Einstein Pathologists Help Identify Threat to Big Cat

Tiger. The word evokes images of ferocious power encased in an orange-black blur of big-cat quickness, equipped with dagger-like teeth and sharp claws. Arguably one of nature's most beautiful large predators, tigers are still no match for humans. Since the beginning of the 20th century, hunting and poaching have decimated tiger populations, causing the extinction of two subspecies and pushing those still remaining to the brink of extinction.

Dr. Denise McAloose in her lab at the Bronx ZooRecently, conservationists began to worry about another sinister threat to tiger survival. Between 2001 and 2010, scattered sightings in Russian villages of Amur tigers (also known as Siberian tigers) that were acting blind and adrift—odd behaviors for the reclusive and powerful cat—sent wildlife scientists scrambling to understand what could be wrong with the affected big cats.

Thanks to a collaborative study by researchers at Einstein, Montefiore Medical Center, the Wildlife Conservation Society (WCS) and Russian health and veterinary organizations, the mystery has now been solved: By testing tissue and conducting genetic analysis of the brain tissue of five dead Siberian tigers—which were either killed on site or dead as a result of disease—the researchers were able to show that the world's largest cats were infected with canine distemper virus (CDV).

A type of paramyxovirus related to measles, CDV causes fever, diarrhea, labored breathing, dehydration, and seizures, and in which death is often due to fatal pneumonia and inflammation of the brain. Although it was first described in domestic dogs in 1905, it is now known that the virus can infect and cause disease and death to potentially all species of land-based carnivores, including foxes, raccoons, bobcat, ferrets, lions and black-footed ferrets. It also can affect some species of marine carnivores, such as seals. The virus also was recently found to infect and cause outbreaks and mortality among species of monkey, most notably rhesus and cynomolgus macaques in Asia.

The tiger CDV study, which was published in the journal mBio, is the first to confirm and partially characterize genetically a form of CDV that is killing the Amur tiger. With fewer than 400 of its kind left in the wild, the Amur tiger is one of the world's most endangered big cats.

"The discovery illustrates the importance of long-term wildlife monitoring and health surveillance in identifying emerging threats in endangered species," noted Dr. Dee McAloose, a lead author on the mBio paper, who is among a handful of wildlife pathologists in the United States. She also is assistant professor of pathology at Einstein and head of pathology at the Bronx Zoo (which is run by the WCS).

Identifying Emerging Threats

"It may come as a surprise to some people that wild animals get disease," noted Dr. McAloose. "But cycles of disease in wildlife occur all the time and, in many cases, like a common cold, the presence of a disease may not be significant either for an individual or a population."

In some cases, however, disease may not only cause death or an outbreak, but can threaten the survival of an entire species or group of species. "The challenge," she said, "is being in the right place at the right time and, most importantly, to be looking in order to notice that something has changed."

She continued, "For Amur tigers, it's because we have been carefully studying their behavior and biology in Russia for over 20 years, so it became clear that something unusual was happening to them."

The Bronx Zoo's pathology department, which dates back to 1902, is one of the oldest in the country and one of only eight zoo-based pathology departments among the 223 zoos and aquariums that are accredited by the Association of Zoos and Aquariums in the United States. And it is one of only three with on-site histology and molecular labs. Most other zoos use one of two commercial pathology services or one of several university-based diagnostic pathology services.

The study researched what was killing Amur , or Siberian, tigers like the one pictured Dr. McAloose's work in the high-tech pathology lab—which sits in the 33,000 square-foot health center tucked away in the northeast end of the zoo—is pushing forward the study of emerging infectious diseases with Amur tigers and dozens of other wild species.

"Our focus is the diagnosis or discovery of diseases that are important, emergent or re-emergent, with specific interest in those that affect wildlife and wildlife conservation," she explained.

A Collaborative Relationship

The Amur tiger study also highlights the invaluable collaborative relationship among Einstein's scientists, physicians and veterinary researchers, who hope to better understand how wildlife health is related to domestic animal health and human health.

Interspecies transmission of pathogens has significant implications for both human disease and for biodiversity. It is increasingly on the rise as humans encroach on wildlife habitats. More than 75 percent of emerging infectious diseases, including many of the world's most significant pandemic outbreaks, can be attributed to a wildlife source.

