Experimental human infection with Asian Taenia saginata metacestodes obtained from naturally infected Korean domestic pigs.

The infectivity of metacestodes of Asian Taenia saginata, now tentatively called Taenia saginata taiwanensis, in human host was confirmed. The metacestodes used in experimental infection were collected from the livers of naturally infected domestic pigs at an abattoir in Cheongju City, Korea. The first gravid proglottid was spontaneously discharged 76 days after infection. Two worms were recovered two years later by chemotherapy. The scolex was unarmed. The number of main uterine branches, varying from 16 to 21, was similar to that of classical Taenia saginata. The liver of pigs was confirmed to be an infection source of Asian T. saginata in Korea.     

The pig as an intermediate host for Taiwan Taenia infection

Eggs (1000-100,000/animal) of Taiwan Taenia were inoculated per os into 14 Small-Ear-Miniature (SEM), 19 Landrace-Small-Ear-Miniature (L-SEM), and 5 Duroc-Yorkshire-Landrace (DYL) pigs. These animals were sacrificed 7-107 days after infection. Thirty-four pigs were found to be infected with Taiwan Taenia cysticerci and the infection rates of SEM, L-SEM, and DYL were 86%, 89% and 100% respectively. The cysticerci recovery rates of SEM, L-SEM and DYL pigs were 27.2%, 1.7% and 0.27% respectively. Cysticerci were recovered only from the livers and none were found in muscles, viscera or other parts of the carcasses. More cysticerci were located in the liver parenchyma (71%) than on the liver surface (29%). Taiwan Taenia cysticerci were smaller than those of classical T. saginata or T. solium. Moreover, Taiwan Taenia cysticerci had 2 rows of rudimentary hooklets on the scolex. The results of this study indicate that young pigs are good intermediate hosts for Taiwan Taenia and that the SEM pig is a satisfactory host for experimental studies with this tapeworm. These results were similar to other studies with different geographic strains of the T. saginata-like tapeworm in the Far East. These strains appear to be the same and possibly a new species.     

Taiwan taenia and taeniasis

Toeniids are large tapeworms, common throughout the world. Two species, Taenia saginata and T. solium are common parasites of man. The adult worms parasitize the small intestine, while immature stages (metacestodes or cysticerci) develop mainly in cattle in the case of T. saginata or pigs in the case of T. solium. Cysticerci of T. saginata rarely develop in man, although humans are easily infected with those of T. solium after eating raw or undercooked infected pork-producing the disease known as cysticercosis. In Taiwan, both the pork and beef tapeworms have been documented among aboriginal peoples - with T. saginata considered the most prevalent species. But, as P.C. Fan discusses here, the 'Taiwan Taenia' has several unusual features - not least the fact that beef is not part of the traditional diet of Taiwan oboriginols.     

Experimental infection of Indonesia Taenia (Samosir strain) in domestic animals

Three 58-day old Small-Ear-Miniature (SEM) pigs, six 36-day old Landrace-Small-Ear-Miniature (L-SEM) pigs, and two 5-day old Holstein calves were each fed 3000 or 30,000 Indonesia Taenia (Samosir strain) eggs and sacrificed 27-195 days after inoculation. A total of 4922 cysticerci were recovered only from the livers of the three SEM pigs (1977 cysticerci) and six L-SEM pigs (2945 cysticerci). The infection rate in pigs was 100%. Cysticerci recovery rates of SEM and L-SEM pigs were 22.0% and 1.6%, respectively. Calves were not susceptible to Indonesia Taenia. More cysticerci were found in the liver parenchyma (L-SEM, 66.4%; SEM, 76.2%) than on the liver surface (L-SEM, 33.6%; SEM, 23.8%) of the infected animals. Most (99.86%) of the cysticerci recovered from the livers of L-SEM pigs were degenerated or calcified but 77.9% of those in the livers of SEM pigs were mature and only 22.1% were degenerated or calcified. Measurements of length, width, diameters of protoscolex, rostellum, and sucker and hooklet pattern indicated that Indonesia Taenia is very similar to Taiwan Taenia and very different from Taenia saginata and Taenia solium. The present findings indicate that Indonesia Taenia and Taiwan Taenia may be the same new species.     

