Control of echinococcosis and cysticercosis: a public health challenge to international cooperation in China

Tribendimidine and albendazole for treating soil-transmitted helminths, Strongyloides stercoralis and Taenia spp.: open-label randomized trial

Background

Tribendimidine is an anthelminthic drug with a broad spectrum of activity. In 2004 the drug was approved by Chinese authorities for human use. The efficacy of tribendimidine against soil-transmitted helminths (Ascaris lumbricoides, hookworm, and Trichuris trichiura) has been established, and new laboratory investigations point to activity against cestodes and Strongyloides ratti.

Methodology/Principal Findings

In an open-label randomized trial, the safety and efficacy of a single oral dose of albendazole or tribendimidine (both drugs administered at 200 mg for 5- to 14-year-old children, and 400 mg for individuals ≥15 years) against soil-transmitted helminths, Strongyloides stercoralis, and Taenia spp. were assessed in a village in Yunnan province, People's Republic of China. The analysis was on a per-protocol basis and the trial is registered with controlled-trials.com (number ISRCTN01779485). Both albendazole and tribendimidine were highly efficacious against A. lumbricoides and, moderately, against hookworm. The efficacy against T. trichiura was low. Among 57 individuals who received tribendimidine, the prevalence of S. stercoralis was reduced from 19.3% to 8.8% (observed cure rate 54.5%, p = 0.107), and that of Taenia spp. from 26.3% to 8.8% (observed cure rate 66.7%, p = 0.014). Similar prevalence reductions were noted among the 66 albendazole recipients. Taking into account “new” infections discovered at treatment evaluation, which were most likely missed pre-treatment due to the lack of sensitivity of available diagnostic approaches, the difference between the drug-specific net Taenia spp. cure rates was highly significant in favor of tribendimidine (p = 0.001). No significant adverse events of either drug were observed.

Conclusions/Significance

Our results suggest that single-dose oral tribendimidine can be employed in settings with extensive intestinal polyparasitism, and its efficacy against A. lumbricoides and hookworm was confirmed. The promising results obtained with tribendimidine against S. stercoralis and Taenia spp. warrant further investigations. In a next step, multiple-dose schedules should be evaluated.

More than a billion people are infected with intestinal worms and, in the developing world, many individuals harbor several kinds of worms concurrently. There are only a handful of drugs available for treatment, and drug efficacy varies according to the worm species. We compared the efficacy of a single oral dose of tribendimidine, a new broad-spectrum worm drug from China, with the standard drug albendazole for the treatment of hookworm, large roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura) and, for the first time, Strongyloides stercoralis and tapeworm (Taenia spp.). Our single-blind randomized trial was conducted in a village in Yunnan province, southwest China. Both drugs showed high efficacy against A. lumbricoides and a moderate efficacy against hookworm. Among 57 tribendimidine recipients, the prevalence of S. stercoralis was reduced from 19.3% to 8.8%, and that of Taenia spp. from 26.3% to 8.8%. Similar prevalence reductions were noted among the 66 albendazole recipients. Taking into account additional infections only discovered at treatment evaluation, the difference between the drug-specific Taenia spp. net cure rates was highly significant in favor of tribendimidine. In view of our promising results, multiple-dose schedules with tribendimidine against S. stercoralis and Taenia spp. should be evaluated next.

Landscape composition and spatial prediction of alveolar echinococcosis in southern Ningxia, China

BACKGROUND

Alveolar echinococcosis (AE) presents a serious public health challenge within China. Mass screening ultrasound surveys can detect pre-symptomatic AE, but targeting areas identified from hospital records is inefficient regarding AE. Prediction of undetected or emerging hotspots would increase detection rates. Voles and lemmings of the subfamily Arvicolinae are important intermediate hosts in sylvatic transmission systems. Their populations reach high densities in productive grasslands where food and cover are abundant. Habitat availability is thought to affect arvicoline population dynamic patterns and definitive host-intermediate host interactions. Arvicoline habitat correlates with AE prevalence in Western Europe and southern Gansu Province, China.

METHODS AND FINDINGS

Xiji County, Ningxia Hui Autonomous Region, borders southern Gansu. The aims of this study were to map AE prevalence across Xiji and test arvicoline habitat as a predictor. Land cover was mapped using remotely sensed (Landsat) imagery. Infection status of 3,205 individuals screened in 2002-2003 was related, using generalised additive mixed models, to covariates: gender; farming; ethnicity; dog ownership; water source; and areal cover of mountain pasture and lowland pasture. A Markov random field modelled additional spatial variation and uncertainty. Mountain pasture and lowland pasture were associated with below and above average AE prevalence, respectively.