"When you talk about highly pathogenic avian influenza, or swine flu, or HIV, West Nile virus, SARS, hanta virus, or monkey pox, all of these are diseases that affect animals and have crossed from animals to humans," said Dr. Tylis Chang, a contributor to the study who is attending clinical pathologist at Montefiore, which is Einstein's University Hospital.

The broader human health community only began to pay attention to this crossover during the past decade. "That's because our knowledge base of infectious agents that affect species other than humans is very narrow," noted Dr. Chang, who also is associate professor of pathology at Einstein and a Wildlife Conservation Fellow at the WCS/Bronx Zoo.

The WCS collaboration with Einstein and Montefiore is helping to change that.

The Power of Molecular Diagnostic Testing

Most recently, Dr. Chang has worked hand-in-hand with Dr. McAloose in building and developing the molecular diagnostics program at the Bronx Zoo.

In 2007, with equipment donated from Montefiore, the duo implemented a pilot program to introduce WCS to molecular diagnostic testing and the valuable role it can play in conservation—including the detection of known or novel DNA or RNA sequences from pathogenic microorganisms such as viruses, bacteria or fungi.

While microscopy—Dr. McAloose's first love—is an age-old tool that can identify whether cells are cancerous or infectious, it usually only narrows down the problem, not specifically identifies it. At the Bronx Zoo, on-site availability of these technologies remove disease diagnostics as a roadblock to conservation, since most commercial laboratories and research labs don't offer molecular testing for many of the pathogens that WCS is interested in screening for.

"The great thing about molecular testing is it can tell you the exact organism, and the exact strain of the organism, and it can give it to you with extraordinary confidence," said Dr. Chang.

Drs. Tylis Chang and Tracie Seimon, members of the Einstein-Montefiore research teamIn the case of the Amur tigers, Dr. Carol Oddoux, who runs the molecular pathology laboratory at Montefiore, contributed to the confirmation of distemper virus in her lab, which helped make the argument for CDV compelling.

A Typical Day at the Zoo

On most days, Dr. McAloose's team of three pathologists, a pathology resident, pathology technician, two histology technicians, a molecular scientist and a molecular postdoctoral fellow, are stationed at the Bronx Zoo's Wildlife Health Center, where they receive, process and review case materials from more than the 20,000 animals representing more than 1,500 species from all five WCS wildlife parks—Bronx Zoo, Central Park Zoo, Queen's Zoo, Prospect Park Zoo, or the New York Aquarium—as well as from more than 500 field conservation projects in over 60 countries, and four oceans, in which the WCS works. Their main goal is to fit together the pieces of puzzles that can help explain why animals are sick and why they die.

"We try to understand why animals die, how they die naturally and the diseases they can get," said Dr. McAloose. "The work we do at the zoo, including necropsy, histology, and molecular diagnostics helps us understand the breadth of diseases that different species are susceptible to and the variations in disease expression between different species."  

That knowledge can be directly applied to animals in the wild and to WCS's conservation efforts. For example, knowing that CDV can and does kill wild tigers, the researchers will now focus on identifying species in Russia that harbor the virus and could be the source of disease in the tigers.

"Once we know that, we can develop more comprehensive strategies to protect the tigers." she said.

Using molecular testing, during the last two years the team also has discovered a dozen new viruses, including a novel herpes virus that has killed pheasants from three different species, and an adenovirus that caused the death of a young North American river otter.

Diseases in wildlife can also be indicators of diseases that affect humans—the proverbial canary in the coalmine.

A Dream Job Helping Animals and Humans

Since her arrival at the WCS in 2001, Dr. McAloose feels fortunate to have been involved in many of the zoo's conservation projects, ranging from health and disease assessments of endangered bog turtles in the Northeast to a mortality investigation of Southern right whales in Patagonia.

Her love for conservation was sparked at a young age after reading The Lorax, by Dr. Seuss, which chronicles the plight of the environment and the Lorax, who speaks for the trees against the greedy Once-ler.

She has landed her dream job, working in pathology related to conservation.

"When I went to vet school it was really as much about doing something to help protect the planet as it was about animals," she said. "And when I looked in the microscope and could see the diseases that I was learning about, I was hooked."