Assessing the burden of Taenia solium cysticercosis and echinococcosis.

This collection of articles provides an account of the papers delivered at the 19th International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP)(held in New Orleans, LA, USA, from 10 to 14 August 2003) in a symposium session on assessing the burden of Taenia solium cysticercosis and echinococcosis organised and chaired by A. Lee Willingham III from the WHO/FAO Collaborating Center for Research and Training on Emerging and other Parasitic Zoonoses in Denmark and Peter M. Schantz from the Parasitic Diseases Division of the US Centers for Disease Control and Prevention, USA. The focus was on the persistence of the zoonotic parasitic diseases cysticercosis, caused by the pork tapeworm T. solium, and echinococcosis,caused by species of the tapeworm Echinococcus, and why these diseases are given very little attention on the national and international agendas in spite of the availability of tools to detect, treat,control and prevent them when it is quite clear in most instances that they are clearly associated with and help perpetuate poverty. A major reason for this is that in many endemic areas the presence and impact of these diseases are not known due to the lack of investigation and information thus policymakers are not aware of their burden and benefits of their control. Documentation is also needed to help increase awareness of the international community and hopefully result in financial and technical support being made available. Thus, burden assessments of cysticercosis and echinococcosis provide an essential evidence base for securing political will and financial and technical support as well as providing a basis for cost-benefit analysis of prevention and control efforts. In order to make an appropriate and full burden assessment one must consider the health, agricultural, social and other impacts of these parasitic zoonoses comprehensively. During the symposium presentations were given concerning current ongoing initiatives to assess the burden of cysticercosis and echinococcosis and examples of the impact of these diseases in both developing and developed countries were provided. In addition, cost factors related to vaccines for these cestode diseases were discussed and the possibilities for technical and financial support from multilateral agencies for assessments and interventions presented.

Proposed diagnostic criteria for neurocysticercosis.

Neurocysticercosis is the most common helminthic infection of the CNS but its diagnosis remains difficult. Clinical manifestations are nonspecific, most neuroimaging findings are not pathognomonic, and some serologic tests have low sensitivity and specificity. The authors provide diagnostic criteria for neurocysticercosis based on objective clinical, imaging, immunologic, and epidemiologic data. These include four categories of criteria stratified on the basis of their diagnostic strength, including the following: 1) absolute--histologic demonstration of the parasite from biopsy of a brain or spinal cord lesion, cystic lesions showing the scolex on CT or MRI, and direct visualization of subretinal parasites by funduscopic examination; 2) major--lesions highly suggestive of neurocysticercosis on neuroimaging studies, positive serum enzyme-linked immunoelectrotransfer blot for the detection of anticysticercal antibodies, resolution of intracranial cystic lesions after therapy with albendazole or praziquantel, and spontaneous resolution of small single enhancing lesions; 3) minor--lesions compatible with neurocysticercosis on neuroimaging studies, clinical manifestations suggestive of neurocysticercosis, positive CSF enzyme-linked immunosorbent assay for detection of anticysticercal antibodies or cysticercal antigens, and cysticercosis outside the CNS; and 4) epidemiologic--evidence of a household contact with Taenia solium infection, individuals coming from or living in an area where cysticercosis is endemic, and history of frequent travel to disease-endemic areas. Interpretation of these criteria permits two degrees of diagnostic certainty: 1) definitive diagnosis, in patients who have one absolute criterion or in those who have two major plus one minor and one epidemiologic criterion; and 2) probable diagnosis, in patients who have one major plus two minor criteria, in those who have one major plus one minor and one epidemiologic criterion, and in those who have three minor plus one epidemiologic criterion.

Hygiene and restraint of pigs is associated with absence of Taenia solium cysticercosis in a rural community of Mexico.

