Operational studies on the control of Taenia solium taeniasis/cysticercosis in Ecuador.

Operational studies on the control of Taenia solium taeniasis/cysticercosis in Ecuador M. Cruz,' A. Davis,2 H. Dixon,3 Z.S. Pawlowski,2 & J. Proanol A large-scale study in Loja and El Oro Provinces, Ecuador, demonstrated that population-based treatment of human taeniasis with a low dose of praziquantel is feasible and effective for the short-term control of transmission of Taenia solium in hyperendemic areas. Chemotherapeutic intervention also effectively pro- moted local preventive measures and contributed greatly to the elaboration of a long-term control pro- gramme. Introduction Two major parasites cause taeniasis in man: Taenia solium (the pork tapeworm) and T. saginata (the beef tapeworm). The adult worms live in the small intes- tine; their eggs are contained in excreted proglottids or faeces, and when ingested by pigs or cattle develop into the larval stages that are termed cysti- cerci. Humans are infected with tapeworm by ingest- ing cysticerci in undercooked pork (T. solium) or undercooked or raw beef (T. saginata). Of the two parasites, T. solium is overwhelm- ingly the more important cause of morbidity, since man can act as both a definitive and intermediate host, becoming infected with T. solium eggs via hands contaminated by contact with stools or the perianal region or from contaminated vegetables or fruit. Autoinfection may occur following the regurgi- tation of gravid proglottids or eggs from the intes- tine to the stomach as, for example, during vomiting, but the frequency of this event is not clear. Ingestion of T. solium eggs by man may produce cysticercosis in different organs, e.g., neurocysticercosis, ocular or dermal cysticercosis, which in turn produce a variety of pathological states and clinical expressions. In neurocysticercosis, these may result in epilepsy, intracranial hypertension, hydrocephalus, psychiatric symptoms, or death (10). While T. solium is found worldwide, the epi- demiological cycle occurs most commonly in ' Centre for Research and Training in Neurosciences (CIEN), Quito, Ecuador. 2 Parasitic Diseases Programme, World Health Organization, 1211 Geneva 27, Switzerland. Requests for reprints should be sent to this address. 3 Epidemiological and Statistical Methodology unit, World Health Organization, Geneva, Switzerland. Reprint No. 492 environments with low socioeconomic or hygiene levels, deficient sanitary facilities, or primitive pig- rearing practices where the animals can gain access to human faeces. In Central and South America the infection occurs in 18 countries (8). The clinical aspects of T. solium taeniasis/ cysticercosis are well known, but much less is appre- ciated about its epidemiology. For example, in Mexico, neurocysticercosis was responsible for nearly 9% of admissions in neurology and neuro- surgical services and was the final diagnosis in 11-25% of patients who were operated on for the removal of brain tumours. Furthermore, cerebral cysticercosis was found in 2.8-3.6% of all autopsies in Mexico City hospitals and was reported as the cause of death in 0.6-1.5% of hospitalized patients (7). In Ecuador, taeniasis/cysticercosis is a serious public health problem, and from 1978 to 1984 the rate of diagnosis of neurocysticercosis in hospitals rose from 0.3 to 2.62 per 1000 patients (2). The results of a previous study indicated, by autopsy, that the prevalence of neurocysticercosis in Cuenca, the capital of Azuay Province, was 1.3% from 1963 to 1981 (1). Also, in a series of mass faecal exami- nations performed in 1984, the prevalence of human taeniasis ranged from 0.03% to 3.23% in the samples examined (6). Furthermore, in Ecuador, 61% of pigs are bred mostly outdoors on small farms of less than 10 hectares; and in 1984 only 48% of pigs were inspected at slaughter by a veterinarian (6). Following a request by the Ecuadorian authori- ties in October 1985, the WHO Parasitic Diseases Programme, in cooperation with the Centre for Research and Training in Neurosciences (CIEN) in Quito, carried out an operational study on the control of taeniasis/cysticercosis in Loja and El Oro Provinces. The objective was to explore the optimal methods needed to reduce the incidence of neuro- Bulletin of the World Health Organization, 67 (4): 401-407 (1989) © World Health Organization 1989 401 M. Cruz et al. cysticercosis in