CONCLUSIONS

Low values of the normalised difference vegetation index indicated sub-optimality of lowland pasture for grassland arvicolines. Unlike other known endemic areas, grassland arvicolines probably did not provide the principal reservoir for Echinococcus multilocularis in Xiji. This result is consistent with recent small mammal surveys reporting low arvicoline densities and high densities of hamsters, pikas and jerboas, all suitable intermediate hosts for E. multilocularis, in reforested lowland pasture. The risk of re-emergence is discussed. We recommend extending monitoring to: southern Haiyuan County, where predicted prevalence was high; southern Xiji County, where prediction uncertainty was high; and monitoring small mammal community dynamics and the infection status of dogs.

Food-borne parasitic zoonoses in China: perspective for control

Food-borne parasitic zoonoses (FBPZs) cause death and serious diseases in humans and animals worldwide, and are of both public health significance and socioeconomic importance. The FBPZ problem is severe in mainland China, where approximately 150 million people are suffering from FBPZs and more people are at risk. Here, the current status of the FBPZ problem in mainland China is reviewed and strategies and measures for effective control of FBPZs are proposed. Major parasitic zoonoses transmitted through consumption of infected or contaminated meat, fish, plants and/or water will be discussed.

Helminth infections and risk factor analysis among residents in Eryuan county, Yunnan province, China

Whilst infections with soil-transmitted helminths are common across China, the public-health significance of Schistosoma japonicum and food-borne helminths is more focalized. Only few studies have investigated the local epidemiology of helminth infections in rural China, including risk factor analysis. We collected stool and blood samples from 3220 individuals, aged 5-88 years, from 35 randomly selected villages in Eryuan county, Yunnan province, China. Stool samples were subjected to the Kato-Katz technique and examined for helminth eggs. Blood samples were tested for Trichinella spp., S. japonicum and cysticerci-specific antibodies. Data on individual and family-level risk factors were collected using questionnaires. The prevalence of Ascaris lumbricoides, Taenia spp., Trichuris trichiura and hookworms was 15.4%, 3.5%, 1.7% and 0.3%, respectively. The seroprevalence of Trichinella spp. was 58.8% and that of cysticercosis 18.5%. The egg positivity rate of S. japonicum in the 13 known endemic villages was 2.7%, and the corresponding seroprevalence was 49.5%. We observed a strong spatial heterogeneity in the families' economic status. S. japonicum infections were more prevalent among the Han than Bai nationality (odds ratio (OR)=3.77, 95% confidence interval (CI)=1.97-7.23) and tobacco growers (OR=3.66, 95% CI=1.77-7.60) and was only found at elevations below 2150 m above sea level. A. lumbricoides and Taenia spp. infections were more prevalent at altitudes above 2150 m when compared to lower settings (OR=1.51, 95% CI=1.24-1.84 and OR=5.32, 95% CI=3.42-8.28, respectively). The opposite was found for T. trichiura (OR=0.31, 95% CI=0.14-0.70). Our findings can guide the design and spatial targeting of control interventions against helminth infections in Eryuan county.

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.

Control of cystic echinococcosis/hydatidosis: 1863-2002

Echinococcosis/hydatidosis, caused by Echinococcus granulosus, is a chronic and debilitating zoonotic larval cestode infection in humans, which is principally transmitted between dogs and domestic livestock, particularly sheep. Human hydatid disease occurs in almost all pastoral communities and rangeland areas of the underdeveloped and developed world. Control programmes against hydatidosis have been implemented in several endemic countries, states, provinces, districts or regions to reduce or eliminate cystic echinococcosis (CE) as a public health problem. This review assesses the impact of 13 of the hydatid control programmes implemented, since the first was introduced in Iceland in 1863. Five island-based control programmes (Iceland, New Zealand, Tasmania, Falklands and Cyprus) resulted, over various intervention periods (from <15 to >50 years), in successful control of transmission as evidenced by major reduction in incidence rates of human CE, and prevalence levels in sheep and dogs. By 2002, two countries, Iceland and New Zealand, and one island-state, Tasmania, had already declared that hydatid disease had been eliminated from their territories. Other hydatid programmes implemented in South America (Argentina, Chile, Uruguay), in Europe (mid-Wales, Sardinia) and in East Africa (northwest Kenya), showed varying degrees of success, but some were considered as having failed. Reasons for the eventual success of certain hydatid control programmes and the problems encountered in others are analysed and discussed, and recommendations for likely optimal approaches considered. The application of new control tools, including use of a hydatid vaccine, are also considered.

