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25 January 2013 Prevalence of Marek's Disease Virus in Different Chicken Populations in Iraq and Indicative Virulence Based on Sequence Variation in the EcoRI-Q (meq) Gene
Salih J. Wajid, Margaret E. Katz, Katrin G. Renz, Stephen W. Walkden-Brown
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Abstract

A cross-sectional survey was conducted in six provinces in southern Iraq to determine the point prevalence of Marek's disease virus (MDV) in different chicken populations followed by sequencing the meq gene for phylogenetic analysis and virulence-associated polymorphisms. A total of 109 samples from unvaccinated flocks were analyzed comprising 52 dust and 30 spleen samples from commercial broiler farms and 27 spleens from local layer chickens purchased in the town markets. The overall prevalence of MDV was 49.5% with no significant differences between provinces (P  =  0.08) or sample types (P  =  0.89). Prevalence ranged from 36.8% in Karbala and Nasiriyah to 65% in Amarah. The percentages of positive samples were 59.1%, 46.7%, and 48.1% in broiler dust, broiler spleen, and layer spleen, respectively. The overall mean (±SEM) Log10 MDV viral copy number per milligram of dust or spleen as determined by quantitative PCR was 1.78 ± 0.19, with no significant differences between provinces (P  =  0.10) or sample types (P  =  0.38). In positive samples only, the overall mean was 3.43 ± 0.18. Sequencing of the meq gene from samples that showed high levels of MDV target in qPCR testing was attempted. Nine samples were sequenced. These sequences were compared with meq sequences of MDVs of different pathotype. All the Iraqi MDVs had a short meq gene of 897 base pairs because of the deletion of 123 bp relative to the reference strain Md5. The Iraqi meq sequences also contained single-nucleotide polymorphisms, resulting in differences in the amino acid sequence. All of the nine Iraqi meq genes encoded two repeats of four-proline sequences. The published negative association between four-proline repeat number and MDV virulence suggests that the Iraqi MDVs are likely to be highly virulent, but this needs to be confirmed by in vivo testing. Taken together, these results indicate that MDV is common in unvaccinated commercial and village chickens in southern Iraq, that there is limited meq gene sequence variation, that all sequenced samples had a short meq with two four-proline repeats, and that this is consistent with a high level of virulence.

Prevalencia del virus de la enfermedad de Marek en diferentes poblaciones de pollos en Irak e indicaciones de que la virulencia está basada en las variaciones de la secuencia del gene EcoRI-Q (meq).

Se llevó a cabo un estudio transversal en seis provincias del sur de Irak para determinar la prevalencia del virus de la enfermedad de Marek (MDV) en diferentes poblaciones de pollo seguido de la secuenciación del gene meq para el análisis filogenético y de polimorfismos asociados con la virulencia. Se analizaron un total de 109 muestras de las parvadas no vacunadas que incluían 52 muestras de polvo y 30 muestras de bazo procedentes de granjas de engorde comerciales y 27 muestras de bazos de gallinas ponedoras locales adquiridas en los mercados de la ciudad. La prevalencia global del virus de la enfermedad de Marek fue de 49.5%, sin diferencias significativas entre provincias (P  =  0.08) o por tipos de muestras (P  =  0.89). La prevalencia fue de 36.8% en Karbala y Nasiriyah hasta 65% en Amarah. Los porcentajes de muestras positivas fueron de 59.1%, 46.7%, y 48.1% en el polvo de las casetas de pollo de engorde, en los bazos de pollos de engorde, y en los bazos de aves de postura, respectivamente. La media general (± error estándar de la media) del Log10 del número de copias virales del virus de Marek por miligramo de polvo o de bazo

American Association of Avian Pathologists
Salih J. Wajid, Margaret E. Katz, Katrin G. Renz, and Stephen W. Walkden-Brown "Prevalence of Marek's Disease Virus in Different Chicken Populations in Iraq and Indicative Virulence Based on Sequence Variation in the EcoRI-Q (meq) Gene," Avian Diseases 57(2s1), 562-568, (25 January 2013). https://doi.org/10.1637/10342-083112-Reg.1
Received: 5 September 2012; Accepted: 1 January 2013; Published: 25 January 2013
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