Avian malaria in a feral-pet pigeon: a case report

Abstract

Background Avian malaria is caused by diverse parasite species of the genus Plasmodium, and it affects various bird species. The occurrence of this disease in wild birds is understudied due to the scarce availability of samples. Hence the pathogenicity in these hosts is not completely known. In addition, feral birds may act as reservoirs bridging the transmission cycle from wild migratory birds to domestic and zoo-kept bird species. We report here the occurrence of P. relictum in a feral pigeon. Case presentation: The bird died unexpectedly, and necropsy revealed an anaemic carcass, with pale organs and hydropericardium. Histopathologic analysis revealed inflammatory infiltrates in lung and liver, and monocytes and Kupffer cells contained hemozoin pigment indicative of phagocytosis of Plasmodium infected erythrocytes. A high erythrocytic infection rate of 18% was evident in tissues and blood vessels in various organs. Furthermore, the thyroid had masses classified as thyroid carcinomas. Immunohistochemistry with anti-P. falciparum HSP70 antibody revealed positive signals in erythrocytes and intravascular leucocytes. Further analysis using Giemsa-stained blood smears revealed a high parasitaemia with an asynchronous infection showing all erythrocytic stages. Molecular diagnosis by PCR identified P. relictum, lineage GRW11 as the etiological agent. The bird presented died most likely due to an acute infection as evidenced by the high blood parasitaemia, leading to major erythrocyte destruction. Further analyses of feral pigeons (n = 22) did not reveal any additional cases with Plasmodium infections. Conclusion While our study suggests that Plasmodium infections are rare in pigeons, host conditions like immunosuppression may have influenced the infection outcome in this fatal case due to the tumour.