Control of Taenia solium cysticercosis/taeniosis

Cysticercosis is emerging as a serious public health and agricultural problem in many poorer countries of Latin America, Africa, and Asia. Caused by the pork tapeworm, Taenia solium, this zoonotic disease forms larval cysts in humans and pigs that can lead to epilepsy and death in humans, reduces the market value of pigs and makes pork unsafe to eat. It occurs where pigs range freely, sanitation is poor, and meat inspection is absent or inadequate, and is thus strongly associated with poverty and smallholder farming. Although theoretically easy to control and declared eradicable cysticercosis remains neglected in most endemic countries due to lack of information and awareness about the extent of the problem, suitable diagnostic and management capacity, and appropriate prevention and control strategies. Human neurocysticercosis occurs when the larval cysts develop in the brain. It is considered to be the most common parasitic infection of the human nervous system and the most frequent preventable cause of epilepsy in the developing world. Thus far the infection has not been eliminated from any region by a specific program, and no national control programs are yet in place. We consider the tools available for combating cysticercosis and suggest simple packages of interventions, which can be conducted utilizing existing services and structures in the endemic countries to provide appropriate and sustainable control of the disease.

Ultrasonographic screening for cystic echinococcosis in sheep in Tunisia

Sheep from the areas of Fondouk-Jeddid, Bir Mchergua and El Fahs, located in the Northeast of Tunisia, were examined by ultrasonography between 2001 and 2004 in order to assess their infection with Echinococcus granulosus, the agent of hydatid disease, and to evaluate this method as an efficient aire for hydatid cysts. A total of 1039 sheep, aged between 1 and 14 years was examined. The highest prevalence was found in sheep aged more than 8 years. The least infected animals were aged between 1 and 2 years. All hydatid cysts detected by ultrasound were located in the liver. In all age-groups, the dead cysts were more numerous than viable cysts. Eighteen positive sheep were autopsied and a comparison between ultrasound and autopsy results was performed. The results showed a prevalence of about 40% for the three areas. Ultrasonography allowed the cysts, deep or superficial to localize in the central or left part in relation to the caudal vena cava of the animals. Consequently, all the cysts were not detected with this technique. This work shows that ultrasonography confirms the importance of ovine hydatid cyst in Tunisia and that its use as a mass screening approach for cystic echinococcosis in sheep could be helpful for the monitoring of this disease in a hydatid control program without great stress for the animals.

Pasture types and Echinococcus multilocularis, Tibetan communities

Our study showed that open pastures had more small mammal burrows than fenced pastures in Tibetan pastoralist communities in 2003. This characteristic was linked to a higher prevalence of Echinococcus multilocularis in dogs and indicates that pasture type may affect E. multilocularis transmission.

Taenia solium: the complex interactions, of biological, social, geographical and commercial factors, involved in the transmission dynamics of pig cysticercosis in highly endemic areas

If a programme for the control of pig cysticercosis is to be effective it has to be based on good data on the local epidemiology of Taenia solium. In 2002-2003, in a cross-sectional study of pig cysticercosis in the Mexican state of Morelos, 1747 pigs that had been born and reared in rural areas of the state were checked for T. solium infection by tongue inspection. The prevalence of cysticercosis in the pigs was found to vary from 0% to 30% according to the municipality from which the pigs came. Although prevalence appeared to be unaffected by the socio-economic status of the municipality, it was relatively high in areas that lacked latrines, and in pigs that were castrated, pregnant and/or of the native (rather than an imported) breed. The results of questionnaire-based interviews with pig owners revealed that most (64.5%) of the rural pigs, whether infected or not, are slaughtered and consumed within the locality where they were reared. The other pigs are sold at low prices to organised traffickers who take the uninspected pigs to neighbouring urban areas for sale. The observed complexity in the factors affecting the transmission of T. solium to the pigs of Morelos state calls for an intervention strategy of matching complexity, initially targeted at those villages with the highest prevalences of pig cysticercosis. The road transport of pigs needs to be better regulated, and the vaccination and genetic improvement of the rural pigs, and delaying the castration of the boars, should all be considered.

Molecular Confirmation of a Case of Multiorgan Cystic Echinococcosis

We report on the results of radical surgery performed on a 10-yr-old Chinese female with multiple echinococcosis lesions and the diagnosis of the infection by imaging, histology, serology, and DNA analysis. Molecular genotyping provided unequivocal proof that the patient was infected with Echinococcus granulosus, the cause of cystic echinococcosis.

