Immunodiagnostic tools for taeniasis

Most diagnostic work conducted on the Taenia species zoonoses has been carried out on the larval stage of Taenia solium in man, reflecting the relative severity of the pathology caused by this stage of that organism. This review will, however, concentrate on the immunodiagnosis of the adult intestinal stages of these parasites in humans. Diagnosis of T. solium will be examined in most detail because of the relative importance of this parasite but relevant work from other cestodes of man and animals will also be discussed. In addition both classical and molecular approaches to diagnosis will be briefly covered. There have been a number of advances in immunodiagnosis of taeniasis over recent years that have improved both diagnostic sensitivity and specificity. Techniques for the detection of Taenia specific coproantigens in human taeniasis infections have been shown to more than double the numbers of T. solium cases accurately diagnosed in epidemiological studies. More recently, work on the serological diagnosis of T. solium have led to the development of a sensitive and specific enzyme linked immuno-transfer blot for the detection of species and stage specific circulating antibodies to adult worm excretory-secretory antigens. Work is ongoing to further improve these assays.     

Fact or hypothesis: Taenia crassiceps as a model for Taenia solium, and the S3Pvac vaccine

Research undertaken over the past 40 years has established many of the general principals concerning immunity to taeniid cestodes. Although much is well understood about the host-protective mechanisms against taeniids and this knowledge has been exploited in studies on vaccine development, many aspects require further investigation or confirmation. Some phenomena have come to be regarded as being well established, while careful analysis of the published data would suggest that they may be better regarded as hypotheses rather than established facts. This review considers one selected issue pertaining to immunity to cestode infections and examines carefully the nature of the evidence that is available to support conclusions that have been made in this area. The issue examined is the use of Taenia crassiceps as a model for cysticercosis in pigs caused by Taenia solium, together with the S3Pvac vaccine, which has been developed based on this model. Strong evidence is found to support the conclusion that defined T. crassiceps antigens can limit intraperitoneal proliferation of the ORF strain of T. crassiceps in mice; however, the potential for these antigens to affect T. solium infection in pigs requires further confirmation.     

Cestode infestations: hydatid disease and cysticercosis

Although humans can be definitive hosts for cestodes (tapeworms), major pathologic conditions occur during cestode larval stages when humans serve as the intermediate host for these parasites. The most relevant forms of human disease caused by cestode larvae are echinococcosis, caused by Echinococcus granulosus (cystic echinococcosis) and Echinococcus multilocularis (alveolar echinococcosis), and cysticercosis, caused by Taenia solium. These infections occur worldwide, but their relevance is particularly high in developing countries, where poor hygiene conditions facilitate the transmission of the parasites. The therapeutic approach is often complex, requiring surgery and/or chemotherapy or, in the case of cystic echinococcosis, percutaneous treatments.     

Community prevalence study of taeniasis and cysticercosis in Bali, Indonesia

Taenia solium, a human cestode parasite endemic throughout most of South-east Asia, causes a number of public health and economic problems. The parasite is endemic in Bali due to a mix of cultural and religious practices. Immunoepidemiological investigation of three rural communities revealed a taeniasis prevalence of 0.72% (3/415). One of the three cases was due to Taenia solium, the other two to Taenia saginata. A further nine cases of Taenia infection were identified from patients from villages surrounding the chosen communities, suggesting that prevalence levels may be higher in other areas. Seroprevalence of human cysticercosis by immunoblot was 1.65% (6/363), though all cases were detected within a single community (6/115; prevalence 5.22%). Several other cases of subcutaneous cysticercosis were identified from local clinics, suggesting continued transmission of Taenia solium in the region. Other intestinal helminth parasites identified within the communities were Ascaris lumbricoides (29.9%), Trichuris trichiuria (33.9%) and hookworm (8.2%).     

