Assessing avian leukosis virus proviral load and lesion correlates in fowl glioma-inducing virus-infected Japanese bantam chickens.

The fowl glioma-inducing virus prototype (FGVp) and its variants, which belong to avian leukosis virus subgroup A (ALV-A), induce cardiomyocyte abnormalities and gliomas in chickens. However, the molecular mechanisms underlying these myocardial changes remain unclear, and ALV-induced tumorigenesis, which is caused by proviral insertional mutagenesis, does not explain the early development of cardiac changes in infected chickens. We established a quantitative PCR (qPCR) assay to measure ALV-A proviral loads in the brains and hearts of FGV-infected Japanese bantam chickens and compared these results with morphologic lesions. Four of 22 bantams had both gliomas and cardiac lesions. Hearts with cardiac lesions had a higher proviral load (10.3 ± 2.7 proviral copies/nucleus) than those without cardiac lesions (0.4 ± 0.4), suggesting that the proviral load in hearts is correlated with the frequency of myocardial changes. Our qPCR method may be useful in the study of ALV-induced cardiomyocyte abnormalities.

Avian retroviral cardiomyopathy induced by infectious molecular clones of avian leukosis viruses (fowl glioma-inducing virus variants).

We previously described cardiomyocyte abnormality caused by Km_5666 strain, a variant of fowl glioma-inducing virus (FGV) prototype, which is an avian leukosis virus (ALV). However, the cardiac involvement appeared to be eradicated from the flock after a few years. An epidemiological survey from 2017 to 2020 was performed to elucidate the current prevalence of the cardiopathogenic strains in this flock. Four of the 71 bantams pathologically examined showed both glioma and cardiomyocyte abnormality, from which three ALV strains were detected. DNA sequencing revealed that several different ALV strains coexisted in each bantam and that the conserved Km_5666 virus fluid also contained at least two different ALV strains. We generated three infectious molecular clones from these samples, named KmN_77_clone_A, KmN_77_clone_B, and Km_5666_clone. The envSU of KmN_77_clone_A shared high sequence identity with that of Km_5666 (94.1%). In contrast, the envSU of KmN_77_clone_B showed >99.2% nucleotide similarity with that of an FGV variant without cardiopathogenicity. Furthermore, Km_5666_clone experimentally reproduced both gliomas and cardiomyocyte abnormality in chickens. From these results, it is suggested that the pathogenic determinant of cardiomyocyte abnormality is located in envSU similar to that of Km_5666. The cloning technique described here is beneficial for evaluating the viral pathogenicity in cases where affected birds are coinfected with several different ALV strains.

Clinically Manifesting, Naturally Occurring Fowl Glioma in a Leghorn Chicken in Germany.

Fowl glioma-inducing virus (FGV), a strain of avian leukosis virus (ALV) subgroup A, is the causal agent of fowl glioma characterized by multiple nodular astrocytic growths, gliosis, and lymphocytic encephalitis. Also associated with FGV infection are cases of cerebellar hypoplasia, perineuromas, and nonsuppurative myocarditis. Though fowl glioma has been recognized in several countries, most reports of FGV infection come from Japan. A 9-mo-old brown leghorn from a German farm with nine leghorns was presented to a veterinarian with an impaired general health with torticollis, tremor, and incoordination. Histopathology revealed multifocal nodular astrocytic growths, gliosis, and a lymphoplasmacytic encephalitis. Immunohistochemically, neoplastic astrocytes showed positivity for anti-ALV antibody. FGV was detected in the brain with nested reverse transcription-polymerase chain reaction (RT-PCR) and subsequent sequencing of PCR product. The remaining eight birds were screened for the presence of ALV with real-time RT-PCR. Four leghorns tested positive for exogenous ALV in nested RT-PCR with an identical nucleotide sequence as the leghorn with neurological symptoms. To the authors' knowledge this is the first report of a natural FGV infection in a brown leghorn in Germany with clinical manifestation.

