Nerve pain, also known as neuropathic pain, refers to pain caused by damage or dysfunction in the nervous system. It is often described as a shooting, stabbing or burning sensation. Nerve pain can be very debilitating and significantly impact one’s quality of life. Some common causes of neuropathic pain include diabetes, shingles, HIV, chemotherapy, and physical trauma. However, parasites are not commonly known to directly cause nerve pain. In this article, we will explore the link between parasites and nerve pain and see if there is any scientific evidence to support parasites as a potential cause of neuropathic pain.
What are Parasites?
Parasites are organisms that live on or inside a host organism and derive nutrients at the expense of the host. There are many different types of parasites, including:
- Protozoa – single-celled organisms like Giardia and Toxoplasma.
- Helminths – worm-like parasites such as tapeworms, roundworms, pinworms.
- Ectoparasites – parasites that live on the external surface of the host e.g. lice, fleas.
Parasitic infections are common globally, especially in developing countries with poor sanitation. However, they can affect people from any region. The most common parasitic diseases in humans are malaria, toxoplasmosis, cryptosporidiosis, and ascariasis.
Parasites can infect various parts of the human body such as the intestines, blood, skin, eyes, and muscles. They can cause inflammation, nutritional deficiencies, toxin release, and mechanical damage. The exact symptoms depend on the type of parasite and area of the body infected.
How Do Parasites Cause Disease?
There are several ways in which parasites can cause disease in the human body:
Nutritional Depletion
Many parasites obtain nutrients from the host’s blood, digestive system, or tissues. This can lead to a lack of essential vitamins, minerals, and nutrients in the body. Deficiencies in vitamin B12, iron, and folate are commonly seen with parasitic infections.
Organ Inflammation and Damage
Parasites release toxic substances and digestive enzymes that damage organs and stimulate inflammatory responses. Chronic inflammation of organs like the liver (hepatic fibrosis) and intestines (enteritis) is common.
Impaired Immune Function
Parasites are able to evade, suppress, or modulate the host immune system for their survival. This makes the host more vulnerable to other infections.
Mechanical Damage and Obstruction
Some parasites like adult roundworms physically obstruct intestines and bile ducts. Larval migration can also damage tissues and organs.
Toxin Release
Parasitic infections are often associated with release of toxic substances in the body. These may include ammonia, enzymes, haemolysins, and eicosanoids.
Link Between Parasites and Nerve Pain
There are a few mechanisms by which parasites could potentially contribute to nerve pain:
Nutritional Deficiencies
As discussed earlier, parasites can cause vitamin B12 and other nutritional deficiencies. These deficiencies are known to cause peripheral neuropathy and nerve damage.
For example, vitamin B12 deficiency affects the myelin sheath surrounding nerves. This can lead to altered nerve conduction and neuropathic pain. Correcting the B12 deficiency generally resolves these symptoms.
Chronic Inflammation
Parasitic infections are often associated with a high inflammatory response. The released cytokines and free radicals can damage nerves over time.
Studies show patients with chronic parasite infections have higher levels of inflammatory cytokines like interleukin-6 (IL-6) and tumor necrosis alpha (TNF-α). These have been linked to nerve pain in other conditions like HIV and shingles.
Cross-Reactivity
There is some evidence that parasite antigens may cross-react with human proteins. This could stimulate autoantibodies that attack the body’s own nerves, causing inflammation and pain.
For example, antibodies against leishmania parasite have been found to cross-react with peripheral nerves in leishmaniasis patients. These autoantibodies could contribute to the nerve damage seen in this disease.
Direct Nerve Damage
A few parasite species are known to directly invade or damage nerves in the body:
- The parasite Trichinella spiralis can penetrate muscle cells and reside inside nerve fibers, causing inflammation.
- Cysticercosis is a tapeworm infection where larval cysts can form in nervous tissue like the brain, spine, and eyes. This can compress nerves and cause surrounding swelling.
