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Do turtles cause any problems for humans?

Turtles eating a dead fish.
Turtles eating a dead fish.

By Stacey Venzel

Mosquitoes and other annoying creatures dubbed pests are unwelcome for a reason, especially when attempts to lessen their impact do not keep them at bay, such as failed attempts with insect repellent. On the other hand, the habits of turtles are, for the most part, minimally invasive to humans and the environment, and those that do cause some concern can be easily controlled, unlike mosquitoes and other pests.

Most of the perceived problems posed by turtles are actually misconceptions, such as a turtle’s role in pond and garden ecology and even Salmonella disease transfer. Some species can cause food poisoning if eaten, become invasive to the environment or harm a human in self-defense, but these risks can be mitigated.

POND PATROL
Aquatic species do feed on fish, ducks and other aquatic prey, but this natural practice does not designate turtles as pests. While fishermen are known to complain about turtles being the reason for a low catch day, no evidence supports this blame-shifting fallacy. In fact, as with opportunistic painted turtles and sliders, many of the fish consumed by turtles are already dead; without turtles as garbage men, cleanup crews, lakes and ponds would reek of rotting fish. Aquatic vegetation is also controlled by herbivorous turtle diets, thereby improving the quality of fishing.

Ducklings and even adult ducks can become victims of a hungry turtle, especially the adventurous and large common snapping turtle, but this behavior is normal. The occasional feathered friend might disappear, but a pond would need to hold hundreds of big, ravenous turtles to see any dent in the duck population.

GARDEN INVADERS
Occasionally, a turtle might wander into your garden and feast on available fruits, vegetables or flowers. They will do so quietly and stealthily, rarely leaving evidence of their invasion behind. Though this habit can be seen as a nuisance, it is important to remember that the turtle likely roamed the area first and the human is the real invader. These low-lying individuals can easily be prevented garden access with a simple chicken-wire fence around the bed of plants.

DISEASES TO HUMANS
While turtles can succumb to a number of illnesses, Salmonella is the leading cause of disease transfer from turtles to humans. However, other animals carry the fever-and-diarrhea-inducing bacteria, too. Reptiles, amphibians and birds are known to harbor Salmonella, which can be transmitted to humans upon contact with an infected animal, typically through feces or from touching regions of the mucous membranes. The latter is the reason for disease outbreaks associated with children and pet turtles as children are more likely to handle the pet inappropriately and not wash their hands after. Elderly and immune-compromised individuals are also at risk.

To avoid contamination from turtles and any aquatic animals, the Center for Disease Controls suggests thoroughly washing your hands after handling the animals.
To avoid contamination from turtles and any aquatic animals, the Center for Disease Controls suggests thoroughly washing your hands after handling the animals.

THE TRUTH ABOUT SALMONELLA
Despite widespread concern about Salmonella’s association with pet or wild turtles, some facts should be made clear. Concern for the transmission via these shelled reptiles led the U.S. Food and Drug Administration to ban the sale of turtles smaller than 4 inches, effective since 1975. The FDA estimates this has prevented 100,000 cases of Salmonella outbreak in children. But a 2014 European study that induced poor hygienic conditions in captive reptile environments—essentially creating breeding grounds for Salmonella — found only 3 percent of turtles contracted the bacteria compared to 17 percent of lizards and 24 percent of snakes.

According to the Centers for Disease Control and Prevention, more than 1 million cases of Salmonella food poisoning are reported annually, the cause linked to ingestion of raw eggs and meat or other unclean food products. Field biologists handle thousands of turtles in a lifetime and never become ill. These and other statistics have led to scientists to conclude that the risks of contracting Salmonella from turtles is low enough that it does not necessitate worry. With Salmonella still being the most notable turtle disease transfer, illnesses spread from turtles to humans are not a major problem.

Additionally, as Salmonella is documented more often in pet turtles than wild caught ones, scientists suggest reduction of the disease could be as simple as eliminating crowded turtle farming because poor conditions and close quarters increase chances of contraction and transmission. If you want to acquire a pet turtle but are concerned about diseases, an alternative to the farm-raised pet store trade is to take on turtle re-homing, adopting a rescued or abandoned non-releasable turtle from an animal rescue or rehabilitation center.

FOOD POISONING FROM TURTLES
Other cases of disease transfer from turtles to humans exist, though they are even more rare in occurrence. A few documented cases of food poisoning in humans have occurred from eating turtles, even when cooked. Common box turtles sometimes feed on poisonous mushrooms, and while the turtle remains asymptomatic, humans have become ill after dining on the turtle’s meat shortly after it has munched on the fungi. Chelonitoxin food poisoning occurs when humans specifically eat sea turtles. As an example, the sponge diet of hawksbill sea turtles has caused humans to get sick.

Longevity of turtles suggests they can accumulate a lot of toxins in their lifetime without being affected. For those species that are not protected under the law from consumption, humans should take care when ingesting individuals that dwell in polluted areas where the build up of heavy metals and toxic chemicals or compounds could be detrimental to a human’s health.

TURTLE INVASION
Released pets are a cause for environmental concern, often resulting in ecological disruption. Similar to how introduced iguanas, tegus and monitor lizards in Florida have become added predators to turtles, ex-pet turtles can also thrive and upset the balance of an ecological niche. Red-eared sliders are the most common pet turtle but often get released into nearby lakes or ponds when owners do not want the pet anymore. This act has put other native pure-bred slider species in danger of extinction due to hybrid breeding with released red-eared sliders.

NINJA TURTLE SELF-DEFENSE
Though their initial reaction is to flee or hide, threatened turtles can chomp down or claw in self-defense. They might appear slow on land but they can react quickly with a bite or scratch. The bite of an alligator snapping turtle can lacerate a finger down to the bone. As painful as the wound might be, proper cleaning and care prevents infection. Unlike venomous snakebites, allergic reactions to bee stings, cat scratch disease from infected cats or bites from rabies vector species like dogs, a turtle’s defense tactics rarely send a person to the hospital. Even though it might leave a mark, a turtle won’t kill you.

LIVING IN HARMONY WITH TURTLES
Weighing the benefits of turtles against the threats, turtles pose little danger to humans. In fact, the trend of who threatens whom is skewed in the other direction. Adopting more harmonious, educated actions when it comes to dealing with turtles can protect both humans and turtles in the future. As biologists Whit Gibbons and Judy Greene write about the turtle-human dynamic, “The problem would be solved if everyone had the attitude that all turtles were special and that humans have a responsibility to protect them at all costs.”

 

Sources:

F Cito, A Cunningham, A Giovannini, Et. Al., “Disease risk assessments involving companion animals: An overview for 15 selected pathogens taking a European perspective,” Journal of Pathology, 2015, http://www.sciencedirect.com/science/article/pii/S0021997515001280.

Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 23, 300, 305-306.

Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 33, 50.

Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 40, 96, 104.

Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 6, 78, 90-98, 107, 129.

Salmonella: Technical information,” Centers for Disease Control and Prevention, March 9, 2015, http://www.cdc.gov/salmonella/general/technical.html.

“Pet turtles: Cute but contaminated with Salmonella,” U.S. Food and Drug Administration, February 2014, http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm048151.htm