Animal Diversity Web

Ge­o­graphic Range

Tae­nia solium, known as the pork tape­worm, is found through­out the world. It is par­tic­u­larly preva­lent in de­vel­op­ing coun­tries where pigs are raised in poor san­i­tary con­di­tions. In the West­ern Hemi­sphere, it is mostly found in South and Cen­tral Amer­ica. Canada, United States, Ar­gentina and Uruguay are four coun­tries from this re­gion that seems to have erad­i­cated the tape­worm, al­though cases of Tae­nia solium in­fec­tion in peo­ple have been ap­pear­ing re­cently. This reap­pear­ance has been at­trib­uted to the grow­ing num­ber of im­mi­grants from coun­tries with tape­worm trans­mis­sion, who are hosts to the T. solium. The tape­worm is also widely found through­out coun­tries in Africa and Asia; how­ever, the num­ber of in­fec­tions is low in pop­u­la­tions of Mus­lim and Jew­ish cul­tures where eat­ing pork is for­bid­den. (Schantz, 2002)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native
• antarctica
  • native
• oceanic islands
  • native

• Other Geographic Terms
• cosmopolitan

Habi­tat

The pork tape­worm has sev­eral dif­fer­ent habi­tats de­pend­ing on the stage in its life cycle. The pread­ult tape­worm and adult tape­worm can be found in the small in­tes­tine of a human host. The proglot­tid seg­ments full of eggs are found in the host feces, and in the ex­ter­nal en­vi­ron­ment where the feces are re­leased. Un­for­tu­nately, there is an in­ad­e­quate amount of re­search that has been con­ducted on the sub­ject of eggs in the ex­ter­nal en­vi­ron­ment. As a re­sult it is dif­fi­cult to as­sess the type of habi­tat the eggs favor. How­ever, tem­per­a­ture is known to ef­fect egg sur­vival. If the habi­tat is colder than 10 de­grees Cel­sius or above room tem­per­a­ture, the eggs can eas­ily per­ish.

The next stage of the tape­worm is the on­cos­phere, and this stage takes place in­side the pig in­ter­me­di­ate host. The habi­tat of the on­cos­phere is the gut and tis­sue of the pig host and con­tin­ues its life stage in the mus­cle and brain of the pig in the cys­ticer­cus stage. The cys­ticer­cus form is also ca­pa­ble of sur­viv­ing in a human host, liv­ing in the mus­cles and the brain. (Pawlowski, 2002; Sciutto, et al., 2000)

• Habitat Regions
• temperate
• tropical
• polar
• terrestrial

• Other Habitat Features
• agricultural

Phys­i­cal De­scrip­tion

The mor­phol­ogy of the adult pork tape­worm is di­vided into three parts: scolex, neck, and stro­bila. The scolex is the head of the tape­worm, po­si­tioned at the an­te­rior end of the or­gan­ism. The scolex acts as an at­tach­ment de­vice with four suck­ers, hooks and ros­tel­lum used to at­tach it­self to the in­tes­tine of the host. The neck is an elon­gated re­gion be­tween the scolex and the strob­lia. The strob­lia con­tains the bulk of the sys­tems of the tape­worm and has an av­er­age length of 2-3 m. It con­sists of mul­ti­ple seg­ments called proglot­tids. As a mo­noe­cious species, every sin­gle proglot­tid con­tains both the male and fe­male re­pro­duc­tive sys­tems. The proglot­tids ma­ture sex­u­ally as they progress in the pos­te­rior di­rec­tion of the stro­bila. The pork tape­worm does not have a di­ges­tive sys­tem, but is com­posed of the fol­low­ing sys­tems: tegu­ment, ner­vous, os­moreg­u­la­tory and mus­cu­lar.

