration, air flows from the caudal air sacs through the major exchange area of the lung, the paleopulmonic parabronchi, instead of bypassing the lungs via the intrapulmonary bronchus. We tested whether the effectiveness of this expiratory flow control mechanism depends on aerodynamic factors, especially convective inertial forces that depend on gas density and flow velocity. In pump-ventilated, anaesthetized geese, a bolus of tracer gas was introduced into both the right and left caudal thoracic air sacs during an end-inspiratory pause. During the first expiration, the rise of tracer levels within the caudal trachea was measured. Valve efficacy was positively correlated with the rate of expiratory gas flow, V·ao (range 8­200 ml s-1). At flows assumed to occur during exercise in geese (V·ao>100 ml s-1), the expiratory valve efficacy was approximately 95 %; it was less effective at lower flows. Surprisingly, the density (rho) of the background gas (rho of He/O2=0.43 g l-1, Ar/O2=1.72 g l-1 or SF6/O2=5.50 g l-1) had no effect on expiratory valving. We suggest two possible mechanisms that might explain this unusual combination of flow dependence without density dependence. (1) If airway geometry changes occurred between experiments with different gases, flow in the vicinity of the expiratory valve may have varied independently from flow measured at the airway opening. (2) Alternatively, valving may depend on dynamic compression of the intrapulmonary bronchus, which could depend mainly on viscous resistance and thus on flow velocity but not gas density.