High concentration of levamisole in the diet of Colossoma macropomum (Pisces: Serrasalmidae) is effective for controlling monogenean parasites / Alta concentração de levamisol na dieta de Colossoma macropomum (Pisces: Serrasalmidae) é efetiva para controlar parasitos monogenea

Abstract This study investigated the effects of diets supplemented with levamisole on monogeneans on the gills of Colossoma macropomum. Fish were fed with diets containing levamisole at concentrations of 0, 300, 600, 900 and 1200 mg kg-1 for 24, 96 and 240 h and the infection by Anacanthorus spatulatus, Notozothecium janauachensis and Mymarothecium boegeri were evaluated. None of the levamisole concentrations caused either mortality or behavioral alterations in fishes during 240 h of feeding. After 24 h of feeding with 1200 mg kg-1 of levamisole, the abundance of N. janauachensis decreased in comparison with treatments of 0, 300, 600 and 900 mg kg-1, as did the abundance of M. boegeri after 240 h of feeding with 1200 mg kg-1 of levamisole. The efficacy of 900 mg kg-1 of levamisole was only 55.7% after 96 h of feeding, but it was 84.6% after 240 h of feeding with 1200 mg kg-1. Our results show that 1200 mg kg-1 of levamisole for 10 days has good anthelmintic efficacy against monogeneans of C. macropomum. Since monogeneans elicit some of the worst problems in C. macropomum, this study has provided evidence of an effective control method that may be used in fish farms.

Resumo Este estudo investigou os efeitos de dietas suplementadas com levamisol na infecção por monogeneas nas brânquias de Colossoma macropomum. Os peixes foram alimentados com dietas contendo 0, 300, 600, 900 e 1200 mg kg-1 de levamisol por 24, 96 e 240 h e os níveis de infecção por Anacanthorus spatulatus, Notozothecium janauachensis e Mymarothecium boegeri, foram avaliados. Nenhuma das concentrações de levamisol causou mortalidade ou alterações comportamentais nos peixes durante 240 h de alimentação. Após 24 h de alimentação com 1.200 mg kg-1 de levamisol, a abundância de N. janauachensis diminuiu quando comparada aos tratamentos com 0, 300, 600 e 900 mg kg-1, bem como a abundância de M. boegeri após 240 h de alimentação com 1200 mg kg-1 de levamisol. A eficácia de 900 mg kg-1 de levamisol foi somente de 55,7% após 96 h de alimentação, mas foi de 84,6% após 240 h de alimentação com 1200 mg kg-1. Os resultados mostram que 1200 mg kg-1 de levamisol durante 10 dias, tem uma boa eficácia antihelmíntica contra monogeneas de C. macropomum. Como monogeneas provocam alguns dos piores problemas em C. macropomum, este estudo forneceu evidências de um método de controle eficaz que pode ser usado em pisciculturas.

The potential of plant and fungal proteins in the control of gastrointestinal nematodes from animals / Potencial de proteínas de plantas e fungos no controle de nematoides gastrintestinais de animais

Abstract Gastrointestinal nematode infection is an important cause of high economic losses in livestock production. Nematode control based on a synthetic chemical approach is considered unsustainable due to the increasing incidence of anthelmintic resistance. Control alternatives such as the use of natural products are therefore becoming relevant from an environmental and economic point of view. Proteins are macromolecules with various properties that can be obtained from a wide range of organisms, including plants and fungi. Proteins belonging to different classes have shown great potential for the control of nematodes. The action of proteins can occur at specific stages of the nematode life cycle, depending on the composition of the external layers of the nematode body and the active site of the protein. Advances in biotechnology have resulted in the emergence of numerous protein and peptide therapeutics; however, few have been discussed with a focus on the control of animal nematodes. Here, we discuss the use of exogenous proteins and peptides in the control of gastrointestinal.

