Taenia solium taeniasis Cysticercosis

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Collaborative Course on Infectious
Diseases January 2008
LECTURE 5 Taenia solium (Taeniasis /
Cysticercosis)
Felipe Fregni ffregni_at_bidmc.harvard.edu
Harvard School of Public Health Faculdade de
Ciências Médicas da Santa Casa de São Paulo
Brazil Studies Program, DRCLAS, Harvard
University
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Objectives

• To discuss the epidemiology of disease
  prevalence, incidence, risk factors, change over
  time
• Understand the reasons that cysticercosis is not
  highly prevalent in poor areas of Brazil
• Compare cysticercosis with the distribution of
  other infectious diseases in Brazil such
  schistosomiasis
• Understand characteristics contributing to make
  this disease highly prevalent in agricultural
  areas (example north of Parana state)
• Describe re-infestation and clinical
  characteristics and also late expression of
  infection (several years after acquisition)
• Understand difficulties of access to diagnosis
  and treatment
• Discuss the relationship of different forms of
  diseases with individual characteristics

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Questions

• What are the different forms of disease
  presentation in humans and how does this
  contribute to the epidemiology of this disease?
• Although cysticercosis is related to extreme
  poverty, why is the incidence of this disease low
  in some poor areas, such as the northeast of
  Brazil?
• What are the important characteristics of the
  human carriers of T. solium that determine the
  persistence of the infection?
• Is eradication possible?
• What are the difficulties of implementing a
  control program for cysticercosis?
• Is this disease only a consequence of extreme
  poverty?

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Why taeniasis/cysticercosis is a significant
public health issue?

• It accounts for 10 of acute neurological
  admissions in endemic areas
• It produces significant livestock production
  losses to pig owners
• An interesting model of zoonotic disease that can
  be applied to other infections diseases

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Basics (1)

• Complex two-host life cycle
• Human beings are the only definitive host (small
  intestines - 2-4 meters long -800-1000 segments)
• Both humans and pigs can act as intermediate
  hosts (larvae or cysticerci)
• Most common in Latin America, Africa and India -
  400,000 people have symptomatic
  neurocysticercosis in Latin America

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Basics of the infection cycle

• Faecal-borne infection
• Tapeworm larval cyst (cysticercus) is ingested
  with poorly infected meat
• Larva escapes the cyst and attaches to the mucosa
  by the scolex
• Feces are contaminated with eggs (persist for
  several days in the environment) - consumed by
  pigs (eggs are hatched and form cysticerci
• Humans are the only definitive host
• Pigs - intermediate host (cysticercal stage)
• However
• Humans - also can be the intermediate host -
  causing cysticercosis (neurocysticercosis) if
  they ingest eggs

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• Two different forms in humans
• Human taeniases
• Human cysticercosis

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Human infection - taeniasis

• The scolex attaches to the mucosa and begins
  forming segments (proglotids)
• After two months of infection, gravid proglotids
  begin to detach from the distal end - excreted in
  the feces
• Each segment contains 60,000 eggs
• Worm causes only minor inflammation to the
  intestine (mild symptoms - abdominal pain,
  distension, diarrhea and nausea - or none at all)

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Human infection - cysticercosis

• Faecal-oral contamination with T. solium eggs
  from tapeworm carriers
• Internal autoinfection is also possible
• The invasive oncosphere (embryos) in the eggs are
  liberated by the action of gastric acid and cross
  the bowel wall (remember - cysticerci are too big
  to cross the bowel wall)
• They establish at small terminal vessels
  (muscles, brain, eye) where they grow to about
  the size of 1 cm in 2-3 months

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Human cysticercosis

• Muscle - small, palpable, movable nodules -
  chests and arms - mild or no symptoms
• Ophthalmic cysticercosis - intraocular cysts
  floating freely in the vitreous humor - decreased
  visual acuity
• Neurocysticercosis - most symptoms are because of
  the inflammatory reaction associated with cyst
  degeneration (that may take years to happen) -
  epilepsy, hydrocephalus, encephalitis, meningitis

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• How to diagnose and treat this condition?
• Differences taeniasis vs. cysticercosis

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Diagnosis - taeniasis

• Visualization of Taenia eggs was the only
  diagnosis until recently - has poor sensitivity
  and difficult to differentiate from taenia
  saginata.
• Best diagnosis - coproantigen detection ELISA
  (detect taenia specific molecules in the feces -
  95 sensitivity and 99 specificity)
• Options
• not efficient and cheap test vs. efficient and
  expensive test

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Diagnosis - cysticercosis

• Depends on the targeted organ
• CNS - CSF immunology, neuroimaging (the scolex
  can be seen)
• Muscle - imaging, bx
• Eye - imaging (ultrasound)
• (serological exam - ELISA)

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Treatment - taeniasis

• Taeniasis - relatively easy for intestinal
  disease - PO drugs - niclosamide and
  praziquantel.
• niclosamide is the choice as it is not absorbed
  however, it is an expensive drug

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Treatment - cysticercosis

• Neurocysticercosis is the main problem
• The problem of the cyst is the inflammatory
  reaction
• Use of parasiticide (praziquantel or albendazole)
  - debatable - aim is to reduce inflammation and
  scar tissue
• palliative treatment to control inflammation -
  corticosteroids, antihistamines

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Epidemiology

• Affect millions of individuals - 2.5 million
  people worldwide carry the T. solium and 20
  million are infected with the cysticerci
• Endemic villages - up to 25 are seropositive and
  10-18 have CT findings suggestive of
  neurocysticercosis

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Latin America and Brazil

• Average seroprevalence in Latin America is 10
• Brazil estimates of 3 - 5.6
• Human neurocysticercosis - estimates of 7 (Latin
  America)
• Swine cysticercosis - 17 of prevalence (Latin
  America)

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OPEN TO DISCUSSION

• How to control taeniasis/cysticercosis?
• Potential difficulties for implementation?

