About Author: Carmel Witte

Posts by Carmel Witte


The Social Network…of Birds

Two bee-eaters appear to be sharing a meal in their aviary.

These two bee-eaters sharing a meal in their aviary are part of the same social network.

The age of social networking has the world communicating through cyberspace on just about anything. We are now connected to a network of people on Facebook and Twitter with whom we tune in daily to see what our friends are up to. In the past hour, my friends on Facebook looked at the nutrition facts on a candy bar (Is that really a good idea?), posted a CUTE photo of a clouded leopard (thanks to my “friend,” San Diego Zoo Global), and humorously referenced her boss mistaking a Kanye West song for the ‘80s hit single “Ghostbusters.” This is my social network.

Scientists are developing new methods to understand how people are influenced by their social network. Who we are connected to in the virtual world and in real life influences different aspects of our own lives, such as whether we vote in elections, our happiness, our weight, and whether we catch the flu or acquire other diseases. In collaboration with James Fowler, Ph.D., a professor at the University of California, San Diego, we are also trying to learn how connectedness influences the spread of disease in bird populations.

Avian mycobacteriosis is a bacterial disease of birds caused by Mycobacterium avium and other related species of mycobacteria. This is a challenging disease of birds, because whenever a case arises, we do not know how far an infection has spread through a group of “connected” birds sharing the same aviary. Traditionally, disease acquisition has been attributed entirely to contact with other infected birds; however, recent studies conducted by the Wildlife Disease Laboratories, a division of the San Diego Zoo Institute for Conservation Research, show that the environment may also be playing an important role in the spread of this disease. So, which is more important, the social network or the environment?

A powerful method of untangling this dizzying question is a social network analysis. Years of careful record keeping has created an archive of data documenting each bird’s aviary and enclosure-mates. These data can be used in conjunction with health history to determine whether the occasional cases of avian mycobacteriosis we see are attributed to a bird’s social network or its environment history. What makes the problem interesting is that the network is dynamic. Similar to how I might change my Facebook network by adding or dropping a friend, one of our birds might change social networks when she moves into a new enclosure to be closer to her new boyfriend (i.e., she drops her old bird “friends” and adds a new bird “friend”). Evaluating these dynamics through time is where social network analysis is remarkably powerful. Ultimately, we hope to uncover the relative contribution of mycobacterial infections due to both the social network and the environment.

We are just beginning this fascinating journey into understanding the influence of social networks on disease dynamics in our animals, so you will have to stay tuned to find out the answers. These answers will allow us to develop better disease-management protocols to mitigate risk to birds at the San Diego Zoo and San Diego Zoo Safari Park, as well as in conservation programs around the world.

Carmel Witte is a researcher with the San Diego Zoo Institute for Conservation Research. Read her previous post, Cutting-edge Science in Historical Surroundings.


Cutting-edge Science in Historical Surroundings

Looking across St. Michael’s bridge, early morning, in Ghent, Belgium.

I stood on the side of Saint Michael’s bridge staring at the stunning city before me: Ghent, Belgium. For four nights I was privileged to live in the beauty of this Central European city and take in all of her cafes, castles, and (my favorite!) chocolate. More importantly, I was there on official San Diego Zoo Global business to join some of the world’s best minds for a short, intensive workshop on molecular epidemiology and attend an influential conference that is held only once every three years: The International Symposium of Veterinary Epidemiology and Economics (ISVEE; endearingly called “iz-v”). It was an amazing opportunity provided by special funds set aside for employee development to meet with, learn from, and establish collaborations with some of the best in the field.

My journey started with the workshop in molecular epidemiology. The course instructors came from distant corners of the globe, including New Zealand, Scotland, and the U.S. to share their expertise with approximately 30 participants. We gathered for 3 days under the dim lights and a vaulted ceiling of wooden beams on the 4th floor (a.k.a. the attic) of a medieval Dominican monastery, Het Pand. This venue was not exactly the white, sterile laboratory from the movies (or the Zoo’s lab!) in which molecular science is usually performed, but I liked the contrast…cutting-edge science in historical surroundings.