Glioma aviar de manifestación clínica y natural en un pollo Leghorn en Alemania. El virus inductor del glioma del pollo (FGV), una cepa del subgrupo A del virus de la leucosis aviar (ALV), es el agente causal del glioma del pollo caracterizado por crecimientos astrocíticos nodulares múltiples, gliosis y encefalitis linfocítica. También se asocian con la infección por este virus, casos de hipoplasia cerebelar, perineuromas y miocarditis no supurativa. Aunque el glioma aviar se ha reconocido en varios países, la mayoría de los informes de infección por el virus inductor del glioma del pollo provienen de Japón. Un pollo Leghorn marrón de nueve meses de edad proveniente de una granja alemana con nueve aves Leghorns fue remitido a una clínica veterinaria con problemas de salud en general, tortícolis, temblores y falta de coordinación. La histopatología reveló crecimientos astrocíticos nodulares multifocales, gliosis y encefalitis linfoplasmocítica. Inmunohistoquímicamente, los astrocitos neoplásicos mostraron reacción positiva para anticuerpos contra el virus de la leucosis aviar. El virus inductor del glioma del pollo se detectó en el cerebro mediante transcripción reversa y reacción en cadena de la polimerasa anidada (RT-PCR) y con secuenciación posterior del producto de PCR. Las ocho aves restantes se examinaron para detectar la presencia del virus de la leucosis aviar mediante RT-PCR en tiempo real. Cuatro aves Leghorn dieron positivo para virus exógenos de leucosis mediante RT-PCR anidada y con una secuencia de nucleótidos idéntica a la del ave Leghorn con síntomas neurológicos. De acuerdo con el conocimiento de los autores, este es el primer informe de una infección natural por el virus inductor del glioma del pollo en un ave Leghorn marrón en Alemania que presentaba manifestaciones clínicas.

Calving-related intradural avulsion injuries of the thoracolumbar spinal nerve roots in a calf.

Calving difficulty may lead to traumatic peripheral nerve injury. A male, 8-mo-old, Japanese Black calf with a history of secondary dystocia as a result of fetal gigantism had lameness and gait disturbance. At autopsy, multifocal dural thickening with adhesions to the adjacent spinal cord was observed at T12-13 and L4-5 vertebral levels. Microscopically, numerous traumatic neuroma-like fascicles of nerve twigs were embedded in the dura mater with abundant collagenous connective tissue. By immunohistochemistry, axons and Schwann cells were confirmed in each nerve fascicle. Our observations suggest that avulsion injuries in the preganglionic fibers of the spinal nerve roots, and secondary spinal cord compression, resulted in the development of neurologic signs.

Multilobular tumor of bone on the forehead of a guinea pig.

Multilobular tumor of bone (MLTB) is an infrequent, slow-growing, bone neoplasm formed predominantly on the head. These tumors can behave as malignant neoplasms clinically and pathologically and can metastasize occasionally. No cases of MLTB in rodents have been reported, to our knowledge. We describe a novel case of an MLTB in a guinea pig. An adult guinea pig had an exophytic mass fixed on the frontal bone, maxilla, and nasal bone. On radiography, the mass had a spherical contour and variable density and was formed on the surface of the cranial bones. The mass was excised surgically. The cut surface was light-yellow to milky-white and had a granular texture with fine fibrous septa. Histologically, the neoplasm had a multilobular pattern, which consisted of many islands of bone and/or cartilage matrix surrounded by small cells and separated by fibrous septa, which closely resembles the equivalent neoplasm in dogs.

Neuropathogenicity of newly isolated avian leukosis viruses from chickens with osteopetrosis and mesenchymal neoplasms.

ABSTRACT The prototype fowl glioma-inducing virus (FGVp) causes fowl glioma and cerebellar hypoplasia in chickens. In this study, we investigated whether a strain of avian leukosis virus (ALV), associated with avian osteopetrosis and mesenchymal neoplasms, is able to induce fowl glioma. We encountered avian osteopetrosis and mesenchymal neoplasms, including myxosarcoma and rhabdomyosarcoma, in Japanese native chickens used for both egg-laying and meat production. These birds were also affected by non-suppurative encephalitis and glioma in their brains. Four ALV strains (GifN_001, GifN_002, GifN_004, GifN_005) were isolated, and a phylogenic analysis of envSU showed that these isolates were classified into different clusters from FGVp and the variants previously reported. Whereas the envSU shared a high identity (94.7%) with that of Rous sarcoma virus (strain Schmidt-Ruppin B) (RSV-SRB), the identity between envTM of GifN_001 and that of FGVp was high (94.5%), indicating that GifN_strains may emerge by recombination between FGVp and other exogenous ALVs. Specific-pathogen-free chickens inoculated in ovo with GifN_001 revealed fowl glioma and cerebellar hypoplasia. These results suggest that the newly isolated strains have acquired neuropathogenicity to chickens.

