Cysticercosis

Cysticercosis is an infection of pig and cattle with larvae of T. solium and T. saginata respectively, which develops after ingestion of ova excreted in human faeces. Both adult and larval stage of Taenia species is most important.

Taeniasis is an intestinal infection of adult tapeworm (Taenia solium and Taenia saginata) following ingestion of contaminated pork and beef.

The intermediate stage of tapeworm is found in muscles of cattle and economic problem to pork and beef industry and public health issues.

Taenia saginata

Morphology

• The length of adult tape worm is 5-15 cm. The scolex has neither rostellum and nor hooks. Which is found in small intestine.
• Metacestode stage-Cysticercus bovis is greyish white about 1.0 cm in diameter and found in skeletal, cardiac muscle, masseter, intercostals muscle, heart and tongue.

Epidemiology

• World wide distribution.
• Abnormal eating habits of cattle due to certain mineral deficiencies (pica) may result in cravings that increase the exposure through the ingestion of faeces.
• Sewage water is an important route of dissemination of infection.
• Birds that consume infected sewage water and disseminate the infection.

Transmission

Transmission in cattle

• Passive ingestion of contaminated pasture.
• Neonatal calves may be infected when they are handled by infected person (with motile proglottids).

Transmission in human  

• Ingestion of raw or under cooked beef (Measely beef).
• Changing of food habits – fast foods.
• If cattle slaughtered 9 months after infection (without reinfection) – infection rate in human beings is very less.

Cysticercosis storm

• In developed countries like Australia and Britain – human sewage is utilized as fertilizer for pasture land in the form of sludge (sedimented or bacterial digested faeces).
• If cattle are exposed to contaminated pasture land immediately after application of sludge. The high incidence of infection of T. Saginata was noticed.

Life Cycle

• An infected human may pass millions of eggs daily, either free in the faeces or as intact segments each containing about 2,50,000 eggs, and these can survive on pasture for several months.
• After ingestion by a susceptible bovine the onchosphere travels via the blood to striated muscle.
•  It is first grossly visible about two weeks later as a pale, semi-transparent spot about l0mm in diameter, but is not infective to man until about 12 weeks, later it has reached its full size of l.0cm, which is enclosed by thin fibrous capsule.
• The longevity of the cysts ranges from weeks to years in muscles.
• When they die they are usually replaced by a caseous, crumbly mass which may become calcified.
• Both living and dead cysts are frequently present in same carcass.
• Man becomes infected by ingesting raw or inadequately cooked meat.
• Development to patency takes place in 2-3 months.

Clinical manifestation

Cattle

• Under natural conditions clinical symptoms are not evident.
• Experimental infection of calves with T.saginata develops myocarditis and heart failure.

Human

• Diarrhoea and hunger pain, but the infection is usually asymptomatic.

Treatment

• Praziquantel has shown efficacy in experimental infection.

Prevention

Immunoprophylaxis against T. saginata

• Homologous vaccine – In-vitro culturing of oncosphere of T. saginata releases secretory and excretory antigen.
• Active immunization in calves- Secretory and excretory antigen administered in calves before infection (after infection there is no useful).
• Passive immunization- Secretory and excretory antigen administered to periparturient cows either through intramuscularly or intra mammary route.
• Calves are immunized while consuming colostrum / milk from immunized dam.

Heterologus vaccine

• In-vitro culturing of oncospheres of T. taeniaformis releases secretory and excretory antigen, which capable of inducing high level protective immunity against heterologus parasite – T. Saginata.
• Intramuscular injection of eggs of T. hydatigena in cattle induces partial immunity against heterologus parasite.

Control

• Maintenance of high standard of human sanitation.
• Compulsory meat inspection.
• Thorough cooking of meat.
• Regulations usually require that infected carcasses are frozen at -10°C for at least 10 days which is sufficient to kill the cysticerci.
• In agricultural practice the use of human sludge as a fertilizer should be confined to cultivated fields or to those on which cattle will not be grazed for at least two years.

Taenia solium

Morphology

• The adult tape worm has scolex, which contain rostellum and two concentric rows of hooks.
• Egg – spherical in shape.
• Metacestode stage – Cysticercus cellulosae  found in pig and man.
• Location – Skeletal and cardiac muscles.

Epidemiology

• Almost similar to T. saginata, differences are:
  • Infection rate – 10 proglottids X 40,000 = 4,00,000 eggs per day.
  • Gravid proglottids do not leave spontaneously from the host and voided passively through faeces.
• Man acts as an IH:
  • Autoinfection – by reverse peristalsis is the most important source of infection.
  • Accidental ingestion of T. solium eggs along with food and water.
  • Nail baiting habits – especially with dirty hands.
  • If man acts as an IH, the life cycle is arrested in metacestode stage itself.

