Pathological and Immunohistochemical Studies of Subclinical Infection of Chicken Anemia Virus in 4-Week-Old Chickens

Abstract

ABSTRACT. Subclinical infection of chicken anemia virus (CAV) at 4 to 6 weeks of age, after maternal antibodies have waned, is implicated in several field problems in broiler flocks. In order to understand the pathogenesis of subclinical infection with CAV, an immunopathological study of CAV-inoculated 4-week-old SPF chickens was performed. Sixty 4-week-old SPF chickens were equally divided into CAV and control groups. The CAV group was inoculated intramuscularly with the MSB1-TK5803 strain of CAV. Neither mortality nor anemia was detected in the CAV and control groups. In the CAV group, no signs were observed, except that some chickens were grossly smaller compared with the control group. Sporadic thymus lobes appeared to be reddening and atrophied. Within the first two weeks p.i. of CAV, there was a mild to moderate depletion of lymphocytes in the thymus cortex and spleen in some chickens. Moreover, lymphoid depletion of the bursa of Fabricius, proventriculus and cecal tonsils was observed. Hyperplastic lymphoid foci were observed in the liver, lungs, kidneys and heart at the 4th week p.i. of CAV. Immunohistochemically, a moderate lymphoid depletion of CD4 + and CD8 + T cells in the thymus cortex and spleen was observed in some chickens within two weeks p.i. of CAV. CAV inclusions and antigens were detected infrequently in the thymus cortex and spleen. It could be concluded that the immunosuppression in subclinical infection with CAV occurs as a result of reduction of cellular immunity.

Immunosuppressive Effects of Chicken Infectious Anaemia Virus on T Lymphocyte Populations Using Flow Cytometry and Hematological Parameters During Experimental Subclinical Infection in Chicks

“…Similarly, flow cytometric analysis of peripheral blood lymphocytes indicated significant decrease of CD4 + CD8 -and CD4 -CD8 + cells in the chicks of CIAV infected group. Such destructive effects on lymphoid organs in adult infected chicks were observed immunohistochemically by other workers during subclinical infection (Smyth et al, 2006;Haridy et al, 2012a). The blood CD4 + CD8 -:CD4 -CD8 + ratio was low (1-1.2: 1) as compared to 1.2-3.25 ratio which may be due to SPF nature of the chicks.…”

“…All these changes were in agreement with the previous reports Latheef et al, 2013). Recent findings have shown that in the adult susceptible birds, CIAV replicates at high concentration in the thymus, and causes characteristic histopathological changes in the thymus, spleen, bursa of Fabricius, proventriculus and caecal tonsils (Kaffashi et al, 2006;Haridy et al, 2012a;Wani et al, 2014). Infections with CIAV increases the susceptibility of birds to secondary (bacterial/viral) infections, depresses vaccinal immunity, aggravates residual pathogenicity of attenuated virus and vaccine strains leading to vaccination failures and various disease outbreaks (Pope, 1991;Adair et al, 1993;Todd, 2000;Dhama et al, 2003;Dhama et al, 2008).…”

“…Also, the co-infection with immunosuppressive pathogens like Marek's disease virus, infectious bursal disease virus increases the severity of CIAV-associated complications to the growing and susceptible adult chicks (Haridy et al, 2012a;Haridy et al, 2012b). Although clinical disease does not occur in adult birds but such infections lead to decrease in body weight gain, contamination of pathogen-free eggs and vaccination failures; besides acting as source of infection to other susceptible birds.…”

“…A recent molecular epidemiological study from India indicated CIAV positivity of 66.6% and 25%, respectively, in 3-7 week and 7-12 week age groups of chickens . Also, recent findings have shown that CIAV can cause characteristic histopathological changes and immunosuppressive effects involving various cytokines in the adult susceptible birds (Haridy et al, 2012a;Wani et al, 2014).…”

Avian Immunosuppressive Diseases and Immunoevasion

“…Adair et al [77] reported that CD3 1 CD8 1 TCRαβ spleen cells constitute the major CIAV-infected population in the spleen. Recently, Haridy et al [78] reported that infection in 4-week-old chickens resulted in a moderate loss of CD4 1 and CD8 1 cells in the spleen and thymus. Infection in 1-day-old chicks causes a more severe depletion of CD4 1 and CD8 1 cells (e.g., [79]).…”