Experimental infection of Philippine Taenia in domestic animals.

In the present study, six 34-44-day-old Small-Ear-Miniature pigs and one 14-day-old Holstein calf were each fed 10,000 Philippine Taenia eggs and sacrificed 27-43 days after inoculation. The infection rate was 100% for both pigs and calf with cysticerci recovery rates of 11 and 6%, respectively. A total of 6431 cysticerci were recovered only from the livers of the six pigs and 597 only from the liver of the calf; more occurred in the parenchyma (pigs 75%, calf 83%) than on the surface (pigs 25%, calf 17%). Mature cysticerci were found in four of the six pigs. A total of 317 cysticerci recovered from the pig livers were mature and the rest were either immature (926), degenerate or calcified (5188). All 597 cysticerci recovered from the liver of the calf were degenerate or calcified. Measurements of length, width, diameter of protoscolex, rostellum, and sucker and hooklet pattern indicated that Philippine Taenia is very similar to Taenia from Taiwan, Korea, Indonesia and Thailand and very different from classical T. saginata and T. solium.     

Experimental infection with Taenia saginata (Poland strain) in Taiwanese pigs.

Two 22-day-old Landrace-Small Ear Miniature (L-SEM) pigs, five 45 to 66-day-old Small Ear Miniature (SEM) pigs, and one 16-day-old Holstein calf were each fed 1000, 3000 or 10,000 Taenia saginata (Poland strain) eggs respectively and killed 34-77 days after inoculation. Four of the five SEM pigs and the Holstein calf were susceptible to this parasite. However, two L-SEM pigs and one SEM pig remained negative. The cysticerci recovery rates for the SEM pig and Holstein calf were 36% and 3%, respectively. All cysticerci from the SEM pigs were found in the livers, more in the parenchyma (89%) than on the surface (11%). Only eleven cysticerci in two SEM pigs were mature and the remainder were either immature, degenerated or calcified. The cysticerci in the calf were distributed throughout the body: leg muscles (248), heart (27), tongue (17), intercostal muscles (14), diaphragm (5), kidney (1) and liver (1). Most (299) of the cysticerci were mature, one was immature and 13 were degenerated or calcified. The length, width, diameter of the protoscolex and sucker of the cysticerci from the calf were larger than those from the SEM pigs. However, the diameter of the rostellum of the latter was slightly larger than the former. Hooklets were not found on any mature cysticercus recovered. The results of the present study provide evidence that the SEM pig can be used as an experimental intermediate host for T. saginata.     

Experimental infection of Thailand Taenia (Chiengmai strain) in domestic animals

Twenty-five gravid proglottides of a Thailand Taenia were obtained from a patient in Chiengmai, Thailand, and brought to our laboratory. The tapeworm was determined to be T. saginata-like by counting uterine branches (mean number 16, range 12-19 on each side). The eggs from these proglottides remained infective under storage at room temperature for 14 days followed by refrigeration (4-8 degrees C) for 131 days. Eight Small-Ear-Miniature pigs and two Holstein calves were each fed with 3000 eggs and sacrificed 12-76 days afterwards. Six pigs became infected and 16 cysticerci were recovered from the livers. Thirteen degenerated/calcified cysticerci were also recovered from the livers of the two calves. More cysticerci were found in the liver parenchyma (55%) than on the liver surface (45%) of the infected animals. Measurements of length, width, diameters of protoscolex, rostellum and sucker and hooklet pattern show that Thailand Taenia is similar to Taenia from Taiwan, Korea and Indonesia but different from T. saginata and T. solium. These findings indicate that Thailand Taenia, Taiwan Taenia, Korea Taenia, and Indonesia Taenia may be of the same species or sub-species.     

A monoclonal antibody-based ELISA for the detection of circulating excretory-secretory antigens in Taenia saginata cysticercosis.