Tae­nia solium egg's have a frag­ile outer shell that can be shed when the egg exits the host's body, leav­ing the on­cos­phere larva ex­posed to the ex­ter­nal en­vi­ron­ment. The on­cos­phere larva is 30 um in di­am­e­ter and is also called the hexa­canth larva since it has six hooks. The larva is a solid mass of cells and sur­rounded by a pro­tec­tive cover called the em­bryophore. This cover pro­tects the on­cos­phere from harsh con­di­tions when the larva is ex­posed to the en­vi­ron­ment. The on­cos­phere de­vel­ops into the cys­ticer­cus form, con­vert­ing from a solid larva to a vesi­cle with an opales­cent fluid. In the cys­ticer­cus form the scolex is dis­cernible, but is in­vagi­nated at this stage. The larva has an outer and inner layer and in be­tween these lay­ers the first signs of organ sys­tem dif­fer­en­ti­a­tion is seen.

The genus Tae­nia has 20 species and Tae­nia solium is often con­fused with Tae­nia sag­i­nata, the beef tape­worm. At the egg stage these two species are in­dis­tin­guish­able, and the dif­fer­en­ti­a­tion be­tween the two species occur at the adult stage. Tae­nia solium has a scolex com­posed of hooks, when com­pared to Tae­nia sag­i­nata. Tae­nia solium is also smaller in size and miss­ing the vagi­nal sphinc­ter. Tae­nia solium also has three lobes in its ovary com­pared to two in Tae­nia sag­i­nata. (Pawlowski, 2002; Sciutto, et al., 2000)

• Range length

  2 to 10 m

  6.56 to 32.81 ft

De­vel­op­ment

Tae­nia solium has six stages in its life cycle: pread­ult tape­worm, adult tape­worm, egg, on­cos­phere, pos­ton­cos­pheral form and cys­ticer­cus. The pread­ult and adult tape­worm occur in the de­fin­i­tive host, the human. These two stages can only occur when the de­fin­i­tive host con­sumes pork in­fected by the cys­ticer­cus stage be­cause the adult must ma­ture in the de­fin­i­tive host's in­tes­tine. The adult tape­worm is the re­pro­duc­tive stage in the life cycle and a sin­gle sex­u­ally ma­ture proglot­tid con­tains an av­er­age of 40,000 eggs. These eggs are shed through the host's feces and then con­sumed by a pig, the in­ter­me­di­ate host. The pig in­gests the human fecal mat­ter under poor san­i­ta­tion con­di­tions. The egg sheds its outer shell and be­comes the on­cos­phere larva. The egg may also shed its outer shell while being ex­pelled from the de­fin­i­tive host. In this sit­u­a­tion, it is the on­cos­phere that is con­sumed by the pig. The larva en­ters the in­ter­me­di­ate host's cir­cu­la­tion sys­tem and is car­ried to mus­cle cells, in­ter­nal or­gans and brain. From these lo­ca­tions, in the in­ter­me­di­ate host, the larva grows into the pos­ton­cos­pheral stage. This stage out­lines the tran­si­tion be­tween the on­cos­phere larva and the cys­ticer­cus larva. The larva be­gins the trans­for­ma­tion into an adult when it reaches the human's in­tes­tine. This trans­fer of host oc­curs when a human eats un­der­cooked pork meat in­fected by cys­ticer­cus. This trans­for­ma­tion into an adult takes an av­er­age of 2 months be­fore the tape­worm can be­come sex­u­ally ma­ture. (Pawlowski, 2002)

• Development - Life Cycle
• metamorphosis
• diapause

Re­pro­duc­tion

Tae­nia solium is a mo­noe­cious species that holds both fe­male and male re­pro­duc­tive sys­tems in­side a sin­gle proglot­tid. (Pawlowski, 2002)

