Tapeworms (cestodiasis)

Nearly all of the cestodes, or tapeworms (class Cestoda in the phylum Platyhelminthes, the flatworms), are parasitic as adults in the intestinal tract of vertebrates. This article discusses the epidemiology, diagnosis, and treatment of taeniasis, diphyllobothriasis, hymenolepiasis, dipylidiasis, and other tapeworm infections.

Seroprevalence of cysticercosis in an Orthodox Jewish community

Neurocysticercosis cases were identified in 1991 in an Orthodox Jewish community. Transmission was linked to tapeworm-infected immigrant housekeepers from countries where Taenia solium is endemic. To evaluate the extent of and risks for locally acquired cysticercosis, a seroprevalence survey was conducted in 9% of the households in this community. Cysticercosis antibodies were detected in 23 (1.3%) of 1,789 persons from 612 families. All 23 seropositive persons were asymptomatic, and no intracerebral lesions were found for the 21 seropositive persons who underwent brain imaging. Seropositivity was associated with female sex (relative risk [RR] = 2.45, P = 0.049), hiring a domestic worker for child care duties (RR = 3.79, P = 0.05), and with employees from Central America (RR = 2.70, P = 0.0001). Exposure to T. solium in this community is unexpectedly high. Widespread employment of domestic workers from endemic regions and high employee turnover contributes to exposure risk.

Em18, a new serodiagnostic marker for differentiation of active and inactive cases of alveolar hydatid disease

We determined whether detection of antibody response against a newly detected epitope, designated Em18, among Echinococcus multilocularis antigens could be a reliable marker for differentiation of active cases of alveolar hydatid disease (AHD) from inactive cases. Fifteen Alaskan patients with either active or inactive lesions of AHD previously confirmed clinically, pathologically, and serologically by the Em2-enzyme-linked immunosorbent assay (ELISA) were used for a blind test by Western blotting. Ten and five cases were considered to be active and inactive cases, respectively. One of the 10 cases classified serologically as active was judged to be inactive based on clinical and pathologic criteria; the patient had a recognizable parasitic lesion, and following short-term treatment with albendazole, a biopsy of the liver showed a degenerated lesion that did not grow in rodents. The five cases judged to be inactive included two confirmed inactive cases with cicatrized lesions and three active cases that showed the weakest values in the Em2-ELISA. The most predominant IgG subclass responding to Em18 was IgG4. In general, there were good correlations between 1) the antibody response against Em18 and the presence of active lesions and 2) the antibody response against Em18 and the Em2-ELISA values.

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.

Echinococcal disease

Diagnosis of infection by the larval stages of Echinococcus granulosus, E. multilocaris, and E. vogeli, has increased in most parts of the world because of improved diagnostic technology, active surveillance, and increasing rates of transmission. Specific immunodiagnostics and sophisticated imaging techniques have made diagnosis more sensitive and specific. Surgery, performed by an experienced team with adequate postoperative support, remains the mainstay of therapy; however, alternative treatments, including chemotherapy and percutaneous cyst drainage, are used increasingly to aid in the management of inoperable echinococcal disease and, in some cases, for primary therapy. This article incorporates data from widely disparate sources and attempts a summary of the state-of-the-art diagnosis and treatment of echinococcal disease.

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.

Cysticercosis surveillance: locally acquired and travel-related infections and detection of intestinal tapeworm carriers in Los Angeles County