hyperendemic areas in Ecuador. Since the general economic and sanitary conditions cannot be improved, and, since indoor pig hus- bandry and regular meat inspection cannot be intro- duced effectively or promptly in the affected areas, the most realistic short-term solution to lower the overall incidence of human neurocysticercosis appeared to be the immediate use of large-scale che- motherapy against human taeniasis (5). A basic assumption was that the high mortality and mor- bidity rates relating to human cysticercosis justify mass chemotherapy of the whole population in a hyperendemic area, defined as one with a point- prevalence rate of greater than 1% taeniasis in man and of > 5% cysticercosis in pigs. The effect of this intervention on the local transmission of T. solium was evaluated by measuring the prevalence of cysti- cercosis in pigs that originated from the treated area. The reduced incidence of human cysticercosis cannot, however, be measured in the short term but rather must be followed over some years. This large-scale chemotherapeutic programme, the first to be organized in a well-controlled study, was also novel because it evaluated the efficacy and the feasibility of population-based chemotherapy. Furthermore, it increased the understanding of T. solium epidemiology, and measured the effect of chemotherapy on the promotion of taeniasis/ cysticercosis control measures in Ecuador. Materials and methods Study areas The studies were performed in Loja and El Oro Provinces in southern Ecuador. Two Andean cantons, Gonzanama and Catamayo, in Loja Prov- ince (located 1500-2000 m above sea level), and two parochial agglomerations, Balsas and Marcabelli in El Oro Province, situated in hilly regions (500- 700 m above sea level) were selected. These areas were categorized as hyperendemic for taeniasis/ cysticercosis, since in 1968-75, 1.0% of inpatients examined in Loja Province Hospital were taenia car- riers (3). Also, in 1982 regular meat inspection detected cysticercosis in 3.9% of pigs slaughtered in El Oro Province and 5.5% in Loja Province (4). Most of the inhabitants of the study areas are engaged principally in agricultural activities, includ- ing cattle and pig breeding. Pigs constitute a funda- mental source of income to the family economy, and it has been estimated that in Loja Province there are 379 215 pigs. Pork is the main source of animal protein and an important feast dish. It is consumed mainly asfritada (fried in its own fat) or cecina (raw, Table 1: Intervention schedule used In the Taenla sollum taenlasls/cysticercosls operational study, Ecuador, 1985-87 Intervention schedule Preparatory phase November 1985-January 1986 January-March 1986 Treatment phase February 1986 March-September 1986 Follow-up phase October 1986 January-March 1987 February 1987 May-October 1987 Organizational activities First pig examination: -in vivo (1117 pigs); and -at slaughter (70 pigs)a First community treatment (10 173 people) Epilepsy study Data processing Anthropological evaluation Second pig examination -at slaughter (113 pigs)8 Faecal examinations (420 people)" Second community treat- ment (739 people)" Data processing a In Gonzanama Canton only. dried strips), both of which can contain invasive cysticerci if not prepared properly. Meat is rarely refrigerated. Medical services are provided mainly through the Ministry of Public Health, with supple- mentation by local private practitioners. The preva- lence of epilepsy was 12.4 per 1000 population in Gonzanama (M. Cruz et al., unpublished results). Study design The studies were organized in three phases, as shown in Table 1, and as discussed below. Preparatory phase (3 months). The provincial authori- ties and local community councils or leaders were contacted, informed about the project, and consulted on optimizing the organizational methods. Pro- fessionally formulated bulletins containing informa- tion pertinent to both pig inspection and human treatment were broadcast daily by radio for 4 months in the study areas. Posters elaborated by experts in social communications were displayed in public places. Finally, an educational leaflet was pre- pared and a copy left in each house visited by field teams. In most of the villages the proposed interven- tion was well accepted. The authorities in Loja Province and in the National University in Loja were successfully approached and provided 64 