Anatomopathological and molecular studies of Marek's disease virus in India

In India, increasing incidence of Marek’s Disease Virus (MDV) outbreaks are being reported even in vaccinated poultry farms. Hence identifying the new emerging pathotype of MDV is necessary for successful control through vaccination. Birds received in the post mortem section of The Avian Disease Laboratory, Indian Veterinary Research Institute, were screened for the presence of MDV by collecting neoplastic tissues, spleen and feather follicles. Screening was carried out by polymerase chain reaction (PCR) and histopathological examination. Among the tested 150 birds’ tissue samples, 35 bird tissue samples were found positive for MDV. Based on pathotyping specific PCR, it was found that 34 birds tissues were affected virulent MDV and one birds tissue was affected with very virulent MDV. Since, HVT vaccine will not protect the very virulent pathotype, combined vaccine of SB-1 and HVT can be administered to control the very virulent MDV. Among the MD infected birds, neoplastic liver is most commonly encountered. Spleen tissue samples was found to be more suitable for the DNA isolation for PCR.

An Overview on Mareks Disease Virus Evolution and Evidence for Increased Virulence in Brazil

Mareks disease virus (MDV) has been shown to be evolving to higher virulence. One of the genetic sites involved in virulence which enables such characterization is the 339-amino acid Meq protein encoding gene (meq). The reemergence of clinical Mareks disease (MD) in vaccinated flocks can be associated to changes in meq. Our studies have shown the presence of very virulent MDV strains in the Brazilian industrial and free-range poultry. We present an overview of MD increasing severity and indicate the necessity of using phylogenetic tools for best accompanying MDV evolution.(AU)

An Overview on Mareks Disease Virus Evolution and Evidence for Increased Virulence in Brazil

Mareks disease virus (MDV) has been shown to be evolving to higher virulence. One of the genetic sites involved in virulence which enables such characterization is the 339-amino acid Meq protein encoding gene (meq). The reemergence of clinical Mareks disease (MD) in vaccinated flocks can be associated to changes in meq. Our studies have shown the presence of very virulent MDV strains in the Brazilian industrial and free-range poultry. We present an overview of MD increasing severity and indicate the necessity of using phylogenetic tools for best accompanying MDV evolution.

Anatomopathological and molecular studies of Marek's disease virus in India

In India, increasing incidence of Mareks Disease Virus (MDV) outbreaks are being reported even in vaccinated poultry farms. Hence identifying the new emerging pathotype of MDV is necessary for successful control through vaccination. Birds received in the post mortem section of The Avian Disease Laboratory, Indian Veterinary Research Institute, were screened for the presence of MDV by collecting neoplastic tissues, spleen and feather follicles. Screening was carried out by polymerase chain reaction (PCR) and histopathological examination. Among the tested 150 birds tissue samples, 35 bird tissue samples were found positive for MDV. Based on pathotyping specific PCR, it was found that 34 birds tissues were affected virulent MDV and one birds tissue was affected with very virulent MDV. Since, HVT vaccine will not protect the very virulent pathotype, combined vaccine of SB-1 and HVT can be administered to control the very virulent MDV. Among the MD infected birds, neoplastic liver is most commonly encountered. Spleen tissue samples was found to be more suitable for the DNA isolation for PCR.(AU)

Ocorrência, co-infecções e diversidade molecular do vírus da doença de Marek em Minas Gerais

A doença de Marek (MD) é uma enfermidade vírica que atinge aves domésticas (Gallus gallus domesticus), causada por um herpesvírus. É uma doença de ocorrência e importância mundial, visto que, possui um grande impacto econômico na indústria avícola em função dos custos de vacinação, mortalidade, condenações de carcaças e diminuição na produção de ovos. Desde o surgimento da avicultura intensificada, especialmente no início do século 20, iniciou-se a evolução de Vírus da Doença de Marek (MDV) para maior patogenicidade. Paradoxalmente, a criação das vacinas no início dos anos 1970, resultou em pressão seletiva que aumentou com a geração de estirpes de progressivamente maior patogenicidade, com diversificação dos quadros patológicos. Nos últimos anos o gene Meq tem atraído a atenção como uma possível causa do aumento da oncogenicidade, o mais importante determinante de patogenicidade de MDV. A caracterização molecular de estirpes brasileiras de MDV revelou a presença de estirpes muito virulentas (vvMDV), tanto da avicultura industrial como de subsistência. Considerando que os agentes infecciosos não se apresentam isoladamente no organismo do animal desafiado, o quadro decorrente de infecções simultâneas é por si só um desafio extremo para a ave, principalmente quando associados aos fatores estressantes da intensificação, como estresse, superlotação, competição social, canibalismo, má nutrição, desconforto térmico e inadequado bem-estar, fazendo com que o sistema imune da ave afetada não consiga debelar a infecção.

