The hot, arid Mojave desert. Yuccas and Joshua trees sparsely dispersed in the foreground. Yellow “caution” tape surrounding the affected area. Photographs being snapped with numbers and rulers.
DTCC research associate:
The victim (adult male tortoise) was found lying in dorsal recumbancy (on the carapace) in front of an empty manmade burrow, urates on the plastron and ground. A fellow male and female tortoise look on from the corner of the tortoise pen.
DTCC pathology tech:
Looks like a case of love……gone wrong … YYYEEEAAAAAAHHHHH!!
Okay, okay, that’s not how my day actually plays out when a dead tortoise is found on site, which luckily isn’t too often, but we do have a pseudo-CSI department here at the San Diego Zoo’s Desert Tortoise Conservation Center (DTCC).
If and when a tortoise is found dead on site, or needs to be humanely euthanized due to a debilitating illness or severe injury, it is immediately brought to the pathology trailer for necropsy. A necropsy is an animal autopsy, and it is performed by me, the pathology technician, as proxy for our pathologist who is based at the San Diego Zoo’s Wildlife Disease Laboratories. The necropsy helps determine the cause of death by examining body lesions or changes in tissues.
I begin a necropsy by verifying the death and identification of the tortoise, taking external measurements (weight, size, etc.), and noting any abnormalities seen on the exterior portions of the tortoise. After the external examination, I perform the internal examination, inspecting the organs, muscles, and joints, taking representative samples from each section for molecular diagnostics and histology. For histology, very thin-cut sections of these tissue samples (~10 µm thick) are mounted and stained on glass slides for microscopic examination of cells, structures, and immune response cells not visible to the naked eye. For molecular diagnostics we isolate DNA out of the tissue samples for real-time PCR, used to detect microorganisms. The samples, along with my gross descriptions (not gross as in disgusting, but gross as in overall) and photographic documentation of the case are sent to the pathologist, who will then interpret all of this information to make a diagnosis of why a tortoise died or the main cause of disease if it was euthanized.
Necropsy is a very useful tool for maintaining the health of a captive population, especially for an animal listed as an endangered species, such as the desert tortoise. By conducting necropsies, we have the opportunity to learn from the unfortunate death of an animal on site. We can see tissue proliferations, severe inflammation, and abscesses that are not externally visible in areas such as the lungs. We also inspect changes to the nasal cavities, an area frequently affected by Mycoplasma agassizii, one of the leading causes of upper respiratory tract disease in tortoises. We can see an excess in production of mineral deposits, such as uroliths (bladder stones) within the urinary bladder that are too large for the animal to pass so they cause a blockage. We can also see endoparasites present within the GI tract that we can sample for identification.
Identifying infectious diseases and disease-causing agents is the first step toward mitigating disease in the remaining population and establishing screening tests. Thus, by investigating the deaths at the DTCC we are able to make more informed decisions regarding how to provide the best care for these animals that are destined to augment the dwindling wild populations.
Larisa Gokool is a research associate at the San Diego Zoo Desert Tortoise Conservation Center. Read her previous post, Meeting Galápagos Tortoises.