A series of monoclonal antibodies (MoAb) produced against excretory and secretory products from 10- and 20-week-old Taenia saginata cysticerci were tested for their ability to detect circulating antigen in a double antibody sandwich enzyme-linked immunosorbent assay (ELISA). Two MoAb, 12G5 and 2H8, proved to be highly reactive with the tegument of viable T. saginata cysticerci and recognized antigenic components of 65, 87 and 100 kDa in immunoblotting. The detection limit of the assay using 12G5 as trapping antibody and 2H8 as a biotinylated indicator antibody was 0.1 ng protein per ml. Although the sensitivity of the test varied from one animal to another, the minimum number of living cysticerci, which could be detected by the ELISA, was 88. Animals harbouring only dead cysticerci gave similar reactions as non-infected control animals. Cross-reactions were only observed with taeniid parasites. The test was able to detect circulating antigen also in sheep and pigs, respectively infected with T. ovis and T. solium and in the serum samples of confirmed cases of human T. solium cysticercosis.     

Vaccination against Taenia solium cysticercosis in pigs using native and recombinant oncosphere antigens.

Pigs were immunised with antigens derived from Taenia solium oncospheres or with a pool of three recombinant antigens from Taenia ovis, and subsequently challenged with T. solium eggs. The native oncosphere antigens induced 83% protection against viable, and 89% protection against the total number of cysticerci established following the challenge infection. Immunisation with the recombinant T. ovis antigens induced 93% protection against the establishment of viable cysticerci, and 74% protection against the total number of cysticerci. These results, and those achieved elsewhere with Taenia saginata and T. ovis, support the possibility of developing a practical vaccine to assist in the control of transmission of T. solium through pigs.     

The 10 kDa protein of Taenia solium metacestodes shows genus specific antigenicity

Genus specific antigenicity of the 10 kDa protein in cyst fluid (CF) of Taenia solium metacestodes was demonstrated by comparative immunoblot analysis. When CFs from taeniid metacestodes of T. saginata, T. solium, T. taeniaeformis and T. crassiceps were probed with specific monoclonal antibody (mAb) raised against 150 kDa protein of T. solium metacestodes, specific antibody reactions were observed in 7 and 10 kDa proteins of T. solium and in 7/8 kDa of T. saginata, T. taeniaeformis and T. crassiceps. The mAb did not react with any protein in hydatid fluid of Echinococcus granulosus and E. multilocularis. This result revealed that the 10 kDa peptide of T. solium metacestodes and its equivalent proteins of different Taenia metacestodes are genus specific antigens that are shared among different Taenia species.     

The Asian Taenia and the possibility of cysticercosis

In certain Asian countries, a third form of human Taenia, also known as the Asian Taenia, has been discovered. This Asian Taenia seems to be an intermediate between Taenia solium and T. saginata since in morphological terms it is similar to T. saginata, yet biologically, as it uses the same intermediate host (pigs), it is more akin to T. solium. Taenia solium causes human cysticercosis, while T. saginata does not. It is not known whether the Asian taeniid is able to develop to the larval stage in humans or not. The arguments proposed by those authors who consider it unlikely that the Asian Taenia causes human cysticercosis are: (a) its molecular similarities with T. saginata; (b) the absence of cases of human cysticercosis in populations where the Asian adult is highly prevalent; and (c) the unsupporting results derived from an experimental infestation study. These three arguments are debated, although bearing in mind that at present there is still no clear scientific data to support that human cysticercosis can be caused by the Asian Taenia.     

The experimental infection of pigs with different numbers of Taenia solium eggs: immune response and efficiency of establishment

Three of 4 pigs inoculated with 10 eggs of Taenia solium became infected. In those pigs infected with larger numbers of eggs, all became infected. Specific antibodies against the metacestodes were found in serum at day 30 postinoculation (PI) in animals that received 1,000 or more eggs and at day 60 in those that received 10 or 100 eggs. The concentration and diversity of antibodies increased up to the day of death in pigs that received 10,000 or 100,000 eggs. All pigs infected with 1,000 or more eggs developed antibodies, but only 40% and 75% of pigs that received 10 and 100 eggs, respectively, developed antibodies. Metacestodes were found in the muscles of 23 of the 27 infected animals. In 35.7% of the pigs that received 1,000 or more eggs, metacestodes were also found in the brain. Most of the metacestodes found in pigs infected with 10 or 100 eggs were caseous, whereas in pigs infected with 1,000 or more eggs the majority of metacestodes were vesicular. This study shows that the severity of T. solium infection and the possible regulation of the immune system-evasion mechanisms depend on the number of metacestodes that succeed in establishing themselves and remain vesicular.     

