Sick of that whining mosquito that never shuts up?

Have a heart. Maybe it’s got a broken leg or a dislocated wing and can’t stop complaining about it.

Australian scientists have shown for the first time that insects “experience chronic pain that lasts long after an initial injury has healed”.

The study, from the University of Sydney, includes the first genetic evidence of what causes chronic pain in fruit flies “and there is good evidence that similar changes also drive chronic pain in humans”.

Why is this significant?

The study appears to reveal how and why pain originates in the body – and for people with chronic pain, that means a potential cure.

The traditional path of treating the symptoms of pain – that is, the discomfort, sometimes crippling – has led to mass dependence on drugs that aren’t good for us.

Even long-term use of paracetamol carries a small risk of causing heart attacks, gastrointestinal bleeds (bleeding inside the digestive system) and impaired kidney function.

And then there’s the opioid crisis – prescription medicine – that’s killing 130 people every day in the US.

The researchers from the University of Sydney believe that the insights gleaned from what causes pain in the fruit fly could change that – by leading to the development of treatments that, for the first time, target the cause and not just the symptoms of chronic pain.

The discovery was made by Associate Professor Greg Neely, whose team of researchers is studying pain at the Charles Perkins Centre with the goal of developing non-opioid solutions for pain management.

In a prepared statement, Dr Neely noted that people don’t really think of insects as feeling any kind of pain.

“But it has already been shown in lots of different invertebrate animals that they can sense and avoid dangerous stimuli that we perceive as painful.

“In non-humans, we call this sense ‘nociception’, the sense that detects potentially harmful stimuli like heat, cold, or physical injury, but for simplicity we can refer to what insects experience as ‘pain’.

“So we knew that insects could sense ‘pain’, but what we didn’t know is that an injury could lead to long-lasting hypersensitivity to normally non-painful stimuli in a similar way to human patients’ experiences.”

Chronic pain is defined as persistent pain that continues after the original injury has healed. It comes in two forms: Inflammatory pain and neuropathic pain.

The study of fruit flies looked at neuropathic ‘pain’, which occurs after damage to the nervous system and, in humans, is usually described as a burning or shooting pain.

In humans, neuropathic pain occurs in conditions such as sciatica, a pinched nerve, spinal cord injuries, shingles, diabetic neuropathy, cancer bone pain and in accidental injuries.

How did they test pain in fruit flies?

In the study, Associate Professor Neely and lead author Dr Thang Khuong damaged a nerve in one leg of the fly.

After the injury was allowed to fully heal, they found the fly’s other legs had become hypersensitive.

“After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives,” said Dr Neely.

Next, the team genetically dissected how this works. Dr Neely said the fruit fly is receiving pain messages from its body that then go through sensory neurons to the ventral nerve cord, the fly’s version of our spinal cord. In this nerve cord are inhibitory neurons that act like a gate to allow or block pain perception.

“After the injury, the injured nerve dumps all its cargo in the nerve cord and kills all the brakes, forever. Then the rest of the animal doesn’t have brakes on its ‘pain’. The ‘pain’ threshold changes and now they are hyper-vigilant,” he said.

The new study supports the theory that chronic neuropathic pain in humans is a result of the brakes coming off for good in the central nervous system, a process called central disinhibition.

Dr Neely said his team were now focused on making new stem cell therapies or drugs that will target this underlying cause with a view to stopping pain for good.