auxiliary staff, as follows: seven physicians, two veterinarians, one public health specialist, 26 students, three social workers, seven sanitary inspectors, six teachers, nine WHO Bulletin OMS Vol. 67 1989 Control of Taenla sollum ta.nlasls/cysticercosls In Ecuador volunteers, and three drivers, all of whose transport to the study area was ensured. In total, 13416 people from 2602 households in two urban areas, nine parochial, and 15 peripheral settlements were included in the studies. The propor- tions of urban, parochial, and peripheral populations under study were, respectively, 13%, 58%, and 29%. During the preparatory stage, 1117 pigs were examined in vivo in Loja and El Oro Provinces, and 70 pigs were inspected carefully after slaughter in Gonzanama Canton to assess the prevalence of porcine cysticercosis. Because of the limited detec- tion rate (3% in Loja Province and 0.9% in El Oro Province), in vivo examinations were not repeated in the follow-up phase of the studies. Large-scale treatment phase (one month). In February 1986, seven teams, each consisting of a physician, a nurse and undergraduate students, carried out house-to-house visits in the study areas. The name, age, and sex of all persons living in the houses were registered, and the occupation of the owner was noted. The teams also characterized the type of house, the local source of water, the toilet facilities, the number of pigs kept, the way in which they were bred, and whether or not they were inspected after slaughter. A leaflet on the planned control of taeniasis/cysticercosis was distributed and verbal health education offered to the inhabitants. Addi- tional information on health status was obtained in order to exclude from the treatment individuals with a history of epilepsy, allergies, pregnant women, or those who were severely ill. The treatment coverage was 75.8% of the population in the households examined. Those selected for treatment and who accepted it were weighed and given a single dose of prazi- quantel amounting to about 5 mg/kg body weight. Since the 150-mg tablets could be divided only into four parts, the actual doses given ranged from 3.4 mg/kg to 8.7 mg/kg body weight, with a mean of 5.2 mg/kg body weight. In most instances, the drug was taken in the presence of a team member. A plastic bag and a piece of soap were left in each house with detailed instructions on how to collect any tapeworms that were expelled after treat- ment. Most of the houses (90%) were revisited during the 48-72 hours after treatment and the inhabitants questioned about any side-effects and whether they had expelled tapeworms. In most instances, the expelled tapeworms were inspected macroscopically and destroyed by burning. Micro- scopic differential diagnosis was not performed, since T. saginata taeniasis was not known to exist in the study area. The forms containing all the field data were col- lected and sent to WHO in Geneva for computerized analysis. Follow-up phase (after 1 year). The follow-up study in January-March 1987 was restricted to that part of Gonzanama Canton from where the most detailed information on human taeniasis and pig cysticercosis was collected. Follow-up consisted of: a second treatment of 739 people (539 of whom had pre- viously been treated and 200 of whom were treated for the first time); faecal examination of 420 people by the Kato-Katz technique (most of those exam- ined had been treated 1 year previously); inspection of meat from 113 pigs killed at the local slaughter- house in Gonzanama using the same technique that was used in the first study in 1986; socio- anthropological studies were carried out by two independent researchers to evaluate peoples' reaction to the mass chemotherapeutic intervention and to characterize their living conditions and behaviour. Because of a lack of local experience in environmental and experimental studies, a search for taenia eggs in soil, water, and on vegetables, as well as an evaluation of their potential infectivity could not be performed. Also, no serological studies were conducted since it was thought that they would con- tribute little to the detection of taeniasis in man and cysticercosis in pigs. Results Large-scale chemotherapeutic Intervention Efficacy and costs. A total of 10173 persons were treated. For 9529 of these individuals, information on worm expulsion was available and 148 (1.6%) reported having expelled