Recent advances in characterization of Echinococcus antigen B

Antigen B (AgB) in hydatid cyst fluid of Echinococcus granulosus is a polymeric lipoprotein of 160 kDa and a highly immunogenic major antigen in echinococcal infection. The antigen is comprised of a group of subunit monomers of approximately 8 kDa in molecular size. Recent studies have revealed that the E. granulosus AgB (EgAgB) shows a high degree of genetic variability and the genes encoding the EgAgB 8-kDa subunit monomers that have been identified to date could be grouped into four clades, corresponding to the genes EgAgB8/1, EgAgB8/2, EgAgB8/3 and EgAgB8/4. It has been suggested that the recombinant EgAgB8/2 (rEgAgB8/2) provides better performance in serodiagnosis of human cystic echinococcosis (CE) than does the recombinant EgAgB8/1 (rEgAgB8/1). The EgAgB has been identified as a protease inhibitor with an ability to inhibit recruitment of neutrophils and exploit activation of T helper cells by eliciting a non-protective Th2 cell response, predominantly in patients with progressive CE. Recently it has been revealed that AgB also exists in the cyst fluid of Echinococcus multilocularis. Five different cDNAs encoding the EgAgB homologues have been identified in vesicles, protoscoleces and/or immature adult worms of E. multilocularis and named as EmAgB8/1, EmAgB8/2, EmAgB8/3, EmAgB8/4 and EmAgB8/5. These genes appeared to be expressed in a developmentally regulated manner in the parasite life cycle. This review focuses on recent advances in molecular biological and immunological characterization of AgB from both of E. granulosus and E. multilocularis.

Veterinary public health activities at FAO: Cysticercosis and echinococcosis

In many developing and transition countries, parasitic zoonoses such as cysticercosis and echinococcosis cause serious human suffering and considerable losses in agricultural and human productivity, thus posing a significant hindrance to their development. Although, effective and reliable tools for the diagnosis, prevention and control of parasitic zoonoses are now available, their implementation has not always been successful in many countries. This is primarily due to the lack of awareness on the presence or impact of the causing parasites (Taenia saginata, Taenia solium and Echinococcus spp.). In addition, often the needed intersectorial cooperation, resource management and political commitment for their control are (also) absent. FAO's regular programme has established a global network of professionals directly involved in zoonotic and food-borne diseases. The network provides a basic framework for the spread of information related to the diagnosis, prevention and control of major zoonotic diseases including cysticercosis and echinococcosis.

Role of chemotherapy of taeniasis in prevention of neurocysticercosis

Neurocysticercosis (NC) is a serious public health problem in Taenia solium endemic areas and in some immigrants and international travelers. A key intervention in preventing NC is elimination of taeniasis by chemotherapy. Currently, two safe and effective taenicides, namely niclosamide and praziquantel, are available. Both are on WHO Essential Drug list, but are often inaccessible in T. solium endemic areas. Natural remedies, still widely used in some endemic areas, are frequently carcinogenic or highly toxic and as such should be discontinued. Chemotherapeutic intervention to control T. solium taeniasis/cysticercosis, whilst theoretically feasible, has several practical obstacles. These include poor public awareness, problems with diagnosing Taenia carriers, poor availability of taenicides where needed and low priority afforded to the control of NC. These can be overcome, respectively, by effective health education, wider use of newly developed coproantigen tests, strengthening of health services infrastructure and essential drugs distribution, and increasing the priority given to prevention of NC, as a leading cause of epilepsy in T. solium endemic areas. Information is accumulating on rational approaches to population-based short-term chemotherapeutic control measures. These are: widely available modern diagnostic tools and taenicides, treatment of any case of taeniasis, confirmed or probable, focus-oriented chemotherapy, irrespective of Taenia species implicated, improved sanitation, cooperation of veterinary and medical services, linkage with programs against epilepsy and cooperation of better educated communities. Now, it remains to take an advantage of existing tools and experience.

Brief historical remarks as an introduction for the international symposium on taeniasis/cysticercosis and echinococcosis

Some historical remarks are made on the background information leading to the international symposium on taeniasis/cysticercosis and echincoccosis with focus on Asia and the Pacific.

Epidemiology of human alveolar echinococcosis in China

Globally human alveolar echinococcosis (AE) is a rare zoonotic helminthic disease confined to the Northern Hemisphere as sporadic infections in rural populations, principally in some areas of North America, west-central Europe, the Near East, Siberia, Central Asia, Japan and China. In China the first human cases were reported from western regions in the 1960s, but most hospital records remain fragmented and inadequate. From the mid-1990s mass screening surveys using portable ultrasound scanners recorded higher prevalences (up to 6% by county) than in any other areas of the world with some village rates as high as 15%. Risk factors identified for AE cases included ethnicity, sex, age and occupation. The role of the dog in transmission of Echinococcus multilocularis to humans now appears to be significant and may be one of the most important risk factor, in combination with landscape/land-use features conducive to maintaining wildlife host populations.