Marek's disease (MD) is a viral disease that affects poultry (Gallus gallus domesticus), caused by a herpesvirus. It is a disease of global importance and occurrence, since it has a great economic impact on the poultry industry due to the costs of vaccination, mortality, carcass condemnations and decreased egg production. Since the emergence of intensified poultry farming, especially at the beginning of the 20th century, the evolution of Marek's Disease Virus (MDV) has started towards greater pathogenicity. Paradoxically, the creation of vaccines in the early 1970s resulted in selective pressure that increased with the generation of strains of progressively greater pathogenicity, with diversification of pathological conditions. In recent years, the Meq gene has attracted attention as a possible cause of increased oncogenicity, the most important determinant of MDV pathogenicity. The molecular characterization of Brazilian strains of MDV revealed a presence of very virulent strains (vvMDV), both from industrial and subsistence poultry farming. Considering that the infectious agents do not appear in isolation in the organism of the challenged animal, the situation resulting from simultaneous alterations is in itself an extreme challenge for the bird, especially when associated with intensifying stressors, such as stress, overcrowding, social competition, cannibalism , malnutrition, thermal discomfort and appropriate wellbeing, making the immune system of the affected bird unable to suppress an infection.

Detecção e caracterização molecular do Vírus da Doença de Marek em Minas Gerais

O vírus da doença de Marek (MDV) é um agente infeccioso que atinge, principalmente, galinhas domésticas (Gallus gallus domesticus), tanto da avicultura industrial quanto de subsistência, causando uma doença inflamatória linfo-proliferativa conhecida como doença de Marek (DM). A doença acarreta em grandes perdas produtivas e econômicas à avicultura tecnificada, com impacto também à avicultura de subsistência. A ocorrência de MD foi reduzida dramaticamente com o uso da vacinação obrigatória dos pintinhos no incubatório desde os anos 1970. A emergência de estirpes de alta e muito alta virulência do vírus de MD (MDV), entretanto, foi relatada em vários países, envolvidas em surtos em plantéis vacinados. No entanto, apesar do Brasil ser o maior exportador mundial de carne de frango, não se conhece o perfil genético molecular de MDV. Descreve-se a caracterização molecular de estirpes de MDV baseada no sequenciamento de parte do gene que codifica a proteína Meq de MDV, em galinhas da avicultura de subsistência e industrial de Belo Horizonte e região metropolitana. Aves com quadro clínico sugestivo de DM foram admitidas no Laboratório de Doenças das Aves e examinadas. De um total de 112 aves positivas para MDV, quinze (13,4%) isolados com potencial patogênico foram detectados, dois sendo caracterizados como MDV de alta virulência (vvMDV), e os demais treze isolados caracterizaram-se como MDV virulentos (vMDV) clássicos. A presença de estirpes de vvMDV pode representar aumento do risco de falha da proteção vacinal nos plantéis industriais. Entretanto, na grande maioria das aves (86,6%) não foi detectado MDV patogênico. De um total de cento e doze galinhas positivas para MDV, setenta e cinco aves apresentaram um quadro de infecção simultânea entre MDV e um ou mais agentes infecciosos. O cenário de infecções simultâneas ou coinfecções entre MDV e outros agentes endêmicos sugere ser representativo da condição comum na epidemiologia das infecções em aves. A caracterização molecular de MDV e a co-infecção por alguns importantes agentes infecciosos é discutida.

Marek disease virus (MDV) is an infectious agent that affects primarily domestic chickens (Gallus gallus domesticus), both of industrial poultry farming as of subsistence, causing a lymphocytic inflammatory disease-known as proliferative Marek disease (MD). The disease causes in productive and economic losses to poultry, but also impact the poultry. The occurrence of MD was reduced dramatically with the use of mandatory vaccination of hatchery chicks since the years 1970. The emergence of strains of high and very high virulence of MD virus (MDV), however, was reported in several countries, involved in outbreaks in vaccinated flocks. However, in spite of Brazil being the world's largest exporter of chicken meat, no known molecular genetic profile of MDV. Describes the molecular characterization of MDV strains based on sequencing of the gene encoding the protein Meq of MDV, in chickens of subsistence and industrial poultry farming of Belo Horizonte and metropolitan region. Birds with clinical picture suggestive of DM were admitted in the laboratory of poultry Diseases and examined. A total of 112 birds positive for MDV, fifteen (13.4%) isolates with pathogenic potential were detected, two being characterized as high virulence MDV (vvMDV), and the remaining thirteen isolates were characterised as MDV virulent (vMDV) classics. The presence of vvMDV strains may represent increased risk of failure of vaccine protection in industrial stocks. However, in the vast majority of birds (86.6%) was not detected MDV pathogen. A total of 112 chickens positive for MDV, 75 birds presented a painting of simultaneous infection between MDV and one or more infectious agents. The scenario of concurrent infections or coinfecções between MDV and other endemic agents suggests be representative of common condition on epidemiology of infections in birds. Molecular characterization of MDV and co-infection by some important infectious agents is discussed