Formication is a generalized description of the condition when a person feels one or more of various sensations on or under the skin, but then nothing is visibly present for any observer to see which could possibly be responsible. Doctors often ascribe this sensation to some form of a neurological or psychological disorder without so much as investigating any of the potential organic diseases that might cause this particular set of sensations.

The specific symptoms grouped under formication is often described as a moving or crawling feeling on the skin, biting or pin pricks, small vibrations or tingling, itching, rash, numbness, or even a burning feeling. This situation is known to be provoked during menopause, while the person is using certain prescribed drugs, or upon the withdrawal from certain recreational drugs or alcohol. Many causes have been hypothesized but none have actually been proven scientifically so the go-to answer is almost always a psychological diagnosis.

Occult Dirofilariasis is one such organic disease which will necessarily cause all these symptoms as a primary set of symptoms of the disease, but since there is currently no test for this disease in humans, the true cause of formication naturally goes untested and untreated in the human population. In the US population there is somewhere between 41.1 and 137.2 Million people that will have already been exposed to this disease[01].

The physical sensations felt by this person can be caused by the parasite living in the veins just under the surface of the skin, which because of their very close proximity to the surface sensory neurons it will be completely indistinguishable for the patient to tell if this kinetic sensation is from something actually on the surface of the skin or just below it. From millions of years of evolution our human brain has been hard-wired to just assume the former since that is where external threats naturally come from. It just feels like its on the surface, not just below the surface where the parasite actually resides.

By definition the default condition in humans is the occult infection as when the parasite molts into the L4 stage it enters the bloodstream where it becomes completely undetectable in humans. The sensations originating from an occult Dirofilariasis infection will always be collocated within a vein found just below the surface of the skin. Doctors should pay close attention to where a patient says they have these sensations because that information could be very important information in getting an ultimate diagnosis. Larger veins in the lower extremities are more common for the larger filaria and the more powerful sensations and may even be measurable[02], however other places like the face and scalp are extremely sensitive and can also be the source of a complaint. The branching tributaries and venous valves throughout the body may be particularly sensitive as well. The doctor should refer to a text book resource of the vascular system before concluding that this is just some kind of a psychological manifestation.

Reasons for the Specific Symptoms of Formication

  • Crawling/motion, vibrations, or tingling – This is the primary set of symptoms cause by the nematode which can be up to six inches in length and moving just under the surface of the skin. There are many different situations which can exacerbate this particular symptom of their motility, as is described below in much more detail.
  • Biting or pin pricks – Since we have no real-time diagnostic imaging tools yet there is no way to know exactly how or why they are digging into the endothelial tissues of the veins but the evidence is that this is a very common symptom. We know from animal studies that Dirofilaria destroy the endothelial layer of tissue in the vascular system of their host, so feeding on this tissue in addition to other circulating proteins, sugars and lipids found in the blood should not be surprising. This constant onslaught is also functionally able to desensitize the host from slapping or biting every time an insect vector might feed, thus leading to the ability for it to transfer more easily in any non-human host. There is literally nothing the host can do to stop this pain so they learn to live with it 24×7.
  • Itching – The itching they are experiencing is due to the chemical messenger histamine which normally drives the Th2 immune inflammatory response used against any parasitic invader. The parasite dumps its secretomes, comprised of miRNA in exosome-like particles[03], directly into the hosts bloodstream in order to circumvent[04] the normal immunological response downstream in the immunological chain of events[05]. The histamines are still secreted by any activated basophils and mast cells so the histamines are there, but the downstream immunological functions that they are meant to trigger to rid themselves of the parasite are disabled by this active immunosuppression. The end result is the accumulation of histamines in the blood and its associated itching.
  • Rash – While the immune system is waging war there will be many toxic compounds and free radicals released into the bloodstream in attempt to wear down the thick coat of carbohydrates off of the exterior of the parasite and these will just drift downstream and causing cellular damage other tissues and blood cells. A whole cascade of immunological changes[04][06][08][09] will happen and in some individuals a rash may be formed in the process.
  • Numbness – Dirofilaria and its endosymbiont causes both hyperglycemia[10] [11] , nerve, and tissue damage. Its physical presence in the vasculature system can also attribute to a loss of blood flow. All these factors can attribute to the feeling of numbness in the extremities but this will generally be a late-stage development.
  • Burning sensation – Given the amount of tissue destruction it should not be surprising there would be extreme irritation in the areas where the filaria are being attacked by the immune cells. When the filaria itself becomes irritated by this onslaught they will often move or gyrate in a way to shake off the attacking immune cells and cause the blood in that vein to move downstream carrying the immune cells away. While this motion persists this will further cause pain by further irritating the inflamed inflammation endothelial lining of the veins in that immediate area.

Types of Filarial Motility

There are several causes for the sensations of filarial motility that cause this primary symptom of formication. The list below is not necessarily complete but is provided as loose framework for understanding the kinetic motivation of the parasite in this disease.