Each seg­ment in the pork tape­worm has its own set of male and fe­male re­pro­duc­tive sys­tems. The fe­male re­pro­duc­tive sys­tem is com­posed of a vagina, sem­i­nal re­cep­ta­cle, ovary, oviduct, vitelline gland, Mehlis glands and uterus. An un­fer­til­ized egg from the ovary is car­ried through an oviduct, where it meets the sperm and be­comes fer­til­ized. The sperm cre­ated in one of the 150-200 testes in the proglot­tid, swims through the vas def­er­ens and into the vagina through the gen­i­tal pore. The gen­i­tal pore is also con­nected to the vagina that leads the sperm to the un­fer­til­ized egg in the oviduct. After fer­til­iza­tion, the vitelline gland and Mehlis gland se­crete a sub­stance that sur­rounds the zy­gote. It is be­lieved that these se­cre­tions form into the em­bryophore. The zy­gote con­tin­ues its de­vel­op­ment in the uterus until the adult tape­worm is ready to expel its eggs into the ex­ter­nal en­vi­ron­ment. While this process is self-fer­til­iza­tion, there have been re­ports of cross fer­til­iza­tion be­tween dif­fer­ent in­di­vid­u­als. (Mar­avilla, et al., 2003; Pawlowski, 2002; Roberts and Janovy, 2009; Sciutto, et al., 2000)

• Key Reproductive Features
• simultaneous hermaphrodite
• sexual
• fertilization
  • internal
• oviparous

• Average number of offspring

  300,000 eggs/day

Lifes­pan/Longevity

It is be­lieved that Tae­nia solium can sur­vive in the in­tes­tine of its de­fin­i­tive host up to 25 years. How­ever, there is con­tro­versy as to the truth of this num­ber and other re­searchers claim that their life span is less than 5 years. Eggs can sur­vive for 8 months, how­ever, en­vi­ron­men­tal con­di­tions usu­ally do not let the eggs sur­vive to the next stage in the life cycle. Al­though there has been lit­tle re­search, tem­per­a­ture is the most im­por­tant en­vi­ron­men­tal fac­tor for the eggs. (Gar­cia, et al., 2003; Hoberg, 2002; Pawlowski, 2002; Roberts and Janovy, 2009)

• Range lifespan
  Status: captivity

  25 (high) years

• Average lifespan
  Status: captivity

  5 years

Be­hav­ior

Tae­nia solium is dif­fer­ent than other species in the genus Tae­nia in that it can use its de­fin­i­tive host (human) as an in­ter­me­di­ate. The on­cos­phere larva can in­fect a human host through ex­ter­nal au­toin­fec­tion, where eggs ex­pelled through fecal mat­ter are in­gested orally. In­ter­nal au­toin­fec­tion, where a larva can in­fect the host with­out being ex­pelled through fecal mat­ter, have yet to be ob­served. How­ever, re­searchers are open to the pos­si­bil­ity of its oc­cur­rence.

The pork tape­worm is a mo­bile species. In its lar­val stage it pen­e­trates the in­ter­me­di­ate host's gut to reach the cir­cu­la­tory sys­tem and mi­grate through­out the body. The adult tape­worm is often fixed by the scolex to the de­fin­i­tive host's in­tes­tine. How­ever, this dy­namic can also be tem­po­rary be­cause the tape­worm is known to mi­grate up and down the small in­tes­tine de­pend­ing on in­gested food, pH and di­ges­tive en­zymes. (Pawlowski, 2002; Roberts and Janovy, 2009; Sci­u­too, et al., 2007)

Tae­nia solium is a soli­tary par­a­site. In most ob­ser­va­tions only a sin­gle par­a­site in­fects an in­di­vid­ual host. How­ever, there are pos­si­bil­i­ties for com­pe­ti­tion be­tween mul­ti­ple tape­worms in­fect­ing the same host. If a host is in­fected by mul­ti­ple pork tape­worms, the tape­worms have greater dif­fi­culty reach­ing sex­u­ally ma­tu­rity. (Con­lan, et al., 2009)