OBJECTIVE: To determine the prevalence and risk factors associated to pig cysticercosis in a rural community of Veracruz, Mexico. MATERIAL AND METHODS: Swine cysticercosis was diagnosed by tongue palpation and circulating antibodies in pigs kept in 178 household backyards. Risk factors were assessed by interviewing owners to collect information on pig breeding conditions and demographic characteristics. RESULTS: None of the 53 pigs studied showed cysts in the tongue, nor antibodies against Taenia solium in Western blot assays. Latrines were available in 91% of the houses and pigs were kept in restrained areas. CONCLUSIONS: The present study shows that pig breeding under restraint with basic hygiene and sanitary conditions, may be effective and practical interventions to restrain Taenia solium in rural communities.

Mass treatment against human taeniasis for the control of cysticercosis: a population-based intervention study.

An intervention study with mass treatment against taeniasis to prevent neurocysticercosis due to Taenia solium in a rural community in Mexico was performed in 1991-96. Information and biological samples were obtained at the beginning of the study, at 6 months and at 42 months after mass treatment with praziquantel at a single dose of 5 mg/kg. Prevalence rates of taeniasis were measured by the detection of Taenia coproantigens and Taenia eggs in faeces; neurocysticercosis was suggested by clinical data and by serum antibodies in humans and also in swine. A reduction of 53% after 6 months and of 56% after 42 months for human taeniasis was seen after treatment. Late-onset general seizures decreased 70%. Anti-cysticercus antibodies in the human population were reduced by 75% after 42 months. Antibodies in pigs also showed a significant reduction of 55% after 6 months. In conclusion, an impact of mass chemotherapy against taeniasis to control cysticercosis in the short and long term was demonstrated. Praziquantel for tapeworm treatment should not be given at doses lower than 10 mg/kg. Late-onset convulsive crisis and specific antibodies are good indicators of neurocysticercosis and of exposure to the parasite, respectively.

A population-based, case-control study of Taenia solium taeniasis and cysticercosis.

A two-phase study was conducted in a rural community in Honduras, to evaluate the association between neurocysticercosis (NCC) diagnosed by computed tomography (CT), epilepsy, seropositivity for antibodies to the cysticerci of Taenia solium [determined by enzyme-linked-immunoelectrotransfer-blot (EITB) assays], intestinal infection with this parasite, and various epidemiological factors. Of the 480 individuals studied in the first phase, 17% were seropositive and 2.5% supplied faecal samples which contained T. solium eggs. In the second phase, 148 individuals (74 of the seropositive subjects from the first phase and 74 matched controls from the seronegatives) underwent CT and neurological examinations. The CT results appeared normal in 110 (74%) of the 148, showed anatomical abnormality in seven (5%), and active or calcified lesions compatible with NCC in 31 (23% of the seropositives and 19% of the seronegatives). Only five of the latter had neurological symptoms (two being epileptics) and only five lived in households in which intestinal taeniasis had been detected. Subject age was significantly associated with NCC-compatible lesions but all the other factors investigated, including seropositivity, showed no significant association with the CT findings. The overall sensitivity of the EITB assays was found to be 55%. Taken together, the present results indicate that, even though it is a valuable tool in determining transmission levels in sero-epidemiological studies, the EITB assay should not be used to predict the existence of NCC or to estimate the prevalence of NCC. The results do provide further evidence that taeniasis and cysticercosis are widely prevalent in Honduras, and indicate that much larger studies of hyper-endemic communities may be necessary if the factors associated with the transmission of T. solium are to be elucidated.

Epilepsy and neurocysticercosis in an Andean community.