Resumo A infecção por nematoides gastrintestinais é uma importante causa de grandes perdas econômicas na pecuária. O controle de nematoides com compostos químicos sintéticos é considerado insustentável devido ao aumento da resistência anti-helmíntica. Alternativas de controle, como o uso de produtos naturais, estão se tornando relevantes do ponto de vista ambiental e econômico. As proteínas são macromoléculas com várias propriedades que podem ser obtidas de uma ampla gama de organismos, incluindo plantas e fungos. Proteínas pertencentes a diferentes classes têm mostrado grande potencial para o controle de nematoides. A ação das proteínas pode ocorrer em estágios específicos do ciclo de vida do nematoide, dependendo da composição das camadas externas do parasito e do sítio ativo da proteína. Avanços na biotecnologia resultaram no surgimento de numerosas terapias de proteínas e peptídeos; no entanto, pouco foi discutido com foco no controle de nematoides parasitos de animais. Na presente revisão foi discutido o uso de proteínas exógenas e peptídeos no controle de nematoides gastrintestinais, os mecanismos sugeridos de ação, e os desafios e perspectivas para o uso dessas biomoléculas como uma classe de anti-helmínticos.

Interação entre nematicidas e herbicidas pré-emergentes no desenvolvimento inicial da cultura da cana-de-açúcar / Interaction between nematicides and pre-emergent herbicide in the initial development of sugar cane / Interacción entre nematicidas y herbicidas pre emergentes en el desarrollo inicial de la cultura de caña de azúcar

O objetivo do trabalho foi avaliar a interação do herbicida tebuthiuron (Combine® 500 SC), com nematicidas carbofuram (Furadan® 350 SC) e benfuracarbe (Pottente®), aplicados no plantio da cultura da cana-de-açúcar (RB 867515). O experimento foi conduzido em casa de vegetação da Universidade Paranaense, em Umuarama ­ PR, no período de abril a agosto de 2014. Foi instalado em vasos com capacidade para 4,5 L, contendo uma planta por vaso, em delineamento inteiramente casualizado, com seis tratamentos e quatro repetições, sendo os tratamentos testemunha (T1), sem aplicação de produtos; aplicação isolada de carbofuran (T2); aplicação isolada de benfuracarbe (T3); aplicação isolada de tebuthiuron (T4); aplicação combinada de carbofuran e tebuthiuron (T5) e aplicação combinada de benfuracarbe e tebuthiuron (T6). O experimento foi submetido a duas avaliações, 45 e 90 dias após o plantio (DAP) sendo que na primeira, as variáveis avaliadas foram altura da parte aérea, número de folhas e número de plantas daninhas por vaso, e, na segunda, altura da parte aérea; número de folhas; número de plantas daninhas; massa fresca e seca da parte aérea; massa fresca do sistema radicular; população final total de nematoides por vaso, calculada pelo somatório de nematoides nas raízes e solo. Quanto ao número de folhas, o tratamento T4 demonstrou fitotoxicidade aos 45 DAP. Os tratamentos T3, T5 e T6 apresentaram as maiores massa fresca e seca da parte área da cana, demonstraram ausência de interação antagônica entre as combinações do herbicida com os nematicidas aos 90 DAP. Os tratamentos T3 e T5 foram eficientes no controle populacional de P. zeae.(AU)