Control of Taenia solium taeniasis/cysticercosis: From research towards implementation

Theoretically, considering the biology of its transmission and reservoirs, global eradication of Taenia solium taeniasis and cysticercosis is feasible. Recently much progress has been made in research on diagnosis, treatment and prevention of human taeniasis and porcine cysticercosis, although more operational research is still needed. In spite of this, global eradication of T. solium infection is still unlikely in the near future. Major obstacles to practical implementation of control measures include low levels of sanitation and health education amongst endemic populations, ineffective health services infrastructure and inadequate socioeconomic development in these areas. The continued public health impact of neurocysticercosis, especially fatalities and epilepsy, force us to identify improved options for control. In order to implement control measures in highly endemic areas the active involvement of medical services in controlling T. solium infection and more effective collaboration between medical and veterinary services is necessary. A switch is suggested from total reliance on meat inspection to active diagnosis and treatment of human taeniasis, protection of pigs against infection, promotion of health education and improved surveillance preparing chemotherapeutic and/or sanitary interventions. This could be implemented in areas where active transmission causes substantial morbidity and mortality provided there is the political will, social support, better financing and an effective organizational framework.

Evaluation of clinical and serological data from Taenia solium cysticercosis patients in eastern Inner Mongolia Autonomous Region, China

Neurocysticercosis (NCC) is one of the major causes of neurological disease in China. ELISA and immunoblotting using glycoproteins purified by preparative isoelectric focusing were used to detect human cysticercosis in Tongliao area, Inner Mongolia, China in 1998. Approximately 89% (39 of 44 inpatients and outpatients with suspected NCC at Tongliao City Hospital) were residents of Inner Mongolia. About 53% were male and 77% were of working age (18-59 years), and 32% were farmers. Immunoblotting and ELISA showed a high correlation. Of the 44 patients, 31 positive by cerebral computed tomography (CT) scan were confirmed serologically to have cysticercosis. In the ELISA, patients with no lesions by CT scan had lower OD values, similar to those of normal serum. These findings confirm that both ELISA and immunoblotting assays are sufficiently sensitive to detect asymptomatic or symptomatic cysticercosis patients.

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.

Echinococcosis: disease, detection and transmission

Echinococcosis is one of the world's most geographically widespread parasitic zoonoses, with transmission occurring in tropical, temperate and arctic biomes. Most human infections are due to Echinococcus granulosus transmitted between domestic dogs and livestock, but this cosmopolitan species also cycles between wild carnivores (principally canids) and wild ungulates. The other species with significant zoonotic potential is E. multilocularis that occurs naturally in fox definitive hosts and small mammal intermediate hosts. These two species cause human cystic or alveolar echinococcosis respectively, which may be considered serious public health problems in several regions including developed countries. This review provides an introductory overview to the Supplement and summarises the biology and epidemiology of these two related cestodes with an emphasis on applied aspects relating to detection, diagnosis and surveillance in animal and human populations, and includes aspects of transmission ecology, and also considers aspects of community epidemiology and potential for control.

Epidemiology of alveolar echinococcosis with particular reference to China and Europe

Human alveolar echinococcosis (AE), caused by the metacestode of the fox tapeworm Echinococcus multilocularis, is the most pathogenic zoonosis in temperate and arctic regions of the northern hemisphere. Prospective collection of human cases in some areas and mass screenings using ultrasound imaging and confirmation with serological techniques have markedly improved our knowledge of the epidemiology of the disease in humans during the past two decades. Transmission occurs when eggs of the tapeworm, excreted by the final hosts (usually foxes but also dogs, wolves and cats), are ingested accidentally by humans or during normal feeding by a variety of rodents and small lagomorphs. However, the species of host animals differ according to regional changes in mammalian fauna. This review mostly focuses on epidemiology of alveolar echinococcosis in those parts of the world where new and more accurate epidemiological data are now available, i.e. China and Europe, as well as on new epidemiological trends that can be suspected from recent case reports and/or from recent changes in animal epidemiology of E. multilocularis infection. The People's Republic of China (PRC) is a newly recognized focus on AE in Asia. Human AE cases were firstly recognized in Xinjiang Uygur Autonomous Region and Qinghai Provinces at the end of 1950s and infected animals were first reported from Ningxia in central China and northeast of Inner Mongolia in the 1980s. E. multilocularis (and human cases of AE) appears to occur in three areas: (1) Northeastern China (northeast focus): including Inner Mongolia Autonomous region and Heliongjiang Province (2) Central China (central focus): including Gansu Province, Ningxia Hui Autonomous Region, Sichuan Province, Qinghai Province and Tibet Autonomous Region and (3) Northwestern China: including Xinjiang Uygur Autonomous Region, bordered with Mongolia, Russia, Kazakhstan and Kyrgyzstan. The highest prevalence of the disease, up to 15 per cent of the population in some villages, is reached in China. In Europe, data from the European Echinococcosis Registry (EurEchinoReg: 1982-2000) show 53 autochthonous cases of AE in Austria, 3 in Belgium, 235 in France, 126 in Germany, 1 in Greece, and 112 in Switzerland, and 15 'imported' cases, especially from central Asia; 14 cases were collected in Poland, a country not previously considered endemic for AE. Improved diagnostic technology, as well as a real increase in the infection rate and an extension to new areas, can explain that more than 500 cases have been reported for these 2 decades while less than 900 cases were published for the previous 7 decades. New epidemiological trends are related to an unprecedented increase in the fox population in Europe, to the unexpected development of urban foxes in Japan and in Europe, and to changes in the environmental situation in many countries worldwide due to climatic or anthropic factors which might influence the host-predator relationship in the animal reservoir and/or the behavioural characteristics of the populations in the endemic areas.

