Marek's Disease in Backyard Chickens, A Study of Pathologic Findings and Viral Loads in Tumorous and Nontumorous Birds

Abstract

Marek's disease (MD) is a major cause of mortality in backyard chickens. The diagnosis of MD is complex, however, and knowledge of Marek's disease virus (MDV) in spontaneous field cases such as in backyard chickens is largely unknown. In this study, 40 backyard chickens with a presumptive MD diagnosis based on histologic lymphoid infiltrations in peripheral nerves with and without lymphomas were investigated. Twenty-eight of the birds were submitted to the diagnostic laboratory for disease explorations, and 12 chickens were from a flock in which some members demonstrated anisocoria and pupil irregularities compatible with ocular MD. Histologic scores were established for brain, peripheral nerves, heart, lung, liver, kidney, and gonad sections, ranging from mild (+) to severe (+++) lymphoid infiltrations. Twelve chickens had gross lymphomas, and all but two chickens had mild to severe peripheral nerve lymphoid infiltrates. There were no age or breed predispositions in the study group. Quantification of serotypes MDV-1, -2, and -3 performed with real-time PCR demonstrated high correlation (R = 0.94) between fresh and fixed spleen specimens, as well as between histopathology scores and MDV-1 viral loads. MDV-2 DNA was detected in a portion of the chickens, likely consistent with naturally occurring virus, whereas the vaccine strain MDV-3 was rarely detected. Significant differences in MDV-1 viral loads between tumorous and nontumorous chickens were observed, in which a ratio of MDV-1 glycoprotein B/glyceraldehyde-3-phosphate dehydrogenase ≥ 0.5 was suggestive of gross tumors in this study. We propose that real-time PCR may be a good tool for MD diagnosis in backyard chickens.

Detection and Molecular Characterization of a Natural Coinfection of Marek’s Disease Virus and Reticuloendotheliosis Virus in Brazilian Backyard Chicken Flock

“…As reports of the MDV strain in Brazil are scarce, even more in backyard chicken flocks, this study remembers the importance of the vigilance. On the other hand, the apparition of MDV in backyard flocks is a common event [51] with the presence of low and high-virulence pathotypes [52,53]. The pathogenicity of the MDV strain detected in this study could be comparable with the highest virulent ones, based on the percentage of mortality (>10%) and the lymphoproliferative lesions observed in necropsy (Figure 1a,b) and histopathologic examination (Figure 2a-d).…”

Spotlight on avian pathology: Marek’s disease

“…Affected birds remain infectious for life continuously shedding the virus into the environment contaminating the poultry house environment. MD has been reported in all poultry-rearing countries (Dunn & Gimeno, 2013;Mete et al, 2016) and a 2004 estimate suggested that MD causes annual losses of up to US$2 billion to the poultry industry (Morrow & Fehler, 2004).…”

Histologic findings and viral antigen distribution in natural coinfection of layer hens with subgroup J avian leukosis virus, Marek’s disease virus, and reticuloendotheliosis virus

“…Coinfection with 2–3 viruses has become an important epidemiologic situation in poultry production. 2,9,14,15,17 Many reports have described and compared histologic changes associated with single virus infection; 1,7,8 however, histologic findings and antigen distribution from naturally occurring cases of coinfection have been reported only rarely.…”