Fungal respiratory infection cause of death in Mute swan

In January 2018 a severe respiratory infection was diagnosed in a mute swan (Cygnus olor) that had been found dead in Harderwijk. The carcase of the juvenile male swan was submitted to the DWHC by the animal ambulance of Ermelo-Harderwijk for investigation into the cause of death. Post-mortem investigation showed that the bird had died as a result of a severe inflammation of the airways and air sacs. The infection had been caused by the fungus Aspergillus fumigatus, leading to a disease known as aspergillosis.

Aspergillus fumigatus

Foto: Afdeling Multimedia faculteit Diergeneeskunde

This fungus is ubiquitous and can cause disease in humans with immunosupression and in other species. particularly birds. Whilst it typically causes respiratory infections, other organs may also be affected. This infection is a common cause of death in captive birds but is less often involved in illness in wild birds (Bernaert, 2010). Whether or not disease develops depends on the amount of fungal spores that the animal inhales and the immune status of the individual – weak animals are particularly susceptible. A range of factors can result in the immune system being weakened: For example, other disease or injuries, starvation, migration and the breeding season (Bernaert, 2010).

Disease course

Infection occurs when an animal inhales fungal spores and often begins in the air sacs. If the immune system is unable to clear the spores then the airways can become damaged or blocked by dead tissue and inflammatory fluids. The windpipe of this mute swan was almost completely covered by white inflammatory material (see picture).

Beernaert L. A., F. Pasmans , L. Van Waeyenberghe , F. Haesebrouck & A. Martel (2010). Aspergillus infections in birds: a review, Avian Pathology, 39:5, 325-331, https://www.ncbi.nlm.nih.gov/pubmed/20954008