A surveillance system for cysticercosis was initiated in January 1988 in Los Angeles County to measure the incidence of the disease, to more accurately assess the level of locally acquired and travel-related infection, and to evaluate household contacts for intestinal tapeworm infection. In three years of surveillance (1988-1990), 138 incident cases were reported for an average crude annual incidence rate of 0.6 per 100,000 population. The highest rates were among Hispanics (1.6/100,000), most of whom were Mexican immigrants. Eight (5.8%) cases were fatal. Nine (6.5%) probable travel-associated cases occurred among persons born in the United States who had traveled to Mexico. Ten (7.2%) autochthonous cases of cysticercosis were documented. Taenia eggs were recovered more commonly in specimens from contacts with cysticercosis cases (1.1%) than in specimens from noncontact patients (0.2%). At least one Taenia tapeworm carrier was found among contacts of five (6.9%) of 72 cysticercosis patients. Carriers were more likely to be found among contacts of patients born in the United States (22.2%) than among those of foreign-born (4.8%) patients (odds ratio = 5.4) Cysticercosis causes appreciable morbidity and mortality in Los Angeles County, principally among Hispanic immigrants. However, these results indicate that both travel-acquired and locally acquired cysticercosis may be more common than previously recognized. Public health followup of cysticercosis cases, including screening of household contacts, can identify tapeworm carriers, who can be treated and removed as potential sources of further infection.

Parasiticidal effect of chemotherapy in alveolar hydatid disease: review of experience with mebendazole and albendazole in Alaskan Eskimos

Evidence that the larval stage of Echinococcus multilocularis in humans is killed by chemotherapy is presented in a review of our 17-year experience with treatment of alveolar hydatid disease in Alaska. The efficacy of chemotherapy was assessed with use of an in vivo assay of parasite viability by means of inoculation of voles, immunohistochemical tests, and histopathologic findings. Of 14 tests performed for nine patients, 12 in vivo assays (86%) were negative after chemotherapy, while only two (17%) of 12 vole tests for seven untreated patients were negative. Regression of arrest of growth of metastatic and primary hepatic lesions, together with their partial-to-complete calcification and prolonged survival times has been observed among patients treated with the benzimidazole compounds. For six who received appropriate chemotherapy, treatment has been discontinued for an average of 4.6 years (range, 3-7 years) without an increase lesion size or other evidence of reactivation.

A trichinosis outbreak among Southeast Asian refugees

The number of cases of trichinosis reported to Centers for Disease Control has declined steadily, with an average of only 44 cases per year from 1984 through 1988. This decline was almost entirely due to a reduction in cases acquired from ingestion of fresh commercial pork. However, from July 21 through September 3, 1990, 90 (72%) of 125 Southeast Asian refugees from six states and Canada developed trichinosis after attending or eating pork sausage taken from a wedding held in Des Moines, Iowa, on July 14, 1990. Eating uncooked sausage prepared at home from commercially obtained pork was associated with the development of this illness (odds ratio = 34.0, p less than 0.001). Analysis by amount of pork consumed was significant (Mann-Whitney U rank sum test, p less than 0.001). This outbreak of trichinosis in Iowa is the fourth reported within the last 15 years among the 900,000 Southeast Asian refugees resident in the United States and one of the largest reported outbreaks in US history. The continued presence of Trichinella spiralis in commercial pork emphasizes the need for further education and control measures for persons whose dietary habits place them at risk for developing trichinosis.

Prevalence and risk factors for Taenia solium taeniasis and cysticercosis in humans and pigs in a village in Morelos, Mexico

In a Mexican village in which Taenia solium infection was known to be endemic, we selected a cluster sample of 368 households (21% of the total) for demographic, environmental, and diagnostic surveys, and medical histories for taeniasis and cysticercosis. Coproparasitologic studies of 1,531 participants revealed infection by Taenia sp. in four (0.3%) individuals; however, 5.8% of the respondents reported a history of having passed tapeworm proglottids in feces. Of 1,552 human serum specimens, 10.8% tested positive in the cysticercosis immunoblot assay. Seropositivity increased with age and reached a maximum in subjects ages 46-55 years. Risk factors associated with seropositivity included a history of passing tapeworm proglottids, frequent consumption of pork, and poor personal and household hygiene (P less than 0.05). A history of seizures was also significantly associated with seropositivity (P less than 0.05); approximately one-third of persons with such histories were seropositive. Of 571 pigs examined by tongue inspection, 23 (4.0%) had cysticerci; infection rates increased with the age of pigs, and were higher in pigs that habitually ran loose or were fed human feces (P less than 0.05). Goodness of fit analysis confirmed that seropositive persons (but not infected pigs) were significantly clustered within households, particularly, in households in which a member reported a history of having passed tapeworm proglottids. The results of this study have identified community behavioral and environmental practices that must be modified to prevent continued transmission of cysticercosis and taeniasis.

