Subgroup J avian leukosis virus infection in turkeys: induction of rapid onset tumours by acutely transforming virus strain 966

Avian Leukosis: Will We Be Able to Get Rid of It?

Avian leukosis viruses (ALVs) have been virtually eradicated from commercial poultry. However, some niches remain as pockets from which this group of viruses may reemerge and induce economic losses. Such is the case of fancy, hobby, backyard chickens and indigenous or native breeds, which are not as strictly inspected as commercial poultry and which have been found to harbor ALVs. In addition, the genome of both poultry and of several gamebird species contain endogenous retroviral sequences. Circumstances that support keeping up surveillance include the detection of several ALV natural recombinants between exogenous and endogenous ALV-related sequences which, combined with the well-known ability of retroviruses to mutate, facilitate the emergence of escape mutants. The subgroup most prevalent nowadays, ALV-J, has emerged as a multi-recombinant which uses a different receptor from the previously known subgroups, greatly increasing its cell tropism and pathogenicity and making it more transmissible. In this review we describe the ALVs, their different subgroups and which receptor they use to infect the cell, their routes of transmission and their presence in different bird collectivities, and the immune response against them. We analyze the different systems to control them, from vaccination to the progress made editing the bird genome to generate mutated ALV receptors or selecting certain haplotypes.

Recent trends in diagnosis and control of Marek's disease (MD) in poultry

Marek's Disease (MD), caused by Marek's Disease Virus (MDV) is a highly contagious oncogenic and neuropathic disease of chickens responsible for great economic losses to the poultry industry all around the world and characterized by development of CD4+T cell lymphomas as well as infiltration of nerves and visceral organs by lymphocytes. MD is one of the most common lymphoproliferative diseases of chickens which cause mononuclear cell infiltration in one or more of the following tissues: peripheral nerves, gonads, lymphoid organs, iris, muscle, skin and other visceral organs resulting into development of tumours in visceral organs, paralysis of legs, wings and neck, grey eye (iris) or irregular pupil, vision impairment, blindness, skin lesions and immunosuppression, all of which can be accompanied by non-specific signs such as anorexia, weight loss and poor performance. Today there are evolving highly pathogenic isolates of MDV around the world capable of overwhelming the protection from currently employed vaccines. Thus MD poses a big challenge to the welfare and wellbeing of the poultry with increased condemnation of carcass, loss of productivity and quality products, leading to huge economic losses. It is also an immunosuppressive disease and causes increased susceptibility to other infections. The present review discusses in brief about the Marek's disease, its etiology, conventional and advance tools and techniques being used for its diagnosis, prevention and control strategies in poultry.

Innovation and discovery: the application of nucleic acid-based technology to avian virus detection and characterization

Polymerase chain reaction (PCR)-based approaches to the detection, differentiation and characterization of avian pathogens continue to be developed and refined. The PCRs, or reverse transcriptase-PCRs, may be general, designed to detect all or most variants of a pathogen, or to be serotype, genotype or pathotype specific. Progress is being made with respect to making nucleic acid approaches more suitable for use in diagnostic laboratories. Robotic workstations are now available for extraction of nucleic acid from many samples in a short time, for routine diagnosis. Following general PCR, the DNA products are commonly analyzed by restriction endonuclease mapping (restriction fragment length polymorphism), using a small number of restriction endonucleases, based on a large body of sequence data. Increasingly, however, nucleotide sequencing is being used to analyze the DNA product, in part due to the expanding use of non-radioactive sequencing methods that are safe and enable high throughout. In this review, I highlight some recent developments with many avian viruses: Newcastle disease virus; circoviruses in canary and pigeon; infectious bursal disease virus (Gumboro disease virus); avian adenoviruses, including Angara disease/infectious hydropericardium virus, haemorrhagic enteritis virus of turkeys, and egg drop syndrome virus; avian herpesviruses, including infectious laryngotracheitis virus, duck plague virus, psittacine herpesvirus (Pacheco's parrot disease virus), Marek's disease virus and herpesvirus of turkeys; avian leukosis virus (associated with lymphoid leukosis or myeloid leukosis, and egg transmission); avian pneumoviruses (turkey rhinotracheitis virus); avian coronaviruses, including infectious bronchitis virus, turkey coronavirus and pheasant coronavirus; astrovirus, in the context of poult enteritis and mortality syndrome, and avian nephritis virus; and avian encephalomyelitis virus, a picornavirus related to hepatitis A virus.

