Small mammals such as gerbils are becoming increasingly popular as pets and today’s owners have a greater understanding of the environmental, nutritional and behavioural needs of these animals. This is reflected in increasing numbers of published papers and data that are now available for small mammals although, unlike other rodent species, there is relatively little information about naturally occurring diseases in pet gerbils. Small mammals have their own unique perspectives on common lesions, even among different subspecies. Nevertheless, it is still possible to apply “first principles pathology” to investigate lesions and form an appropriate differential list, just as is done for other domestic species.
Small mammals have their own unique perspectives on common lesions, even among different subspecies
The importance of species and strain
Numerous species of gerbil exist, although only a few are commonly kept as pets. They live as monogamous pairs or in small groups, and their lifespan is typically three to four years. The most common species which are kept as pets in the UK are the Mongolian gerbil (Meriones unguiculatus) and the fat-tailed gerbil (Pachyuromys duprasi). However, different species and strains show differing behaviours and resistance to disease, so it is important to include the species of gerbil on the submission form, along with the age and sex of the animal, just as for other species.
Case study
Recent histopathology submissions from gerbils primarily involved neoplastic skin lesions. Most of the lesions involved the ventral scent glands, although lesions from other parts of the body were also submitted. In this brief report, we describe an unusual presentation of squamous papilloma with a concurrent squamous cell carcinoma.
The patient was a two-year-old male gerbil who presented with a 20 x 17mm hairless growth in the umbilical region. This consisted of a well-demarcated papillomatous lesion composed of squamous cells, with marked hyperkeratosis with some areas of crusting (Figure 1). There was marked hypergranulosis of the squamous cells, as well as the proliferation of the basaloid layer. Underlying the papillomatous lesion there was a markedly infiltrative lesion composed of poorly differentiated squamous cells, arranged individually or in solid trabeculae, within a fibrous stroma (Figure 2). Neoplastic cells were highly pleomorphic and showed high mitotic activity. The papillomatous lesion was entirely removed, but there were extensive areas of malignant squamous cells extending to the deep margin of the section. A diagnosis was made of a poorly differentiated squamous cell carcinoma (SCC) arising from a papilloma.
Final thoughts
Although cutaneous papillomas and carcinomas are recorded in Mongolian gerbils, this was an unusual lesion. Neoplastic skin lesions involving the scent glands can be sebaceous adenomas, epitheliomas or carcinomas, including SCC. They can become ulcerated and infected, leading to significant debilitation. Malignant lesions can be locally invasive and can also metastasise to the regional lymph nodes and lungs.
Progression from squamous papilloma to SCC has been recorded in rabbits and four-toed hedgehogs, but little is known about this progression in Mongolian gerbils
Progression from squamous papilloma to SCC has been recorded in rabbits and four-toed hedgehogs, but little is known about this progression in Mongolian gerbils. Likewise, the development of papillomas due to infection with papillomavirus, as in humans and other domestic species, has also not yet been reported in gerbils.
