“Leeches are allies of medicine, but in Mexico they are not used due to prejudices.”

▲ Leech specimens from the National Helminth Collection, Institute of Biology, National Autonomous University of Mexico. Photo by Cristina Rodríguez

Eirinet Gómez

La Jornada Newspaper, Tuesday, November 11, 2025, p. 5

Leeches are recognized for their effectiveness in applying grafts in countries such as Turkey, Spain, the United States, and Great Britain; however, their application remains marginalized in Mexico due to prejudice, lack of knowledge, and lack of regulation.

“Mentioning them may cause rejection, but when a tissue becomes congested and cannot eliminate the blood it receives, there is no drug or surgical procedure that can match the effect of a leech,” says Luis Rodrigo Reynoso, a reconstructive plastic surgeon.

From a hospital in Peru, at the end of a surgical day, Rodrigo Reynoso answered La Jornada's call. "I'm probably the only surgeon in Mexico who uses leeches," he points out, and then explains that he discovered the practice in Turkey during his training.

After confirming their effectiveness, and as part of his thesis, he decided to investigate how to implement them here. This search led him to contact Alejandro Francisco Oceguera Figueroa, from the Institute of Biology at the National Autonomous University of Mexico (UNAM), who is dedicated to the study of these organisms.

“I looked for local species, but the ones we have here consume very little blood, less than a milliliter, which makes them clinically inefficient,” he explains.

Leeches are worms belonging to the group of annelids, or segmented worms. Among the more than 600 species that exist, Hirudo medicinalis —native to Europe, Asia, and North Africa—is the one most used in medicine because of its ability to consume up to 10 milliliters of blood.

Its therapeutic use dates back to ancient civilizations in Egypt, Mesopotamia, and Classical Rome, continuing until the 20th century when scientific advances led to its decline. However, in the 1960s, a greater understanding of the properties of its saliva led to its reintroduction into medical practice.

In the 1980s and 90s, pioneers in reconstructive surgery used them to achieve successful grafts and transplants. By 2000, their use had expanded to the treatment of osteoarthritis, rheumatoid arthritis, and degenerative arthritis in Sweden, Spain, and the United States.

In the case of reimplantations of ears, fingers, and skin fragments, Rodrigo Reynoso explained that it is common for there not to be enough veins to nourish and drain the area, which causes congestion, putting limbs at risk or compromising the patient's health.

There, the leeches act as a living drainage system, since when placed on the transplanted area they connect with their suckers and begin to draw blood. This reduces inflammation and allows the tissue to oxygenate; in addition, they release an anticoagulant substance through their saliva.

“Once the leech is full, it automatically detaches from the patient, but it leaves an anticoagulating effect on the tissue that remains for some time. This is very beneficial so that the area continues to drain, doesn't become congested, and doesn't die.”

After 10 years of experience and more than 20 surgeries in which he used leeches, Rodrigo Reynoso highlighted three successful clinical cases: the reimplantation of an ear to a patient – ​​a difficult area, due to the coagulation of the vessels –, the transplantation of a toe to the hand after an accident and the reconstruction of a nose after a horse bite.

“This therapy is normally used for about five to seven days, until the body begins to generate new circulation,” he explains.

They require regulation and protocols

The expert in reconstructive surgery points out that in countries where its use has become popular, such as the United States, its implementation is regulated and they have protocols, which establish everything from the use of laboratory leeches and their medical implementation, to the incineration after their use.

“One of the major risks is infection at the site where the leech will be placed, because they carry bacteria in their stomachs that could escape from the digestive tract and contaminate the flap.” To address this issue, a prophylactic antibiotic is administered, he emphasizes.

He mentions that during the application of leeches, they usually detach themselves once they are full – after 15 to 30 minutes – but if this does not happen or you want to interrupt the suction, you should put a drop of soapy water or alcohol on it, “never pull them off, because the suckers could remain attached and cause an infection.”

In Mexico, Rodrigo Reynoso lamented, the use of leeches remains marginal due to three obstacles: there are no farms, no protocols, and no regulations. “When I tried to formally introduce them, the Ministry of Environment and Natural Resources and the Federal Commission for Protection against Sanitary Risks stopped me because they thought I wanted to release an exotic species,” he recalled.

The surgeon emphasizes the need for reforms in the law, so that they are recognized as medical devices and from there it is accredited who can use them and what the protocols for their use are.

Another barrier to overcome is cultural resistance, because when the need to use leeches is presented to the patient, the first reaction is rejection. “They find it disgusting, but I show them success stories, explain that the leeches come from a laboratory, and outline the entire protocol for their use, and then they agree,” he says.

“When they see that only a leech can save their ear or their finger, they change their minds,” he adds.

Rodrigo Reynoso advocates that the General Health Council and the Ministry of Health, in coordination with medical associations, promote legal reforms that encourage the creation of a properly accredited leech farm, and promote medical training.

“Hopefully one day we will stop seeing them as mere larvae and recognize them as allies of medicine,” the surgeon concluded.

