ILAR Journal Online, Volume 38(1) 1997: Unusual Mammalian Models

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ILAR Journal V38(1) 1997
Unusual Mammalian Models

Introduction
Ralph B. Dell

Researchers today are using more sophisticated animal models in biological research--unusual species, traditional laboratory animals with a defined microbial status, or animals that have been genetically modified. New models and new technology create special protocol review challenges for institutional animal care and use committees (IACUCs) and special veterinary care and husbandry issues for the animal care staff. Each of the 5 papers in this issue of ILAR Journal describes a special animal model and explores some of the IACUC and husbandry issues associated with it. These particular models were selected because of their uniqueness and relevance. The selection process was not meant to be exclusionary and, in fact, other uncommon models are available such as some amphibians and reptiles (see ILAR Journal 37[4]) and some mammals like voles and shrews. Because unusual models are being developed continuously, as the ILAR Journal Editorial Board becomes aware of new models, it will include them in the "Animal Models" department. If any reader knows of an uncommon or unusual animal model, please contact Ms. Mara Glenshaw, the Journal's Managing Editor.

The first paper (by Drs. VandeBerg and Robinson) discusses the origin, current genetic status, and uses of the laboratory opossum (Monodelphis domestica). These readily available animals are particularly well suited for use in studies of melanoma, hypercholesterolemia, and the development of arteriosclerosis and angiogenesis and corneal cancer. Because they are altricial, developmental studies are also done on their extremely immature young. An increasing number of researchers are using the laboratory opossum and considerable baseline data are now available. M. domestica are easily cared for in standard rodent cages and can be fed standard pelleted fox laboratory diet.

Next, Dr. Jackson provides a review of unusual laboratory rodent species such as voles, deer mice, ground squirrels, cotton rats, degus, woodchucks, and mastomys (Dr. Jackson). This article focuses on the uses, special husbandry needs, and infectious disease risks associated with wild rodents. Wild rodents have been used to study environmental impact, nutrition (such as atherogenic diets), and infectious diseases (such as sleeping sickness, poliomyelitis, and filariasis). In particular, the woodchuck is a popular model for studies of hepatitis and the development of hepatocellular carcinoma. Most of these species can be housed in standard polycarbonate caging on contact bedding. An important consideration for IACUCs and for veterinary care and husbandry staff is the potential risk of transmission of infectious diseases including hantavirus, viral hemorrhagic fevers, borreliosis, babesiosis, and ehrlichiosis.

Drs. Buchl, Keeling, and Voss describe the establishment of a specific pathogen-free (SPF) nonhuman primate colony. Their colony is specifically free of simian immunodeficiency virus, simian retroviruses 1-5, simian T lymphocyte virus, and Cercopithecine herpesvirus 1 (B virus). The SPF colony was established by identifying virus-free animals, implementing a well-conceived and well-executed breeding program, and testing frequently for each of the agents in order to detect and cull positives. Clearly these animals require a special housing area to preserve their SPF status, similar to SPF rodent housing within a facility that maintains animals with other opportunistic infections. In light of the fact that B virus is lethal to humans, IACUCs and the Occupational Health Service should consider whether personnel working with SPF primates (wearing protective gloves, mask, and face shield) as they would when working with animals from a conventional colony.

Drs. Safron and Gonder discuss the meaning of SPF for swine and how this SPF status is achieved and maintained. While production of SPF swine will reduce the number of infectious agents, total elimination of disease is not guaranteed. Clearly, testing must be performed to ensure that the animals are free of infectious other than indicator diseases. Since farm management practices could affect herd health, further testing must be performed to ensure that the animals are free from confounding pathogens. A number of veterinary care issues and husbandry factors that can also impact the suitability of SPF swine for biomedical research are described in this article.

Finally, Dr. Gordon describes transgenic technology and emphasizes the special problems that this technology has created for IACUCs, veterinary and husbandry staff, and investigators. The infectious disease potential of retroviral vectors is small due to species specificity and the fact that modern vectors are constructed in a way that minimizes the risk. The animal care staff needs to be aware that some transgenes may cause unforeseen health problems for transgenic animals. Several specific models are discussed to illustrate these problems. Extensive breeding may be necessary to establish the transgene in all cells. Embryo freezing is a method of preserving a transgenic line but requires special facilities, skilled people, and a way of keeping costs to a minimum if this technique is to flourish. A few of the ethical issues created by the technology are discussed in this article.

Thus, this issue of ILAR Journal contains information for IACUCs, veterinarians, animal care staff, and investigators who are currently working with or plan to work with these uncommon or unusual animals. While the articles are surveys, they are heavily referenced and should provide access to relevant literature for those who wish to pursue any of these special topics.