Case of fatal Histomonas meleagridis infection (blackhead disease) in two peafowl (Pavo cristatus) in Greece.

Histomonosis is a parasitic disease caused by Histomonas meleagridis, a protozoan that can lead to necrotizing typhlitis and hepatitis in several bird species. Currently, only a few cases have been reported in peafowl; therefore, limited information is available regarding the pathogenicity of the parasite. in this species. The present study aimed to investigate a case of histomonosis in peafowl originating from a free-range farm, housing various avian species and other animals. In November 2022, two peafowl, aged 4 and 8 months, were submitted for necropsy at the Unit of Avian Medicine, Aristotle University of Thessaloniki (AUTH). One week prior to presentation, peafowl showed depression, anorexia, and apathy. On postmortem examination, the liver was enlarged and exhibited multifocal, circumscribed necrotic lesions. The caeca were grossly distended, with yellowish content, necrotic foci, ulceration in the wall, adhesions with adjacent organs, and evidence of peritonitis. Histomonosis was suspected based on the post-mortem examination. To confirm the diagnosis, parasitological examination was performed on faecal samples, while tissue samples from the intestine, liver, and spleen were collected for histopathological examination. Parasitological examination revealed numerous spherical protozoa with a diameter of 8-14 μm, morphologically similar to H. meleagridis. Histopathological examination demonstrated ulcerative necrotizing typhlitis and necrotizing hepatitis. Furthermore, Periodic acid-Schiff (PAS) histochemical staining revealed trophozoites morphologically similar to H. meleagridis. The lack of commercially available treatments and limited knowledge of the prevalence of this parasite among domestic and free-living birds in Greece highlight the importance of implementing strict biosecurity measures on backyard and free-range poultry farms to prevent the establishment of endemic infections.