Cysticercosis/taeniasis in Asia and the Pacific

Three taeniid tapeworms infect humans in Asia and the Pacific: Taenia solim, Taenia saginata, and Taenia asiatica. Although there is continuing debate about the definition of a new species, phylogenetic analyses of these parasites have provided multiple lines of evidence that T. asiatica is an independent species and the sister species of T. saginata. Here we review briefly the morphology, pathology, molecular biology, distribution and control options of taeniasis/cysticercosis in Asia and the Pacific and comment on the potential role which dogs may play in the transmission of T. solium. Special attention is focused on Indonesia: taeniasis caused by T. asiatica in North Sumatra, taeniasis/cysticercosis of T. solium and taeniasis of T. saginata in Bali, and taeniasis/cysticercosis of T. solium in Papua (formerly Irian Jaya). Issues relating to the spread of taeniasis/cysticercosis caused by T. solium in Papua New Guinea are highlighted, since serological evidence suggests that cysticercosis occurs among the local residents. The use of modern techniques for detection of taeniasis in humans and cysticercosis in humans, pigs and dogs, with the possible adoption of new control measures will provide a better understanding of the epidemiology of taeniasis/cysticercosis in Asia and the Pacific and lead to improved control of zoonotic and simultaneously meat-borne disease transmission.     

Biotechnology research on cestodes in the Philippines, Malaysia, and Indonesia

There are essentially no reports on the use of modern biotechnological methods on the study of cestode parasites in the Philippines, Indonesia or Malaysia. The only recent reports of cestode studies in these countries have been on reports of new species in animals and on prevalence rates of cestode parasites in humans; Taenia solium and cysticercosis, Taenia saginata and Hymenolepis nana, etc. Reports on the use of biotechnology has emanated from outside the area on cestodes of humans and animals, and some of these methods could be used to study cestodes in this part of the world.     

Human Taeniasis and cysticercosis in Asia

CONTEXT: Human Taeniasis caused by the pork, Taenia solium, or beef, T saginata, tapeworm arises after eating pork or beef contaminated with metacestodes, the larval stage of these parasites. Taeniasis with T solium can lead to neurocysticercosis and threaten others by accidental ingestion of eggs released from asymptomatic Taeniasis patients. The 2003 World Health Assembly declared that T solium is of worldwide public-health importance, and that it is an eradicable parasitic disease worldwide. Adult taeniid tapeworms expelled from people in almost all Asian countries appeared to be T saginata (the so-called Asian Taenia), even though they ate pork. The organism is now named T asiatica, and has been found in Taiwan, Korea, China, Vietnam, and Indonesia. But it has been difficult to differentiate T saginata from beef and Asian Taenia from pork. STARTING POINT: Marshall Lightowlers and colleagues (Int J Parasitol 2003; 33: 1207-17) recently demonstrated that recombinant oncosphere vaccines against several taeniid cestodes, including T ovis, T saginata, T solium, and Echinococcus granulosus, are highly effective. Protection was almost 100%, in the laboratory and in the field. These researchers found several common features, including a predicted secretory signal sequence, and one or two copies of a fibronectin type III domain, each encoded by separate exons within the associated gene. WHERE NEXT? Molecular and immunological techniques, including vaccine research and development of animal models for differentiation of taeniid species in humans, have greatly advanced over the past decade. The clinical importance of infections by these taeniids, including T asiatica, in humans, and the potential for cysticercosis attributable to T asiatica in humans, needs further study.     

Short report: secondary transmission in porcine cysticercosis: description and their potential implications for control sustainability

Taenia solium taeniasis/cysticercosis is one of few potentially eradicable infectious diseases and is the target of control programs in several countries. The larval stage of this zoonotic cestode invades the human brain and is responsible for most cases of adult-onset epilepsy in the world. The pig is the natural intermediate host, harboring the larvae or cysticerci. Our current understanding of the life cycle implicates humans as the only definitive host and tapeworm carrier (developing taeniasis) and thus the sole source of infective eggs that are responsible for cysticercosis in both human and pigs through oral-fecal transmission. Here we show evidence of an alternative pig-to-pig route of transmission, previously not suspected to exist. In a series of four experiments, naive sentinel pigs were exposed to pigs that had been infected orally with tapeworm segments (containing infective eggs) and moved to a clean environment. Consistently in all four experiments, at least one of the sentinel pigs became seropositive or infected with parasite cysts with much lower cyst burdens than did primarily infected animals. Second-hand transmission of Taenia solium eggs could explain the overdispersed pattern of porcine cysticercosis, with few pigs harboring heavy parasite burdens and many more harboring small numbers of parasites. This route of transmission opens new avenues for consideration with respect to control strategies.     

