The pig as an experimental host of Taenia saginata (Ethiopia and Madagascar strains)

Towards a cysticercosis-free tropical resort island: A historical overview of taeniasis/cysticercosis in Bali

Taeniasis and cysticercosis are known to be endemic in several Indonesian islands, although relatively little recent epidemiological data are available. As most Indonesian people are Muslims, taeniasis/cysticercosis caused by the pork tapeworm, Taenia solium, has a restricted presence in non-Muslim societies and is endemic only among some Hindu communities on the island of Bali. Bali has long been known to be endemic for taeniasis/cysticercosis; almost a century ago levels of cysticercosis of 20-30% were described in cattle and 2-3% in pigs. Few studies of taeniasis/cysticercosis were undertaken in Bali prior to a series of research programs commenced since the 1990s. Both Taenia saginata and T. solium continue to be endemic in Bali. Molecular studies have revealed that all T. saginata-like tapeworms detected in Bali are T. saginata. No evidence has been found for the presence of Taenia asiatica in Bali. Economic, sanitary and education improvements across much of the island over the past decades have been associated with a decline in the amount of transmission of T. solium such that the parasite now seems to be restricted to the eastern part of the island, a small area on the northeastern slope of Mt. Agung, the highest mountain in Bali. The living environment including sanitation and hygiene condition in this endemic area remains relatively poor especially during the half-year dry season, and pigs continue to roam freely. In this review, historical records and ongoing projects towards elimination of taeniasis/cysticercosis in Bali are reviewed to provide a better understanding of the present situation of taeniasis/cysticercosis in Bali towards a future, cysticercosis-free tropical resort island.

Pig as a favorable animal for Taenia saginata asiatica infection

The epidemiology of Taenia saginata in some parts of Asia is confusing, in that beef does not appear to be the source of infection. In some areas, beef is either not available or not eaten raw, whereas pork at times is eaten uncooked. In light of this situation, we have exposed pigs and other animals to infection with strains of T. saginata to establish their ability to serve as intermediate hosts. Eggs of Taiwan Taenia, Korea Taenia, Indonesia Taenia, Thailand Taenia, Philippines Taenia, Ethiopia Taenia, and Madagascar Taenia were fed to 83 pigs of three strains: 43 Small-Ear Miniature (SEM), 34 Landrace Small-Ear Miniature (L-SEM), and 6 Duroc-Yorkshire-Landrace (DYL). We also fed the eggs to 10 Holstein calves, 17 Sannean goats, and 4 monkeys (Macaca cyclopis). We succeeded in infecting SEM (infection rate 88%, cysticercus recovery rate 19.1%), L-SEM (83%, 1.1%), and DYL (100%, 0.3%) pigs with Taiwan Taenia; SEM (100%, 1.7%), L-SEM (100%, 5.6%), and DYL (100%, 0.06%) pigs with Korea Taenia; SEM (100%, 22%) and L-SEM (100%, 1.6%) pigs with Indonesia Taenia; SEM (75%, 0.06%) pigs with Thailand Taenia SEM (100%, 11%) pigs with Philippines Taenia; SEM (80%, 0.005%) pigs with Ethiopia Taenia; SEM (100%, 0.2%) pigs with Madagascar Taenia. Holstein calves became infected with Taenia from Taiwan (100%, 1.1%), Korea (100%, 0.03%), Thailand (100%, 0.2%), and the Philippines (100%, 6%); however, the cysticerci of Taenia from Korea, Thailand, and the Philippines were degenerated and/or calcified. Sannean goats became infected with Taenia from Taiwan (33%, 0.01%) and Korea (50%, 0.02%), while monkeys became infected with Taenia from Taiwan (50%, 0.01%). However, the cysticerci were degenerated and/ or calcified. Therefore, these strains of pig seem to be favorable animal models for experimental studies of T. saginata-like tapeworms, with the SEM pig the most favorable.

PCR tools for the differential diagnosis of Taenia saginata and Taenia solium taeniasis/cysticercosis from different geographical locations

The potential value of PCRs in the species-specific diagnosis of have been investigated, using samples of T. saginata and T. solium from different geographical areas. The PCRs examining inter-species differences were based on the sequence of the HDP2 DNA fragment, specific for T. saginata/T. solium, and the sequence of the rDNA internal transcribed spacer 1 and spacer 2 (ITS-1 and ITS-2). This PCR analysis of DNA isolates confirmed morphologic diagnosis and allowed the speciation of samples too small or fragmented for morphologic identification, with clear and consistent inter-species differences between T. saginata (twenty-two) and T. solium (three) geographical isolates. Possible intra-species genomic variability, within these species, was similarly studied through analysis of PCR amplification products (PCR-RFLP) and only encountered one exceptional T. saginata isolate from Kenya, which yielded a unique PCR-RFLP pattern, different from T. saginata DNA of Mexican (one sample) and Spanish (seven samples) origin.

