A plague on snakes

HARLINGEN — Herpers, as snake enthusiasts call themselves, are always on the lookout for new acquaintances in low places.

When herpetologist Mayra Oyervides is in the field, her days are spent hiking and flipping over logs, debris and ground cover in hopes of discovering a hidden snake whiling away the daylight hours.

Night-time is prime time for hunting, however, and as she drives along Texas roads and byways the task can take from 7 p.m. until 11 a.m. the next day.

Some of the snakes, drawn to the warmth of the asphalt, are alive.

Others have succumbed to vehicle traffic, and these she catalogs, taking measurements, weights, photos, noting temperature and humidity and even moon phase.

She collects the dead snakes and deposits them as scientific vouchers in vertebrate museums to help with further reptile studies.

Oyervides is on the faculty of Schreiner University, and has been the go-to snake expert in

the Valley for the Texas Parks and Wildlife Department for the past decade.

But in the past two years, her field work has taken a twist, and she is finding more and more snakes covered in lesions.

Snake fungal disease has reached the Rio Grande Valley.

“I’ve seen it across a number of snake species, and there really hasn’t been any indication as to any species not being susceptible to it,” she said in a recent interview.

New Hampshire link

Snake fungal disease was first documented in timber rattlesnakes in 2006 in New Hampshire, which given its cold and bitter winters, is at the northern limit of where these pit vipers can survive.

As they left their communal den, the snakes were discovered to have lesions on their bodies.

Since that time, snake fungal disease has been widely reported across the eastern United States and into the Midwest, the South and, as of last year, Texas. Using DNA analysis of preserved lab specimens at vertebrate museums, researchers have now determined the earliest occurrence of snake fungal disease was in 1986.

Initially it was thought to be spreading, but some researchers believe it has always infected snakes in many regions, and is only being reported more widely because people are looking for it.

“I suspect we’ll continue to get it in other states as people recognize it as a problem,” said Jeffrey Lorch, a microbiologist with the U.S. Geological Survey at the National Wildlife Health Center who has studied snake fungal disease.

Mortality associated with the fungal disease in wild snakes without the intervention of human treatment is estimated to be about 40 percent, according to one Illinois study. The USGS’s Lorch, though, thinks the number is probably on the high side, although he concedes there is little data on wild snake populations infected with snake fungal disease.

Although the fungus is a different strain, it appears to mimic the effect of the fungus which causes white-nose syndrome in bats because both fungi manage to infect multiple bat and snake species.

In all, about two dozen different snake species are known to be susceptible to the disease.

Snake fungal disease also has been found in captive and wild snakes in the United Kingdom and Germany, as well as in some captive snakes in Australia.

Here in the Valley

Oyervides says several Texas glossy snakes she collected in Hidalgo County (she has permits to keep them) showed evidence of lesions and she took one home.

“After three or four months it purposely kept shedding over and over and over and over,” Oyervides said. “I removed the water bowl and only would offer it water like once every couple of days, and then I took the water bowl out to reduce the humidity in the cage and I put the heat up to stay constantly pretty warm and dry.

“It healed up completely,” she added.

Her experiment gives her hope the climate in Texas may be beneficial in helping snakes fight off the fungal disease. Outside of our wet fall weather in South Texas, the rest of the year tends to be hot and dry, and those conditions may be optimal for snake survival.

Something has changed

Just why snakes are suddenly becoming infected by a common and widespread fungus with which they have co-existed for millennia isn’t clear.

Did the fungus somehow change? Has something in the snakes changed? Or has the environment they live in been altered by human impact or by something else?

Clint Guadiana is curator of reptiles at Gladys Porter Zoo in Brownsville. While he hasn’t seen any cases of SFD in wild snakes in the Valley, or perhaps more importantly for him, in the zoo’s collection of reptiles, he voiced the opinion of most experts confronting such a complex biological puzzle.

“It could be environmental, it could be caused by humans, we just don’t know,” he said.

The complexity of the different factors involved in snake fungal disease and the short time it’s been studied haven’t allowed time for proper research, Oyervides said.

“I would say it’s a combination of things,” she said. “We have data that shows that the fungus has been here in snakes since 1986 but it wasn’t causing mass mortality.

“It wasn’t an issue until something in the environment either changed to induce this pathogen to become more prevalent or more virulent to infect the snakes, or something in the snakes is stressing them out so much that their immune systems somehow are being compromised,” she added.

Fungus worldwide

One of the most prominent red flags which snake fungal disease has raised is the fact it isn’t the only fungus rampaging through wildlife worldwide.