- African trypanosomes infect the central nervous system and cause a condition called sleeping sickness, which presents with neurological symptoms.
However, most common parasites like intestinal worms do not directly infect or damage nerves.
Scientific Evidence on Parasites Causing Neuropathic Pain
There is limited research specifically examining if parasitic infections can cause neuropathic pain syndromes. Most evidence on this topic is indirect. Here is a summary of the key scientific studies:
Case Reports
There are a handful of case reports linking rare parasites like schistosomes and filarial worms to nerve pain symptoms like burning limbs, pins and needles sensation, and hypersensitivity. However, these case reports are limited in scope.
Animal Studies
A 2017 study in rats showed that a tapeworm infection led to chronic inflammation and nerve damage in the gut. This was associated with visceral hypersensitivity – a sign of nerve pain.
Another rodent study found the parasite Toxoplasma gondii triggered neuropathic pain through activation of spinal cord microglia cells.
However, animal findings do not always translate to humans.
Epidemiological Studies
A cross-sectional study in India compared chronic pain symptoms in 239 people with and without filariasis. Nerve pain symptoms were significantly higher in the filariasis group, affecting 43% of individuals.
Another large study in Brazil evaluated pain complaints in over 1700 children. Children with intestinal parasites were 2-3 times more likely to experience chronic abdominal pain compared to uninfected children.
While these studies show an association, they cannot prove parasites caused the reported nerve pain.
Clinical Trials
There are currently no clinical trials assessing if eradicating parasites improves neuropathic symptoms. This type of study would provide the strongest evidence of a causal link.
Overall, the current research in humans is limited. More systematic studies are needed to clarify if parasitic infections can trigger neuropathic pain.
Common Parasites Unlikely to Cause Neuropathy
Based on available evidence, the most common parasites like Giardia, Entamoeba, Strongyloides, Hookworm do not frequently cause neuropathy.
These organisms mostly reside in the gut and do not directly infect nerves or neural tissue. They are also readily treated with anthelmintics.
Rarer parasites like Schistosoma, Onchocerca filarial worms, and cyst-forming tapeworms have better evidence linking them to neuropathic symptoms. But even for these, reported cases are uncommon.
Diagnosing Parasite-Induced Neuropathy
There are no formal diagnostic criteria for parasite-induced neuropathy. It would be suspected if:
- Symptoms of unexplained nerve pain are present
- The individual lives in or travelled to an endemic area for parasitic diseases
- Stool or blood tests confirm a current parasitic infection
- There are no other causes for neuropathy identified
Diagnostic tests may include:
- Blood tests for antibodies or antigens
- Microscopic examination of stool, tissue or CSF samples
- Skin snip test for filarial worms
- Neuropathic pain questionnaires
- Nerve conduction studies
- Electromyography
- MRI or CT scan to visualize neural lesions
Treatment is directed at eradicating the underlying parasite with anti-parasitic medication. Pain medications and nerve modulators may provide symptomatic relief.
Preventing Parasitic Infections
Some tips to avoid contracting parasitic infections include:
- Practicing good hygiene – wash hands before eating, cook food thoroughly, wash/peel fruits and vegetables
- Avoid contaminated water and undercooked meat
- Wear shoes outdoors to avoid hookworm infection
- Control insect vectors like mosquitoes and ticks
- Deworm pets regularly
- Screen and treat high-risk groups like workers, travelers, immigrants
Public health measures like improved sanitation, vector control, health education, and food/water safety are key for reducing parasitemia rates globally.
Conclusion
There is limited evidence that certain parasitic infections may be associated with nerve pain, likely through nutritional deficiencies, inflammation, and rare direct nerve damage. However, the data in humans remains scarce. Most common parasites do not appear to directly cause neuropathy. Better quality research is required to establish if eradicating parasitic infections can improve neuropathic symptoms. Regardless, preventing parasitic diseases has immense public health benefits.