Identification of Taenia asiatica in China: molecular,morphological, and epidemiological analysis of a Luzhai isolate

Multiple analysis has characterized a recently described tapeworm of people, Taenia asiatica, in mainland China. Six adult tapeworms collected from people of the Zhuang minority residing in the southern part of China (Luzhai isolate) were comparatively analyzed with other tapeworms from people: T. asiatica (n = 2, South Korea), T. saginata (n = 1, Poland; n = 1, Korea), and T. solium (n = 1, People's Republic of China). Experimental infections with eggs from the Luzhai isolate in pigs and cattle produced cysticerci, each with a hookletless scolex and with wartlike formations on the external surface of the bladder wall. There were rostellar protrusions in the scolices of adult worms. Random amplified polymorphic DNA analysis using 3 arbitrary primers produced bands identical to those of the Korean T. asiatica. Conversely, T. saginata and T. solium exhibited different banding patterns. Phylogenetic relationships inferred from the complete nucleotide sequences of the internal transcribed spacer 2 placed the Chinese tapeworms consistently within the T. asiatica clade by 96% bootstrapping value in the maximum likelihood analysis, 96% in maximum parsimony, and 100% in neighbor joining. These collective data demonstrate that T. asiatica is sympatrically distributed with the other 2 species of Taenia in the human host in mainland China.     

Early stages of development of the Taenia solium metacestode in pigs

In order to identify the early stages of Taenia solium metacestodes, 12 pigs were each fed 100,000 viable eggs and later killed and necropsied at different times after infection. Hematoxylin-eosin (HE) and immunohistochemical techniques (IHCs) were used to identify onchospheres and cysticerci in different tissues. At 2 days postinfection (dpi) structures compatible with onchospheres were found in the lumen of the small intestine, and in the mesenteric blood vessels and lymph nodes. At 4 dpi, these same structures were observed in the small intestine, the liver, and skeletal muscles. Between 6 and 39 dpi, they were found only in skeletal muscles. Between 2 and 6 dpi the postonchospheres were circular and oval shaped and measured between 6 and 34 x 27 microm. From 14 to 39 dpi, well-developed metacestodes 550 x 750 microm were observed. IHCs support the identification of early stages of T. solium.     

Antigenic components of Taenia saginata and their relevance to the diagnosis of bovine cysticercosis by immunoelectrophoresis.

22 antigenic components of Taenia saginata proglottides were detected by immunoelectrophoretic (IEP) study. Cross-absorption of the hyperimmune serum, raised in rabbits against T. saginata, with heterologous and host antigens showed that two thirds of these components were not specific for the cestode. Among the calves experimentally infected with T. saginata eggs, 3 precipitation patterns in IEP were identified depending on the evolutionary stage of the infection. The hydrosoluble extract of T. saginata was used as antigen. A short precipitating arc present near the antigen well and appearing 3 to 4 weeks post-infection of the calves and a long precipitating arc extending towards the anodic end of the slide and appearing in later stages of infection were found of high diagnostic value. No false-positive reaction or cross-reaction were found. Among the calves harbouring less than 50 cysticerci, false-negative reactions were seen.     