Pathological characteristics of thyroid glands from Japanese Black Cattle living in the restricted area of the Fukushima Daiichi Nuclear Power Plant accident.

To study the effect of ionizing radiation on thyroid glands, 66 Japanese Black cattle residing in the restricted area of the Fukushima Daiichi Nuclear Power Plant in 2013-2017 were pathologically examined. There were no clinical symptoms of thyroid disease in these cattle. Three cases of goiter and seven of atrophy were found in two among the four farms examined. Cases of goiter exhibited normal morphological structure without mass or nodule formation in thyroid glands. Cellular atypia or capsular invasion of the follicular epithelium was absent. The estimated integrated dose of external radiation in goiter cases ranged from maximum 797 mSv to minimum 24 mSv. All lobules in the seven atrophic thyroid glands were affected, but pathological findings, such as inflammatory cell infiltration or stromal fibrosis, were not observed. The estimated integrated dose of external radiation in atrophic thyroids ranged from maximum 589 mSv to minimum 8 mSv. Immunohistochemical analysis of anti-nitroguanosine and the TUNEL method in goiter and atrophic thyroid glands did not reveal any positive findings. The present study indicates that there was no significant relationship between a radiation effect and pathological findings in any thyroid glands.

Yersinia infection in two captive guereza colobus monkeys (Colobus guereza).

Two guereza colobus monkeys (Colobus guereza) reared in a zoological garden in Japan suddenly died of multifocal fibrinonecrotic gastroenteritis and septicemia associated with infection by Yersinia spp. It was necessary to microbiologically differentiate Yersinia frederiksenii and Y. enterocolitica. We described the pathological findings and discuss the causal agent to emphasize the need to revert to using a combination of multiple examinations for diagnosis.

Extralobar pulmonary sequestration in two pinniped species.

Two cases of extralobar pulmonary sequestrations from a walrus (Odobenus rosmarus) and a Steller sea lion (Eumetopias jubatus) are described in the present study. Grossly, an independent, soft unilocular cystic mass was found within the abdominal cavities of both animals, adherent to the diaphragm in O. rosmarus and attached to the cardia of the stomach in E. jubatus. Histopathologically, the cysts were lined by pseudostratified ciliated columnar epithelium with abundant goblet cells, while the wall comprised of glands, hyaline cartilage, bronchiole- and alveolus-like structures, smooth muscles, and large, well-developed elastic and muscular arteries. The pinniped cases presented are exceptionally rare and to the best of the authors' knowledge, marks the first descriptions of this congenital anomaly in wildlife.

Pathological findings of Japanese Black Cattle living in the restricted area of the Fukushima Daiichi Nuclear Power Plant accident, 2013-2016.

Fifty-one Japanese black cattle from four farms in the evacuation zone of the Fukushima nuclear accident were examined pathologically during the period, 2013-2016. We found no evidence of a radiation effect on pathological findings in any of these autopsy cases, although nine cases (3.7%) of enzootic bovine leukosis (EBL) and three cases (1.2%) of goiter were diagnosed. Estimated integrating dose of external exposure in EBL cases ranged from a maximum of 1200 mSv to a minimum of 72 mSv. Clinically, five cases showed wobble, dysstasia or paralysis. Exophthalmos was observed in three cases. Macroscopically, enlarged lymph nodes, multiple irregular masses of intra-abdominal and intrapelvic adipose tissue, diffuse thickening of the abomasal submucosa with ulceration, and numerous white nodules of myocardium were observed. Histologically, neoplastic lymphoid cells were extensively proliferated and infiltrated in the lesions. Lymphoid tumor cells showed mature or large lymphoblastic appearance. Immunohistochemically, tumor cells were positive for BLA-36, CD20 and CD5, and negative for CD3. Three cases showed diffuse enlargement of the thyroid gland with no mass or nodule lesion. Histologically, diffuse proliferation of follicular epithelium was observed with preservation of normal structures. There were no malignant findings such as cellular atypia or invasion to capsule.

Assessment of contrast-enhanced ultrasonography of the hepatic vein for detection of hemodynamic changes associated with experimentally induced portal hypertension in dogs.