Molecular cloning, expression, and serological evaluation of an 8-kilodalton subunit of antigen B from Echinococcus multilocularis

Full-length cDNA and genomic DNA encoding an 8-kDa subunit of antigen B from Echinococcus multilocularis (designated EmAgB8/1) were isolated from an E. multilocularis metacestode cDNA library and a protoscolex genomic DNA library, respectively. The open reading frame of the cDNA clone encodes a polypeptide comprising 85 amino acids with a 20-amino-acid NH(2)-terminal signal sequence, which was confirmed following N-terminal sequencing of the native antigen. Reverse transcription-PCR analysis revealed that the clone encoding EmAgB8/1 is predominantly transcribed in larval E. multilocularis. The gene consists of two exons (encoding the signal sequence and mature protein) separated by a 91-bp intron. The mature form was expressed in Escherichia coli, and its antigenic reactivity was compared with that of a counterpart, an 8-kDa subunit of antigen B from Echinococcus granulosus (EgAgB8/1) by Western blotting and enzyme-linked immunosorbent assay (ELISA) with serum samples from patients confirmed to have cystic echinococcosis (CE) and alveolar echinococcosis (AE). Recombinant EmAgB8/1 showed positive reactions in Western blots with 81.3% (65 of 80) of serum samples from CE patients and 40.6% (26 of 64) of serum samples from AE patients, while recombinant EgAgB8/1 showed positive reactions with 86% (43 of 50) and 42% (19 of 45) of the serum samples from these CE and AE patients, respectively. By the ELISA, both EmAgB8/1 and EgAgB8/1 exhibited similar positive reactions with 88% (44 of 50) of serum samples from CE patients and 37.8% (17 of 45) serum samples from AE patients. Statistical analysis revealed that the sensitivity of EmAgB8/1 was comparable to that of EgAgB8/1 for the serodiagnosis of echinococcal diseases. There was no cross-reaction with sera from patients with cysticercosis, which often cross-react when native antigens are used for serodiagnosis.

DNA differential diagnosis of taeniasis and cysticercosis by multiplex PCR

Multiplex PCR was established for differential diagnosis of taeniasis and cysticercosis, including their causative agents. For identification of the parasites, multiplex PCR with cytochrome c oxidase subunit 1 gene yielded evident differential products unique for Taenia saginata and Taenia asiatica and for American/African and Asian genotypes of Taenia solium with molecular sizes of 827, 269, 720, and 984 bp, respectively. In the PCR-based detection of tapeworm carriers using fecal samples, the diagnostic markers were detected from 7 of 14 and 4 of 9 T. solium carriers from Guatemala and Indonesia, respectively. Test sensitivity may have been reduced by the length of time (up to 12 years) that samples were stored and/or small sample volumes (ca. 30 to 50 mg). However, the diagnostic markers were detected by nested PCR in five worm carriers from Guatemalan cases that were found to be negative by multiplex PCR. It was noteworthy that a 720 bp-diagnostic marker was detected from a T. solium carrier who was egg-free, implying that it is possible to detect worm carriers and treat before mature gravid proglottids are discharged. In contrast to T. solium carriers, 827-bp markers were detected by multiplex PCR in all T. saginata carriers. The application of the multiplex PCR would be useful not only for surveillance of taeniasis and cysticercosis control but also for the molecular epidemiological survey of these cestode infections.

