Chicken Infectious Anemia

INTRODUCTION The disease is characterized by aplastic anemia and generalized lymphoid atrophy with concomitant immunosuppression and frequently is complicated by secondary viral, bacterial, or fungal infections.

ETIOLOGY Classification Recently, the virus has been classified as the only member of the genus Gyrovirus of the Circoviridae

Transmission Chicken infectious anemia virus spreads both horizontally and vertically. Horizontal transmission is very likely based on the presence of high concentrations of virus in the feces of chickens for 5—7 weeks after infection

Age Resistance Age resistance develops rapidly during the first week of life and becomes complete by 3 weeks or even earlier in immunologically competent chickens.

Incubation Period In experimental infections, anemia and distinct histologic lesions can first be detected at 8 days after parenteral inoculation of virus. Clinical signs generally develop after 10—14 days, and mortality starts at 12—14 days after inoculation

Clinical Signs The only specific sign of CIAV infection is anemia, with a peak at 14—16 days postinoculation. Anemia is characterized by hematocrit values ranging from 6—27%. Affected birds are depressed and can become pale. Weight gain isdepressed between 10— 20 days after experimental infection. Affected birds may die between 12—28 days postinoculation.

If mortality does occur, it generally does not exceed 30% If mortality does occur, it generally does not exceed 30%. Surviving chicks completely recover from depression and anemia by 20— 28 days after infection, although retarded recovery and increased mortality may be associated with secondary bacterial or viral infections. Secondary infections, causing more severe clinical signs, are frequently seen in field cases

Pathology Lesions associated with CIA may vary dependent on the route of infection, age of exposure, viral dose, and immune status of the host.

A. Control thymus (top) and thymus with chicken infectious anemia virus (CIAV)–induced atrophy (bottom) B. Femur with normal dark red bone marrow (top) and femur with pale aplastic bone marrow (bottom)

C. Gangrenous dermatitis (blue wing disease). D C. Gangrenous dermatitis (blue wing disease). D. Hemorrhages in thigh and leg muscles.

E. Hemorrhages in breast muscle. F. Hemorrhages in proventriculus.

Gross Lesions Thymic atrophy, sometimes resulting in an almost complete absence of thymic lobes, is the most consistent lesion especially when chicks develop age resistance. The thymic remnants may have a dark reddish color. Bone marrow atrophy is the most characteristic lesion seen and is best evaluated in the femur

In a small proportion of birds, the size of the bursa of Fabricius may be reduced. In many cases, the outer bursal wall appears translucent. Hemorrhages in the proventricular mucosa and subcutaneous and muscular hemorrhages are sometimes associated with severe anemia

DIAGNOSIS Isolation and Identification of CIAV Serology

INTERVENTION STRATEGIES Management Procedures Vaccination