Effect of an in ovo infection with a Dutch avian leukosis virus subgroup J isolate on the growth and immunological performance of SPF broiler chickens

The effect of an in ovo infection with a Dutch isolate of avian leukosis virus subgroup J (ALV-J) on the growth of specific pathogen free (SPF) broiler chickens was analysed. During this study, possible immune suppressive effects of ALV-J were assessed by measuring delayed-type hypersensitivity with keyhole limpet haemocyanin (KLH), natural killer (NK) cell activity, the production of radicals of nitric oxide (NO) by macrophages, humoral immune response against Newcastle and infectious bursal disease vaccine viruses, and automated total and differential leukocyte counts. In an attempt to elucidate the underlying causal mechanisms of the induced growth retardation, 3,3',5-triiodothyronine (T3) concentrations in serum were measured. Four experiments were conducted. In experiment 1, ALV-J-injected birds were compared with ALV subgroup A (ALV-A)-injected and negative control chickens. In experiment 2, ALV-J-injected birds were only compared with negative controls. Finally, in experiments 3a and 3b, ALV-J-injected chickens were compared with negative controls and a group of chickens in which only 10% of birds had been injected with ALV-J. Birds were injected in ovo at day 7 of incubation with 10(4) median tissue culture infectious dose (TCID(50)) ALV-J or ALV-A, except in experiment 3a where 10(2) TCID(50) ALV-J was injected. Significant growth suppression was found in all 100% of ALV-J-infected groups. The average growth retardation of ALV-J-infected birds compared with negative controls at 6 weeks of age was approximately 8, 11, 2.5 and 6% for the four successive experiments performed. The delayed-type hypersensitivity test against KLH of ALV-J-infected birds showed a tendency towards lower wattle thickness; however, the difference with controls was not significant (P > 0.05). The same was true for NK cell activity and NO production by macrophages, although the difference was not significant. The total and differential leukocyte counts performed on blood samples from birds at 3, 4 and 6 weeks of age as well as the humoral immune response against Newcastle and infectious bursal disease vaccine viruses did not show significant differences between treatment groups either. Only the number of basophils were significantly higher (P = 0.02) in ALV-J-infected birds at 3 weeks of age. No significant lower T(3) levels were found in ALV-J-infected birds in weeks 2 and 3 (experiment 2) and weeks 3 and 5 (experiment 3b); however, at 4 weeks (experiment 2) and 6 weeks (experiment 3b) of age, T(3) levels were significantly lower suggesting mild hypothyroidism in these broilers. In conclusion, the present experiments show the occurrence of significant growth retardation in SPF broilers after an ALV-J in ovo infection. The various studies performed to assess the immune competence of ALV-J-infected chickens did not show significant differences in immune responsiveness. The assays on cellular immunity showed a tendency to a lower response in ALV-J-infected birds, but these differences were not statistically significant.

Acutely transforming avian leukosis virus subgroup J strain 966: defective genome encodes a 72-kilodalton Gag-Myc fusion protein

Avian leukosis virus subgroup J (ALV-J), the most recent member of the avian retroviruses, is predominantly associated with myeloid leukosis in meat-type chickens. We have previously demonstrated that the acutely transforming virus strain 966, isolated from an ALV-J-induced tumor, transformed peripheral blood monocyte and bone marrow cells in vitro and induced rapid-onset tumors, suggesting transduction of oncogenes (L. N. Payne, A. M. Gillespie, and K. Howes, Avian Dis. 37:438-450, 1993). In order to understand the molecular basis for the rapid transformation and tumor induction, we have determined the complete genomic structure of the provirus of the 966 strain. The sequence of the 966 provirus clone revealed that its genome is closely related to that of HPRS-103 but is defective, with the entire pol and parts of the gag and env genes replaced by a 1,491-bp sequence representing exons 2 and 3 of the c-myc gene. LSTC-IAH30, a stable cell line derived from turkey monocyte cultures transformed by the 966 strain of ALV-J, expressed a 72-kDa Gag-Myc fusion protein. The identification of the myc gene in 966 virus as well as in several other ALV-J-induced tumors suggested that the induction of myeloid tumors by this new subgroup of ALV occurs through mechanisms involving the activation of the c-myc oncogene.