Echinococcosis on the Tibetan Plateau: prevalence and risk factors for cystic and alveolar echinococcosis in Tibetan populations in Qinghai Province, China

Infections by larval stages of tapeworms of the genus Echinococcus (echinococcosis or hydatid disease) are zoonotic infections of major public health importance throughout much of the world. Humans become infected through accidental ingestion of eggs passed in faeces of canid definitive hosts. Tibetan populations of China have some of the highest documented levels of infections by both Echinococcus granulosus and E. multilocularis, the causes of cystic and alveolar echinococcosis, respectively. In this study we measured the prevalence of cystic (CE) and alveolar (AE) echinococcosis disease in Tibetan communities in Qinghai, Province, China, and identified putative risk factors for both infections in these communities. 3703 volunteers in three predominately Tibetan counties of Qinghai were surveyed between June 1997 and June 1998. Parasitic lesions were diagnosed by imaging of characteristic space-occupying lesions in abdominal organs (ultrasound) or the lungs (radiographs). Specific serodiagnostic assays (Dot-ELISA and Em2-ELISA) were performed on sera of positively imaged subjects to further distinguish the disease agent. All participants completed a questionnaire documenting age, sex, education level, occupation, lifestyle (nomadic or settled), slaughter practices, drinking water source, hygienic practice and association with dogs. Data were analyzed using SAS version 8. 6·6% of the volunteers had image-confirmed infection with E. granulosus (CE) and 0·8% had E. multilocularis (AE) infection. The significant univariate factors for echinococcal infection (both CE and AE) included livestock ownership, Tibetan ethnicity, female gender, low income, herding occupation, limited education, water source, age greater than 25 years old, poor hygienic practices, offal disposal practices and dog care. Multivariate analysis revealed that livestock ownership was a significant risk factor for both forms of the disease, as well as age greater than 25 years, female gender, herding occupation, and being nomadic (vs semi-nomadic or settled). No additional significant risk factors were identified among the 344 nomadic participants. Being female and being older than 25 years of age were significant factors among the 1906 semi-nomadic participants. Among the 1445 settled participants, allowing dogs to sleep indoors was statistically significant. Issues such as inadequate assessment of animal ownership, selection bias, disease misclassification, and loss of information may have led to reduction in strength of some risk factor associations and need to be addressed in future epidemiologic analysis of echinococcosis in this population.

Perspective on control options forEchinococcus multiloculariswith particular reference to Japan

Following a brief introduction of recent advances in molecular and immunological technology for detection of persons and animals infected withEchinococcus multilocularisand an overview of the current situation of alveolar echinococcosis (AE) in Japan, perspectives on control options are discussed with reference to different epidemiological situations. AE is considered the most serious parasitic zoonosis in temperate and arctic regions of the northern hemisphere. The number of human cases differs drastically among regions. While high numbers of patients are apparently associated with highE. multilocularisprevalence in domestic dogs, e.g. in parts of Alaska and western China, the number of cases is moderate or low in areas where the parasite is mainly transmitted by wild canid species (e.g. in central Europe or temperate North America). However, the severity of the disease, the absence of curative treatment for most cases, the high cost of long-term chemotherapy and the anxiety caused for the population in highly endemic areas call for the development of preventive strategies even in regions where human AE is rare. Furthermore, in view of (1) drastically increasing numbers and infection rates of foxes involved in transmission ofE. multilocularis, and (2) increasingly close contact between humans and foxes e.g. in Europe and Japan, there is considerable concern that AE incidences may in future increase in these regions. Control options depend on a variety of factors including the species of canid principally responsible for transmission and the socio-economic situation in the region. Where domestic dogs (stray or owned) are the principal hosts forE. multilocularis, control options can include those applicable toE. granulosus, i.e. reduction of the number of stray dogs, registration and regular preventive chemotherapy of owned dogs, and information campaigns for the population promoting low-risk behaviour for man and dogs. WhereE. multilocularisis mainly transmitted by wild canids, the situation is far more difficult with preventive strategies still being in trial stage. Integrated control measures could include prevention information campaigns, restricting access of pet animals (dogs and cats) to rodents, chemotherapy of foxes on local or regional scales, and strategies to minimize contacts between people and foxes.

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.

