Neurocysticercosis is a condition which arises, chiefly in the brain, after the ingestion of pork tapeworms, and it is a common medical problem in the developing countries of the world, as well as those countries where citizens from those underdeveloped countries emigrate.
The precise culprit in neurosis is the pork tapeworm taenia solium, and the reaction exhibited by any given human host depends on where the larvae of this tapeworm are situated and what kind of concentration there is at the infestation site.
Reactions from the host vary significantly in severity and can include headaches, focal neurologic symptoms, localized muscle pain and abnormal nodules, visual disturbances, and even violent seizures.
This tapeworm infection is the most common parasitic infection around the entire globe, with an estimated 50 million people being victimized at any one point in time. It is endemic to India, Asia, South America, Mexico, Central America, and parts of Africa.
While the infection itself is referred to as cysticercosis, the neurologic manifestation of it is properly termed neurocysticercosis. No other infection of the brain is more prevalent around the world than this one, and even in the United States, more than 1,000 new cases are diagnosed every year. It remains the number one cause of seizures among adults globally and has yet to be brought under medical control.
It should be borne in mind that by the time any symptoms appear which are truly traceable to neurocysticercosis, the infection has already been in progress for several years, in at least one location in the body. This kind of ‘silent infection’ will be continued until the degeneration of the taenia solium cysts release the larval antigens, at which time symptoms begin to appear near the specific location of the infection site.
Because there are so many possible infection sites around the body, symptoms can literally appear almost anywhere and can have a tremendous variance in degree. Because of this broad range of possible symptoms, it can be very difficult to diagnose neurocysticercosis unless symptoms are so pronounced as to be almost indisputable.
Symptoms can appear as inflamed skin at various locations, sometimes accompanied by noticeable nodules which have no other apparent origin. An unusual constraint or limitation of muscle movement at specific locations can also be symptoms of the disease, especially when no injury has occurred at that site and there is no history of limited movement in that area. Eye movements, for instance, can become limited, and vision can become blurred when infection occurs in the general area around the eyes.
The most noticeable and the most violent symptoms observable are generally triggered by infections which lodge themselves somewhere in the brain. Depending on which part of the brain is afflicted with the infection, the functions specifically managed by that section of the brain are highly likely to be negatively impacted. As previously mentioned, one of the most common types of reaction is a seizure, sometimes even an epileptic seizure.
The most common of all symptoms of neurosis is epilepsy, accounting for as much as 70% of all forms of the infection, both in adult-onset epilepsy and in childhood epilepsy as well. In situations where a single lesion is in place at an infection site, seizures tend to be less severe in nature, and when multiple lesions are in place, much more severe episodes of epilepsy are frequently triggered.
Strokes are another manifestation of vascular damage or hemorrhaging in arteries where lesions have impacted a particular site. Such strokes and mini-strokes are generally observable as involuntary movements like twitching or jerking, or disturbances to ambulatory movements.
In some cases, the concentration of lesions at an infection site can be so pronounced that it leads to symptoms akin to dementia, although some scientists argue that this is due more to intracranial hypertension than to the actual number of parasites afflicting brain tissue. As such, it can be difficult to diagnose neurocysticercosis rather than the more obvious dementia, especially if the victim is at an age where dementia is more likely.
When any of these symptoms are manifested and become observable over a period of time, there are several methods available which can help with the accurate diagnosis of neurocysticercosis. One such strategy is magnetic resonance imaging, which is very good at the detection of spinal, brainstem, or ventricular lesions which have developed in the body. For the detection of lesions around the eyes, ultrasonography is particularly useful and carries a high degree of accuracy.
In almost all cases, the most definitive way to determine whether observable symptoms are in fact associated with neurocysticercosis is via biopsy of the skin, muscle, or brain tissue which is thought to be affected. However, since this is also the most invasive method, a biopsy is not generally one of the first procedures undertaken. Other less invasive means are generally employed first, with biopsy being reserved as a last alternative for detection.
The pork tapeworm taenia solium begins life at the larval stage in pigs and can be transferred to humans via undercooked pork when taenia solium cysts are ingested. These larvae attach themselves to the human digestive system, and simply feed on available host nutrients until they mature into adult tapeworms. When humans ingest the tapeworm eggs, they become the final hosts of the parasites in their larval stage and inevitably develop cysticercosis.
