In 1995 a new, fatal disease of racing pigeons was described in Belgium. It began in October, 1992 and was characterised by sudden death in pigeons of all ages (note!). There were very few clinical signs in affected birds prior to death -- occasionally, there was fluid, yellow diarrhoea and vomiting. However, the main sign was sudden death which occurred within 24 hours of the onset of illness, with none of the obviously sick birds surviving longer than 48 hours. Antibiotic treatment had no effect on the outcome of this disease. Losses in individual lofts was variable but usually amounted to 30%.

At post mortem examination of these birds, veterinarians found that about 15% had a yellow, pale, swollen liver that exhibited a red sheen as the most characteristic change. Microscopic examination of these livers revealed widespread localized or more diffuse areas of death of this tissue. As well, there were characteristic structures called inclusion bodies in the nuclei of affected liver cells.

Investigation of the field situation showed that, although this illness occurred initially in one age group in 65% of affected lofts, in about 70% of the cases, the disease finally spread to all ages of birds in these lofts. Losses of birds in affected lofts were usually about 30%, but in some cases, reached 100%. The investigators were astounded that in lofts in which these acute deaths occurred, pigeons that did not die remained completely normal, with no sign of clinical illness. Even youngsters in the nest grew normally if they were able to feed themselves or were raised by other pigeons, after their parents had died.

Special examinations of the livers of affected birds by means of an electron microscope determined that the cause was likely an adenovirus (pronounced ADD-enovirus).

The disease reported this year from Belgium is the second known adenovirus-caused condition to affect pigeons. The first one (called Type I) was discovered in 1976, and was associated with disease in young pigeons during the first half of the year, with peak frequency in June. Clinically, in this type, there is watery diarrhoea and weight loss. Intestinal bacteria called E.coli often complicate this adenoviral infection, and results in a more severe diarrhoea, as well as vomiting and occasionally, death.

This adenovirus-E. coli combined disease is usually successfully treated with appropriate antibiotics which deal with the E. coli infection. In birds that die from this combined disease, the liver often appears grossly normal, or only mildly affected.

However, microscopically, there are characteristic inclusion bodies of adenoviral infection in cells of the liver (Figure .) Extensive death of liver is not seen in this condition. Gross evidence of enteritis (inflammation of the intestines) is usually present.

By contrast, the adenoviral disease described in Belgium in 1995 (called Type II), causes extensive destruction of the liver, and sudden death of affected birds within 48 hours of the onset of illness. All ages of birds are affected in Type II. If a number of young birds begin to vomit and have diarrhoea, and are off colour, it would be fair to consider this adenoviral- E.coli combined disease as a good possibility. Further examinations of dead birds by your veterinarian and diagnostic laboratory will help to confirm the diagnosis, and will likely result in a better approach to antibiotic therapy.