OBJECTIVE To assess the use of contrast-enhanced ultrasonography (CEUS) of the hepatic vein for the detection of hemodynamic changes associated with experimentally induced portal hypertension in dogs. ANIMALS 6 healthy Beagles. PROCEDURES A prospective study was conducted. A catheter was surgically placed in the portal vein of each dog. Hypertension was induced by intraportal injection of microspheres (10 to 15 mg/kg) at 5-day intervals via the catheter. Microsphere injections were continued until multiple acquired portosystemic shunts were created. Portal vein pressure (PVP) was measured through the catheter. Contrast-enhanced ultrasonography was performed before and after establishment of hypertension. Time-intensity curves were generated from the region of interest in the hepatic vein. Perfusion variables measured for statistical analysis were hepatic vein arrival time, time to peak, time to peak phase (TTPP), and washout ratio. The correlation between CEUS variables and PVP was assessed by use of simple regression analysis. RESULTS Time to peak and TTPP were significantly less after induction of portal hypertension. Simple regression analysis revealed a significant negative correlation between TTPP and PVP. CONCLUSIONS AND CLINICAL RELEVANCE CEUS was useful for detecting hemodynamic changes associated with experimentally induced portal hypertension in dogs, which was characterized by a rapid increase in the intensity of the hepatic vein. Furthermore, TTPP, a time-dependent variable, provided useful complementary information for predicting portal hypertension. IMPACT FOR HUMAN MEDICINE Because the method described here induced presinusoidal portal hypertension, these results can be applied to idiopathic portal hypertension in humans.

In situ detection of GM1 and GM2 gangliosides using immunohistochemical and immunofluorescent techniques for auxiliary diagnosis of canine and feline gangliosidoses.

BACKGROUND: GM1 and GM2 gangliosidoses are progressive neurodegenerative lysosomal storage diseases resulting from the excessive accumulation of GM1 and GM2 gangliosides in the lysosomes, respectively. The diagnosis of gangliosidosis is carried out based on comprehensive findings using various types of specimens for histological, ultrastructural, biochemical and genetic analyses. Therefore, the partial absence or lack of specimens might have resulted in many undiagnosed cases. The aim of the present study was to establish immunohistochemical and immunofluorescent techniques for the auxiliary diagnosis of canine and feline gangliosidoses, using paraffin-embedded brain specimens stored for a long period. RESULTS: Using hematoxylin and eosin staining, cytoplasmic accumulation of pale to eosinophilic granular materials in swollen neurons was observed in animals previously diagnosed with GM1 or GM2 gangliosidosis. The immunohistochemical and immunofluorescent techniques developed in this study clearly demonstrated the accumulated material to be either GM1 or GM2 ganglioside. CONCLUSIONS: Immunohistochemical and immunofluorescent techniques using stored paraffin-embedded brain specimens are useful for the retrospective diagnosis of GM1 and GM2 gangliosidoses in dogs and cats.

Persistence of chicken anemia virus antigen and inclusions in spontaneous cases of Marek's disease visceral lymphomas in broiler chickens at slaughterhouses.

The chicken anemia virus (CAV) and Marek's disease virus (MDV) infect chickens worldwide; a single or dual infection by these viruses has a great impact on poultry production. In the present study, we examined the existence of CAV antigen and its inclusions in Marek's disease (MD) lymphomas in chickens in the slaughterhouses of Iwate prefecture, Japan. Forty-nine spleens and 13 livers with different degrees of nodular lesions were histopathologically examined at our laboratory. Grossly, the tested organs showed various sizes and anatomical architectures. Based on the cellular morphology and the infiltrative nature of the neoplastic lymphocytes, MD was confirmed in 76% (37/49) of the spleens and 92% (12/13) of the livers. The lesions of MD, according to the pattern of lymphocytic accumulation in the affected organs, were divided into multifocal, coalesced and diffuse. CAV intranuclear inclusion bodies were detected within the small and the large bizarre lymphocytes of the MD lymphomas in 2 livers and 9 spleens, and the immunostaining test for CAV confirmed the persistence of CAV antigens and inclusions in the neoplastic cells. This study demonstrated the persistence of CAV infection within the neoplastic cells of naturally occurring MD lymphomas in chickens.

Contrast-enhanced ultrasonographic findings in three dogs with pancreatic insulinoma.