  • In response to a host immunological attack – When the host’s own immune system is trying to do its job the filaria may become perturbed and begin undulating within the blood vessel. This action would shake off some of the attacking immune cells and force some measure of blood to flow downstream which then lessens the time period in which each immune cell is in contact and is able to do its damage. The cytotoxic compounds use to degrade the cuticle coating of the parasite are then instead released into the blood stream thus causing cellular damage downstream of the parasite. Any drug or chemical compound that increases the amount of alternately activated macrophages (e.g. Thuja[12], Biociden[13][09]) or otherwise boosts the immune system activity may actually increase this specific filarial activity. Moxidectin will decrease this same activity through mild paralysis but will not kill any adult parasite.
  • Temperature – The filaria appear to be sensitive to temperature and will begin moving more violently when the temperature is increased. Using therapeutic ultrasound at the 3.5 Watts/cm2 will begin to get them aroused but so far there is no definitive proof that this is detrimental to their health and can also be uncomfortable for the person as well.
  • Stimulants – Drugs such as amphetamines, methylphenidate (Ritalin), or dextroamphetamine, not only have an effect on the host but also on the nematodes[14] residing within that host. In fact nematodes are often used in drug research laboratories because they have many of the same biological pathways that humans do, and nematodes are much easier and cheaper to study. Logically it should not be surprising that stimulants would have such an effect.
  • Drug Withdrawal – Nematodes do get hooked[15] on illicit drugs just the same as humans do. When the host is going through a bad withdrawal there should be little surprise that the parasite will be going through the exact same issues. When the nematode becomes irritable it is going to complain every bit as much as its host.
  • Space restriction – Anytime the filaria is restricted or pinched within the cavity of the vein it is living in it is going to try to get loose. When the person lays down for the night there will be a shift in the orthostatic blood pressure which will then shift how much room is physically available in all the veins and the filaria will then seek a new position giving more room. Pressing a finger against a blood vessel hard enough might get one to thrash around to try and free itself. Moving an arm or a leg in specific ways might cause one to even move to another location to lessen this perturbation. For example, placing a hard brimmed hat tightly on the head may cause filaria in the scalp region to thrash and move to another location nearby.
  • Normal Taxis – This is the normal mode for the parasite to migrate to another region of the hosts body. The larger filaria will likely remain in the same location in the lower extremities because that is where the room for them is maximized due to orthostatic pressure. Smaller filaria may migrate more often and this may sometimes give a sensation like a spider web being stretched across the face. Male filaria tend to be smaller and will still still seek a female for mating even though in humans there is nearly zero chance for their offspring to survive. Procreation is burned right into their genes, so this sex drive does not stop just because they are in a non-productive in a given host.
  • Copulation – When the male filaria seeks out a female for mating purposes it doesn’t know that the microfilaria prodigy will never survive in a human host. It is still still driven to carry out its life-cycle regardless of the final fate of being within in a dead-end host. When the female finds its resting place in the veins close to the external surface of the skin it may be quite far up towards the smaller capillaries where the blood flow and thus all nutrients needed by her originate. As long as she is not far enough forward to cause blood pressure in the vein to build up then she will likely be comfortable for a long time. For the male to mount the female for copulation the male first needs to be along side of the female, by squeezing tightly into in the restricted space in that vein next to her. If the immune system has been attacking her recently then this endothelial cell lining may be inflamed and painful to the host and this inflammatory pain will be noticed. The stretching of the inflamed vascular tissues can be quite painful. In addition, because of their anatomical differences in the placement of their sex organs the male must be further forward than the female for their mating appendages to line up, and this causes the male to push even farther forward where there may not be sufficient space for him. As he pushes even more into that restricted space the blood pressure will begin to back up and make all the local tissues begin to swell as he drives himself deep into the very thin venous structures thus causing enormous pain to the host. This pain can be intense and is punctuated because he can not push consistently against the hosts own blood pressure. This swelling and intense pushing against the blood flow can be extremely painful.

The general intensity of this formication will mirror the adult filarial activity which increases from around 9am and peaks later around 1am[16]. This later intensity seems to mirror the activity cycle of mosquitoes as the purpose of these vibrations is to undulate to expel the prodigy of microfilaria, even though they do not circulate in humans this circadian rhythm is ingrained into their biology. This lack of microfilarial circulation is likely due to the immune system completely eradicating the stage L1 microfilaria while any remnants of this may be filtered out by the capillaries of the lungs. A late evening spike in activity may cause the patient to have trouble falling asleep at night, causing general sleep deprivation, irritability, and thus problems focusing on things during the day.


[01] – Dirofilaria exposure based on 2020 Census age distribution and known animal infection rates.

[02] – Direct detection of vibrations from a filaria in the dorsal metatarsal vein using a modified geophone sensor.

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