# Pulmonary Vascular Proliferative Lesions in Wild Korean Raccoon Dogs (Nyctereutes procyonoides): Description of 13 Cases

## TL;DR

This study describes unusual lung blood vessel growths in wild Korean raccoon dogs, possibly linked to long-term parasite infections.

## Contribution

The paper provides the first detailed pathological characterization of pulmonary vascular proliferative lesions in wild Korean raccoon dogs.

## Key findings

- Lesions appeared as finger-like projections in lung blood vessels and were histologically benign.
- Most affected raccoon dogs had parasitic infections like heartworm and scabies, suggesting a link to chronic irritation.
- Special stains and immunohistochemistry confirmed the endothelial origin and non-cancerous nature of the lesions.

## Abstract

Pulmonary vascular growths inside blood vessels are unusual in animals, and very little is known about them. In this study, we examined 13 wild Korean raccoon dogs that were found to have these abnormal tissue growths in the lungs. We aimed to understand what these growths look like, what may cause them, and whether they are connected to other health problems. We found that many raccoon dogs had small finger-like projections growing inside the lung blood vessels. Most of these animals were also infected with parasites, such as heartworms in the chest and mites on the skin, which can cause long-term irritation and vasculitis, respectively. Under the microscope, the growths appeared to be made of harmless (non-cancerous) cells forming small papillary structures. These findings suggest that long-term irritation from parasitic infections may contribute to these unusual lung lesions. This information is valuable for wildlife health monitoring and helps veterinarians and researchers better understand diseases affecting raccoon dogs.

Pulmonary vascular proliferative lesions are rarely reported and poorly characterized in animals. In this study, we describe 13 cases identified in wild Korean raccoon dogs (Nyctereutes procyonoides), suggesting a higher-than-expected incidence in this species. Gross examination revealed villous projections within the lumina of pulmonary vessels, sometimes accompanied by pneumonia, hemorrhage, or Dirofilaria immitis (heartworm) infection. Most affected animals also presented with thick, dark gray cutaneous crusts associated with scabies infestation. Histopathologically, the lesions consisted of papillary proliferations within thickened vascular lumens. Special stains (Masson’s trichrome and Elastic Verhoeff–Van Gieson) demonstrated a single layer of endothelial cells lining fibromuscular and collagenous thick cores. Immunohistochemistry confirmed endothelial origin and benign proliferative nature, with positive expression of CD31, collagen types I, III, and IV, and proliferating cell nuclear antigen (PCNA). To date, pulmonary vascular proliferative lesions have not been well documented in N. procyonoides, and baseline pathological data, including findings from special stains, are lacking. These findings indicate that pulmonary vascular proliferative lesions may be underrecognized in raccoon dogs and suggest a likely association with chronic vascular injury related to parasitic infections. Further studies are warranted to elucidate the underlying mechanisms and contributing factors.