Department of Pathology Newsletter

Einstein and Bronx Zoo Pathologists Find Rare Amur Tigers Affected by Canine Distemper

 Dr. Dee McAloose, assistant professor of pathology at Einstein, and head of pathology at the Bronx Zoo with Amur tiger.  Photo: Julie Larsen Maher
Dee McAloose, DVM, with a young Amur tiger at the Bronx Zoo. Dr. McAloose lead the study that identified Canine Distemper Virus in Siberian Tigers in Russia. Photo: Julie Larsen Maher

Amur tiger
Less than 400 Amur tigers remain in the wild. Photo: Julie Larsen Maher
TIGER. The word evokes images of orange and black stripes, blazing eyes, dagger-like teeth, sharp claws and power. They are arguably one of nature’s most beautiful top predators, but are no match for humans. Since the beginning of the twentieth century, hunting and poaching have decimated tigers, causing the extinction of two subspecies and pushing those still remaining to the brink of extinction.

Recently, conservationists began to worry about another sinister threat to tiger survival. Between 2001 and 2010, scattered sightings of Amur tigers (also known as Siberian tigers) in Russian villages acting blind and adrift - odd behaviors for the reclusive and powerful cats – sent wildlife scientists scrambling to know why. 

Now the mystery has been solved, thanks to a collaborative study by researchers at the Wildlife Conservation Society (WCS), Albert Einstein College of Medicine, and Russian health and veterinary organizations.

They found that the world’s largest cats were infected with canine distemper virus (CDV), a type of paramyxovirus related to measles.

Histologic examination (testing tissue) and genetic analysis of the brain tissue of five dead Siberian tigers – either killed on site or dead as a result of disease - showed they were infected with the viral disease, which causes fever, diarrhea, labored breathing, dehydration, and seizures, and in which death is often due to fatal pneumonia and encephalitis.

First described in 1905 in domestic dogs, it is now known that CDV can infect and cause disease and death in many and potentially all species of terrestrial carnivores, for example, foxes, racoons, bobcat, ferrets, lions, endangered black-footed ferrets, and some species of marine carnivores, including seals.  It also recently jumped taxonomic groups to infect and cause outbreaks and mortality in monkeys (Rhesus and cynomologus macaques) in Asia.

The tiger CDV study, which was recently published in the journal mBio, is the first to confirm and genetically partially characterize a CDV that is killing the Amur tiger – a species that with fewer than 400 animals left in the wild, is one of the world’s most endangered cats on the planet.

Dr. Dee McAloose, VMD, a lead author on the mBio paper, who is an Assistant Professor of Pathology at Einstein, and Head of Pathology at the Bronx Zoo, which is run by the WCS, said the discovery illustrates the importance of long-term wildlife monitoring and health surveillance in identifying emerging threats in endangered species.

Identifying emerging threats

“It may come as a surprise to some people that wild animals get disease. 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,” said Dr. McAloose, a graduate of University of Pennsylvania School of Veterinary Medicine, who is among a handful of wildlife pathologists in the country - and fewer than 20 at zoos in the United States. 

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.

“For Amur tigers, it’s because we have been carefully studying their behavior and biology in Russia for over 20 years that it became clear that something unusual was happening to them,” Dr. McAloose added.

Dr. Dee McAloose at her microscope at the Bronx Zoo

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 or one of several university-based diagnostic pathology services.

Her work in the high-tech pathology lab - which sits in the 33,000 square-foot health center tucked away in the north east end of the Bronx 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 impact wildlife and wildlife conservation," Dr. McAloose said. 

And it has powerful implications beyond the animal kingdom.

A collaborative relationship 

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

One of the reasons is that interspecies transmission of pathogens has significant implications for both human disease and for biodiversity, and is on the rise as humans increasingly encroach on wildlife habitats. Over 75% of emerging infectious diseases, including many of world’s most significant pandemic outbreaks can be traced to a wildlife source.

tylis Chang
Dr. Tylis Chang collaborated on Amur tiger study

“When you talk about highly pathogenic avian influenza, or swine flu, or HIV, West Nile virus, SARS, hanta virus, or monkey pox, to name a few, all of these are diseases that affect animals have crossed from animals to humans,” said Dr. Tylis Chang, an Attending Pathologist at MMC, Associate Professor of Pathology at Einstein, and Wildlife Conservation Fellow at WCS and Bronx Zoo, who contributed to the Amur tiger study.

But only in the last decade or so has the broader human health community paid notice.