The aim of the study was to evaluate the interaction of the herbicide tebuthiuron (Combine® SC 500), with the following nematicides: carbofuran (350 Furadan® SC) and benfuracarb (Pottente®) applied during the planting of cane sugar (RB 867515). The experiment was conducted in a greenhouse at Universidade Paranaense in Umuarama - PR, from April to August 2014. The crop was started in 4.5-L vases containing one plant per vase, in a completely randomized design with six treatments and four replications, namely control treatments (T1), with no application of products; isolated application of carbofuran (T2); isolated application of benfuracarb (T3); isolated application of tebuthiuron (T4); combined application of carbofuran and tebuthiuron (T5) and combined application of benfuracarb and tebuthiuron (T6). The experiment was submitted to two assessments, at 45 and 90 days after planting (DAP). On the first assessment, the variables analyzed were shoot height, number of leaves and number of weeds per vase. The second assessment analyzed shoot height; number of leaves; number of weeds; fresh and dry weight of shoot; fresh weight of the root system; total final population of nematodes per vase, calculated by the sum of nematodes in the roots and soil. Regarding the number of leaves, the T4 treatment showed phytotoxicity at 45 DAP. The T3, T5 and T6 treatments had the highest fresh and dry weight of the aerial part of the sugar cane; with absence of antagonistic interaction between the combinations of herbicide and nematicides at 90 DAP. The T3 and T5 treatments were effective in controlling the population of P. zeae.(AU)

El objetivo del estudio ha sido evaluar la interacción del herbicida tebuthiuron (Combine® 500 SC), con nematicidas carbofuram (Furadan® 350 SC) y benfuracarbe (Pottente®), aplicados en plantío de caña de azúcar (RB 867515). El experimento ha sido dirigido en el área de vegetación de la Universidad Paranaense, en Umuarama - PR, en el período de abril a agosto de 2014. Se ha instalado en floreros con capacidad para 4,5 L, conteniendo una planta por florero, en delineamiento enteramente casualizado, con seis tratamientos y cuatro repeticiones, siendo los tratamientos testigo (T1), sin aplicación de productos; aplicación aislada de carbofuran (T2); aplicación aislada de benfuracarbe (T3); aplicación aislada de tebuthiuron (T4); aplicación combinada de carbofuran y tebuthiuron (T5) y aplicación combinada de benfuracarbe y tebuthiuron (T6). El experimento ha sido sometido a dos evaluaciones, 45 y 90 días después del plantío (DAP) siendo que en la primera, las variables evaluadas fue la altura de la parte aérea, número de hojas y el número de plantas dañinas por florero, y, en la segunda, altura de la parte aérea, número de hojas, número de plantas dañinas; masa fresca y seca de la parte aérea; masa fresca del sistema radicular; población final total de nematodos por florero, calculado por la suma de nematodos en las raíces y suelo. Cuanto al número de hojas, el tratamiento T4 demostró citotoxicidad a los 45 DAP. Los tratamientos T3, T5 y T6 presentaron mayor masa fresca y seca en la parte aérea de la caña, demostraron ausencia de interacción antagónica entre las combinaciones de los herbicidas con los nematicidas a los 90 DAP. Los tratamientos T3 y T5 fueron eficientes en el control poblacional de P. zeae.(AU)

Eficácia de Chenopodium ambrosioides (erva-de-santa-maria) no controle de endoparasitos de Coturnix japônica (codorna japonesa) / Effectiveness of Chenopodium ambrosioides (santa maria herb) for controlling Coturnix japonica (japanese quail) endoparasites

O objetivo foi testar in vitro e in vivo a eficácia da planta medicinal Chenopodium ambrosioidesLinnaeus, 1786 (erva-de-santa-maria), nas formas fitoterápica e homeopática, como meios alternativos para o controle de endoparasitos de Coturnix japonica Temminck & Schlegel, 1849 (codorna japonesa), um sério problema que afeta a criação e desempenho de aves domésticas, ocasionando morte quando muito intenso, retardo de crescimento, redução de índice de conversão alimentar e aumento na suscetibilidade às doenças infecciosas. As metodologias utilizadas foram preconizadas por Coles et al. (1992), creditada pela World Association for the Advancement of Veterinary Parasitology (WAAVP). A pesquisa evidenciou a presença dos gêneros Ascaridiae Eimeria. O ensaio in vitro demonstrou alta taxa de redução na inibição de eclosão de ovos de Ascaridiasp. (100,00%) e significativa taxa de redução na destruição de oocistos de Eimeriasp. (47,06%). O ensaio in vivodemonstrou alta taxa de redução na contagem de ovos de Ascaridiasp. nas fezes (100,00%) e expressiva taxa de redução na contagem de oocistos de Eimeriasp. nas fezes (60,33%). Chenopodium ambrosioides mostrou em certos momentos superioridade frente ao produto tradicional (Thiabendazole/Mebendazole) e índices superiores aos preconizados pelo Ministério da Agricultura do Brasil e Organização Mundial da Saúde como indicativos de eficácia.