• Key Behaviors
• sessile
• motile
• solitary

Com­mu­ni­ca­tion and Per­cep­tion

There has not been a spe­cific dis­cov­ery of the meth­ods of com­mu­ni­ca­tion be­tween dif­fer­ent in­di­vid­u­als in this species. Even the ways tape­worms per­ceive dif­fer­ent en­vi­ron­ments are un­clear. How­ever, there is a nerve gan­glia in the scolex and a sen­sory sys­tem linked to touch and chem­i­cal stim­uli. (Roberts and Janovy, 2009)

• Perception Channels
• tactile
• chemical

Food Habits

Tae­nia solium like all other Ces­toda do not have a di­ges­tive sys­tem. As a re­sult, they use their tegu­ment to ab­sorb their needed nu­tri­ents from the host they are in­fect­ing. Their tegu­ment along the en­tire body is equipped with struc­tures sim­i­lar to mi­crovilli in cer­tain or­gan­isms. These struc­tures called mi­crotriches can be used to in­crease the sur­face area of the worm's tegu­ment, al­low­ing for a greater amount of nu­tri­ent ab­sorp­tion from the host. (Roberts and Janovy, 2009)

Pre­da­tion

Tae­nia solium does not have any known preda­tors.

Ecosys­tem Roles

Tae­nia solium is a par­a­sitic tape­worm that in­fects pigs and hu­mans. The cys­ticerci stage in the life cycle can cause med­ical and vet­eri­nary prob­lems in its pig host. Porcine cys­ticer­co­sis, the in­fec­tion of cys­ticerci in pigs, have been found to be mostly asymp­to­matic. This is be­cause most pigs are killed be­fore the cys­ticerci enter the de­gen­er­a­tive stage, which is known to cause symp­toms. (Gar­cia, et al., 2003)

• Ecosystem Impact
• parasite

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

There are no pos­i­tive ben­e­fits for hu­mans.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Tae­nia solium is one of the most dan­ger­ous tape­worms to hu­mans, be­cause hu­mans can act as a de­fin­i­tive and in­ter­me­di­ate host. The con­di­tion where a human is used as a de­fin­i­tive host for an adult tape worm is called tae­ni­a­sis. This con­di­tion is usu­ally asymp­to­matic in hu­mans and non­fa­tal. At times there are a few mild symp­toms such as ab­dom­i­nal pain, al­tered ap­petite, di­ar­rhea, con­sti­pa­tion, hunger pains and weight loss.

The fatal in­fec­tion for hu­mans is cys­ticer­co­sis, where the human acts as an in­ter­me­di­ate hosts for the cys­ticerci. This stage can occur through ex­ter­nal au­toin­fec­tion of the host. Al­though there is no ev­i­dence for in­ter­nal au­toin­fec­tion, it is a pos­si­ble way for the human to be in­fected with the on­cos­phere. In this con­di­tion, the cys­ticerci can in­fect any organ in the body and the ex­tent of the symp­toms caused by cys­ticer­co­sis de­pend largely on the lo­ca­tion of in­fec­tion. The most com­mon areas of in­fec­tion are sub­cu­ta­neous con­nec­tive tis­sues, the eye and the brain. In­fec­tion to sub­cu­ta­neous con­nec­tive tis­sues rarely pre­sent symp­toms and is non­fa­tal. In­fec­tion to the eye can cause blind­ness in the host. The most dan­ger­ous area of in­fec­tion is in the cen­tral ner­vous sys­tem, termed neu­ro­cys­ticer­co­sis. When cys­ticerci mi­grate to the brain they can cause epilepsy, in­tracra­nial hy­per­ten­sion and can mimic a brain tumor to the host. The most dan­ger­ous stage in cys­ticer­co­sis is when the cys­ticer­cus larva dies. The larva's de­gen­er­a­tion can cause an in­flam­ma­tory re­sponse in the body that could be fatal to the host.

