What has always fascinated me and never ceases to stir up my curiosity is how diseases work: what goes on in the battle between host and intruder(s), what determines the outcome of the interaction, and how can I figure out the events leading up to death. My curiosity landed me in veterinary school in Berlin, Germany, which answered many questions and raised even more. A few years later, I had the great opportunity to pack my bags and fly to San Diego to join an amazing team of wildlife pathologists, epidemiologists, and scientists at the San Diego Zoo Institute for Conservation Research Wildlife Disease Labs—the wildlife crime scene investigators. We work behind the scenes as detectives of animal health.
As we walk through some of the aspects of a disease investigation, I am sure you will soon realize that the process is much more complex than what I can put into a few words here.
Crime scene: The body. Yes, the immediate surroundings, environment, and health history of the individual can provide important evidence. Therefore, the animal care staff and zoo veterinarians are questioned. They provide valuable information on the health, behavior, and social interactions the animal had leading up to its death. The body itself is delivered to the Wildlife Disease Labs where postmortem (after death) investigations unfold.
Criminals: The “criminals” or causes of disease are manyfold. They include microorganisms such as viruses, bacteria, and parasites. Some parasites use an animal’s body as part of their life cycle. Certain nematodes, for example, take long journeys through the body while leaving trails of lesions. They are swallowed, break through the intestinal wall, wander via the liver to the lung, get coughed up, and escape the host. If the parasite gets lost in the body it can end up in abnormal tissues, such as the brain.
Even “normal” cells of the body can go rogue and can cause disease. For example, tumor cells lose the ability to play by the rules and expand into neighboring space or travel to new locations (metastasis), and immune cells that cannot distinguish between self and other end up attacking its own body (autoimmune diseases).
Profiling: Systematic analyses are required to narrow down the pool of suspects. A necropsy (autopsy on an animal) is performed so the pathologists can examine the entire body from nose tip to tail tip. They look at every organ system for abnormalities and take small sections of all tissues to view under the microscope. This enables identification of patterns and evidence—the ultimate clues pointing to what is going on and what group of criminals is responsible.
In some cases, microorganisms leave unique patterns of lesions that are known to be caused by this one entity. These lesions are known as pathognomonic, and the agents causing them are easier to convict than microorganisms with elaborate master plans of attack and destruction.
Tools of conviction: Once the profile is set and the list of suspects reduced, the suspicion needs to be verified. We use molecular techniques to identify microorganisms. Specifically, we isolate and sequence their DNA (their genetic code). There are large databases of DNA sequences of all known microorganisms available for researchers to use as comparison and find a match, similar to the large fingerprint database used by the FBI.
Implications: The health and welfare of the animals are a number one priority for San Diego Zoo Global. Investigating causes of death within the population will identify if there is an emergence of a significant disease problem that requires immediate intervention.
By Josephine Braun, D.V.M., scientist, Wildlife Disease Laboratories