Abstract
Image 1
D. Perianal pruritus
The image shows the nematode Passalurus ambiguus, the rabbit pinworm, in this case detected in a domestic pet rabbit. P. ambiguus is found in the cecum or colon. Adults are 5 to 10 mm long, threadlike oxyurids that may be detected in both hard feces and cecotrophs. P.ambiguus exhibits prominent lateral alae (Image 1a; arrows) and a muscular esophagus (Image 1b; arrowhead). Although even heavy burdens of the parasite are frequently nonpathogenic, young rabbits with high numbers of P. ambiguus may exhibit perianal pruritus. Oxyuris equi is another oxyurid parasite that may similarly cause pruritic perianal dermatitis in affected horses.
Additional reading: Harcourt-Brown F. Digestive system disease. In: Meredith A, Lord B, eds. BSAVA Manual of Rabbit Medicine. 1st ed. Quedgeley, England: British Small Animal Veterinary Association; 2014:168–190.
Contributor: Katherine Hughes, University of Cambridge, UK
Image 2
B. Calicivirus
Rabbit hemorrhagic disease (RHD) is caused by a calicivirus with high mortality and morbidity rates in wild, farm, and pet rabbits. The primary histological lesion is acute necrotizing hepatitis (Image 2); the necrosis can be periportal or random. Hemorrhages can occur in the lungs, heart, and kidneys. RHD has no treatment. Different pathogenic viral strains have been identified and are grouped into GI.1a-d and GI.2 genotypes, also known as classic RHDV and RHDV2 (or new variant), respectively. None of the other viruses listed cause acute hepatic necrosis in rabbits.
Additional reading: Harcourt-Brown N, Silkstone M, Whitbread TJ, et al. RHDV2 epidemic in UK pet rabbits. Part 1: clinical features, gross postmortem and histopathological findings. J Small Anim Pract. 2020;
Contributor: Filipe Fontes Pinto. HIPRA, Malveira, Portugal & School of Medicine and Biomedical Sciences (ICBAS), University of Porto, Portugal
Image 3
D. Graphidium strigosum
Graphidium strigosum is a rabbit nematode parasite that is predominantly found in the stomach. One study of wild rabbits in the United Kingdom (as was this case) indicated a prevalence of 78%. It is suggested that this nematode occurs infrequently in North America. G. strigosum nematodes are red and filiform. Histologically, the cuticle has conspicuous ridges, and the intestine is composed of multinucleated cells (Image 3). Males exhibit chitinized brown spicules. Trichuris leporis and P. ambiguus nematodes are typically found in the cecum and colon. Cittotaenia pectinata is a cestode occurring in the small intestine of rabbits.
Additional reading: Allan JC, Craig PS, Sherington J, et al. Helminth parasites of the wild rabbit Oryctolagus cuniculus near Malham Tarn, Yorkshire, UK. J Helminthol. 1999;
Contributor: Katherine Hughes, University of Cambridge, UK
Image 4
A. Gram
Encephalitozoon cuniculi is an important pathogen of rabbits, with granulomatous encephalitis and nephritis being the most common lesions. Although clinical disease is most common in dwarf rabbits, E. cuniculi is considered enzootic in all domestic and laboratory rabbits. Microscopic examination of the brain in this sudden death case revealed multifocal granulomas characterized by focal aggregates of macrophages and multinucleated giant cells surrounded by moderate numbers of lymphocytes and plasma cells. Although in some cases the agent can be seen on routine hematoxylin and eosin stain, Gram stain facilitates the identification of 1.5 to 2.5 μm, round to ovoid, dark blue spores (Image 4).
Additional reading: Rodríguez-Tovar LE, Villarreal-Marroquín A, Nevárez-Garza AM, et al. Histochemical study of Encephalitozoon cuniculi spores in the kidneys of naturally infected New Zealand rabbits. J Vet Diagn Invest. 2017;
Contributor: Fernanda Castillo-Alcala, Massey University, New Zealand
Veterinary Pathology invites submission of exceptional gross or microscopic images for consideration as an Image Challenge, along with a multiple-choice question and answer. For details, see the Instructions to Authors on the journal website.