Het Pand is the medieval Dominican Monastery where the molecular epidemiology course was held, Ghent, Belgium.

Molecular epidemiology is a specialized subfield of epidemiology (see Epidemi-what?) that requires unique tools and techniques to uncover patterns of disease transmission at the genetic level. My interest in this topic stems from the Zoo’s Molecular Diagnostic Laboratory. The lab was established in 1999 as part of the Wildlife Disease Laboratories to fulfill a need to develop diagnostic tests suitable for our animals and to improve our ability to identify and control important diseases. As one of the only zoo-based molecular diagnostic labs in the world, it has been instrumental in the development of diagnostic tests and animal disease research. For example, in 2007 a generous grant from the Ellen Browning Scripps Foundation allowed us to carry out a large study to describe herpesviruses in hoofed mammals (antelope, deer, goats, sheep, cows, and similar species). These herpesviruses can cause a fatal disease called malignant catarrhal fever when they are passed from animals that naturally carry the virus to new, susceptible hosts. Molecular methods can be used to look at the genetic similarities between viruses found in different animals to determine who is passing them to whom. This is where the epidemiology comes in.

Looking for patterns within molecular data (i.e., patterns across changes in DNA) requires methods that are new to me as an analytical epidemiologist. Thus, my goal in attending the course was to develop a working knowledge of such techniques to further improve the Wildlife Disease Laboratories’ ability to answer some pressing conservation questions. On the second day I was introduced to a new data analysis technique called Analysis of Molecular Variance (or “AMOVA” for short). Such a technique will allow me to extend our valuable data on herpesviruses and ask new or additional questions like: “Are animals in multispecies exhibits more likely to transmit the virus to each other?” Such an analysis could have a big impact on providing information that helps zoos better manage endangered species in the presence of this known disease.

A view of Maastricht, looking over the Meuse river.

Following the workshop, my travels then took me 90 miles east to the Belgium-Netherlands border where I joined 1,000 conference participants in Maastricht, The Netherlands, for 5 days of everything-animal-related epidemiology. Maastricht is a beautiful, historic-yet-modern city on the banks of the Meuse River that is famous for the birthplace of the European Union and the single European currency, the euro. My days in Maastricht consisted of attending talks on the latest work in the field, while the evenings presented opportunities to meet veterinary epidemiologists from around the world and engage in discussions of their research projects and areas of expertise.

I was honored to be a representative of San Diego Zoo Global at this venue and share some of our notable conservation work in epidemiology. Experiences like these provide me with better capabilities for using science to save species.

Carmel Witte is a senior research coordinator at the San Diego Zoo Institute for Conservation Research. Read her previous post, Investigating Primate Malaria in the Amazon.


Investigating Primate Malaria in the Amazon

A microscope slide shows the malarial parasite in a red blood cell red (see arrow) of a sampled primate.

When I first met Marina Bueno, I was instantly drawn to her excitement and passion for research in conservation medicine, a field that blends aspects of wildlife conservation, wildlife health, and human health. Marina is a veterinarian and doctorate scientist who works with the University of São Paulo’s Laboratory of Wildlife Comparative Pathology in the School of Veterinary Medicine and Animal Sciences. She also works with TRÍADE, a Brazilian organization for conservation medicine research, and Instituto Pri-Matas, a nonprofit organization conducting a project with golden-headed lion tamarins. Last summer, Marina spent extended time training in our Molecular Diagnostics Lab, learning how to improve DNA isolation techniques for some of her work. This is where we first discussed potential opportunities for collaboration on her projects investigating primate malaria in the Amazon.

Brazil’s Amazon region is seeing large-scale, human-induced (often referred to as anthropogenic) environmental changes that affect people and wildlife habitat. In a study conducted by Marina and collaborators, primates were surveyed across two protected field sites in the Amazon that are currently under severe anthropogenic pressure due to large construction projects that include the building of roads and dams. The idea was to sample South American primates in these sites to better understand what diseases they have and how these diseases could impact primate conservation and human health in these areas.

Marina Bueno samples primates in the Amazon for potential diseases.