Taeniasis vs cysticercosis infection routes

Although cysticercosis caused by Taenia solium(T. solium) is considered a neglected disease, its life cycle has been well known for more than two centuries. T. solium not only causes cysticercosis but also taeniasis in humans. These two diseases have totally different infection routes. To acquire taeniasis(the presence of the adult stage of T. solium in the intestine), humans have to ingest the larval stage(cysticercus) that infects a variety of organs and viscera in pigs, its intermediate hosts. Therefore, taeniasis is acquired when eating raw or undercooked infected pork. The adult stage in the human intestine release eggs that contain a hexacanth embryo, the oncosphere. If humans accidentally ingest the eggs of T. solium, the released oncospheres penetrate the intestine and become cysticerci. Therefore, cysticercosis is acquired by the ingestion of eggs that contaminate water, vegetables, hands etc. These facts should not be forgotten to avoid misinformation in scientific publications.     

猪带绦虫六钩蚴TSO18基因研究进展

猪囊尾蚴病是一种严重危害人类健康的人兽共患寄生虫病,疫苗是预防控制猪囊尾蚴病的重要手段.TSO18基因是猪带绦虫六钩蚴阶段重要的免疫原基因,被认为是最具有前途的疫苗候选基因.该文综述了猪带绦虫六钩蚴TSO18基因的分子生物学及其疫苗开发的研究进展.     

Taeniasis/cysticercosis in a Tibetan population in Sichuan Province, China

The results of a preliminary survey of taeniasis/cysticercosis in Yajiang County, Ganze Tibetan Prefecture in southwest Sichuan Province, China, indicated a very high prevalence of taeniasis (22.5%), with Taenia saginata as the dominant species. There was also a significant occurrence of late-onset epilepsy (8.5% prevalence and 16.4% seropositive for Taenia solium antibodies) attributable in large part to probable neurocysticercosis caused by T. solium. The poor sanitation and hygiene in this Tibetan community likely contributed to a high risk of human cysticercosis despite a low level of T. solium taeniasis (actually no T. solium carriers were detected amongst the 21 proven Taenia carriers). In addition, three taeniasis cases were confirmed by DNA genotyping as Taenia asiatica, which is the first report of this tapeworm in Tibetans, the first report for Sichuan Province and only the third report for mainland China.     

猪带绦虫六钩蚴TSO45W基因工程疫苗研究进展

囊虫病是一种危害严重的人兽共患寄生虫病。研制有保护性作用的疫苗将是控制和消灭该病的有效方法,猪带绦虫保护性抗原的研究是猪囊虫病免疫的基础。45W蛋白是猪带绦虫六钩蚴时期的重要抗原,但天然45W抗原来源有限,限制了其应用,而基因工程重组抗原的应用可解决质量控制和抗原来源的问题。本文就近年来国内外对猪带绦虫六钩蚴TSO45W基因工程疫苗的研究进展作一综述。     

Taeniasis and cysticercosis in Asia and the Pacific: present state of knowledge and perspectives

Several topics on taeniasis and cysticercosis in Asia and the Pacific are overviewed. In Asia and the Pacific, three human taeniid species have been recognized: Taenia solium, Taenia saginata and Taenia asiatica. The first topic is on evolution of T. solium. Mitochondrial DNA polymorphisms of T. solium worldwide are discussed with emphasis of two specific genotypes: American-African and Asian. The second topic is recent major advances in sero- and molecular-diagnosis of T. solium cysticercosis in humans, pigs and dogs. The third is the present situation of T. solium taeniasis/cysticercosis in Papua (Irian Jaya), Indonesia. The forth is the present situation of T. solium cysticercosis and T. saginata taeniasis in Bali, Indonesia. The fifth is the present situation of T. asiatica taeniasis in Asia and the Pacific and in North Sumatra, Indonesia. The sixth is on the debate of the exact definition of T. asiatica. Because T. asiatica can not be differentiated from T. saginata morphologically, it is time to re-evaluate T. saginata in Asia and the Pacific. New and broad-based surveys across this region are necessary from epidemiological and public health perspectives, based on evidence.     