Human Neurocysticercosis Case and an Endemic Focus of Taenia solium in Lao PDR

A male patient with neurocysticercosis was identified in Montai Village, Xay District, Oudomxay Province, Lao PDR in February 2004. He had a history of diagnosis for neurocysticercosis by a CT scan in Thailand after an onset of epileptic seizure in 1993. A pig in the same district was found to contain Taenia solium metacestodes (=cysticerci); the slaughtered pig body contained more than 2,000 cysticerci. In addition to morphological identification, molecular identification was also performed on the cysticerci by DNA sequencing analysis of the mitochondrial cox1 gene; they were confirmed as T. solium metacestodes. The patient is regarded as an indigenous case of neurocysticercosis infected in an endemic focus of T. solium taeniasis/cysticercosis in Oudomxay Province, Lao PDR.     

Oncospheres of Taenia solium and T. saginata asiatica develop into metacestodes in normal and immunosuppressed mice.

Normal and immunosuppressed mice were infected with oncospheres of Taenia saginata asiatica and T. solium. Although normal ICR mice were not susceptible to these two parasites, cysticerci were recovered from the immunosuppressed ones following venous injection. For T. s. asiatica, immunosuppressed ICR mice had an infection rate of 12.5% and six cysticerci of this parasite were recovered from three males. After injection of T. solium oncospheres, a high infection rate of 57% was obtained and 23 cysticerci were collected from 13 male immunosuppressed ICR mice. The immunosuppressed C57 mice had the highest infection rate (100%) and cysticercus recovery rate (2.4%) for T. solium. The infection rate and cysticercus recovery rate in six normal C57 mice were 40% and 3% respectively. The immunosuppressed ICR, Balb/c and C3H mice were also susceptible to T. s. asiatica.     

Protective immunity against Taenia crassiceps murine cysticercosis induced by DNA vaccination with a Taenia saginata tegument antigen

This study investigated the protective capacity of the recombinant Taenia saginata Tso18 antigen administered as a DNA vaccine in the Taenia crassiceps murine model of cysticercosis. This Tso18 DNA sequence, isolated from a T. saginata oncosphere cDNA library, has homologies with Taenia solium and Echinococcus sp. It was cloned in the pcDNA3.1 plasmid and injected once intramuscularly into mice. Compared to saline-vaccinated control mice, immunization reduced the parasite burden by 57.3-81.4%, while lower levels of non-specific protection were induced in control mice injected with the plasmid pcDNA3.1 (18.8-33.1%) or a plasmid with irrelevant construct, pcDNA3.1/3D15 (33.4-38.8%). Importantly, significant levels of protection were observed between the pcDNA3.1/Tso18 plasmid and pcDNA3.1/3D15 plasmid immunized mice. Mice immunized with pTso18 synthesized low levels of, primarily IgG1 sub-class, antibodies. These antibodies were shown to recognize a 66 kDa antigen fraction of T. crassiceps and T. solium. Splenocytes enriched in both CD4+CD8- and CD4-CD8+ T cells from these vaccinated mice proliferated in vitro when exposed to antigens from both T. solium and T. crassiceps cestodes. Immunolocalization studies revealed the Tso18 antigen in oncospheres of T. saginata and T. solium, in the adult tapeworm and in the tegument of T. solium cysticerci. The protective capacity of this antigen and its extensive distribution in different stages, species and genera of cestodes points to the potential of Tso18 antigen for the possible design of a vaccine against cestodes.     

Taenia saginata: differential diagnosis of human taeniasis by polymerase chain reaction-restriction fragment length polymorphism assay

Speciation of Taenia in human stool is important because of their different clinical and epidemiological features. DNA analysis has recently become possible which overcomes the problems of differentiating human taeniid cestodes morphologically. In the present study, we evaluated PCR coupled to restriction fragment length polymorphism to differentiate Taenia solium from Taenia saginata eggs present in fecal samples from naturally infected patients. A different DraI-RFLP pattern: a two-band pattern (421 and 100 bp) for T. saginata and a three-band pattern (234, 188, and 99 bp) for T. solium was observed allowing the two species to be separated. The lower detection limit of the PCR-RFLP using a non-infected fecal sample prepared with a given number of T. saginata eggs was 34 eggs in 2 g stool sediment. The 521 bp mtDNA fragment was detected in 8 out of 12 Taenia sp. carriers (66.6%). Of these, three showed a T. solium pattern and five a T. saginata pattern.