Seroepidemiologic study of toxocariasis and strongyloidiasis in institutionalized mentally retarded adults

Serologic surveys for Toxocara canis and Strongyloides sp., as well as stool examinations for intestinal parasites, were conducted in a home for mentally retarded adults. Evidence of parasitic infection was found in 30 (28.3%) of 106 residents; nine (8.5%) had positive toxocaral serology (enzyme-linked immunosorbent assay[ELISA]), 1 (0.9%) had positive serology for Stronglyoides sp. (ELISA), and 21 (19.8%) had parasites in stool (including Stronglyoides stercoralis in the patient with positive serology). Most of the residents with positive toxocaral serology lived in the same apartment and used to play with dogs. Parameters found to be significantly associated with positive toxocaral serology were pica behavior and eosinophilia (P less than 0.05). Mental retardation requiring institutionalization appears to be a risk factor for toxocariasis and other parasitic infections in adults as it is for children.

Epidemiologic observations on porcine cysticercosis in a rural community of Michoacan State, Mexico

The prevalence of and risk factors for Taenia solium infection (cysticercosis) in pigs were studied in a rural community in Michoacan State, Mexico. Visual inspection of the tongues of 216 pigs revealed cysticerci in 14 (6.5%). The prevalence was slightly higher in male (10/105) than female pigs (4/110) (P = 0.06) and increased with age (P less than 0.05). The most important risk factors for infection in pigs were access to human feces at a public washing area (P = 0.004), the presence of an indoor latrine (P = 0.05) and indiscriminate disposal of human feces around the pig owner's household (P less than 0.1). Effective and long-lasting control of the transmission of T. solium from humans to pigs must include measures to deny pigs access to human feces, a change which is likely to be resisted because of the traditional and functional aspects of established pig-rearing practices.

Current status of food-borne parasitic zoonoses in the United States

Although not a major public health problem, food-borne parasitic zoonoses in the United States are the cause of numerous diseases that occur widely in the population. The most common food-borne parasitic diseases in the United States are trichinosis, toxoplasmosis, taeniasis/cysticercosis, diphyllobothriasis, and anisakiasis. Since 1947, when the US Public Health Service began to record statistics on trichinosis cases in humans, the numbers of reported cases in the United States have declined markedly, from an average of about 400 with 10-15 deaths reported each year in the late 1940s, to an average of 57 per year with three deaths overall in the 5 years 1982-1986. Each year throughout the world, Toxoplasma gondii infects millions of persons, who contract it either by eating raw or poorly cooked meat from infected animals such as hogs or sheep or by ingesting soil contaminated with cat feces. In the United States between 400 and 10,000 infants are born each year with congenital toxoplasmosis. Toxoplasmic encephalitis, marked by dementia and seizures, has become the most commonly recognized cause of central nervous system opportunistic infection in AIDS patients. Intestinal taeniid tapeworm infection acquired in the United States is almost entirely caused by Taenia saginata, the beef tapeworm. Neurocysticercosis, caused by larvae of the pork tapeworm Taenia solium, is diagnosed in hundreds of persons in the United States every year. Nearly all patients are immigrants or travelers from Mexico and other disease-endemic areas. Diphyllobothriasis and anisakiasis both have increased in recent years in association with increasing popularity of raw fish dishes. Adequate prevention and control of food-borne parasitic zoonoses require continued and improved programs to educate consumers, producers and medical practitioners.

Laboratory diagnosis of cysticercosis

Human cysticercosis is caused by cystic tissue larvae of Taenia solium acquired by ingesting the eggs of the T. solium tapeworm. The diagnosis of human cysticercosis can be made by radiologic imaging, tissue biopsy, or serology. Radiologic imaging, including MRI and CT, currently is the most effective means for diagnosis.