BACKGROUND: Taenia solium neurocysticercosis (NCC) has been documented as one of the major causes of epilepsy in developing countries. However, methodological limitations have hindered the evaluation of the epidemiological relationship between cysticercosis and epilepsy at the community level. METHODS: We used the WHO protocol for epidemiological evaluation of neurological disorders to conduct a door-to-door survey among 2723 residents of San Pablo del Lago, an Ecuadorean rural community in which T. solium taeniasis/cysticercosis was known to be endemic. The WHO protocol was complemented by neuroimaging and immunological tests to confirm the diagnosis of this infection. RESULTS: In all 31 people suffering from active epilepsy were detected (prevalence 11.4 per 1000, 95% CI:7.7-15.4); 26 agreed to undergo a computer tomography (CT) examination, and 28 agreed to have blood drawn for serodiagnosis. Fourteen of the 26 (53.8%) had CT changes compatible with NCC and six of the 28 (21.4%) tested positive in the enzyme-linked immunoelectro-transfer blot (EITB) assay. In a seizure-free random sample of this population, 17 of 118 (144 per 1000) subjects examined by CT and 10 out of 96 (104 per 1000) examined by EITB had evidence of this infection. The differences between the epilepsy group and the random sample of the population were statistically significant (OR = 6.93, 95% CI: 2.7-17.5, P < 0.001) for CT diagnosis, but not for EITB results (OR = 2.75, 95% CI: 0.8-7.1, P > 0.12, NS). CONCLUSIONS: These findings confirm that T. solium NCC is a significant cause of epilepsy at the community level in Andean villages of Ecuador. It is important to initiate effective public health interventions to eliminate this infection, which may be responsible for at least half of the cases of reported epilepsy in Ecuador.

[Epidemiology of cerebral cysticercosis in an Andean community in Ecuador]. / Epidémiologie de la cysticercose cérébrale dans une communauté des Andes en Equateur.

Taenia solium neurocysticercosis (NCC) has been documented to be an underlying cause of epilepsy, intractable headaches, hydrocephalus, dementia and other serious neurological conditions in many countries of Central and South America. However, methodological limitations had prevented the assessment of the true prevalence of this condition at the community level. We conducted a house-to-house neuroepidemiological survey of 6,118 residents of an Andean community. This information was used to target neuroimaging (CT-scan) and immunodiagnosis (enzyme-linked immunoelectrotransfer blot assay, EITB) tests in individuals suspected of harbouring Taenia solium NCC. In the rural population, NCC was confirmed in 8 out of 47 examined by CT-scan (17%) and in 6 of 42 examined by EITB (14%). In the urban population, NCC was confirmed in 35 of 147 examined by CT-scan (23.8%) and in 28 of 124 examined by EITB (22.6%). In a sample of relatives of patients with documented cerebral cysticercosis, 20 out of 81 examined by CT-scan (25%) and 12 of 79 (15%) examined by EITB had NCC. Finally, CT scans were performed for 83 school children from urban areas, and 9 (11%) were diagnosed as harbouring NCC. In a community-based study, cysticercosis appears to be much more frequent than initially thought, when CT examination is used as the "gold standard" for diagnosis.

Development and evaluation of a health education intervention against Taenia solium in a rural community in Mexico.

A comprehensive study was undertaken in a rural community in the state of Morelos, Mexico to evaluate health education as an intervention measure against Taenia solium. An educational program was developed to promote recognition and knowledge of the transmission of the parasite and to improve hygienic behavior and sanitary conditions that foster transmission. The effects of educational intervention were evaluated by measuring changes in knowledge and practices and prevalence of human taeniasis and swine cysticercosis before and after the campaign. The health education strategy was implemented with the active participation of the population based on the information obtained from a sociologic study. A questionnaire was designed and used before, immediately after the intervention, and six months later. Statistically significant improvements occurred in knowledge of the parasite, its life cycle, and how it is acquired by humans; however, changes in behavior related to transmission were less dramatic and persistent. The prevalences of cysticercosis in pigs at the start of the education intervention were 2.6% and 5.2% by lingual examination and antibody detection (immunoblot assay), respectively, and approximately one year after the intervention they were 0% and 1.2% (P < 0.05). These changes were accompanied by significant reductions in the reported access of pigs to sources of infection and freedom to roam. We conclude that health education, developed along with community involvement, reduced opportunities for transmission of T. solium in the human-pig cycle.