▲ Leech samples collected in the country and kept at the Institute of Biology of the UNAM. Photo by Cristina Rodríguez

Eirinet Gómez

La Jornada Newspaper, Tuesday, November 11, 2025, p. 6

A bacterium found in a leech endemic to Mexico could help us fight antibiotic resistance, reported researcher Deyanira Pérez Morales, from the Center for Genomic Sciences of the National Autonomous University of Mexico, whose headquarters are located in Cuernavaca, Morelos.

“In leeches, we find a bacterium of the genus Chryseobacterium that produces compounds with antibacterial activity. Interestingly, it inhibits the growth of Staphylococcus aureus , a very common pathogenic bacterium in hospital infections that already shows resistance to multiple antibiotics,” he noted.

In an interview with La Jornada , Pérez Morales explained that antimicrobial resistance, "the loss of effectiveness of medications (antibiotics, antivirals, antifungals) to combat infections," constitutes a relevant public health problem worldwide.

He added that the excessive and improper use of these drugs in both humans and animals has caused pathogens to become resistant, and mentioned that it is a serious situation because we are running out of therapeutic options to treat infectious diseases.

“There have already been reports of people dying because they were infected with bacteria resistant to all antibiotics available on the market,” he warned.

This health emergency led her to focus her scientific work on searching leeches for new molecules with antibacterial activity. “All animals live in symbiosis with millions of bacteria in our bodies, but leeches are different; they have very few species in their microbiota,” she explained.

Under that hypothesis, "their bacteria could produce compounds that prevent the growth of others."

The researcher collected specimens of Haementeria officinalis in the lagoon of the municipality of Coroneo, in Guanajuato. Once in the laboratory, she extracted the contents of the crop, a part of the intestine, identified about 40 species of bacteria, and then focused on 10.

He then cultured these bacteria in specific media and tested them against pathogenic bacteria using an inhibition assay (a laboratory test). When a leech bacterium successfully inhibits a pathogenic bacterium, an “inhibition zone” forms—a visible area where the harmful bacterium cannot grow.

To identify the bacteria taken from the leeches, they extracted their DNA and amplified the 16S gene, a test that allows them to determine which genus each one belongs to; this is how they found Chryseobacterium , which showed antibacterial activity against Staphylococcus aureus , a bacterium that can cause a wide variety of diseases.

“The most interesting thing is that it inhibited clinical strains of methicillin-resistant Staphylococcus aureus ,” the academic highlighted.

These strains are listed by the World Health Organization as priority pathogens for research and development of new antibiotics. “It is urgent to find new molecules that inhibit the growth of these resistant strains,” stressed Pérez Morales, for whom this discovery is significant because it revives an ancient practice: “the medicinal use of leeches in countries like Egypt or Greece” from a modern perspective.

“In this case, we are talking about using a natural resource from Mexico, the endemic leech, in which an antibacterial molecule has been identified,” he emphasized.

Based on this discovery, Pérez Morales, along with his master's student Brianda Hernández, is now working to isolate the molecule to study its cytotoxicity, first in laboratory larvae and in the future in human cells.

“This step is crucial if we want to test it as a new molecule to combat infectious diseases in humans,” the scientist explained.

One possible additional use, he added, would be as a disinfectant to help eliminate antibiotic-resistant bacteria on surfaces or on farms where long-lasting pathogens have also been detected.

"If its effectiveness and safety are confirmed, this molecule could open a new path in the fight against antibiotic resistance," he concluded.

Eirinet Gómez

La Jornada Newspaper, Tuesday, November 11, 2025, p. 6

The leech has become an unexpected ally in understanding how the human brain works. Its neurons, which share similar mechanisms and genes with ours that have been maintained throughout evolution, allow us to observe live how serotonin, a key neurotransmitter that regulates mood, sleep, emotions, and attention, is released.

José Arturo Laguna Macías, a doctoral student in biomedical sciences at the Institute of Cellular Physiology of UNAM, explained that through these invertebrates they have been able to study step by step the complex process by which neurons communicate and better understand how brain activity is organized.

In an interview with La Jornada , he explained that they used leeches in this research because they share small, functional "parts" in common, such as ion channels that allow the passage of molecules, calcium sensors, and vesicle fusion machinery, among others.

Serotonin release

The leech's nervous system, unlike ours and that of mammals, is segmented into 21 ganglia connected by nerve cords that run from the animal's head to its tail, like a string of beads. Each ganglion contains 400 neurons with a stereotyped distribution, making it easy to distinguish a pair of large, serotonergic Retzius neurons (named after their discoverer, Gustaf Retzius).

“These neurons are ideal for observing how serotonin is released from the soma (the neuron's body) because we can extract them and keep them in culture, stimulate them, record their activity, and inject solutions while observing them under a microscope.”

Initial laboratory work has allowed them to map this release pathway from the soma and its key components, which depends on calcium and requires the mobilization of its components. Lagunas Macías is now focused on identifying the proteins that execute the release of serotonin from the somatic membrane.

“Proteins are like tools that the cell manufactures from a gene, and each one performs a specific task, for example, detecting calcium, moving vesicles, joining membranes. The next step is to move from the level of tools to that of instructions: to find out which genes and which signaling pathways coordinate each stage of the process and when they are turned on or off in response to different signals,” he explained.

Defining this type of neuronal communication, the researcher mentioned, allows us to understand how the brain regulates its state and perceives the world.