Chicken Anaemia Virus

Chicken Anaemia Virus

Sep 18, 2013

Chicken Anaemia Virus (CAV) or Chicken Infectious Anaemia Virus

CAV is a small virus that is found all over the world. It is very resistant to disinfectants and it is generally considered to be present to a greater or lesser extent on all chicken farms.  The virus is only known to infect chickens. Chickens can become infected at any age, however chickens will only develop the clinical disease if they are infected before 3 weeks of age.  There is good news though, because antibodies that the chick gets from it’s mother are completely protective against the disease, and these antibodies last for 3 weeks.

It is therefore very important that the breeder birds are exposed to the disease before they begin to lay. If the birds are exposed to CAV before lay 2 things happen. Firstly the breeders produce antibodies which stops them from transmitting the virus to the chicks via the egg. Secondly these same antibodies protect the chicks from virus which may be on the farm to which they are going. It is for these reasons that the breeder flocks are normally vaccinated between 13 and 15 weeks of age.  To make sure that this vaccination has been done correctly blood samples taken at 16 weeks are tested for antibodies to the disease.

If breeder birds are not properly immunised and therefore do not have antibodies when they start to lay eggs two possible situations are possible in the chicks. The first is that the chicks will not have any antibodies and can then become infected when they arrive on the farm. The second possibility is that the breeder flock becomes infected and then they actually give the virus to the chick through the egg. Both of these situations are potentially disastrous and will be discussed in the next blog piece.

If chickens become infected with CAV what will you actually see on the farm? Generally the mortality will begin to increase around 10 – 12 days of age and peak between 17 and 24 days of age. On post mortem a wide range of problems can be seen. This is because the virus affects the chickens’ ability to make blood. Blood has a number of components to it including red blood cells, white blood cells and platelets.

If just CAV is involved then the birds will be pale (no red blood cells) and will often also show bleeding through the whole body, particularly under the skin and in the muscles. The problem is that CAV rarely acts alone and there are often other diseases which are made much worse by CAV. This is because the white blood cells which fight off disease in the chicken are also decreased. If the chicken cannot fight off other diseases then these run rampant through the chicken and can be the ultimate cause of death.

Low white blood cells form part of a syndrome that is called immunosuppression. Infectious Bursal Disease, also known as Gumbro, also causes immunosuppression. To complicate the picture even more Gumboro can also cause bleeding in the bird the same way that CAV can.

This means that diagnosing CAV is not an easy task and will involve a thorough investigation by a veterinarian to determine the underlying cause. An investigation into CAV will involve collecting information from both the affected farm and the breeder farm from where the chicks came from.

There is no cure for CAV and so once again we rely on properly vaccinating our birds. Always remember with diseases that prevention is better than cure!