A fungus called Batrachochytrium dendrobatidis (BD) causes chytridiomycosis, also known as chytrid (pronounced KIT-trid).

For 30 years chytrid has been slaying vast populations of the world’s frogs and salamanders, and estimates are it is pushing at least 200 species toward extinction.

Still another fungus causes white-nose syndrome in bats. Like snake fungal disease, it was first reported in the northeastern United States, in 2007, and has had a devastating impact on bat colonies in colder climates where long winters mean extended cave hibernation.

It is believed these extended periods of close quarters among bats as they hibernate, combined with the cold temperatures, allow the fungal disease to flourish. It has killed an estimated 5 million to 7 million bats in the United States.

“People like to lump these things all together, because they’re fungal diseases and they are emerging, but I think a lot of them are emerging due to different mechanisms,” said the USGS’s Lorch.

“White-nose syndrome, for example, in bats, that’s kind of another big-name fungal one right now, we know that that pathogen was introduced to North America and it’s native to Eurasia,” he added. “The idea being that when you release a pathogen in an area where the hosts have never seen it before, that’s often when you get really high mortality because the hosts don’t have any immunity to it and they haven’t co-evolved to sort of live alongside it.”

White-nose syndrome was detected in the Texas Panhandle region one year ago in three bat species — the tri-colored bat, cave myotis and Townsend’s big-eared bat.

So far, bats here are not showing symptoms of the actual disease, Texas Parks and Wildlife Department biologists say. The hope is milder winters in Texas will spare bat colonies from the same level of devastation caused by white-nose syndrome in more northerly latitudes.

Biologists helping

Snake fungal disease, at least initially, was believed to have been passed exclusively from environment to snake. But now scientists are finding snake-to-snake transmission is also possible.

“Field people or biologists now have to be careful if they’re handling different animals at one time, either wearing gloves or just cleaning up properly in-between each species they’re picking up,” said Guadiana, who said his Brownsville zoo has strict protocols on handling animals, particularly if they have just come on-site from other zoos.

Oyervides has been doing that for years, she said, and wears a fresh pair of disposable gloves with each snake she encounters in her field work.

“It definitely is contagious and of course we see a lot more of it once they start coming out of their dens from overwintering,” she said. “It’s highly, highly contagious.”

In her case, she’s taken some good-natured jokes from other herpetologists and snake enthusiasts for wearing gloves in the field while handling snakes.

“Some people think I’m crazy because they’re like, ‘why the gloves?’” she said. “It’s because I have first-hand knowledge of what happens if you hold one snake that’s infected, the whole rest of the night all the snakes that you collect, and if you’re unprotected or you haven’t sanitized correctly, are now subject to snake fungal disease.”

Dead snake, good snake?

In Texas, with its population of large and poisonous snake species, many people’s first reaction to a major snake die-off might be good riddance.

Yet there would almost assuredly be unexpected consequences involving such upheaval in the natural balance within an ecosystem.

Snakes both poisonous and non-poisonous are ferocious predators of rodents. Although we don’t usually see these nocturnal inter-species battles, the loss of a predation lid on rat and mice populations could easily send these sometimes disease-carrying mammals into our yards and our homes.

So is the only good snake a dead snake?

“Obviously, my response is biased, but no, it’s not the proper response,” Oyervides said.

“We’d have an increase, obviously, in the populations of a number of rodents,” she added, and that could cost Valley residents more than just a higher annual pest-control bill.

“Insects, mammals, some birds, we would definitely see an imbalance in the food chain,” Oyervides said. “But as far as human-related problems, we would almost certainly see an increase in hanta disease, hantavirus, and all these different rodent-transmitted diseases which is a main, main problem because we create a lot of trash, we create a lot of piles of this and that, which is perfect habitat for rodents.”

Lorch works in Wisconsin and, in the Midwest, Lyme disease infects humans and is carried by rodents which are kept in check by snakes. He also notes it is curious to see the different attitudes people now apply to bats and snakes.

“Snakes are still considered by many to be one of those malign species of wildlife,” he said. “Twenty to 30 years ago, people would have said the same thing about bats and public perception toward bats has largely changed.”

Public education campaigns have removed or at least reduced the stigma bats have been tagged with for thousands of years as people come to appreciate the numbers of insects they consume and their role as pollinators.

“Snakes haven’t really gotten to that level yet,” he said.

“Even in someone like myself, who is interested in snakes and was before this disease got so much attention, when I see a snake the first thing that happens is my heart jumps, just as everyone else’s does, and then it takes a few seconds for me to get into that mode of, ‘oh I need to catch this thing,’” he said.

“It’s just funny that that innate fear is so deep there,” Lorch added.