PIP: Neurocysticercosis is an important health problem in Mexico, as well as in many other countries of Latin America, Asia, and Africa where conditions permit completion of the cestode's life cycle in pigs and humans. A study was conducted in a rural community in the state of Morelos, Mexico, to determine whether health education could be an effective measure against Taenia solium. An educational program was developed with community input to promote recognition and knowledge of the transmission of the parasite and to improve hygienic behavior and sanitary conditions which foster transmission. The effects of the educational intervention were then assessed by measuring changes in knowledge, practices, and the prevalence of human taeniasis and swine cysticercosis before and after the campaign. Statistically significant improvements occurred with regard to knowledge of the parasite, its life cycle, and how it is acquired by humans. However, changes in behavior related to transmission were less marked and persistent. Lingual examination and antibody detection found cysticercosis among 2.6% and 5.2% of pigs, respectively, at the start of the intervention. At approximately 1 year after the intervention, prevalences had declined to 0% and 1.2%. The decline was accompanied by significant reductions in the reported access of pigs to sources of infection and freedom to roam.

Proposal of diagnostic criteria for human cysticercosis and neurocysticercosis.

Taenia solium cysticercosis is a major public health problem in several areas of the world. While the disease has a recognized etiologic agent, its definitive histological diagnosis is not possible in most cases because this parasite tends to lodge in cerebral tissues where routine biopsy is not feasible. Therefore, the diagnosis of human cysticercosis (and neurocysticercosis) should rest on the proper interpretation of the patients' symptoms together with data provided by radiological studies and immunologic tests for the detection of anticysticercal antibodies. Unfortunately, the pleomorphism of this parasitic disease creates confusion when non-specific clinical, radiological, or immunologic criteria alone are used to detect cases among populations or to diagnose hospitalized patients with neurological manifestations. We propose a chart of diagnostic criteria for human cysticercosis that objectively permit clinicians and health care workers to evaluate clinical, radiological, immunologic, and epidemiologic data of patients. The chart uses four degrees of criteria: absolute, major, minor, and epidemiologic, that were selected on the basis of their individual diagnostic strength. Interpretation of such criteria will result in three categories of diagnostic certainty: definitive, probable and possible, according to the likelihood that cysticercosis is present in a given person.

Parasitic infection in malnourished school children: effects on behaviour and EEG.

This paper describes a study of 194 children (aged 9-13) from a mountain village in Ecuador who were infected with one or more species of intestinal helminth or protozoan parasite. In addition to parasite load, the assessment consisted of a battery of psychological and neuropsychological tests, an EEG examination, measures of iodine level, presence of goitre and level of nutrition. We found that, in general, parasite infection, as measured at the baseline level, was not associated with cognitive impairment. The intensity of infection with A. lumbricoides, however, was correlated with the level of verbal ability and with inhibition-control aspects of cognitive behaviour. Multivariate analysis with level of nutrition, EEG status and parasite burden showed a consistent main effect of the degree of nutrition on neuropsychological performance, particularly the language, problem solving and inhibition-control dimensions.

Human subcutaneous Taenia solium cysticercosis in an Andean population with neurocysticercosis.

Subcutaneous involvement by the larval stages of the pork tapeworm Taenia solium in patients suffering from neurocysticercosis (neurocysticercosis) is well-described. It has been a clinical but undocumented impression that subcutaneous nodules are less common in cases of neurocysticercosis in Latin American than in Africa or Asia. We report on the absence of subcutaneous nodules found in a screened population of 2,891 residents of an Andean village in Ecuador with a prevalence rate for neurocysticercosis of 144 per thousand. Thirty-four patients with multiple intracranial calcifications and or cystic or encephalitic parenchymal lesions of neurocysticercosis were examined and questioned about subcutaneous nodules. Only one patient described nodules and this computed tomography plain films are presented. Several hypotheses are presented as to why nodules may be less common in this Andean community with a high prevalence of neurocysticercosis.

Community-based epidemiological investigations of cysticercosis due to Taenia solium: comparison of serological screening tests and clinical findings in two populations in Mexico.