a taenia. The expulsion rate was, however, probably higher, since some individ- uals may not have noticed the partly or totally digested tapeworm, may not have wished to report the expulsion, or were not revisited by a study team 2-3 days after receiving a dose of praziquantel. The follow-up studies carried out in Gonzanama showed that of the 539 people who were re-treated with the drug in 1987, none expelled a tapeworm again; these results include 12 persons who were infected during the first intervention. Also, of 420 people who had a faecal examination during the follow-up phase, two were positive for taenia eggs; however, neither had been treated before, since they were not resident in Gonzanama during the chemotherapeutic interven- tion. This suggests that expulsion of a tapeworm rep- resented a cure in most if not in all the cases. It also indicates that the single dose of about 5 mg of prazi- quantel per kg body weight is effective in treating taeniasis; furthermore, those who expelled tape- WHO Bulletin OMS Vol. 67 1989 403 M. Cruz et al. worms received 3.4-7.3 mg of the drug per kg (mean, 5.1 mg/kg), while those who did not, received 3.4-8.7 mg/kg (mean, 5.2 mg/kg). The average cost of treating an adult was US$ 0.30 at the 1986 retail price of praziquantel to United Nations agencies. In Ecuador the average cost of the drug to treat one case of human cysti- cercosis was estimated to be US$ 187, and in Mexico in 1982 the average cost of hospitalizing a patient with the disease was US$ 2173.8 By law, infected pigs are usually destroyed, which means the loss of US$ 50-150 per animal depending on the weight at slaughter. The follow-up veterinary studies performed in Gonzanama demonstrated that one year after inter- vention the prevalence of cysticercosis in slaughtered pigs dropped from 11.4% to 2.6%. Three infected pigs were found at follow-up, but all were over 1-year old and thus might have been infected before the intervention or originated from households that were not covered by the chemotherapeutic project. Safety, coverage, and acceptance of the Intervention Side-effects relating to the treatment were not recorded consistently and could therefore not be analysed statistically. However, to the best of our knowledge, all side-effects were transient and mild; more serious was a case of seizures and also a case of dysentery that may not have been related directly to the treatment. The potential effect of a single small dose of praziquantel on neurocysticercosis could not be evaluated since individuals known to have epi- lepsy were excluded from the study. Many of those with epilepsy were treated with niclosamide at a later date. The treatment coverage of 75.8% (10 173 people were treated out of 13416 included in the studies) was satisfactory. Children below 6 years of age, preg- nant women, and a few individuals with certain medical contraindications were not treated. A small number of people, however, were not treated for other reasons, e.g., they were temporarily absent or did not comply with the treatment. Two hundred of those who missed treatment in Gonzanama in 1986 were treated for the first time in 1987 and two of these individuals were found to be infected with taenia. This suggests that an early chance of treat- ment should be offered to all those who are not able or willing to participate in population-based treat- ment at the first intervention. " Gemmell, M. et al., ed. Guidelines for surveillance, prevention and control of taeniasis/cysticercosis. Unpublished document WHO/VPH/83.49. The treatment was well accepted by the local population. The socioanthropological study in Gon- zanama revealed that 90% of the people who had been treated and interviewed were interested in the continuation of the project. Only in one settlement, where the information campaign was not particu- larly active, and one of the local leaders opposed the project, did 50% of the population interviewed show no interest in further participation. Epidemiological observations Prevalence and distribution of taenlasis in the study areas The post-treatment assessment showed that the prevalence of taeniasis in those treated was at least 1.6% (Table 2). This proportion might well be higher because of under-reporting of tapeworm expulsion and the 75.8% treatment coverage. The infection rate increased slightly with age from 1.3% among 5-9- year-olds to 2.2% in those > 60 years of age. Females were more commonly infected (1.9%) than males (1.2%). Taeniasis was unevenly distributed throughout the study areas; the infection rate was highest in Gonzanama Canton (2.2%) and lowest in Balsas and Marcabelli (1.1 %). The disease was more common in peripheral (2.4%) than in parochial (1.2%) or urban areas (1.0%). At the settlement level, no tapeworm Table 2: Assessment of the effect of the treatment given for taenlasls/cysticercosis, by age, sex, and location In the study areas, Ecuador No. of individuals Expelled Did not expel a taenia a taenia Total Age (years) 0-4 0 6 6 5-9 23 (1.3)8 1726 1749 10-19 48 (1.6) 2921 2969 20-39 31 (1.3) 2424 2455 40-59 30 (1.8) 1588 1618 )60 16 (2.2) 716 732 Total 148 (1.6) 9381 9529 Sex: Male 55 (1.2) 4602 4657 Female 93 (1.9) 4779 4872 Area: Urban 12 (1.0) 1146 1158 Parochial 67 (1.2) 5380 5447 Peripheral 69 (2.4) 2855 2924 Canton Gonzanama 62 (2.2) 2699 2761 Catamayo 41(1.6) 2490 2531 Balsas/Marcabelli 45 (1.1) 4192 4237 a Figures in parentheses are percentages. 404 WHO Bulletin OMS Vol. 67 1989 Control of Taenla sollum ta.nlasls/cysticercosis In Ecuador was reported to have been expelled in five localities, whereas in another five (out of a total of 26) the infection rate was 7.4%, 9.7%, 13.6%, 19%, and 21.1%, respectively; this may indicate a clustering of infection. Taeniasis also had a tendency to occur in some families; the prevalence among 734 people treated in "infected" households was 20.2%, and more than one taenia carrier was found in 24.3% of "infected" households. Analysis of the infection rate by household indicated that 4.8% of examined and treated households had one or more taenia carriers. The distribution of taeniasis was statistically dependent on household size (7.1% of households with seven or more people had one or more carriers) but was not dependent on economic or sanitary indices such as the type of house, water source, toilet availability, and whether pigs were bred at home (X2 test, P > 0.05). Rate of reinfection with T. sollum The lack of new infections among the 539 people treated and re-examined in 1987, a year after the initial chemotherapeutic intervention, and the rela- tively constant prevalence of taeniasis by age, as esti- mated by the expulsion of a tapeworm after treatment (Table 2), suggest that the rate of reinfec- tion with T. solium in the study area was low. This might be taken to imply that the early repetition of treatment in endemic areas may be unnecessary. However, this is only valid if maximal population coverage during the first chemotherapeutic interven- tion can be assured. Discussion Control of neurocysticercosias In man Effect on the transmission and reservoir of Infectlon. The expulsion of a tapeworm by at least 148 carriers defi- nitely reduced the exposure to T. solium eggs both for man and pigs in the study areas. With a relatively low reinfection rate, this human reservoir of infection would remain diminished for several years even in the absence of other control measures. However, since the large-scale intervention covered only 12.3% of the total population of three cantons, one cannot expect that it will greatly affect the rate of infection of pigs in provincial slaughterhouses that cater for larger areas. Promotional activities. The studies carried out in Loja and El Oro Provinces promoted governmental, pro- vincial, and local preventive and control activities. These were achieved through many meetings with civil, military and religious authorities, as well as community councils and leaders. A regional com- mittee for control of taeniasis/cysticercosis has been formed in Loja Province (COVITEC) to coordinate further control activities in the region. Among members are staff from the Veterinary Medicine School of the National University in Loja, the National Institute for Mother and Child, the Educa- tion Institute for Agrarian Reform, the Loja Prov- ince Directorate for Health, and the Loja Branch of the Ecuadorian House of Culture, as well as repre- sentatives from the Municipal Councils of Gonza- nama and Catamayo. The committee has contacts with the Governor of Loja, the Ministry of Agricul- ture, and the Ministry of Health and cooperates with the Inter-American Development Bank and non- governmental organizations. A seminar on the control of taeniasis/cysticercosis was organized in Loja in November 1985 and two volumes of