Diseases and conditions


This disease is associated with many species of birds, but is predominantly found in songbirds. In songbirds it is often referred to as ‘thick liver disease’. The liver becomes enlarged and round. Because the skin of small birds is so thin and transparent, the liver can actually be seen through the skin of the mid-abdomen in the form of a large dark spot.


The disease is caused by Atoxoplasma serini, a single-celled parasite closely related to coccidia. In contrast to the coccidia, which primarily cause problems in the intestines, A.serini is found in more parts of the body.

It starts in the blood cells and spreads to other organs, including the liver, spleen and intestines.

Adult birds can be carrier of the parasite while themselves showing little or no signs of illness. The faecal matter does, however, contain oocysts (small egg-like cysts) allowing them to infect other birds and their own young.

Young birds are more prone to illness after infection. The symptoms are difficult to recognise. The birds lose some of their weight, ruffle into a ball and can have diarrhoea. The enlarged liver can often be seen through the skin as a dark spot. Young birds can become acutely sick and severe infection can cause a death rate of up to 80%.

Treatment is complicated because the parasite infests areas where there is little to no access for medication (for instance in tendons and joints). After stopping medical treatment, it's quite possible that the disease comes back because the inaccessible parasites multiply again.

Infection occurs when the bird ingests oocysts. The sick birds then discharge them with the faeces.


Diagnosis is difficult as sick birds do not have the oocysts in their stool every day. As a result, a faecal examination will not always result in an accurate diagnosis.

The best way to find the pathogen is by examining the liver and spleen of the bird after it has died. The parasites located in the organs can be detected under a microscope. In addition, the condition of the deceased bird can also provide a strong suspicion of the disease.



Medication is used to kill the parasites, although the problem still remains that birds can easily become infected again and it is difficult to eradicate all parasites.


One treatment method that has seen positive results is treating the birds 2 days a week, then waiting for 5 days before recommencing treatment. This is repeated for a period of 2 months. This seems to have the greatest effect on diminishing the influence of the parasite.



In addition, proper hygiene in the enclosure is very important. This prevents the birds from being able to ingest too many oocysts and reinfecting themselves. Despite the extensive treatment method, it is still very difficult to entirely get rid of the parasite from an aviary.