We compared a plate enzyme-linked immunosorbent assay (ELISA) with an immunoblot--or enzyme-linked immunoelectrotransfer blot--assay (EITB) for the identification of cases of human neurocysticercosis due to Taenia solium and of risk factors for this disease in two Mexican villages. Findings related to age- and sex-specific seroprevalence, risk factors for transmission, and associated morbidity differed significantly according to the assay used. Rates of EITB positivity were significantly higher among persons with a history of convulsions than among those without such a history (29% vs 8%; P < .05); in contrast, ELISA results were negative for all persons with a history of convulsions. The association of seizures with neurocysticercosis in this population was strengthened by the higher rate of abnormal findings compatible with neurocysticercosis on computed tomography of the brain among individuals with a history of convulsions than among those without such a history (70% vs 14%; P < .001). In summary, EITB was more sensitive and specific than ELISA for epidemiological studies of neurocysticercosis.

Epidemiological investigation of Taenia solium taeniasis and cysticercosis in a rural village of Michoacan state, Mexico.

We performed a survey for taeniasis and cysticercosis among persons living in a Mexican village where Taenia solium infection in pigs was known to be enzootic. A standardized questionnaire was administered in all 577 households to obtain medical histories and information on demographic and environmental factors and on risk factors associated with transmission of infection. Serum and/or stool specimens were obtained from 1005 volunteers and examined for cysticercosis antibodies and intestinal parasites. Faecal examination of 828 participants revealed infection by Taenia sp. in 2 (0.2%). Three additional cases of taeniasis were detected in individuals who evacuated proglottids after treatment with praziquantel. Of 1005 human serum specimens, 49 (4.9%) were positive in the cysticercosis immunoblot assay. Seropositivity increased with age and reached a peak in subjects aged 46-55 years (P < 0.05). A history of seizures was significantly associated with seropositivity (P < 0.05); approximately 25% of persons with such histories were seropositive. Histories of headache, dizziness, trembling, blurred vision, and vomiting were also significantly associated with positive immunoblot assays. This study has demonstrated previously undiagnosed morbidity associated with T. solium neurocysticercosis and identified community behavioural and environmental practices that must be modified to prevent continued transmission of cysticercosis and taeniasis.

La erradicabilidad potencial de la teniasis y la cisticercosis / Taeniasis and cysticercosis control

Adaptado de una presentación a la 5a. Reunión del Grupo Internacional de Trabajo para la Erradicación de Enfermedades, Washington, D.C, marzo de 1992

Potential eradicability of taeniasis and cysticercosis

This contribution will also be published in Spanish in the Bol. Oficina Sanit. Panam. Vol. 116(6)

Neurocysticercosis in an Orthodox Jewish community in New York City.

BACKGROUND AND METHODS: From June 1990 through July 1991, intracerebral infection with the larval stage of the pork tapeworm Taenia solium was diagnosed in four unrelated persons in an Orthodox Jewish community in New York City. None of the patients had eaten pork, and only one had traveled to a country in which T. solium infection was endemic. We investigated this outbreak, screened serum samples from family members and household contacts for antibodies to cysticercosis, and examined stool specimens from household employees for eggs of taenia species. RESULTS: The four patients had recurrent seizures and brain lesions that were radiologically consistent with the presence of cysticerci. The diagnosis was confirmed in two patients by a brain biopsy, and in two by immunoblot assays for cysticercus antibodies. Of 17 immediate family members screened serologically, 7 from two families had cysticercus antibodies. Magnetic resonance imaging of the brain showed cystic lesions in two of the seropositive family members, one of whom had had a seizure. Examinations of six domestic employees from all four households revealed an active infection with taenia species in one and a positive serologic test in another. Since these women had recently emigrated from Latin American countries where T. solium infection is endemic, they were the most likely sources of infection in the members of these households. CONCLUSIONS: A diagnosis of neurocysticercosis should be considered in patients with seizures and radiologic evidence of cystic brain lesions, even in those who do not eat pork and who have not traveled to a country in which T. solium infection is endemic. Recent emigrants from countries in which T. solium infection is endemic should be screened for tapeworm infection in their stools before they are employed as housekeepers or food handlers.