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Severe necrotic dermatitis in the combs of line 63 chickens infected with Marek’s disease virus

Heidari, Mohammad, Wang, Dan, Fitzgerald, Scott D., Sun, Shuhong
Avian pathology 2016 v.45 no.5 pp. 582-592
Mardivirus, Micrococcus, T-lymphocytes, cellulitis, chickens, connective tissues, dermatitis, etiological agents, histopathology, inducible nitric oxide synthase, interleukin-12, interleukin-18, interleukin-6, interleukin-8, macrophages, necrosis, neoplasms, oncogenes, quantitative polymerase chain reaction, spleen, viruses, wattles
Marek’s disease virus (MDV), the aetiological agent of Mareks' disease (MD), is a highly cell-associated oncogenic α-herpesvirus that replicates in chicken lymphocytes and establishes a latent infection within CD4 ⁺ T cells. We investigated the possible effect of MDV infection on the exacerbation of necrotic dermatitis in the combs of MD-susceptible (7 ₂) and MD-resistant (6 ₃) chicken lines at 21 days post infection. MDV-infected birds of line 6 ₃ are relatively resistant to tumour development but exhibit an unusual necrosis of combs, wattles, and footpads that is intensified when infected with MDV. Chickens from line 7 ₂, on the other hand, are highly susceptible to MDV infection and tumour development. Real-Time PCR analysis revealed that IL-6, IL-8, IL-12, IL-18, iNOS, and IFNγ were all up regulated in the comb tissues of MDV-infected susceptible line 7 ₂ with no visible necrotic damage. With the exception of IL-8 and iNOS, the expression of all the other tested genes was barely detected in the necrotic combs of the resistant line 6 ₃. Real-Time PCR analysis revealed the MDV meq oncogene transcripts in the spleen tissues of both infected lines but in the comb tissues of only the susceptible line 7 ₂. A significant infiltration of macrophages and lymphocytes was detected in the comb tissues of both resistant and susceptible lines. Histopathological analysis also showed thinning and erosion of epidermis and inflammation, lympho-plasmocytic infiltration, heterophilic, and histocytic cellulitis within the connective tissues of the necrotic combs. Gram stain of the sectioned frozen comb samples exposed the presence of Gram-positive micrococcus.