Zoo InternQuest is a seven-week career exploration program for San Diego high school juniors and seniors. Students have the unique opportunity to meet professionals working for the San Diego Zoo, Safari Park, and the Institute for Conservation Research, learn about their jobs, and then blog about their experience online. Follow their adventures here on the Zoo’s Website!
This week, interns had the opportunity to meet with Megan McCarthy, Resident Zoological Pathologist, and Yvonne Cates, Histology Technician, to learn about what happens to an animal after it dies. Animals from both the Zoo and Safari Park come to the Wildlife Disease Labs to be examined in order to try to determine the cause of death. The most common animals are small birds, but the pathologists work with deceased animals as large as an elephant.
Megan McCarthy is a Resident Zoological Pathologist at the Zoo. She first received an undergraduate degree in economics before deciding to go back to school to study to be a vet. After graduating from vet school from NC State, Dr. McCarthy applied to UC Davis to do a residency program to learn about being a zoo pathologist. She currently works with five other zoological pathologists at the zoo.
Interns first walked to the Wildlife Disease Lab, part of the Zoological Hospital and Biological Research Center, to began to explore the process of examining a deceased animal. Here, Dr. McCarthy showed us a presentation depicting what she does every day and why it is important to pay attention to the animals that have passed. Included in the presentation were three cases that the interns worked through to determine the possible cause of death of each animal.
Half of Dr. McCarthy’s job involves working at her microscope and analyzing tissue samples on the cellular level. As a pathologist, she looks at possible pathogens found in an animal that may have been the cause of death. In some cases, such as when dealing with a virus, Dr. McCarthy is unable to see the true pathogen and instead looks for signs that the pathogen did pass through the specific area. Those working in molecular pathology will take this a step further and use a scanning electron microscope to analyze the sample on a molecular level.
After a quick introduction, interns walked to the histology lab to find out what it takes to make the samples of animal tissue visible under the microscope. There are many steps that go into preparing these slides, and a great deal of care goes into it. One slip up could prevent the zoological pathologists to properly analyze the sample for the animal’s cause of death.
Yvette Cates is a Histology Technician in charge of preparing the samples. In the containers are tissue samples taken by the zoological pathologists from various parts of the deceased animals. The tissue samples are currently being ‘fixed’ by using formalin to denature the proteins and stop the process of the tissues breaking down.
After fixing, the samples are put into this machine to remove the excess water and replace the open spots with paraffin. This process takes 6 to 8 hours, so Ms. Cates leaves the machine to do its job overnight. The paraffin makes the tissue samples last for a long time; some of the tissue samples in the histology lab are from over 30 years ago.
After being sliced, the tissue samples are moved to this machine to stain different parts of the cells. Each color will highlight a different structure when placed under the microscope. Some of the stains are made in the histology lab by following a recipe, and others are ordered from various places across the country.
Once stained, the tissue sample slides are ready to be examined by the zoological pathologists. Each case requires a different amount of slides, with a small frog requiring only a couple and a large elephant requiring dozens. This is because more samples are taken from various parts of the same tissue to ensure a good representation of the organ as a whole.
Occasionally, a different type of process needs to be done to show the animal’s structure as a whole. In the case of this frog, all of the tissues were left transparent and only the skeletal structure was stained. This frog had some leg abnormalities, so only staining the skeletal structure made it easier to find where the problem started.
Next, interns visited the building where the necropsies take place. A necropsy for an animal is used in the same way that an autopsy would be used for humans. The deceased animals are taken here to receive a gross examination and have samples taken from various parts of their anatomy.
Before entering the necropsy room, interns were required to wear plastic shoe coverings to prevent contaminants from entering the building. In between every animal necropsy, tools and tables are sanitized to prevent the spread of disease and to help properly determine the animal’s specific cause of death. When leaving the necropsy building, it was also required for interns to step through a footbath.
Lastly, Dr. McCarthy showed us some preserved samples taken from animals. Here, a horn is being compared to an antler in terms of bone structure and composition. Other animal sections included a section of a deer’s brain, a cross section of an elephant’s foot, and a skull from a hippo.
Week Five, Fall 2015