Verminotic pneumonia in South American fur seal (Arctocephalus australis) in Southern Brazil

Abstract

Verminotic pneumonia caused by Parafilaroides spp. nematodes is an underreported disease in beached South American fur seals, with scant literature available on the characteristics of parafilaroidiasis, the nematode itself, as well as its occurrence in pinnipeds in Brazil. The present work aims to identify, describe and detail the histological features of the infection and molecular characteristics of verminotic pneumonia in the South American fur seal. Twenty-six specimens of Arctocephalus australis, found dead on the northern coast of Rio Grande do Sul in 2021, were analysed. These animals were identified and submitted to necropsy and histology. For the molecular identification of metastrongylids, lung fragments were subjected to DNA extraction, polymerase chain reaction targeting the Internal transcribed spacer 2 (ITS-2) gene and subsequent sequencing. In total, 12 animals presented with parasites in the lung parenchyma on histological evaluation, and only 1 showed a granulomatous lung lesion at necropsy. Microscopically, the nematodes were found mainly in the alveoli, associated with little or no inflammatory response, and they had morphological characteristics compatible with metastrongylids. Six ITS-2 gene quality sequences were obtained; after comparative analysis via BLAST, they showed similarity with sequences obtained from Parafilaroides sp. Therefore, verminotic pneumonia caused by Parafilaroides represents an important differential diagnosis of lung disease in South American fur seals found on the northern coast of Rio Grande do Sul.

Keywords: Arctocephalus australis; ITS-2; Parafilaroides; metastrongylids; pinnipeds.

Graphical abstract

Fig. 1.

Verminotic pneumonia by Parafilaroides sp. in the South American fur seal. Multiple, whitish nodules measuring 0.5–2.5 cm in the lung lobes (3 cm bar).

Fig. 2.

Histology of verminotic pneumonia caused by Parafilaroides sp. in the South American fur seal. (A) Metastrongylids composed of a thin eosinophilic cuticle; a thin hypodermis where the lateral cords are inserted (arrows) is observed. In the pseudocoelomic cavity, there are several sections of intestine composed of a single cell layer (asterisks) (50 μm bar), haematoxylin and eosin (H&E) stain. (B) Female nematode containing larvae eggs inside the uterus and sperm deposit (asterisk) (20 μm bar), H&E stain. (C) Cross-sections of female nematode parasites with intrauterine larval eggs are observed, organized in groups and located in the alveolar spaces, generating marked alveolar emphysema with the absence of an inflammatory infiltrate. Adjacent to the emphysematous areas, the parenchyma is moderately atelectatic (100 μm bar), H&E stain. (D) Bronchiole lumen with nematode cross-section. Female, with a female reproductive system and eggs hatched inside the uterus (20 μm bar), H&E stain. (E) Degenerated parasitic sections, with and without larval eggs, and surrounded by mononuclear inflammatory cells and fibrin (50 μm bar), H&E stain. (F) Nodular lesion with a granulomatous appearance, characterized by eosinophilic fibrillar material, associated with a mononuclear inflammatory infiltrate and cellular debris, and surrounded by fibrous connective tissue (100 μm bar), H&E stain.

Fig. 3.

Maximum-likelihood phylogenetic tree 2. Performed with the Hasegawa–Kishino–Yano model with a gamma distribution (+G) of partial sequences of the ITS-2 gene. The numbers in the branches indicate bootstrap values. Only bootstrap values >50 are counters. The numbers displayed next to the species name are the GenBank^® accession numbers of the sequences used. The generated sequences for the Parafilaroides sp. are in bold, indicated by a black circle.