Definitive host

• Cysticercus reaches small intestine and become changed in to adult worm. Adult worm lay the eggs (prepatent period –100 days) – not much pathogenic changes.

Intermediate Host

• Cysticercus reaches small intestine and become changed in to adult worm. Adult worm lay the eggs (prepatent period –100 days) – not much pathogenic changes.

Life cycle

Humans develop intestinal infection with adult worms after ingestion of contaminated pork or may develop cysticercosis after ingestion of T. solium eggs (making human intermediate hosts).

• Humans ingest raw or undercooked pork containing cysticerci (larvae)
• After ingestion, cysts evaginate, attach to the small intestine by their scolex, and mature into adult worms in about 2 months.
• Adult tapeworms produce proglottids, which become gravid; they detach from the tapeworm and migrate to the anus.
• Detached proglottids, eggs, or both are passed from the definitive host (human) in feces.
• Pigs or humans become infected by ingestion of embryonated eggs or gravid proglottids in fecal contaminated food. Autoinfection may occur in humans if proglottids pass from the intestine to the stomach via reverse peristalsis.
• After eggs are ingested, they hatch in the intestine and release oncospheres, which penetrate the intestinal wall.
• Oncospheres travel through the bloodstream to striated muscles, brain, liver, and other organs, where they develop into cysticerci causes cysticercosis.
• In man C. cellulosae primarily found on subcutaneous tissues and secondarily on brain and ocular cavity.

Clinical manifestation

Pig

• Clinical signs are inapparent.

Human

• Adult worms may cause mild gastrointestinal symptoms or passage of a motile segment in the stool.
• Cysticercosis is usually asymptomatic unless larvae invade the CNS, resulting in neurocysticercosis. Infection in the brain (cerebral cysticercosis) may result in severe symptoms due to mass effect and inflammation induced by degeneration of cysticerci and release of antigens, which can cause seizures and various other neurologic signs like increased intracranial pressure, hydrocephalus, altered mental status or aseptic meningitis.
• Cysticerci may also infect the spinal cord, muscles, subcutaneous tissues and eyes.
• Substantial secondary immunity develops after larval infection.

Diagnosis

• Neurocysticercosis may be recognized on brain imaging studies (computerized axial tomography (CAT) and MRI techniques. The cysticerci mostly found in ventricle of the brain.
• Fewer than half of patients with neurocysticercosis have adult T. solium in their intestines and thus eggs or proglottids in their stool.
• Finding of antibody to cysticerci in the cerebrospinal fluid.

Treatment

Pig

• Albendazloe @ 50 mg/kg – effective against mature metacestode.
• Praziquantel @ 50 mg/kg – highly effective against both mature and immature metacestodes.

Human

• Symptomatic treatment of neurocysticercosis with corticosteroids, anticonvulsive agents, and in some situations, albendazole or praziquantel also can be used.
• Adult worms can be eliminated with praziquantel @10mg/kg b.wt and Niclosomide 2g (total dose).
• Surgical removal of cyst.

Prevention and control

• Treating of infected persons (especially animal handlers).
• Public education and hygiene.
• Proper meat inspection – made multiple incisions of suspected carcasses.
• Through cooking of meat.
• Freezing of carcasses
  • – 5°C for 15 days
  • – 10°C for 9 days
  • – 15 to – 30°C for 6 days

Taenia hydatigena

• This is the largest tapeworm found in dogs and wild canids
• The onchosphere is infective to sheep, cattle and pigs are carried in the blood to the liver in which they migrate for about four weeks before they emerge on the surface of this organ and attach to the peritoneum. Within four weeks each oncosphere develops into cysticercus tenucollis (metacestode stage).
• Infection is prevalent particularly in sheep but, infection generally only detected at meat inspection infrequently; however, large numbers of developing cysticerci migrate contemporaneously in the liver of the sheep or pig producing ‘hepatitis cysticercosa. This condition resembles acute fascioliasis, which is often fatal. Occasionally developing cysticerci are killed, when sheep are previously exposed to infection.

Pathology

• The subscapsular phase of liver is studded with greenish nodules around 1cm dia.

Diagnosis

• Faecal examination for onchosphere or gravid segments in faeces.

Treatment

• Praziquantel, mebendazole, fenbendazole, nitroscanate, and dichlorophen.