Chicken Anaemia Virus (CAV) Infection

[ chicken infectious anaemia, Blue wing disease , Anaemia dermatitis syndrome , Haemorrhagic aplastic anaemia syndrome]

• 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 :

• CAV (Chicken anaemia virus ) of Gyrovirus genus of Anelloviridae family
• [ non-enveloped , -ve sense circular DNA ]

Transmission :

• Disease usually during the first 3 weeks of life.

a. Vertical :

• When breeders flocks get infected during the production period ; this occurs especially in younger flocks .

b. Horizontal :

• Through infected organic material or contaminated equipment
• Chickens at any age are susceptible to infection by :
• Oral route
• Respiratory route
• Incubation period :
• CAV is not highly contagious and takes a few weeks to spread through an entire flock.
• IP is relatively long under field condition
• Under experimental infection :
• First signs of anaemia and histologic lesion are seen 8 days after parenteral inocul;ation of virus
• CS generally develop after 10-14 days
• Mortality – 12-14 after inoculation

Pathogenesis :

Virus   ➦   oral / respiratory route

                          ⬇

       Principle sites of replication are hemocytoblasts in bone marrow ,  precursor T cells in the cortex of thymus , dividing Tcd4 and Tcd8 cells in the spleen .

Replication and destruction of hemocytoblasts in bone marrow

                           ⬇

Decrease production of RBC and WBC

                          ⬇

                    Anaemia

Replication and destruction of T-cells     ➦  immunosuppression

• CAV can be found latent in SPF flocks where viruses are detected in ovaries , oviduct , testicles , and spleen of birds without obvious seroconversion until the birds come into production .

Clinical signs :

• Anaemia ( PCV ≤ 27)
• Paleness
• Anorexia
• Lethargy
• Depression
• Watery and slowly clotting bird
• Reduced weight gain
• High mortality rates resulting from secondary complicating infections ( generally 10-20% , but as much as 60% )
• Anaemia , leukopenia and pancytopenia seen often on blood smears

Gross :

• Organs are pale
• Thymus is generally atrophied ( sometimes absence of thymic lobes )
• Bursa of fabricius may be small .
• Bone marrow is pale or yellow
• Hemorrhages may be present in or under skin and in muscles and other organs
• Lesions associated with secondary infections may be present
• Hemorrhages in proventricular mucosa and subcutaneous and muscular hemorrhages are sometimes associated with severe anaemia
• Gangrenous dermatitis on feet , legs wings or neck
• Acute ,mycotic pneumonia
• Discoloured liver and kidney

• Focal lesions ( wings ) appear as ecchymotic skin hemorrhages
• Lesions turn blue and may break, releasing serosanguineous exudate which  is prone to secondary bacterial infections leading to gangrenous  dermatitis
• This can be especially notorious at end of wings ; hence named “Blue wing disease “
• Tips of wings may appear hemorrhagic and necrotic

Microscopic  lesion :

• Lymphoid cell population are depleted in primary primary and secondary lymphoid organs
• Severe lymphocytic depletion in thymic cortex
• Granulocytic and erythrocytic compartments in bone marrow are atrophied or hypoplastic .

Diagnosis :

• Clinical signs
• Gross lesion
• Demonstration of seroconversion in parent flock
• Isolation and identification of virus in lymphoblastoid cell line
• Serology