All con­di­tions caused by Tae­nia solium cause huge eco­nomic losses for coun­tries af­fected by this species. It has been es­ti­mated that in Mex­ico alone, $15 mil­lion US dol­lars are spent per year in hos­pi­tal ex­penses for neu­ro­cys­ticer­co­sis. This tape­worm also re­sults in se­vere losses for the meat in­dus­try. In Mex­ico, half of the swine in­dus­try is es­ti­mated to be lost to porcine cys­ticer­co­sis and the eco­nomic losses are about $43 mil­lion per year. (Gar­cia, et al., 2003; Roberts and Janovy, 2009)

• Negative Impacts
• injures humans
  • causes disease in humans
• causes or carries domestic animal disease

Con­ser­va­tion Sta­tus

Tae­nia solium is not an en­dan­gered species. Re­searchers are con­stantly try­ing to find ways to con­trol this species as it is a major par­a­site in the human pop­u­la­tion.

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

Ash­ley Chung (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Heidi Liere (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, John Marino (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, Barry OCon­nor (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, Renee Mul­crone (ed­i­tor), Spe­cial Pro­jects.

Ref­er­ences

Con­lan, J., K. Vongxay, S. Fen­wick, S. Black­sell, R. Thomp­son. 2009. Does in­ter­spe­cific com­pe­ti­tion have a mod­er­at­ing ef­fect on Tae­nia solium trans­mis­sion dy­nam­ics in South­east Asia?. Trends in Par­si­tol­ogy, 25 (9): 398-403.

Gar­cia, H., A. Gon­za­lez, C. Evans, R. Gilman. 2003. Tae­nia solium cys­ticer­co­sis. Lancet, 362: 547-556.

Hoberg, E. 2002. Tae­nia tape­worms: their bi­ol­ogy, evo­lu­tion and so­cioe­co­nomic sig­nif­i­cance. Mi­crobes and In­fec­tion, 4: 859-866.

Mar­avilla, P., V. Souza, A. Valera, M. Romero-Val­dovi­nos, Y. Lopez-Vi­dal, J. Dominguez-Alpizar, J. Am­bro­sio, S. Kawa, A. Fisser. 2003. De­tec­tion of ge­netic vari­a­tion in Tae­nia solium. The Jour­nal of Par­a­sitol­ogy, 89 (6): 1250-1254.

Pawlowski, Z. 2002. Basic bi­ol­ogy and trans­mis­sion. Pp. 1-15 in G Singh, ed. Tae­nia Solium cys­ticer­co­sis: from basic to clin­i­cal sci­ence. Chandi­garh, India: CABI Pub­lish­ing.

Roberts, L., J. Janovy. 2009. Ger­ald D. Schmidt & Larry S. Roberts' Foun­da­tions of Par­a­sitol­ogy. New York, NY: Mc­Graw-Hill.

Schantz, P. 2002. Tae­nia solium cys­ticer­co­sis: an overview of global dis­tri­b­u­tion and trans­mis­sion. Pp. 63-73 in G Singh, ed. Tae­nia Solium cys­ticer­co­sis: from basic to clin­i­cal sci­ence. Chandi­garh, India: CABI Pub­lish­ing.

Sci­u­too, E., A. Chavar­ria, G. Fragoso, A. Fleury, C. Lar­ralde. 2007. The im­mune re­sponse in Tae­nia solium cys­ticer­co­sis: pro­tec­tion and in­jury. Par­a­site Im­munol­ogy, 29: 621-636.

Sciutto, E., G. Fragoso, A. Fleury, J. La­clette, J. Sotelo, A. Aluja, L. Var­gas, C. Lar­ralde. 2000. Tae­nia solium dis­ease in hu­mans and pigs: An an­cient par­a­sito­sis dis­ease rooted in de­vel­op­ing coun­tries and emerg­ing as a major health prob­lem of global di­men­sions. Mi­crobes and In­fec­tion, 2 (15): 1875-1890.