Cysticercosis

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Cysticercosis

• Dan Imler
• Morning Report

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EPIDEMIOLOGY

• Cysticercosis is caused by the metacestode or
  larval stage of Taenia solium, the pork tapeworm.
  
• Approximately 50 million people are believed to
  have cysticercosis worldwide.
• This is probably an underestimate since many
  infections are not diagnosed.
• NCC is the most common cause of adult-onset
  seizures in developing countries

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EPIDEMIOLOGY

• Cysticercosis is endemic in many areas,
  particularly in several countries in Central and
  South America, sub-Saharan Africa, India, and
  Asia.
• The prevalence of NCC varies within these
  countries and is often higher in rural areas,
  especially in places where pigs are raised and
  where sanitary conditions are suboptimal.
• Seroprevalence rates in certain rural South
  American communities are as high as 10 to 25
  percent

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EPIDEMIOLOGY

• Cases of cysticercosis are also seen in
  nonendemic countries, particularly in those that
  have significant numbers of immigrants.
• In a prospective study of 1801 radiographically-im
  aged patients who presented with seizures to 11
  university-affiliated emergency departments in
  the United States over a two-year period,
  neurocysticercosis was the etiologic agent in 38
  patients (2.1 percent).
• The rate was higher (5.7 percent) in emergency
  departments from Los Angeles, Phoenix, and
  Albuquerque, which had a higher percentage of
  immigrant Hispanic patients among the eleven
  hospitals.
• In a mortality study using data from the National
  Center for Health Statistics, a total of 221
  cysticercosis deaths were identified in the
  United States from 1990 to 2002 62 percent of
  the patients had emigrated from Mexico.

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TRANSMISSION

• Humans develop cysticercosis by ingestion of eggs
  of T. solium, and consequently the risk of
  acquiring cysticercosis relates to proximity to
  individuals infected with the T. solium tapeworm.
• Those infected with adult T. solium can serve as
  a source of eggs in one of two ways
• Their egg-containing feces can contaminate water
  supplies in endemic areas. If the water is used
  to irrigate fruits and vegetables, eggs are
  ingested with the contaminated food.
• Alternatively, T. solium carriers can contaminate
  food directly the eggs are sticky and can often
  be found under the fingernails of tapeworm
  carriers. Food prepared by the T. solium carrier
  can therefore be contaminated with eggs and lead
  to cysticercosis in the consumer.

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So when in a pig farm in Mexico please Wash your
Hands!
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TRANSMISSION

• People who have never been to countries endemic
  for cysticercosis can also develop infection.
• In such cases a search for the source patient
  with a tapeworm infection should be performed.
• As an example, neurocysticercosis was reported in
  an Orthodox Jewish community in New York City in
  1992 when four cases were identified from four
  separate households.
• An investigation revealed active infection in the
  domestic employees from all four households
  these source patients had recently immigrated
  from Latin American countries where T. solium is
  endemic.

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TRANSMISSION

• In patients harboring adult T. solium tapeworm in
  their intestine, feces can also serve as a source
  of fecal-oral autoinoculation.
• However, only 5 to 40 percent of patients with
  cysticercosis have an adult worm in their
  intestine, and most individuals with intestinal
  tapeworm infection do not develop symptomatic
  cysticercosis.
• Autoinfection in patients with taeniasis by
  regurgitation of proglottids into the stomach and
  release of eggs has been proposed as another
  possible mechanism for the development of
  cysticercosis, but this has not been proven.

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LIFE CYCLE

• Once eggs are ingested by humans, the embryos are
  released in the small intestine and invade the
  bowel wall.
• From there, they disseminate hematogenously to
  other tissues and develop into cysticerci over a
  period of three weeks to two months.
• Cysticerci are liquid-filled vesicles consisting
  of a membranous wall and a nodule containing the
  invaginated scolex.
• The scolex has a head armed with suckers and
  hooks and a rudimentary body.
• Humans with cysticercosis are incidental
  intermediate dead end hosts.