Cysts can attach themselves to the spinal column, eyes, skeletal muscle, subcutaneous tissue, and the brain, which is where 60 to 90% of all infections occur. The least common sight for cyst attachment and larvae development is around the eyes, where no more than 3% of all infection occurs.
The concentration of cysts at a given location in the body can be anywhere from one to many hundreds, and symptoms do not appear immediately because the larvae encrust themselves as a defense mechanism against destruction by the host. This condition can literally last four years with no observable signs or symptoms of the infection. Symptoms only finally appear because the degenerating cysts cannot maintain their protective encrustation indefinitely, and ultimately release larval antigens.
These larval antigens do produce a host response, often in the form of inflamed sites on the skin. When this activity takes place in the brain, it becomes much more dangerous and can cause headaches, neurologic abnormalities, seizures, and symptoms which mimic those of Parkinson’s disease.
When the cysts occur in ventricular areas, they can often grow large enough to cause cranial nerve palsies or obstructive hydrocephalus due to nerve entrapment. When infections occur around the eyes, it can lead to retinal detachment or limitation of eye movements. At other locations around the body, infections may be manifested as noticeable discomfort or pain in specific muscle groups.
All of these manifestations of neurocysticercosis are caused by the same thing though – the ingestion of undercooked pork containing the taenia solium tapeworm.
Treatments for neurocysticercosis are as varied as the locations of the infections and the symptoms themselves. In some cases where infection is suspected, a policy of watchful waiting is employed until symptoms become more pronounced and treatable. The program of treatment decided upon must always assess several different factors, starting with site location and symptoms, but also including the concentration, developmental stage, and size of the cysts.
In cases where isolated muscular or subcutaneous tissue is the extent of observable damage, sometimes no specific treatment is even undertaken unless the victim is in such a state of pain that he/she feels treatment is warranted. In situations like these, an incision can be made in the skin, followed by complete removal of the cysts.
For sites located around the eyes, anti-parasitic therapy is generally used in tandem with steroids as a means of removing constraints upon ocular muscles, and relieving inflammation. For more extreme cases, surgical incision can be an option, although always in consultation with a qualified ophthalmologist.
It is considerably more complicated and risky to treat subarachnoid and ventricular neurocysticercosis, although the simplest form of treatment will generally be the first tactic tried. A program of medication including steroids and high-dose albendazole is generally the first attempt at treatment. Even so, there is a risk of inflammation at the site, which makes consultation desirable with an expert on infectious diseases. Surgical incision is again an option, depending on the sensitivity of the location itself, and the risk imposed to the patient.
It is always more risky to treat parenchymal neurocysticercosis because functional tissue is so much more delicate and critical to overall body operation than simple connective tissue. However, it is parenchymal neurocysticercosis which has been studied and researched more than any other kind of infection, so associated treatments and their effects are also better known than for other infection types.
Again, the treatment for such manifestations of parenchymal neurocysticercosis will first begin with a seven-day course of albendazole or praziquantel, after which the effects of treatment will be observed and documented. Depending on the effectiveness of medications, other strategies may then be employed.
When there’s a high concentration of infection, medications are generally not used because of the danger of overwhelming inflammatory response, which in turn can trigger seizures in greater numbers, and of greater severity. To deal with the inflammation aspect of an infection site, steroids are commonly used, and this program of medication can go on for months and sometimes even several years for an infected patient.
Prevention of neurocysticercosis is a topic which has been focused on to a great extent by the Center for Disease Control and the Prevention Working Group on Parasitic Diseases. Both of these organizations classify neurocysticercosis as a potentially eradicable disease if a concentrated effort were to be made on removing the source of infection.
The first area of prevention thought to be necessary is on preventing the spread of the pork tapeworm, taenia solium. One of the best ways of accomplishing this is to decrease the number of pork tapeworm carriers, which would thereby reduce the parasite eggs which are shed during meat inspection and meat preparation.
Another tactic necessary for the prevention arsenal of neurocysticercosis will be to reduce or eliminate the exposure of pigs to human feces because it is porcine ingestion of human feces that propagates the cycle of tapeworm production, which is ultimately passed back to humans.
An additional focus in the prevention scheme would be to develop a vaccine which is highly effective against taenia solium, hopefully eradicating the tapeworm from all pigs used in agriculture. Already some studies have shown notable success in the development and use of such vaccines in pigs, but widespread use has not yet been achieved, for logistical reasons and because research results have yet to achieve universal agreement and approval.