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AFTER DISCUSSION

• Methods for controlling taeniasis/cysticercosis
• Pig vaccination
• Pig treatment
• Human carriers mass treatment
• Health education

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Mass treatment

• Pros - single dose, PO
• Cons - cost and acceptance / difficulties
  (re-infection) / might increase infection rate
  during treatment
• Who to treat?
• Infection focus - any locality with a high
  prevalence of cysticercotic pigs?
• Any farm supplying cysticercotic pigs?
• Any patient with late onset epilepsy?
• Any case of detected or probably taeniasis?

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Treatment for pigs?

• Advantage - remove established infection and
  avoid economic losses at slaughter - diagnosis
  with tongue palpation
• Drugs do not lead to complete parasite
  elimination
• Drug residuals in pigs - is it safe?
• Vaccination for pigs
• issues (i) appropriate formulation (ii)
  production of a stable vaccine (iii)
  understanding of efficacy (iv) price

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Economic factors - domestic pig raising

• Domestic pig raising, taeniasis and human
  cysticercosis are intimately related - pigs are
  cheap and easily marketable - convenient source
  of meat or money
• Pigs also eat pasture and garbage
• Endemic regions - 30-60 of pigs are infected
• Pig production has doubled in the last 20 years
  in Africa
• Owners usually detect infection in vivo and them
  sell these cheaper pigs to unofficial slaughter
  houses or kill them at home

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Pig culling

• Abattoir inspection and confiscation - however
  pigs are killed clandestinely in many areas and
  also mild infections are not easily detected
• Economic issues - control efforts need to
  purchase diseased meat at the market price and
  process it in a safe manner.

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Health education

• Association of cysticercosis prevalence and
  unsanitary rearing of pigs, inability to
  recognize infected pigs and insufficient
  knowledge of transmission
• Education hand washing, defecating in fields,
  corralling of pigs
• Ex. Community in Mexico - although almost
  everybody could identify cysticercosis in pigs,
  only 0.7 knew how pigs were infected

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Past experiences - health education

• Study in two rural communities (3000 inhabitants
  each)
• Community A - health education only
• Community B - health education and mass treatment
• (health education - promoted knowledge of
  transmission of taeniasis/cysticercosis, improved
  hygiene and sanitation)
• RESULTS - Community A
• Swine cysticercosis rate
• Before 2.6, 5.2, 4.8 (lingual examination,
  antibody detection and postmortem examination)
• After - 0, 2 and 0 (respectively)
• Human infection (coproantigen test) 0.78, 0.51
  and 0.41 (before, one year later and after 42
  months
• RESULTS - Community B
• Swine cysticercosis rate
• Before 4.1, 7.5, 9.3
• After - 0.7, 3.2, 0.9
• Human infection (coproantigen test) 0.79, 0.97
  and 0.7

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Education for domestic pig raising

• Knowledge might not influence actions as strongly
  as does the immediate economic benefit of
  maintaining pigs in a cheap but unhealthy manner

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Eradication

• Pros human is the only carrier, there a
  relatively simple treatment
• Other issues
• 1) Technical - lack of a simple diagnosis, lack
  of an easily available treatment (costs)
• 2) Societal poor community cooperation and
  sanitary education
• 3) Political low priorities and debatable
  strategy
• CDC - eradication cannot be achieved in the near
  future - only regional elimination

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Difficulties to implement control programs

• (i) Taeniasis in humans may go unnoticed
• (ii) Taeniasis is also a mild infection, which
  does not prompt the carrier to get rid of a
  tapeworm even when it is diagnosed.
• (iii) Traditional laboratory diagnosis of
  tapeworm infection in humans has poor accuracy
  and other modern coproantigen tests have not been
  introduced to the market and are expensive
• (iv) Treatment rates are frequently low
  -appropriate medicines are not available in many
  endemic areas
• (v) Several human behavioral factors -
  traditional preferences for raw pork consumption
  and indiscriminate, unsanitary defecation,
• (vi) Inadequate local levels of information on
  taeniasis/cysticercosis
• (vii) There is clear economic motivation for
  small scale pork producers to minimize commercial
  losses associated with infected carcass
  condemnation at official slaughter

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Political will

• The public health impact of human cysticercosis
  in some regions is serious (significant social
  and financial costs)
• Neurocysticercosis can potentially affect any
  person (rural or urban area)
• Contamination with eggs can also be common in
  urban centers
• Control measures can be implemented regionally
• Efficacy of schemes can be measured in sentinel
  or slaughtered pigs

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Is this disease only a consequence of poverty?

• Eradication of extreme poverty - would reduce
  subsistence pig rearing
• Achievement of universal primary school education
  - increase knowledge about risky behaviors in
  relation to T. solium transmission
• Gender equality and empowering women - decrease
  risk of taenia infection at home - reducing
  consumption of contaminated meat and personal
  hygiene
• Combating major infection diseases
• Improvement of sanitation