分子分类结合形态学方法对云南大理带绦虫的鉴定

目的 鉴定云南大理洱源(E1-E2)、鹤庆(H1-H2)、双廊(SL)、挖色(WS)带绦虫的种.方法 首先对大理分离株带绦虫成虫进行形态学鉴定,从成虫节片中抽提DNA,PCR扩增线粒体DNA细胞色素B(mtDNA-Cyth)的部分序列并测序;结合GenBank中已知猪带绦虫、牛带绦虫和亚洲带绦虫mtDNA-Cytb序列,经DNAMAN软件处理后构建系统发育树状图.结果大理带绦虫E1的形态和牛带绦虫相似,系统发育树显示大理分离株E1、E2、SL、WS带绦虫标本与亚洲带绦虫的遗传距离最接近,距牛带绦虫较远,与猪带绦虫则更远.大理分离株H1、H2带绦虫标本与猪带绦虫的遗传距离最近,距牛带绦虫和亚洲带绦虫则较远.结论 经形态学和分子生物学鉴定,云南大理分离株E1、E2、SL、WS带绦虫标本属于亚洲带绦虫,而H1、H2株带绦虫标本属于猪带绦虫.     

Vaccines for prevention of cysticercosis

Neurocysticercosis due to Taenia solium infection is an important cause of human morbidity and mortality. Despite the availability of effective anthelmintics, the disease remains prevalent in many parts of the world and there is a need for new and improved measures for control of the infection. An effective vaccine to prevent infection in pigs, the parasite's natural intermediate host, would be a valuable new option to assist with T. solium control. Several approaches are being used currently towards the development of a T. solium vaccine and these approaches are reviewed briefly, with emphasis on the use of recombinant oncosphere antigens. Highly effective vaccines have been developed against cysticercosis in sheep and cattle caused by Taenia ovis and Taenia saginata, respectively. This success has encouraged the adoption of a similar strategy for T. solium. The recent finding that one oncosphere antigen, TSOL18, can induce complete protection against T. solium infection in pigs, highlights the potential for development of a practical vaccine. A vision is proposed for the development of a safe, effective, inexpensive vaccine for pigs, which can be administered in an edible form. Through an international collaborative effort, research is progressing towards the realisation of such a vaccine and its use to reduce the global burden of neurocysticercosis.     

Antibody responses and epitope specificities to the Taenia solium cysticercosis vaccines TSOL18 and TSOL45-1A

Taenia solium is a cestode parasite that causes cysticercosis in humans and pigs. This study examined the antibody responses in pigs immunized with the TSOL18 and TSOL45-1A recombinant vaccines against T. solium cysticercosis. Immunization with these proteins induced specific, complement-fixing antibodies against the recombinant antigens that are believed to be associated with vaccine-induced protection against T. solium infection. Sera from immunized pigs were used to define the linear B-cell epitopes of TSOL18 and TSOL45-1A. Prominent reactivity was revealed to one linear epitope on TSOL18 and two linear epitopes on TSOL45-1A. These, and oncosphere antigens from other taeniid cestodes, contain a protein sequence motif suggesting that they may show a tertiary structure similar to the fibronectin type III domain (FnIII). Comparison of the location of linear antigenic epitopes in TSOL18 and TSOL45-1A within the proposed FnIII structure to those within related cestode vaccine antigens reveals conservation in the positioning of the epitopes between oncosphere antigens from different taeniid species.     