Abdominal ultrasonography is one of the most common diagnostic imaging modalities used for dogs with suspected insulinoma; however, pancreatic masses are clearly identified in fewer than half of affected dogs and benign pancreatic nodules can be difficult to differentiate from malignant ones. The purpose of this prospective study was to describe contrast-enhanced ultrasonography (CEUS) characteristics of confirmed pancreatic insulinoma in a group of dogs. Inclusion criteria were as follows: (1) repeated hypoglycemia (blood glucose levels <60 mg/dl, twice or more); (2) elevated blood insulin levels with hypoglycemia; (3) pancreatic nodules detected with conventional ultrasonography; and (4) histological confirmation of pancreatic islet cell carcinoma. Immediately following conventional ultrasonography of the entire abdomen, CEUS of the pancreatic nodule and adjacent parenchyma was performed using contrast-specific technology pulse inversion imaging and perflubutane microbubble contrast agent. Three dogs met inclusion criteria. Pancreatic nodules in all the three dogs became more clearly demarcated after injection of the contrast agent. Each nodule showed different enhancement patterns: markedly hyperechoic for 5 s, slightly hyperechoic for 1 s, and clearly hypoechoic for over 30 s. These results were not in complete agreement with previously reported CEUS findings in human patients with insulinoma. All nodules were surgically resected and histopathologically confirmed as malignant insulinomas. Findings from the current study indicated that contrast-enhanced ultrasound may help to increase conspicuity of pancreatic insulinomas in dogs and that enhancement characteristics may be more variable in dogs than in humans.

Astrocytic growth through the autocrine/paracrine production of IL-1ß in the early infectious phase of fowl glioma-inducing virus.

Fowl glioma is characterized morphologically by multiple nodular astrocytic growth with disseminated non-suppurative encephalitis. The disease is caused by fowl glioma-inducing virus (FGV) and its variants, belonging to subgroup A of avian leukosis virus (ALV-A). Fifty-seven FGV variants have so far been isolated from Japanese fowls and these variants have a variable degree of glioma inducibility. However, how these ALVs induce glioma with different degrees and frequencies has not been fully elucidated. In this study, we investigated the relationship between intracerebral viral replication and astrocytic growth in the early infectious phase. Replication abilities of two ALV strains, Sp-53 (a FGV variant) and ALV-based replication-competent vector RCAS(A) without glioma inducibility, were compared in the brains of C/O specific pathogen free chickens at 35 days of age. Sp-53 replicated faster than RCAS(A), and the histological score and the level of interleukin (IL)-1ß in brains increased depending on the level of intracerebral viral RNA. Up-regulation of IL-1ß was also demonstrated in primary cultured astrocytes. These results suggest that the astrocytic growth in this phase is enhanced through the autocrine/paracrine production of IL-1ß in the FGV-infected astrocytes.

Congenital cerebellar dysplasia in White Leghorn chickens (Gallus gallus domesticus).

Congenital cerebellar anomalies have been rarely reported in birds. We examined cerebellums with disorganized folia from seven specific-pathogen-free White Leghorn chickens (Gallus gallus domesticus). Islands of heterotopic cortex were distributed from the deeper cortices to the medulla in the cerebellum. The characteristic lesions were composed of randomly admixed components of the cerebellar cortex, including Purkinje cells, a molecular layer and granular cells. Immunofluorescent analysis revealed Purkinje cells with haphazardly extended dendrites and a lack of Bergmann's glial fibres in the foci. Chicken parvovirus, Aino virus and avian retrovirus were not detected in the affected birds by polymerase chain reaction. This is the first report of cerebellar dysplasia in chickens possibly caused by a genetic abnormality.

Cardiac pathology and molecular epidemiology by avian leukosis viruses in Japan.

