Many thanks to my veterinary colleague Dr Gordon Chalmers of Canada for much of this information.
There are two types of Adeno virus that infect pigeons. Type 1 mainly affects young pigeons and principally involves the digestive tract, causing diarrhoea and vomiting. Many of these birds recover. Type 2 affects older pigeons and frequently involves the liver, with most birds that become unwell dying within 24 hours.
A paper published in 1995 by several Belgian veterinarians described a new fatal disease of racing pigeons in that country. It began in October 1992 and was characterised by sudden death in pigeons of all ages. Some birds displayed watery yellow diarrhoea and vomiting before death. However, the main sign was sudden death, which occurred within 24 hours of the onset of illness, with none of the sick birds surviving longer than 48 hours. Losses from one loft to another varied but often were around 30%. In some cases, they reached 100%. In 18 months from January 1993, nearly 1000 pigeons that died of the disease were examined at the University of Gent, Belgium. These birds had hepatitis (liver inflammation) with extensive death of liver tissue microscopically. Examination revealed that the cause was Adeno virus.
The spread of Adeno virus in a loft was unusual in that it usually started in a single age group but then spread to birds of all ages. Other birds that had been in intimate contact with the dead birds often remained well. Even youngsters in the nest grew normally if they were able to feed themselves after their parents had died.
Subsequent testing showed that only immunosuppressed birds (those in which the immune system’s function was compromised) were vulnerable to the disease. However, the exact cause of the immunosuppression was unclear. Researchers have suggested that the Adeno virus that causes a disease in chickens had mutated or changed slightly to allow it to adapt to pigeons and cause this serious new disease. Definitive diagnosis is made by microscopic examination of tissues in which, with special stains, the viral particles can be seen as inclusion bodies within the birds’ cells. An antigen detection test is also available through AvianLabs as a QUICK test and is being increasingly used.
This type of Adeno virus infection is rare in Australia but is occasionally diagnosed as a cause of ill health and death through histopathology. Adeno virus rarely causes disease unless there are other immunosuppressive factors at work.
The disease reported in 1995 is now called Adeno virus type 2. The first (type 1) was discovered in 1976 and is associated with disease in young pigeons (compare this with the type 2 form of the disease). In this type there is a watery diarrhoea and weight loss. E. coli often complicates this Adeno virus infection and results in a more severe diarrhoea as well as vomiting and occasionally respiratory symptoms. The disease has a low death rate and some birds can spontaneously recover. Affected birds lose condition and, if racing persists, results are poor and there are increased losses. There is also decreased resistance to other diseases. The disease was reported in Great Britain in 1994 and 1995. Large numbers of infected birds were reported by Dutch pigeon veterinarian Henk DeWeerd in south-west Holland by the end of 1991. Whereas Adeno virus type 2 infection does not respond to antibiotics, this Adeno virus-E coli combined disease, often abbreviated to Adeno-coli syndrome, is usually successfully treated with antibiotics. If birds are autopsied, there is obvious enteritis (bowel inflammation) but the liver can look normal and extensive death of liver tissue is not seen microscopically. There are, however, the characteristic viral inclusion bodies. Adeno virus type 1 is also uncommon in Australia. Only a few cases have been seen at my clinic. Cases were managed by ensuring that the loft environment and management were good and that all secondary diseases, notably wet canker and coccidia, were treated in order that the birds were best able to clear the virus. Treating any concurrent secondary problems and providing ongoing good care often leads to a dramatic improvement in the birds. The concurrent E. coli can be treated with appropriate antibiotics. In-contact birds are treated with probiotics.