The Living Dead: Keeping Wildlife Alive Through Scientific Use of Biomaterials
Department of VM-PMI, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
Despite significant advances in understanding the diseases of wildlife over the last few decades, wildlife populations continue to be impacted by recurrent, endemic or emerging diseases. A few high-profile endangered species have been extensively studied, but disease investigations in most species have been neglected of necessity because of limited resources. As more species become endangered, there will be little information on the historic diseases and genetic composition of those species which will serve as a background against which to interpret pathologic findings. For example, when the Channel Island fox (Urocyon littoralis) began to decline precipitously during the mid-1990s and disease was suspected as contributing to that decline, we had no information on the historic and endemic diseases of this population when it was thriving, so that the parasites, serologic evidence of viral exposure, and diseases disclosed during the population decline could not be put into perspective.
While large epidemics in wildlife are usually investigated, many smaller epidemics, genetic diseases or toxicoses likely go unnoticed. The future brings an even more dismal scenario in which loss of genetic diversity, habitat degradation, greater habitat restriction, and exposure to exotic pathogens will cause disease to play a greater role in wildlife losses while the resources to investigate these diseases remain limited. In the future, solving complex questions of disease ecology will need to include assessment of genetic traits, demographics, and environmental conditions in light of historic characteristics of healthy populations. These studies will require information and resources that will not be available unless we begin to collect data and archive biomaterials now.
Pathologists are quintessential pack-rats and have traditionally viewed dead animals as packages of information and future opportunity. Many field veterinarians and wildlife biologists also maximize sample collection when animals are handled. This culture of preservation and archiving needs to pervade all aspects of animal conservation so that resources are available in the future. The usefulness of archived wildlife biologic samples has been documented in several recent disease investigations. During investigation of the 1994 canine distemper epidemic in Serengeti lions, archived serum samples disclosed that lions in this region had been exposed to CDV over a decade earlier, but without the high mortality noted in the 1994 epidemic, thereby indicating that a more pathogenic strain had emerged. While investigating the cause of the Channel Island fox decline in the late 1990s, frozen archived foxes that had died before 1994 were submitted to the pathology survey so that diseases and parasites detected in foxes before the decline could be excluded from investigations.
When carcasses are encountered in the field, many useful samples can be collected with little effort. Preserving tissue samples in formalin or freezing whole bodies or organs are the simplest, most reliable and useful methods of biomaterial collection. Formalin is inexpensive and available worldwide, and formalin-fixed tissues are useful for molecular identification of infectious agents and toxin analyses, as well as for histopathology. Feces can be collected in formalin to identify parasites or parasitic ova or in alcohol to identify parasites, measure steroid hormones, or perform genetic analyses from exfoliated enterocytes. Frozen or dried hair samples also provide cells for genetic analyses. Whole blood can be collected in appropriate buffers and stored at room temperature or frozen for genetic analyses of the host or hemoparasites in the host. Blood smears can be easily prepared and air dried for a hemogram or for hemoparasite identification. Blood adsorbed onto Nobuto Blood Filter Strips® can later be extracted for serologic tests. Serum also can be separated from blood by field centrifuges that are powered by car batteries or simply by gravity. Access to freezers or liquid nitrogen for storage of blood and tissues can often be arranged by networking with regional veterinarians or labs who usually are enthusiastic about collaborating with wildlife projects.
Collecting and preserving living biomaterials from wild animals in the field is limited by access to laboratory equipment, a means to power that equipment, and for dead animals, by timely access to animal carcasses. Preserving gametes and somatic cell lines is not feasible in most situations because their viability depends on harvesting cells soon after death and then careful step-down freezing of single cell suspensions. However, gametes and cells from small skin biopsies, if taken by sterile technique, can remain viable in tissue culture medium temporarily, providing time for transport to a laboratory for appropriate processing. A skin biopsy can then sometimes yield fibroblast cell cultures that are valuable for genetic assessments.
One of the greatest challenges facing successful biomaterial banking from wildlife is training of field personnel to collect samples appropriately. To maximize the collection of useful biomaterials, biologists, park wardens, and other personnel who live and work where wild animals are handled need to be convinced of the value of collecting biomaterials and then trained in appropriate methods. The Necropsy Procedures for Wild Animals was created for this purpose and is available free of charge on the Web <http://www.vetmed.ucdavis.edu/whc/Necropsy/TOC.html> (VIN editor: link could not be accessed on 2/12/21). Another challenge is developing policies that maximize the use of biomaterial archives. Archives of tissues and slides, as well as databases, are costly to develop and maintain, so that currently only a few archives exist, such as those at the Smithsonian Institution, San Diego Zoo, or in faculty laboratories at universities. Determining who owns the animal tissues in these archives and who should have access to these materials and information is a complex issue. These materials represent a considerable investment of time and money on the part of the investigators, yet progress in disease research requires use of tissues in collaborative projects. Prioritizing research requests for access to these materials is best done by committees of informed stakeholders, so that the valuable tissue resources are not used inappropriately. The IUCN CBSG in collaboration with Endangered Wildlife Trust has initiated a series of Genome Resource Banking workshops to address some of the complex issues of biomaterial banks.
So, harvest, collect, preserve, photograph, freeze, and store whatever tissues possible whenever you are handling wild animals. These archives will prove invaluable in animal health investigations and may determine the future of some species.