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NEUROCYSTICERCOSIS

• Cysticerci in the brain are initially viable but
  do not cause much inflammation in surrounding
  tissues this phase of infection is usually
  asymptomatic.
• The host develops a state of immune tolerance to
  the parasite, and cysticerci can remain in this
  stage for many years.
• Clinical manifestations frequently develop when
  an inflammatory response develops around a
  degenerating cysticercus.
• It is not known what triggers this degeneration,
  but after a variable number of years, the cyst
  seems to lose its ability to modulate the host
  immune response.

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NEUROCYSTICERCOSIS

• Postmortem studies in endemic areas suggest that
  80 percent of neurocysticercal infections are
  asymptomatic.
• Consequently, many cases are never diagnosed or
  are found accidentally during imaging procedures.

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NEUROCYSTICERCOSIS

• If symptoms are present, these are mainly due to
  mass effect, an inflammatory response, or
  obstruction of the foramina and ventricular
  system of the brain.
• The symptoms of NCC depend upon the stage, site,
  and number of cysticerci.
• The most common symptoms include seizures, focal
  neurological signs, and intracranial
  hypertension.

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NEUROCYSTICERCOSIS

• The peak of NCC has been estimated to occur three
  to five years after infection, but it can be
  delayed for gt30 years.
• After a variable period of degeneration, cysts
  can become calcified and may then become
  inactive.
• Once they are calcified, they may cease to cause
  symptoms or may serve as a focus for epileptic
  activity.
• Patients frequently have cysts in more than one
  location, and it is not uncommon to have active
  and inactive cysts present in the same patient.

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Ocular cysticercosis

• Ocular cysticercosis occurs in approximately one
  to three percent of all infections.
• Patients with ocular cysticercosis may have
  parasites located in the subretinal space or
  vitreous humor.
• These are often asymptomatic, but inflammation
  around degenerating cysticerci can threaten
  vision by causing chorioretinitis, retinal
  detachment, or vasculitis.
• Parasites may also be present in the anterior
  chamber or may affect the conjunctiva or
  extraocular muscles.
• Ocular cysticercosis should be excluded by a
  proper ophthalmologic examination in all patients
  with NCC prior to initiating therapy.

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Subcutaneous and intramuscular cysticercosis

• Cysticerci can develop in almost any body site,
  but tend to have a predilection for muscle or
  subcutaneous tissues.
• Cysticerci at these sites are usually
  asymptomatic, but the patient may notice
  subcutaneous, pea-like or walnut-sized nodules.
• Subcutaneous nodules are more common in patients
  from Asia and Africa than from Latin America.
• In cases of major muscle involvement, acute
  myopathy can develop. Both subcutaneous and
  intramuscular cysts often undergo calcification
  and may be detected incidentally when radiographs
  are performed for unrelated problems.
• Cysts have also been found in the heart.
  Depending upon the location of the cysts, these
  may be asymptomatic or may result in arrhythmias
  and/or conduction abnormalities

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Routine laboratory tests

• Most patients with cysticercosis have no specific
  diagnostic finding on routine blood counts and
  liver function tests.
• Individuals with cysticercosis often have no
  peripheral eosinophilia unless a cyst is leaking,
  in which case the eosinophilia may be pronounced.
• Stool examinations can be performed however,
  eggs are typically not found, since the majority
  of people diagnosed with cysticercosis do not
  have a viable T. solium tapeworm in their
  intestines.

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Brain imaging

• Any case of suspected NCC should be evaluated
  with a computed tomographic (CT) scan or magnetic
  resonance imaging (MRI).
• The appearance can depend upon the location and
  stage of the lesion(s) and upon the host immune
  response.
• In some patients, the radiologic appearance is
  specific for cysticercosis. The pathognomonic
  lesion is one in which a scolex can be identified
  as a mural nodule within the cyst. There will
  often be other areas of punctate calcification
  seen in association. However, the appearance on
  imaging by CT or MRI is frequently nonspecific,
  and it may not be possible to differentiate NCC
  from other brain lesions, such as abscesses or
  malignancies.

