Air sac trematodes: Morishitium polonicum as a newly identified cause of death in the common blackbird (Turdus merula)

Abstract

Necropsy of two free-ranging common blackbirds ( Turdus merula ) found dead in central Italy revealed the presence of a high number of cyclocoelid flukes in the coelomatic cavity. Cyclocoelid flukes primarily infect avian respiratory system. Histologically, air sac walls were covered with a fibrinous exudate containing degenerate heterophils, many trematodes and some colonies of Gram-positive cocci. The superficial bronchi and parabronchi were markedly distended, and the adjacent pulmonary parenchyma was congested and collapsed. Trematodes, surrounded by a mild suppurative to pyogranulomatous inflammatory reaction, were also observed on the pericardial, intestinal, kidney and hepatic serosal surfaces. The death of the two examined birds was likely due to the high parasite load and associated severe lesions. At parasitological examination, flukes showed a tongue-shaped elongate body, tapered anteriorly and rounded posteriorly, of 2,088–2,314 μm in width and 8,268–11,830 μm in length. The mouth was slightly oval and sub-terminal, with a small oral sucker. The oval pharynx measured 250–309 μm, and the two caeca joined posteriorly. Two large (550–702 μm × 450–520 μm) globular testes were situated obliquely to each other, whereas an oval (250 × 300 μm in mean) or round (about 334 μm in diameter) intertesticular ovary was placed in a longitudinal straight line with the testes. The ootype was about 110 μm in diameter, while the brown-yellow eggs measured 131.5 × 73.9 μm in mean. The genital pore was post-pharyngeal, while the symmetrically arranged vitelline glands were not confluent posteriorly. Morphoflogical diagnosis led to the identification of Morishitium polonicum , a cyclocoelid fluke species that typically inhabits the air sacs of blackbirds. The morphological diagnosis was corroborated by molecular phylogenetic analysis of the mitochondrial (CO1, ND1) DNA loci. The present study provides the first report of pathological lesions and death caused by M. polonicum in birds.

Parasitofauna survey of song thrushes (Turdus philomelos) from the eastern part of Spain

“…Although mild associated lesions were showed in most infected animals in this study, only one bird revealed a massive infection (72 adult trematodes in the coelomic cavity) with severe damage in several organs (tracheitis, aerosaculitis, enteritis and hepatitis). This trematode has been previously described on Turdidae from different European countries such as Spain [1], Poland [14] or Italy [4]. Birds get infected through the consumption of wetland-associated mollusks.…”

“…Birds get infected through the consumption of wetland-associated mollusks. Although there is scarce information about the pathology related to M. polonicum infection, airsacculitis, bronchitis and peribronchitis have been recently described in Turdus merula [4]. However, this is the first report of severe enteric and hepatic lesions associated to M. polonicum infection in Turdidae.…”

“…Although corporal condition of evaluated thrushes was not affected, probably due to the low intensity of parasitism derived from an evolutionary adaptation [16], under stressful conditions (migration) the consecutive immunosuppression can compromise the health status of Turdus when pathogens are present, making it difficult for birds to travel long migratory distances [23]. There is scarce information related to thrushes parasitofauna both in Europe and concretely in Spain, since most of studies have been traditionally focused on viral processes [6,7] or only in one parasitic species, mainly M. polonicum [1,4]. Because the parasitic richness of migratory birds could be higher than the one of resident specimens [24], it is important to consider the results in the present study to evaluate their consequences on the thrushes' migration [24][25][26].…”

“…Different helminths (trematodes, cestodes, nematodes, and acanthocephalan) have been previously isolated from several anatomical regions of Turdus spp. [3][4][5]. These birds have been widely studied as reservoirs of some viral pathogens (e.g., highly pathogenic influenza aviar and usutu virus; [6,7]), but it is still unclear their role as reservoir of parasites for domestic poultry, humans or other game bird species.…”

First finding of Morishitium polonicum (Trematoda, Cyclocoelidae) in Turdus merula and Coccothraustes coccothraustes in Russia

“…The typical host of the parasite is Turdus philomelos Brehm, 1831. Morishitium polonicum was previously registered in thrushes in Poland (Machalska, 1980;Sulgostowska & Czaplinska, 1987), Italy (Visconti et al, 1988;Bona et al, 1995;Galosi et al, 2019), the Czech Republic (Sitko et al, 2017), and Spain (Jaume-Ramis & Pinya, 2018). The parasite was also noted in Armenia, Azerbaijan, Georgia, and Uzbekistan as Neocyclocoelum elongatum (Harrah, 1921) (Feizullaev, 1980).…”