“Our knowledge base of infectious agents that affects species other than humans is immensely weak," he said.

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 WCS’ Bronx Zoo.

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

While microscopy - Dr. McAloose’s first love – is an age-old tool used to identify disease, whether cells are cancerous or infectious, for example, it can sometimes only narrow down the problem, not specifically identify 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.

Baby guenon
Genetic testing helped determine abnormalities in a baby guenon

“The great thing about molecular is it cannot only tell you the exact organism, it can tell you the exact strain of the organism - and it can give it to you with extraordinary confidence,” Dr. Chang said.

In 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 of CDV compelling.

Collaborations between the WCS and Montefiore also include an investigation by Dr. KH Ramesh, who runs Montefiore’s Cytogenetics Laboratory, into genetic abnormalities that may have contributed to severe craniofacial defects, including cleft palette, in a baby guenon, a type of old-world monkey endemic to sub-Saharan Africa. While an obvious defect was not apparent using karyotyping – an organized profile of an organism’s chromosomes - it confirmed the number of chromosomes in the species; information that appears only in one medical publication.

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 post-doctoral fellow, are stationed at the Bronx Zoo’s Wildlife Health Center receiving, processing and reviewing case materials from more than the 20,000 animals representing more than 1500 species from all five WCS wildlife parks - Bronx Zoo, Central Park Zoo, Queen’s Zoo, Prospect Park Zoo, or the New York Aquarium, or from more than 500 field conservation projects in over  60 countries - and four oceans - in which the WCS works .  Their goals are to fit together the pieces of a puzzle to explain why an animal or animals are sick and why they die. 

Her team recently performed the necropsy on Gus, the beloved, aged white polar bear who lived at the Central Park Zoo. Their primary finding was cancer.

“We try to understand why animals die, how they die naturally and the diseases they can get,” Dr. McAloose said. “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 difference in disease expression between different species.”

molecular pathology post doc
Dr. Tracie Seimon in the molecular pathology lab at Bronx Zoo

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, they will now focus on identifying species in Russia that harbor the virus and are the source of disease for tigers.

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

In the last two years, using molecular testing, the team has also discovered a dozen new viruses, including a novel herpes virus that has killed pheasants from three different species, and a novel 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 coal mine.

Identifying West Nile Virus  

In that regard, one of the Zoo’s biggest discoveries of a zoonotic disease was in 1999, when crows were literally falling dead out of the sky in Queens.  Around the same time, other birds in the WCS zoos died suddenly, including flamingos, pheasants, cormorants and a bald eagle, also died suddenly. When examined, all of the birds had encephalitis, inflammation of the brain. Coincidentally, people in New York were also dying from viral encephalitis.

Dr. Tracey McNamara, Dr. McAloose’s predecessor, who examined the animal samples, worked closely with collaborators at the US Army Medical Research Institute of Infectious Disease to determine the birds all died from West Nile Virus. The virus had never been diagnosed in the western hemisphere, but had been known to infect birds and people in parts of Asia, Europe, and Africa.

Saving the Kihansi spray toads 

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.

Kihansi spray toad
Female Kihansi spray toad with toadlet. Photo Julie Larsen Maher

One recent successful conservation project was the reintroduction of 2,000 Kihansi spray toads (KST) to Tanzania’s Kihansi Gorge. The tiny toad, which weighs less than 1 gram and is smaller than a penny when fully grown, was only first discovered during the construction of a dam in 1996. The only place on the planet where the toad existed was in 24-acre area along the edges of the waterfall that was to be damned, which ultimately led to extinction of the toad in the wild. Luckily for the toads however, in 2000, 400 toads were collected and transferred to the Bronx and Toledo zoos, where they were successfully bred over the next decade. In 2010, the Kihansi spray toads were restored to their natural habitat.

Dr. McAloose’s role and that of her staff at WCS, was to ensure, through histology and molecular diagnostic testing, that the toads were not only healthy and fit for reintroduction, but that they weren’t carrying any pathogens that would threaten other native species.

“Because a small group was brought to the zoo, where they were protected and able to breed, we were able to save the species from extinction,” Dr. McAloose said.

Meanwhile, with so much adorableness on a daily basis, it’s hard to not get attached to her work companions.   Dr. McAloose fondly recalled two of her favorite zoo pals: a Sumatran rhino named Rapunzel, whose remains were donated to the American Museum of Natural History, and a 50-year-old milky eagle owl who had bright pink eyelids.

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.

And she has landed her dream job coupling pathology with conservation.

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





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