scienti- fic papers on the subject were published. The authorities in Balsas and Marcabelli, which in the meantime have received the administrative status of canton, have requested the continuance of the control activities and offered all possible local support. The WHO/CIEN studies were well covered by radio broadcasts and by journalists, and as a result the population was kept informed about the feasi- bility of the project and the results. Following this action, some communities expressed their willingness to participate actively in the long-term control mea- sures that were scheduled to follow the short-term therapeutic intervention. The data on the sanitary conditions in Loja and El Oro Provinces were collected for the first time in the area and have already been used by national and international agencies working on the improvement of living conditions in the study areas. Conclusions The operational studies reported, which represent a novel approach to controlling T. solium taeniasis/ cysticercosis, confirm the feasibility of using large- scale chemotherapeutic intervention, but also pose several problems, which require further investiga- tions. Some of these are outlined below. * An improved definition of the hyperendemicity of T. solium taeniasis/cysticercosis is required together with a definition of a T. solium focus, which would lead to better selection of the areas for population- oriented chemotherapy and more strongly justify the need for selective chemotherapeutic intervention. * The optimal dosage, timing, and evaluation pro- cedure for the chemotherapeutic intervention need to be studied further. WHO Bulletin OMS Vol. 67 1989 M. Cruz et al. * A more detailed formulation of the contra- indications to praziquantel in large-scale interven- tions is required; this would include the effect of a single and low dose of the drug on neuro- cysticercosis, since epileptics were excluded from the present studies. * A long-term evaluation of this single intervention should be carried out. * The role of T. solium egg reservoirs in contami- nated soil and water in possible early reinfection should be investigated. * The next steps in controlling taeniasis/ cysticercosis, after a transition from hyperendemicity to endemicity has been achieved, need to be investi- gated. The present studies demonstrate that, over the evaluation period, a single dose of praziquantel (about 5mg/kg body weight) is effective in control- ling the prevalence of T. solium taeniasis in man and in reducing the transmission of infection to pigs. The project fulfilled the short-term objective of taeniasis/ cysticercosis control measures-the reduction of mortality and morbidity caused by neuro- cysticercosis (11). In addition, it partly fulfilled the long-term objective-to diminish the prevalence of taeniasis in man and of cysticercosis in pigs. Apart from the direct effect on human health, the interven- tion has also had a positive effect on the economy for farmers by reducing financial losses caused by condemnation of pig-infected carcasses. In the past, only limited use was made of labor- atory diagnostic tests, i.e., microscopy or serology, in order to clarify the epidemiology of taeniasis/ cysticercosis. The large-scale chemotherapeutic inter- vention that we have described is therefore a good procedure for surveying the prevalence and distribu- tion of taeniasis in areas that are hyperendemic for neurocysticercosis. The experience gained in these studies demon- strates that the survey methodology, which collected data only at the provincial or regional level, is of limited value in selecting areas or villages for chemo- therapeutic intervention. Intervention at village or farm level needs more detailed data, which may or may not be available from hospitals, clinics, medical laboratories, or slaughterhouses. If cooperation between veterinary services and local medical clinics can be achieved in defining foci of T. solium infection (taeniasis as well as cysticercosis), chemotherapy can be targeted towards the farms from which infected pigs originate or towards the villages that show a high rate of pig cysticercosis. Such a control policy is recommended for future activities in the other hyper- endemic foci in Loja and El Oro Provinces as well as in other Ecuadorian provinces, and it may also be useful in other countries where human neuro- cysticercosis is a problem. Acknowledgements