Institute develops antidote for four species that can cause intense pain in people stung in rivers and the sea
Toxins from scorpionfish spines can cause alterations in heart rate
Kris Mikael Kristeria / Wikimedia Commons
Over the past 30 years, whenever she goes to the beach, biologist Mônica Lopes Ferreira of the Butantan Institute takes the opportunity to collect poisonous fish. Back in the lab, she and her team extract the poison to develop serums and treat victims of accidents caused by certain kinds of sea and river fauna. So far, the group has had success with the yellow catfish (Cathorops spixii), common along the entire Brazilian coast, the Amazon River stingray (Potamotrygon orbignyi), the niquim or northeastern toadfish (Thalassophryne nattereri), and a close relative of the lionfish, the scorpionfish (Scorpaena plumieri), found on Atlantic reefs. Ferreira and physician Vidal Haddad Júnior, from São Paulo State University (UNESP), Botucatu campus, chose these species because they frequently cause injuries, according to reports from fishermen from coastal villages in Brazil’s Northeast and North regions.
The team’s serums—already tested on mice—are produced like those used to treat snake or scorpion bites, i.e., tiny doses of venom are inoculated into horses, from which antibodies are then extracted to treat people. Their tests on mice have shown that the serums prove effective in stopping the effects of toxins from these four species, which the researchers describe in an article published in May in the International Journal of Molecular Sciences. New tests and larger-scale production, however, depend on whether the Brazilian Ministry of Health (MS) will recognize fish accidents as a relevant public health problem.
From 2007 through 2013, according to the most recent survey published in 2015, the MS recorded 4,118 accidents involving river and sea animals, including urchins and jellyfish, or 1.6 incidents per day. “Since reporting isn’t mandatory, the real number is certainly much higher,” says Haddad, one of the authors of the survey, which was published in 2015 in the Journal of the Brazilian Society of Tropical Medicine.
There are almost 200 known species of poisonous fish that cause accidents in Brazil, and this number is slowly increasing. “Recently, we added the spotted sorubim [Pseudoplatystoma corruscans]—used to make “breaded bait” hors d’oeuvres in Brazilian bars—to the venomous list,” he adds.
In medical registries, around 70% of all poisonous fish accidents are attributed to freshwater stingrays, which are probably reported most because the wounds are deep and painful. Based on their own observations, however, Haddad and Ferreira consider freshwater catfish to be the species that cause the most accidents, as they are found along the entire coast as well as in rivers.
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Of the 126 fishermen in the municipality of Miranda, in Mato Grosso do Sul, 38 had been injured by catfish and, in Corumbá, 111 of the 355 fishermen reported injuries caused by freshwater catfish, according to a study published in 2018 in the Journal of the Brazilian Society of Tropical Medicine. On beaches, fishermen often discard small catfish onto the sand, which may be stepped on by beachgoers.
Having studied these accidents for 30 years, Haddad has observed that people do not usually seek medical attention because, in general, the pain from the stings goes away after a few hours, even though the toxins in the venom could cause serious medical harm. “Bacterial infections are common in these wounds and can lead to serious complications such as amputation and sepsis,” he notes. Ferreira adds: “Doctors rarely identify the true cause of these injuries, which are mistaken for cuts from broken glass or crab bites, which aren’t poisonous and don’t cause serious injuries. Some doctors are surprised when I tell them that fish have venom.” The fact that these fish are not mentioned in medical reports makes the work difficult.
In partnership with the Health Department of Santa Catarina, Ferreira has given lectures to health professionals to increase the reporting of fish accidents. The biologist has also helped to produce educational pamphlets for general distribution. Haddad, in turn, in 2007 published a manual for health professionals called Animais aquáticos potencialmente perigosos do Brasil: Guia médico e biológico (Potentially dangerous aquatic animals in Brazil: A medical and biological guide).
While working towards his doctorate, as an attending physician in the emergency room in Ubatuba between 1998 and 1999, Haddad found that it wasn’t just fish that disrupted the lives of residents and tourists. There, the most common accidents, around half of them, were caused by sea urchins, which live in colonies of up to 12 specimens, among rocks, and have no poisonous effect on humans. The spines are removed using two thick needles, without anesthesia. “I’ve seen patients with as many as 50 urchin spines, which really slows down the emergency room queue,” says Haddad.
Butantan biologist Ferreira has seen some dramatic episodes. Years ago, at a health center in Maceió, the capital of Alagoas State, she encountered a tailor who, 20 days earlier, had been fishing in the Mundaú lagoon on the city’s outskirts when a catfish swinging at the end of his pole stabbed his hand. The effect of the fish venom was so intense that some of his muscles were already necrotic and unable to move 20 days later when he went to the clinic. The attending physician had to amputate the index and middle fingers of the tailor’s right hand, and he had to seek early retirement.
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Ferreira reports having met shellfish collectors on the coast of Alagoas who were unable to work for months after being lanced by the spines of the niquim (venomous toadfish), a fish that buries itself in shallow waters. Divers are also frequent victims: “People have a bad habit of touching what they observe and will also touch scorpionfish, hidden in the reefs,” she says. The venom from this species is the only one that has a systemic effect on the body—not just the sting site—and can cause respiratory and heart problems.
These poisons are made up of proteins, which are added to toxins in the fish’s skin mucus, which are secreted to protect the animals against pathogens. In some fish, such as stingrays, the stinger is covered by skin and coated by mucus. The toadfish is the only one of these fishes that actively injects venom, like snakes. It contracts the muscles of glands that inject its venom through four hollow spines, two on its sides and two on the back. These are what most frequently injure people who overlook the fish and accidentally step on it.
Fish poisons work in a similar way. As soon as they enter the bloodstream, they create an intense contraction of the arteries and veins. This closing of blood vessels causes swelling, skin redness, inflammation, tissue death, and bacterial infections. “The interruption of circulation is probably what causes the intense pain, which patients describe as excruciating,” comments Haddad.
Although used as synonyms, the terms poison and venom express different behaviors, warns biologist Carlos Jared, also from Butantan: “Venomous animals, such as snakes, attack, bite, and inject venom when they go to feed or defend themselves. Fish only use poison as a form of defense when they are stepped on or bitten.” Pufferfish (Takifugu sp.), in addition to producing poison, inflate their bodies, giving predators the impression that they are much larger than they appear and impossible to eat. Their toxins are in the skin and organs such as the liver, which are removed before human consumption.
A freshwater stingray, which can inflict deep, painful woundsKlaus Rudloff / biolib.cz
In 1982, the closing of the floodgates at the Itaipu hydroelectric plant created an immense lake that inundated the Sete Quedas Falls, which until then had formed a natural barrier to stingrays. Given a clear pathway, they moved up the Paraná River and into the Paranapanema River and continued to spread.
“Around 2005, we collected the first stingrays in the Tietê River and today almost a third of its course is populated by these fish,” reports Haddad. He predicts that the stingrays will advance further via the Tietê River and reach Minas Gerais.
During the breeding season, in July and August, stingrays migrate from deeper sections of the river to shallower areas and bury themselves in the mud. The footfalls of visitors on the riverbed trigger a reflex muscle contraction in the fish, which have one to four stingers in their tail that are difficult to remove if they become embedded in a victim’s leg. Haddad recommends shuffling the feet when wading along these riverbeds, especially in the Pantanal and Amazon rivers, to scare away stingrays.
The recommended treatment against accidents with poisonous fish consists of immersing the affected limb in the hottest water tolerable, removing the stinger or thorn and any debris that has broken off in the injured person’s body, washing the wound with soap and water, seeking medical help, and taking prescribed medicines and applying bandages until the wound heals.
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