Population-based survey of taeniasis along the United States-Mexico border

Taenia solium and T. saginata are zoonotic tapeworms of substantial medical and economic importance. Although human taeniasis is widely recognised as an endemic problem in Mexico, its presence in the United States is poorly understood. The first population-based study to estimate the prevalence of human infection with Taenia tapeworms along the Texas-Mexico border has recently been conducted. Households were interviewed in the Texan city of El Paso and in the neighbouring Ciudad Juárez, in Mexico. Faecal samples from household members were then checked for Taenia eggs by flotation and/or for Taenia copro-antigens in an ELISA. The overall prevalence of taeniasis in this border region was found to be 3% but, compared with the residents of Juárez, El Paso residents were 8.6-fold more likely to be tapeworm carriers. The interviews revealed some important differences between the two study sites, particularly the more frequent use of anthelminthic drugs on the Mexican side of the border. These findings have implications in terms of the planning of effective health-education campaigns to decrease the prevalence of taeniasis in the human populations along the Texas-Mexico border.     

Vaccination of pigs to control human neurocysticercosis

Taenia solium taeniasis/cysticercosis is a zoonotic disease complex in which the pig is an obligate intermediate host. The infection is widespread, particularly in the developing world, and neurocysticercosis is a major cause of human neurologic disease where the parasite is endemic. Despite easy availability, effective anti-parasitic drugs have not been deployed effectively to control disease transmission. We have investigated a vaccine strategy to prevent parasite infection of the pig intermediate host. Such a strategy would interrupt the parasite's life cycle and eliminate the source of infection for humans. Two recombinant antigens selected from the parasite oncosphere life cycle stage were tested in vaccination trials in pigs that were challenged orally with Taenia solium eggs. Both antigens were highly effective in protecting the pigs against infection with the parasite (98.6% and 99.9% protection, respectively). No viable cysts were found in eight pigs vaccinated with one of the antigens. A recombinant subunit vaccine based on oncosphere antigens has the potential to improve the available control measures for T. solium and thereby reduce or eliminate neurocysticercosis.     

云南西部三地带绦虫生物多态性分子遗传学标记的研究

目的利用分子遗传学标记对采自云南西部楚雄、大理和怒江三地带绦虫进行生物多态性研究。方法取云南楚雄株、大理株、怒江株和贵州从江株成虫节片,抽提线粒体DNA,PCR扩增线粒体DNA细胞色素B（mtDNA-Cytb）序列部分区段,并测序;结合GenBank中已知猪带绦虫和亚洲带绦虫mtDNA-Cytb序列,构建系统发育树。结果序列分析显示云南大理和怒江带绦虫mtDNA-Cytb序列部分区段完全一致,同源性为100%;云南楚雄和贵州从江带绦虫mtDNA-Cytb序列部分区段基本一致,同源性为99%。系统发育树显示云南怒江和大理带绦虫与台湾亚洲带绦虫的遗传距离较近,距云南楚雄、贵州从江牛带绦虫较远,与猪带绦虫则更远。结论云南大理和怒江带绦虫属于亚洲带绦虫,云南楚雄带绦虫属于牛带绦虫。mtDNA-Cytb序列分析可以用于带绦虫生物多态性研究。     

云南保山、普洱带绦虫mtDNA ND1基因序列测定及分析

目的对云南保山、普洱地区带绦虫标本进行鉴定。方法选取带绦虫成虫节片,抽提虫体基因组DNA ,PCR扩增mtDNA ND1基因序列,并测序;结合GenBank中已知的亚洲带绦虫、牛带绦虫、猪带绦虫mtDNA ND1基因序列,经DNA MAN软件处理后构建系统发育树状图与同源树状图。结果带绦虫系统发育树与同源 树状图显示P1、P2、B3、B6、B7、ND与N2的同源性最近。B1、B2、B4、B5、YZ与Y1的同源性最近。ZD与Z3 的同源性最近。结论云南保山存在亚洲带绦虫与牛带绦虫;普洱存在牛带绦虫。mtDNA ND1基因序列可用 于三种带绦虫的分类鉴定。