Control of Chicken Anemia Virus Infections in Chickens

Disease overview

• caused by the Chicken Anaemia Virus (CAV)

• can infect chickens of all ages but only young chicks may develop clinical signs

• virus can be isolated from different organs but targets mainly the thymus
• impairing the maturation of T lymphocytes
• immunosuppression

Epidemiology

• Worldwide
• Natural hosts : Chicken
• Turkeys : CAV been isolated
• Quails : CAV antibodies
• Spread of the virus
• Not highly contagious (take few weeks to spread through an entire flock)
• Horizontal transmission : infected organic material or contaminated equipment
• Vertical transmission
• Transmission : occur during 3 – 6 weeks after infection

Epidemiology

• Morbidity and mortality rates are high
• The most severe clinical signs are seen

• Chickens develop age resistance to disease
• Still remain susceptible to infection

> 2-3 weeks

2 weeks

< 2 weeks

Clinical signs

• mainly seen in young birds (<2 weeks of age)
• depressed and huddle under the heat source
• appear less developed for their age and anaemic

• Immunosuppression
• CAV infection impairs the immune system, affecting and multiplying in most lymphopoietic organs
• CAV enhances the effect of other immunosuppressive agents such as Marek’s Disease and IBD

Introduction

• Maternal Immunity
• Maternally derived antibodies (MDA)
• The level of protection is directly related to the level of MDA
• MDA develop
• field infections : do not guarantee high and homogenous levels of MDA
• vaccination : the best way of promptly obtaining high and homogenous levels of MDA

• Minimum protection level
• A minimum level of MDA is needed to stop vertical transmission
• MDA titer of > 8 log2

Vaccination

• The backbone of protection against CAV
• Only live vaccines are used
• mass vaccination (e.g., drinking water),wing web administration or s.c. or i.m. injection.
• induce long lasting systemic immunity

Vaccination program

• Broilers and layer pullets : Currently broilers and layer pullets are not commonly vaccinated against CAV in the field. Early protection is achieved by vaccination of the breeders though MDA

Vaccination program

• Breeders :
• 8-16 weeks of age
• Care should be taken to ensure that vaccination results in high levels of maternally derived antibodies throughout the production period.

Higher MDA levels at the beginning of the fattening period guarantee a longer protection in the progeny

http://www.chicken-anemia.com/publications.asp [Accessed 7 June 2017]

Biosecurity

• Minimize the risk of introducing the virus

• Basic management : limited controlled site access, separate footwear and equipment for each site/house, and footbaths at the entrance to sites/houses...

• Dry clean : removal and disposal of all organic material
• Wet clean : removal of all organic material
• Disinfection :formaldehyde, chlorine releasing agents, or quaternary ammonium compounds
• minimizing virus (and lowering infective dose) in the environment

• The downtime between successive flocks : a minimum of 10 days