Experimental studies on the pathway for migration and the development of Taiwan Taenia in domestic pigs

The pig is the most favorable experimental intermediate host of Taiwan Taenia. Cysticerci in infected pigs are located in the liver except for a few extrahepatic ones. The present study was designed to investigate the pathway of migration of the oncospheres of Taiwan Taenia in the pig. In the first group, each of 5 Small-Ear-Miniature (SEM) and one Landrace-Small-Ear-Miniature (L-SEM) pigs were injected with 5000 hatched oncospheres into the ear vein. Three SEM and one L-SEM pigs were found to harbor 88 degenerated or calcified cysticerci only in the liver 51-81 days after injection. In the second group, each of 3 L-SEM pigs were injected with 5000 hatched oncospheres into the jugular vein. One of the 3 pigs was found to have 5 cysticerci (2 mature and 3 degenerated or calcified) only in the liver at 89 days post-injection. In the third group, each of 4 SEM, three L-SEM, and 3 L-SEM pigs were injected with 10,000, 10,000, and 5000 hatched oncospheres, respectively, directly into the portal vein after surgical opening of the abdominal cavity. All 10 pigs were found to be infected with a total of 1088 cysticerci (44 mature and 1044 degenerated or calcified) only in the liver 23-62 days after injection. Although the sites of injection in these three groups were different, the liver was the only final location of the cysticerci. These findings give strong evidence that the oncospheres migrate to the liver through the venous circulation and develop in this organ.

The prevalence of Taenia solium metacestodes in pigs in northern Tanzania

Eighty three carcasses of pigs were examined at three abattoirs in Moshi, Arusha and Mbulu in northern Tanzania. Taenia solium metacestodes were found in all the three abattoirs with an overall prevalence of 13.3%. During routine meat inspection in Kiboroloni, Moshi 6.2-6.9% of the pigs were found to harbour T. solium metacestodes. The mean number of hooks on the protoscolices was 27 and the length of the small hooks varied from 105 microns to 130 microns while that of the larger hooks varied from 168 microns to 174 microns confirming that the cysts were metacestodes of T. solium. Although cystlike lesions were recovered from livers of both pigs and cattle, no hooklets of sizes in the range of 5-37 microns were found indicating that no Taiwan Taenia metacestodes were recovered during carcass examination.

Experimental infection of pigs and cattle with eggs of Asian Taenia saginata with special reference to its extrahepatic viscerotropism

Asian Taenia saginata, tentatively called Taenia saginata taiwanensis, has been described to be infected in its metacestode stage only in the liver of intermediate host animals. Experimentally, however, we found that the metacestodes of the Asian Taenia saginata are also infected in other viscera than the liver of pigs (Landrace-Duroc-Hampshire) 4 days to 4 months postinoculation (PI). Viscerotropism of cysticercosis was apparent because a majority (70.7%) of the non-calcified cysticerci were found in the livers while a minority were found in extrahepatic organs such as the omentum (19.2%), lungs (8.1%) and serosa of colon (2.0%). When experimentally infected to cattle, Asian T. saginata cysticerci were also observed calcified in the livers. On the other hand, classical Taenia saginata metacestodes infected the muscles and viscera of the Holstein-Friesian cattle whereas no infection was observed in experimental pigs. Extrahepatic metacestodes of Asian T. saginata, which were obtained from an experimental pig were confirmed to be infective to a male volunteer. This extrahepatic viscerotropism of Asian T. saginata metacestodes in experimental pigs explains well the transmission modes of Asian T. saginata among people considering the eating habits.

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 pigs with a Taenia species from Korea: parasitological and serological aspects

Belgian Landrace piglets were experimentally infected with eggs of a Taenia sp. of Korean origin. At autopsy, metacestodes were present only in the livers. The proportion of degenerated metacestodes increased from 12%-39% at 5 weeks to 94%-100% at 10 weeks after infection. A sandwich enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies raised against the excretory-secretory products of T. saginata metacestodes detected circulating antigen in the sera of the pigs at 1 week post-infection. A good correlation was found between the presence of viable metacestodes and the detection of circulating antigen; the latter disappeared as the metacestodes died off. However, the antibodies were detected only after 3 weeks of infection and onwards until the necropsy of the pigs.