The cooperation of the research workers, medical and veterinarian authorities, provincial and local adminis- trators and volunteers, physicians, social workers and sanitary inspectors, university students, and all others who contributed to this operational study, is gratefully acknowledged. Specially prepared 150-mg tablets of pra- ziquantel were kindly donated by Merck AG, Darmstadt, Federal Republic of Germany. This project was sup- ported by funds made available by the Director-General, World Health Organization, Geneva. Resume Equateur: Etudes operationnelles sur la lutte contre la teniase/cysticercose a Taenla sollum Un projet de lutte a grande 6chelle contre la tenia- se a Taenia solium chez I'homme, comportant a la fois des activites educatives et une chimiothe- rapie a l'echelon de la population, a ete mene dans les provinces de Loja et d'EI Oro, Equateur, de 1985 a 1987 pour essayer d'endiguer la forte endemicite de la neurocysticercose humaine. Des agents de sante publique et des etudiants se sont rendus dans plus de 2600 foyers de deux regions urbaines et de 9 paroisses et 15 localites p6riphe- riques, ou ils ont distribue du mat6riel destine a l'education sanitaire. Dix mille cent soixante-treize personnes au total ont e traitees avec une dose unique de praziquantel (allant de 3,9 a 8,7 mg/kg de poids corporel; dose moyenne, 5,2 mg/kg de poids corporel). Le traitement a ete bien accueilli et bien tol6re. Sur les 9529 personnes ayant de- clare avoir retrouve des vers dans leurs selles, 148 (1,6%) ont expulse un tenia. Le retraitement ult6- rieur de 539 personnes et l'analyse des selles de 420 autres ont confirme que le taux de guierson 'etait 'eleve'. La transmission locale de l'infestation a T. solium a considerablement regresse; par exemple, le pourcentage de cysticercose chez les porcs abattus pour la viande est passe de 11,4% avant intervention chimioth6rapeutique c 2,6% dans une region reexaminee un an apres la mise en place du programme de traitement. L'etude a montre que T. solium se r6partissait de fa9on ine- gale dans les provinces de Loja et d'EI Oro, que chez I'homme les cas de teniase avaient tendance WHO Bulletin OMS Vol. 67 1989406 Control of Taenla sollum taenlasis/cysticercosls In Ecuador A Otre concentr6s dans certaines families et qu'il y avait un faible taux de r6infestation un an apr6s le traitement. Ces r6sultats confirment qu'une chi- mioth6rapie de la teniase humaine A 1'6chelon de la population est r6alisable, qu'elle permettra a court terme d'endiguer la transmission de T. solium dans les foyers c t6niase/cysticercose et qu'une telle m6thode favoriser a 6galement l'implantation de mesures de lutte et de pr6vention & long terme. References 1. Cordero, L. & Ugalde, J. [Cysticercosis]. Tribune medica, Quito, 29-32 (1984) (in Spanish). 2. Erazo, F. & Alvarez, J.R. [Prevalence and epidemio- logical follow-up of taeniasis and cysticercosis]. Revista ciencias veterinarias, 5: 51-81 (1985) (in Spanish). 3. Jlmenez, S.B. [Zoonotic cysticercosis caused by C. cellulosae]. Boletin de la Oficina Sanitaria Pan- americana, 80(5): 403-411 (1976) (in Spanish). 4. Morales, A. [Prevalence of Cysticercus cellulosae in pigs slaughtered in Loja abattoir]. Revista ciencias veterinarias, 5: 33-50 (1985) (in Spanish). 5. Pawlowskl, Z.S. Large-scale use of chemotherapy of taeniasis as a control measure for Taenia solium infections. In: Geertz, S. et al., ed. Helminth zoo- noses. Dordrecht, M. Nijhoff, 1987, pp. 100-105. 6. Rulz, P. [Teniasis cysticercosis in Ecuador]. Revista de divulgacion cientifica, Ecuador, 1: 85-98 (1986) (in Spanish). 7. Sartl-Gutlerrez, E.J. et al. Taenia solium taeniasis and cysticercosis in a Mexican village. Tropical medicine and parasitology, 39: 194-198 (1988). 8. Schenone, H. et al. Epidemiology of human cysti- cercosis in Latin America. In: Flisser, A. et al., ed. Cysticercosis: present state of knowledge and per- spectives. New York, Academic Press, 1982, pp. 25-38. 9. WHO Technical Report Series No. 637, 1979 (Parasitic zoonoses: report of a WHO Expert Com- mittee with the participation of FAO). 10. WHO Technical Report Series No. 666, 1981 (Intestinal protozoan and helminthic infections: report of a WHO Scientific Group). 11. WHO Technical Report Series, No. 749, 1987 (Prevention and control of intestinal parasitic infec- tions: report of a WHO Expert Committee). WHO Bulletin OMS Vol. 67 1989 407