They found that approximately 20 percent of surveyed primates carried a malaria-causing parasite, Plasmodium brasilianum. While infection with primate malaria generally does not harm the primates, there has been speculation that some of the primate-specific malarial parasites may not be so primate-specific. Some scientists believe that mosquitoes feeding on primates infected with Plasmodium brasilianumcould transmit the malarial parasite to humans when they bite a human host.

Marina’s research documents these malaria infections in primates, providing recommendations to closely monitor the human and primate populations for Plasmodium brasilianum infection in these areas of severe anthropogenic pressure, a situation that has been known to promote human malaria epidemics. The investigation also recommends that primates be tested for the presence of malaria infection before being relocated to other areas of Brazil for conservation or translocation projects so as not to inadvertently introduce malaria into areas where it has been eradicated.

Working collaboratively with scientists from around the world is a role that our Wildlife Disease Laboratories naturally falls into with its multidisciplinary group that includes veterinary pathologists, scientists, a molecular diagnostic laboratory, a histology laboratory, and an epidemiologist. Epidemiology expertise was provided for this particular collaborative project on primate malaria in the Amazon region. The study will be published soon in a peer-reviewed journal.

We are excited about our collaborations with our Brazilian counterparts in their quest to conserve one of the most ecologically diverse areas of the world and their search for harmony between human progress and wildlife conservation.

Carmel Witte is a senior research coordinator at the San Diego Zoo Institute for Conservation Research. Read her previous post, Epidemi-what?

The above photos are printed with permission from Marina Bueno.



Micronesian kingfishers are highly endangered and seemingly quite susceptible to the avian mycobacteriosis disease.

Whenever I am asked “What do you do for a profession?,” I am often confronted with a familiar, perplexing look followed by a request for clarification: “Epidemi-what?” Epidemiologist. The first thing that seems to enter people’s minds is “epidermis,” the top layer of skin. But, no, I don’t study skin. An epidemiologist studies causes and patterns of disease and health in populations (think epidemic). But what does that really mean, and what role does this funny word play in wildlife conservation?

The field of epidemiology has its roots in human health and is something that most of us are exposed to every day. All of those health-related statistics (such as the ones that say that if you have high cholesterol, then you are more likely to develop heart disease) are generated by epidemiologists. Basically, the epidemiologists look for differences in frequencies of heart disease between groups that do and do not have high cholesterol. As you can guess there are probably a lot of other things that could affect whether someone develops heart disease. The art of epidemiology is dealing with those “other” things through the use of special scientific study designs and analytical techniques. Instead of people and heart disease, my subjects are animals and their health issues.

Epidemiologist Carmel Witte studies causes and patterns of disease and health in zoo animal populations.

One of my first projects was investigating avian mycobacteriosis. This bacterial bird disease has long been thought of as highly contagious: if one bird in an aviary acquires the disease, the fear is that it will quickly spread to all of the other birds. The management implications are significant, causing a halt to breeding of all endangered species living in entire aviaries. So, we decided to ask the simple question, “Is this disease really super-contagious?”

I began tackling this question by using archived animal health data generated by San Diego Zoo Global’s pathologists and veterinarians. I searched records from the past 20 years to identify all of the cases of mycobacteriosis that we ever had. Then, I analyzed thousands of bird records to see what kinds of exposure all of the collection birds had to the relatively small group of 79 infected birds. What I found was rather interesting: up to 96 percent of all birds coming into contact with a disease-carrying bird never developed mycobacteriosis. The conservation implications for this are big: it is likely that mycobacteriois isn’t super-contagious, and zoos probably don’t need to halt breeding when a case is diagnosed.

This avian mycobacteriosis project is just one of many that I continue to tackle with the Wildlife Disease Laboratories’ team. Some other projects include studying feline herpesvirus infections in cheetahs and investigating transmission patterns of herpesviruses and mycobacterial infections in hoofed animals. In all of these projects, my mission is to use epidemiology to help remove disease as a roadblock to conservation and solve pressing health problems in animals. Now that you know exactly what a zoo epidemiologist does, the next time you hear that funny word, you will have the privilege of bypassing the “Epidemi-what?”!

Carmel Witte is a senior research coordinator at the San Diego Zoo Institute for Conservation Research.