Epidemiological studies suggest that retroviruses, including human immunodeficiency virus type 1, are associated with cardiomyopathy and myocarditis, but a causal relationship remains to be established. We encountered unusual cardiomyocyte hypertrophy and mitosis in Japanese native fowls infected with subgroup A of the avian leukosis viruses (ALVs-A), which belong to the genus Alpharetrovirus of the family Retroviridae and mainly induce lymphoid neoplasm in chickens. The affected hearts were evaluated by histopathology and immunohistochemistry, viral isolation, viral genome sequencing and experimental infection. There was non-suppurative myocarditis in eighteen fowls and seven of them had abnormal cardiomyocytes, which were distributed predominantly in the left ventricular wall and showed hypertrophic cytoplasm and atypical large nuclei. Nuclear chains and mitosis were frequently noted in these cardiomyocytes and immunohistochemistry for proliferating cell nuclear antigen supported the enhancement of mitotic activity. ALVs were isolated from all affected cases and phylogenic analysis of envSU genes showed that the isolates were mainly classified into two different clusters, suggesting viral genome diversity. In ovo experimental infection with two of the isolates was demonstrated to cause myocarditis and cardiomyocyte hypertrophy similar to those in the naturally occurring lesions and cardiac hamartoma (rhabdomyoma) in a shorter period of time (at 70 days of age) than expected. These results indicate that ALVs cause myocarditis as well as cardiomyocyte abnormality in chickens, implying a pathogenetic mechanism different from insertional mutagenesis and the existence of retrovirus-induced heart disorder.

Enhancement of antibody production against rabies virus by uridine 5'-triphosphate in mice.

Extracellular nucleotides such as adenosine 5'-triphospate (ATP) and uridine 5'-triphosphate (UTP) interact with P2 purinergic receptors on the surface of phagocytic cells and induce various physiological reactions. In this study, the production of antibody in mice immunized with an inactivated rabies vaccine containing these nucleotides was investigated. Injection of inactivated rabies vaccine with UTP, but not with ATP, induced significantly higher serum antibody production in mice. The enhancement of antibody production by UTP was inhibited by an anti-P2Y4 receptor antibody. In an air pouch experiment, UTP treatment increased the number of monocytes and macrophages infiltrating the pouch and up-regulated the gene expression of IL-4 and IL-13 in the regional lymph nodes. These results suggested that UTP admixed with rabies vaccine activates Th2 cells and induces a humoral immune response. Furthermore, the survival rate of mice immunized with a rabies vaccine admixed with UTP before rabies virus challenge was slightly higher than that of control mice. In conclusion, UTP can act as a vaccine adjuvant to enhance antibody production against the rabies virus in mice.

CXCL12 improves immune responses to neurotropic virus propagation in the CNS by attracting antibody secreting cells.

A previous study showed that increases in chemokine expression and recruitment of antibody secreting cells (ASCs) in the CNS after intracerebral immunization contributed to the suppression of a neurotropic virus. In this study, intracerebral chemokine injection was used to investigate the usefulness of chemokines for controlling neurotropic viruses. Both CXCL12 and a cocktail chemokine (a mixture of CXCL9, 10, 12 and 13) attracted antigen-specific ASCs more strongly than CXCL9, 10 and 13 in an in vitro chemotaxis assay and in vivo intracerebral chemokine injection experiments. Mice pre-treated intracerebrally with CXCL12 and the cocktail chemokine showed an increased survival rate after intracerebral infection with rabies virus. These results suggest that intracerebral CXCL12 injection induces the migration of ASCs and suppresses the neuropathogenicity of rabies virus in the CNS.

Epidemiological study of fowl glioma-inducing virus in chickens in Asia and Germany.

Fowl glioma-inducing virus (FGV), which belongs to avian leukosis virus (ALV) subgroup A, induces fowl glioma. This disease is characterized by multiple nodular gliomatous growths of astrocytes and has been previously reported in Europe, South Africa, Australia, the United States and Japan. FGV and FGV variants have spread to ornamental Japanese fowl, including Japanese bantams (Gallus gallus domesticus), in Japan. However, it is unclear how and where FGV emerged and whether FGV is related to the past fowl glioma in European countries. In this study, the prevalence of FGV in European, Asian and Japanese native chickens was examined. FGV could not be isolated from any chickens in Germany and Asian countries other than Japan. Eighty (26%) out of 307 chickens reared in Japan were positive by FGV-screening nested polymerase chain reaction and 11 FGV variants with an FGV-specific sequence in their 3' untranslated region were isolated. In addition, four other ALVs lacking the FGV-specific sequence were isolated from Japanese bantams with fowl glioma and/or cerebellar hypoplasia. These isolates were considered to be distinct recombinant viruses between FGV variants and endogenous/exogenous avian retroviruses. These results suggest that the variants as well as distinct recombinant ALVs are prevalent among Japanese native chickens in Japan and that FGV may have emerged by recombination among avian retroviruses in the chickens of this country.