What Does Cancer Smell Like? These Animals Can Sniff It Out

A beagle exploring the scent of the forest. Dogs are just one of many creatures with extraordinary noses that can detect signs of human diseases such as COVID and cancer.

The next time you're frustrated that ants have taken over your kitchen, maybe take a moment to think about their amazing perceptual abilities.

These tiny animals can detect markers of diseases such as cancer. In fact, ants are just one of many creatures whose senses detect signs of human disease: dogs, rats, bees, and even tiny worms.

Here's what we know about these animals and their amazing abilities.

business ant

Formica fusca, a species common in Europe, can be studied to detect breast cancer in urine .

Research from France's Sorbonne University Paris Nord, published this year in the Proceedings of the Royal Society B, shows that ants can learn to distinguish the odor of urine from mice with breast cancer tumors from healthy mice.

Ants and other animals detect signs of disease by detecting a variety of volatile organic compounds, or VOCs. These chemicals are produced in many ways and can be found in the air you breathe, sweat, urine and blood. Disease can change the VOCs we emit, causing different odors. By placing the cane next to the crab sample, the ants learn to recognize its smell, a process known as operant conditioning.

"We were surprised by the speed of the ants. An ant can be made in ten minutes," said lead author Baptiste Piqueret, currently a postdoctoral researcher in Chemical Ecology at the Max Planck Institute in Germany.

After training the ants, the scientists placed the insects in petri dishes containing urine samples from tumors and healthy mice. They spend 20% more time on cancer samples.

Ants use their olfactory receptors to smell odor-causing chemicals on their antennae. Perfume is their main form of communication, explains study author Patrizia d'Ettorre, ethologist at the Sorbonne Paris Nord University.

They "recognize group members by body odor" and use pheromones, often in small concentrations, to communicate in disorienting series of complex signals.

These ants also don't bite and are “cheap to buy and keep. Honey and insects die and the ants are happy,” said Piqueret. This makes them excellent candidates for this type of work.

D'Ettor said the exact chemical in the ant's scent is unknown, which is often the case in other animals that taste cancer.

Man's best friend

Dogs can be trained to sniff out a variety of cancers, including melanoma, breast and gastrointestinal cancers, and several human infectious diseases, including malaria and Parkinson's disease. In the US, dogs are working to search for COVID-19, including at several schools in California, several locations in Massachusetts, and at a Miami Heat basketball game.

They can also sniff out infectious diseases in other animals, including chronic wasting disease, which affects the deer's brain and can be fatal.

"It destroys deer, and the only way to detect it is through necropsy," said Cynthia Otto of the University of Pennsylvania School of Veterinary Medicine.

However, dogs can be trained to detect disease in deer droppings, according to research Otto wrote about in the journal Prion . Otto said researchers believe dogs could smell the infectious agent in these and other cases.

"We've done pilot studies on bacterial infection, and if we train dogs about the bacteria themselves, the dogs can respond to samples from infected people," he said. The British charity Medical Detection Dogs has trained dogs to detect a record 28 diseases, including some bacterial.

What is different from cancer detection is that dogs can detect "how the body reacts to cancer cells", including the smell of an immune response or something else. "Or it could be the cancer itself, we don't know for sure," said Otto.

They may also recognize more than one scent, or different dogs may pick up on different scents. In the ovarian cancer study that separated odors into different groups, "different dogs responded to different parts," says Otto.

detective mouse

Another animal used to detect explosives is the giant African rat.

In 2004, Belgian non-profit APOPO shipped trained African giant rats to Mozambique "when the rats were first accredited to foreign mine standards," says Cindy Fast. , is responsible for organizational training and innovation. Since then, they have helped seven countries clear more than 150,000 mines.

Tanzania, where APOPO is headquartered, has no landmines, but is one of the 30 countries with the highest TB rates.

Lily Shallom, the organization's communications manager, said that "APPO research shows that they have detected a variety of odors from Mycobacterium tuberculosis , the bacterium that causes tuberculosis.

Like the ants, the rats received a food reward if they identified a sample of TB in human sputum during training. After training, they act as a safety net, a backup for technicians.

Each mouse "analyzed more than a hundred patient samples in about 20 minutes," said Fast, which would have taken human researchers four days. They are rewarded if they identify patterns that have been identified as positive. However, if the rat reports a sample that has tested negative, it is sent for evaluation with a more expensive test.

According to APOPO, since the program started, rats have detected more than 23,000 cases that were missed by local medical clinics.

"They improve disease detection by about 50% compared to their clinical counterparts," said Fast, boasting of the hairy diagnoses.

Testing bees for COVID-19

As if bees weren't helping us enough, Dutch researchers have shown that bees are good at tracking down SARS-CoV-2, the virus that causes COVID-19.

Bees smell like ants with their sense organs and are very sensitive to smells. Scientists at the Wageningen Bioveterinary Research Laboratory in the Netherlands took real bees and placed them in a special "beekeeper," a plastic head box with room for wings and body movement. They smell the different samples and taste the sweetness when they roll their tongues in response to the COVID positive material. Over time, they will perform these actions without receiving a reward.

Like ants, they can be trained in minutes and tested in seconds.

It is not yet known exactly what the smell of bees in samples infected with SARS-CoV-2 is. The researchers suggest that the bees could be useful in remote communities where traditional testing may be difficult.

Smart worm

Smaller than a bee, the nematode Caenorhabditis elegans , a sand-like creature about the size of a grain of sand, is often used in laboratory research. It has very similar disease genes to us, and is a valuable model organism for scientific research. It is also transparent, so its biological processes can be easily seen under a microscope.

The body has also been shown to have the ability to detect cancer. A Japanese study found it could detect pancreatic cancer cells and an Italian study found it could detect breast cancer cells.

In both cases, the worms can approach samples containing cancer cells and avoid healthy cells. A Japanese biotechnology company is offering N-Nose, a cancer screening test in which people submit a urine sample and have it checked for worms.