Everything about Cysticercosis totally explained
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Cysticercosis, or
neurocysticercosis, is the most common
parasitic infestation of the
central nervous system worldwide. Humans develop cysticercosis when they ingest
eggs or
larvae of the
tapeworm Taenia solium. The eggs and larvae are usually found in fecally-contaminated water and undercooked pork.
Humans are the definitive host for
T. solium, which means that the adult tapeworms are found only in the intestine of humans. It is possible for a human to be infested by
T. solium (
taeniasis) without having cysticercosis; in this case the tapeworm lives in the
jejunum and regularly lays its eggs. These eggs don't have the capacity to invade tissue, and they're excreted with the rest of that person's feces. In areas of poor sanitation, swine (and humans) ingest the eggs, which may contaminate the water supply.
The eggs are capable of hatching once ingested. The larvae of
T. solium are able to invade tissue, and enter the bloodstream. From there, they're able to spread to many organs (
skeletal muscle,
heart,
eye,
brain,
spinal cord) and form cysts in tissue called cysticerci. They can't grow into adult worms in this state, and remain indefinitely encapsulated in tissue. Cysticerci are commonly found at autopsy in asymptomatic inhabitants of endemic areas.
Humans may ingest the eggs or larvae directly from contact with fecally contaminated food or water (common). In rural areas where cysticercosis is common, pigs ingest the eggs by the same means. When pigs eat the eggs, the larvae hatch and disseminate and form cysticerci in the striated muscle, which can be the infective source of cysticercosis for humans who later consume that pork. This describes why swine are the intermediate host of
T. solium: pigs eat the eggs laid by the tapeworms that live in the gut of infested humans.
Humans with
taeniasis contract cysticercosis in the same manner; they're also capable of
autoinfection by
vomiting. In the latter case, eggs laid by their infesting tapeworm are pushed back into the stomach. When these eggs pass back into intestines, the larvae hatch and the infestation proceeds as usual.
See also Taenia solium and Taenia saginata.
Symptoms
In muscles, cysts cause painless
swelling or create nodules under the skin. If cysts form in the eye, they can impair vision by floating in the eye and can cause
blindness by causing swelling and detachment of the
retina. Heart lesions can lead to
abnormal rhythms or
heart failure (rare). The most dangerous symptoms are a result of encystment in the
central nervous system.
According to a
Centers for Disease Control and Prevention Division of Parasitic Diseases, in neurocysticercosis (cysticercosis of the brain), "
seizures, and
headaches are the most common symptoms. However, confusion, lack of attention to people and surroundings, difficulty with balance,
hydrocephalus (compression of the brain tissue due to obstruction of cerebrospinal fluid flow) may also occur." Often, there are few symptoms until the parasite dies. When the parasite dies, the host's
immune system detects the worm's remains and attacks them, causing swelling and
scarring. This is what causes most of the symptoms. Spinal cord lesions can lead to partial loss of
motor control,
weakness, and even
paralysis.
When death occurs, it's most often due to involvement of the brain resulting in
hydrocephalus,
cerebral edema, cerebral compression, or
epileptic seizures.
Diagnosis
Neurocysticercosis is difficult to
diagnose in its early stage and may be apparent only when the first neurological symptoms start, or when a
CT scan, or an
MRI of the
brain is performed for other reasons.
Antibody tests or a
biopsy of the affected area may be necessary to complete the diagnosis.
Treatment
The anti-parasitic drugs
Praziquantel and
Albendazole may be used to treat neurocysticercosis.
Steroid anti-inflammatory medication is also often used in conjunction to reduce the
swelling (brain edema) that results from immune system attacks on dead worms. It is still controversial whether patients benefit from treatment, because live cysticerci don't provoke seizures; only dead or dying parasites invoke an inflammatory response and seizures. In theory, therefore, treating a patient with drugs that kill living parasites can induce seizures in someone who is otherwise well and seizure-free; likewise, treating someone with seizures may not have any effect on outcome as the parasites are already dead and no improvement can be expected. A
meta-analysis of 11 trials suggest that's that there's probably some small benefit to patients who have active lesions, but no benefit to those with only dead or inactive lesions.
If the cyst is in certain locations, such as the eye or the brain, steroids may be started a few days before the antiparasitic, in order to avoid problems caused by swelling. If swelling and immune response are not controlled, the treatment itself can be lethal, so the medication is given in low dosages over several days. Sometimes surgery may be needed to remove the infected area or cysts, but this may be impossible when they're located in areas of difficult or dangerous surgical access. Also, some medications may treat symptoms, such as seizures or irregular heartbeat without affecting the worms.
If the cysticerci have
calcified in the brain, or if there's only one lesion, treatment isn't considered beneficial.
Prevention
It is possible to avoid infection with
T. solium by avoiding undercooked pork and food and water contaminated with human feces. Extra care should be taken in places with poor hygiene or
meat inspection laws. Freezing infested pork for a prolonged period will also kill cysticerci.
If a person is already infected with
T. solium, they can avoid cysticercosis by treating the infection in the small intestine early, by not ingesting their own feces, and by not vomiting, as this brings eggs to the stomach so they form cysticerci in the small intestine.
References in Popular Culture
Further Information
Get more info on 'Cysticercosis'.
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