Echinococcosis

Echinococcosis is a near-cosmopolitan zoonosis caused by adult or larval stages of cestodes belonging to the genus Echinococcus (family Taeniidae). The two major species of medical and public health importance are Echinococcus granulosus and Echinococcus multilocularis, which cause cystic echinococcosis and alveolar echinococcosis, respectively. Both are serious and severe diseases, the latter especially so, with high fatality rates and poor prognosis if managed incorrectly. Several reports have shown that both diseases are of increasing public health concern and that both can be regarded as emerging or re-emerging diseases. In this review we discuss aspects of the biology, life cycle, aetiology, distribution, and transmission of the Echinococcus organisms, and the epidemiology, clinical features, treatment, and diagnosis of the diseases they cause. We also discuss the countermeasures available for the control and prevention of these diseases. E granulosus still has a wide geographical distribution, although effective control against cystic echinococcosis has been achieved in some regions. E multilocularis and alveolar echinococcosis are more problematic, since the primary transmission cycle is almost always sylvatic so that efficient and cost-effective methods for control are unavailable.

Immunodiagnostic and molecular approaches for the detection of taeniid cestode infections

This article summarizes the most recent advances in techniques and applications for the detection of taeniid cestode-infected persons or animals. In addition, the use of molecular approaches for strain identification and control of parasite transmission is discussed.

Evaluation of use of recombinant Em18 and affinity-purified Em18 for serological differentiation of alveolar echinococcosis from cystic echinococcosis and other parasitic infections

To further evaluate recombinant Em18 antigen (rEm18) for immunodiagnosis of human alveolar echinococcosis, 208 serum samples were examined by enzyme-linked immunosorbent assay (ELISA). To comparatively assess the results of rEm18-ELISA, ELISA and immunoblot analysis with two affinity-purified native antigens were also performed with 45 selected serum samples. The results indicate that rEm18 is highly useful for serodiagnosis.

The control of human (neuro)cysticercosis: which way forward?

Taenia solium cysticercosis, and its public health and economic consequences, appears to be a growing problem in poor areas of Africa, Asia and Latin America where people eat pork and traditional pig husbandry is practiced (and expanding). Its burden is counted in terms of human disease (mainly neurocysticercosis related epilepsy) and economic losses, in a context of both commercial and traditional subsistence pig farming. Although substantial fragmentary information seems to be available from local settings, national and global burdens due to T. solium cysticercosis are still to be comprehensively assessed. With regard to control, several strategies have been checked out at a small or medium scale and have proven to be successful. Yet, no intervention programmes have been implemented so far at the national level with proven success. Although T. solium cysticercosis is considered to be a potentially eradicable disease, there is no evidence yet that it is feasible and recommendable to envisage this within a reasonable time frame. However, it appears realistic to aim for the rapid definition of a simple package of interventions, which can routinely be carried out by existing services and structures, and will give an optimal, long-term return in terms of burden relief. Also, a number of international initiatives and opportunities currently exist in which a more pro-active attitude towards the control of T. solium cysticercosis can be integrated and promoted. Commitment of both national and local authorities to control the disease needs to be convincingly solicited and, as for most zoonotic diseases, an interdisciplinary approach is essential.

Serologic and molecular diagnosis of zoonotic larval cestode infections

Neurocysticercosis, cystic echinococcosis and alveolar echinococcosis are the three major zoonotic larval cestodiases worldwide and threatening human life. Early therapeutic treatment based on early differential diagnosis at the early stage of infection and epidemiological surveillance with the expectation for control and prevention are the keys for improvement of quality of human life. Recent advances in (1). differential serodiagnosis of these three diseases, (2). molecular identification of human taeniid species and (3). polymorphism of mitochodrial DNA highly informative for future molecular epidemiology are reviewed in this article.

Evaluation of an enzyme-linked immunosorbent assay (ELISA) with affinity-purified Em18 and an ELISA with recombinant Em18 for differential diagnosis of alveolar echinococcosis: results of a blind test

Alveolar echinococcosis (AE) is the most potentially lethal parasitic zoonosis of the nontropical areas in the northern hemisphere, where cystic echinococcosis (CE) is also endemic. Both AE and CE are highly endemic in China, and both serologic detection of echinococcosis, either AE or CE, and differentiation of AE from CE are crucial problems. Evaluation of Western blot analysis (WB) and enzyme-linked immunosorbent assay (ELISA) for the Em18 antigen, using affinity-purified and recombinant Em18, was carried out "blindly" using 60 human sera from patients diagnosed in France. The results were compared with those obtained using a commercially available Echinococcus WB immunoglobulin G (IgG) kit developed in France. The Em18 WB and Echinococcus WB IgG showed very similar results for detection of AE. Both affinity-purified Em18 or a recombinant Em18 WB and Echinococcus WB IgG seem useful for identification of AE, and the latter seems appropriate for both AE and CE, whereas affinity-purified Em18 ELISA and the newly developed recombinant Em18 ELISA appear to be suitable for detection of AE, especially for epidemiological surveys.