Unlocking the Secrets of Cells

Looking through my microscope at the round purple smudges inside cells of a boreal toad were enough to tell me that this was not going to be an ordinary investigation for the Amphibian Disease Laboratory. 

A few days earlier we had received the samples from a zoo from the Midwest asking for help in determining why several toads out of a group of 40 had died unexpectedly. The boreal toad Anaxyrus boreas boreas is an endangered species from Colorado, New Mexico, and Wyoming. Large survival assurance populations in zoos and government facilities are an important safeguard to help prevent extinction. These were no ordinary toads and determining the cause of the disease outbreak would be the first step towards preventing additional deaths.

So what about the purple smudges inside those cells?  To a veterinary pathologist, those smudges are called “inclusion bodies” and the first thing we think when seeing them is: infection with a virus.  In particular, these inclusion bodies resembled those formed by a ranavirus. 

However, while the ranaviruses are known for causing disease outbreaks in wild amphibians and more recently as a cause of deaths in wild turtle populations, very little is known about the occurrence and risks of ranavirus for captive amphibians and survival assurance populations.  If the boreal toads had a ranavirus infection, we (and the zoo they came from) would be entering unknown territory. However, it would be a great opportunity to gather important new information for maintaining healthy amphibian survival assurance populations.

Within a few days, our laboratory staff including Dr. Megan Jones, a postdoctoral fellow in amphibian pathology, Research Technician Isa Navarrete, and Dr. Mark Schrenzel of the Wildlife Disease Laboratories’ Molecular Diagnostics lab used a PCR technique to detect ranavirus DNA in tissue samples and additional samples examined with an electron microscope (we call it the “Big Eye”) demonstrated characteristic viral particles. The diagnosis was confirmed, but sequencing of the virus DNA revealed something unexpected: the boreal toad virus was likely to not only be a new, undescribed species, but also could be related to ranaviruses not previously found in the United States! 

How did a new species of ranavirus possibly from outside the U.S.  end up in a population of endangered toads? It turns out that the toads were housed in a room with other species of amphibians from many other parts of the world in what is called a “cosmopolitan” collection.  In this case, a virus that doesn’t cause problems for its natural host species made a jump to naïve boreal toads, which were susceptible to developing severe disease.

An example on a global scale is the introduction of the chytrid fungus Batrachochytrium dendrobatidis to new locations as the result of amphibian trade resulting in devastating declines and extinctions of wild amphibian populations.

The goal of the Amphibian Disease Laboratory is to help minimize the risk of important diseases like chytrid fungus and ranavirus infection for amphibian conservation efforts. With initial support from a National Leadership Program grant by the Institute for Museum and Library Services, we have been able to provide efficient, low-cost disease testing to zoos and biologists that work with amphibians, and have helped to draft guidelines for biosecurity practices that prevent transmission of disease in amphibian survival assurance populations and introduction of these diseases to new locations. Download the free Amphibian Disease Control Manual here.

You can help by never releasing pet amphibians into the wild and if you are considering buying an amphibian as a pet, insist that the pet store certify that their frogs are free of harmful infections like the chytrid fungus.

Allan Pessier, Senior Scientist, Wildlife Disease Laboratories