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MRI versus CT scanning

• MRI is preferred over CT scanning, since MRI is
  more sensitive in detecting small lesions,
  brainstem or intraventricular lesions,
  perilesional edema around calcific lesions, and
  is better at visualizing the scolex.
• MRI is also more useful in evaluating
  degenerative changes in the parasite.
• However, CT scanning is cheaper and is better at
  detecting small areas of calcification.
• A reasonable practical approach is to perform a
  CT scan first followed by an MRI in patients with
  inconclusive findings or in those patients with
  negative CT scans where a strong clinical
  suspicion of cysticercosis persists.

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Serology

• All patients with suspected cysticercosis should
  have serologic testing. As with all serologic
  tests, results need to be interpreted with
  caution in individuals from highly endemic areas
  where a positive serology may be due to past
  infection and may not prove current active
  disease.
• Negative serology lowers the suspicion for
  cysticercosis, but does not exclude the diagnosis
  in patients with a compatible clinical
  presentation and radiographic findings.
• Two types
• Enzyme linked immunoelectrotransfer blot assay
  (sensitivity 83 to 100)
• Serologic testing on CSF (86 sensitivity)
• Antigen testing (ELISA 85 to 100 sensitivity)
• LP usually normal

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Anticonvulsant therapy

• Patients with NCC who present with seizures, or
  are considered to be at high risk for recurrent
  seizures, should be given anticonvulsants there
  has been a lot of clinical experience with
  carbamazepine or phyenytoin.
• The appropriate duration of anticonvulsant
  treatment for this disorder is still under
  debate, and ongoing trials will address this
  question.

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Anthelminthic Therapy Risk

• Antiparasitic therapy can lead to serious
  morbidity and mortality, particularly in patients
  with a large number of lesions.
• Treatment of neurocysticercosis can be associated
  with an exacerbation of neurologic symptoms due
  to increased inflammation around the rapidly
  degenerating cyst.
• The inflammation can be so severe that it can
  lead to disability or death of the patient.
• Consequently, corticosteroid therapy is
  beneficial in certain circumstances

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Potential benefits

• There are conflicting studies as to whether
  antiparasitic therapy leads to better seizure
  control or improved resolution of cysts.
• Not all studies have shown a clear benefit of
  antiparasitic therapy over symptomatic management
  alone however, many of these studies were not
  blinded or controlled and subject to bias.

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Potential benefits

• The only randomized, double-blind,
  placebo-controlled trial published since this
  analysis, assigned 120 patients with living
  cysticerci in the brain and seizures treated with
  antiepileptic drugs to either albendazole plus
  dexamethasone or double placebo.
• The patients were followed for 30 months or until
  they were seizure-free for six months after their
  antiepileptic drugs had been tapered.
• The study demonstrated the following results
• Resolution of intracranial cystic lesions were
  more common in the treatment arm.
• The number of patients experiencing generalized
  seizures declined in the treatment arm however,
  no benefit was seen in those patients
  experiencing partial seizures.

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Preventing human tapeworm infections

• Prevention of tapeworm infections in humans can
  serve to decrease the source of egg carriers.
  Tapeworm infections can be prevented by
• Inspection of pork for cysticerci, which are
  visible in raw meat
• Freezing or adequately cooking meat to destroy
  cysticerci pickling and salting are not adequate
• Administering antiparasitic agents to pigs

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Preventing infections in pigs

• Preventing the transmission of cysticercal
  infections to pigs can be accomplished by
• Changing pig-raising practices in endemic areas
  by confining the animals and not allowing them to
  roam freely to avoid contact with infectious eggs
  excreted in human feces
• Improved sanitary conditions and proper disposal
  of human stool
• Preliminary studies suggest vaccination of pigs
  may also be feasible

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Preventing egg transmission to humans

• A number of mechanisms exist for interrupting the
  transmission of eggs to humans including
• Education regarding routes of transmission
• Good personal hygiene and hand washing prior to
  food preparation
• Identifying human carriers of tapeworms, possibly
  through a history of proglottid passage, and
  instituting targeted treatment
• Mass community anthelminthic programs to treat
  tapeworm carriers.

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Resources

• Uptodate
• Epidemiology and transmission of cysticercosis
• Clinical manifestations and diagnosis of
  cysticercosis
• Treatment and prevention of cysticercosis