The aim was in vitro and in vivo to test the effectiveness of Chenopodium ambrosioides Linnaeus, 1786 (santa maria herb) medicinal plant, in regard to phytotherapeutic and homeopathic forms as alternative methods to control Coturnix japonica Temminck & Schlegel, 1849 (japanese quail) endoparasites. The parasitosis is a serious problem affecting domestic poultry raising and performance causing death, delay in grow, food conversion rate reduction and increase of susceptibility to infectious diseases. Methodologies were advocated by Coles et al. (1992), corroborated by World Association for the Advancement of Veterinary Parasitology (WAAVP). Presence of the genera Ascaridia and Eimeria was displayed by this survey. In vitro essay demonstrated high reduction rate on eggs eclosion inhibition of Ascaridia sp. (100.00%) and significant reduction rate on oocyst destruction of Eimeria sp. (47.06%). In vivo essay demonstrated high fecal egg counting reduction rate of Ascaridia sp. (100.00%) and expressive fecal oocyst counting reduction rate of Eimeriasp. (60.33%). C. ambrosioides showed upper rates front traditional product (Thiabendalol/Mebendazol) as well as to those ones advocated by the Brazilian Ministry of Agriculturel and the World Health Organization as effectiveness indicative.

Tolerability of ivermectin in gnathostomiasis.

At present, no universally-accepted effective treatment for cutaneous gnathostomiasis is available. At the Hospital for Tropical Diseases, Mahidol University, albendazole 400 mg twice a day for 14 days is commonly prescribed for patients diagnosed with cutaneous gnathostomiasis. The efficacy of albendazole to induce outward migration of the parasite was less than or around 20% in 2 studies. Research for alternative, more efficacious treatment, is needed. In this prospective open-labeled study, we assessed the safety of ivermectin in 20 Thai patients diagnosed with cutaneous gnathostomiasis. Ivermectin, one time only, at dosages of 50, 100, 150, or 200 microg/kg bodyweight, was given orally to 4 groups of patients, 5 patients each group. Adverse events were recorded and laboratory tests were obtained before and after treatment. No serious adverse events occurred in this study. Forty adverse events were possibly related to ivermectin. The adverse events were malaise (35%), myalgia (30%), drowsiness (30%), pruritus (20%), nausea/vomiting (20%), dizziness (15%), diarrhea (15%), feeling of shortness of breath (10%), feeling of palpitations (10%), constipation (5%), anorexia (5%), and headache (5%). These adverse events were self-limited and not dose-related. Laboratory abnormalities were found in 3 patients (15%). Transient microscopic hematuria, pyuria, and mildly elevated liver enzymes were found in 1 patient each. Ivermectin single dose, of 50,100, 150, and 200 microg/kg bodyweight, is considered safe in Thai patients. Future trials of ivermectin on human gnathostomiasis may be performed using dosages up to 200 microg/kg bodyweight.

El tratamiento antihelmíntico selectivo frente al tratamiento masivo: experiencia en dos comunidades hiperendémicas / Selective vs. mass treatment with antihelminthic drugs: experience in two hyperendemic communities

OBJETIVO: Evaluar la prevalencia e intensidad de las infecciones por geohelmintos en niños de dos comunidades hiperendémicas tratadas con técnicas antihelmínticas diferentes: una con tratamiento selectivo o individual, y la otra con tratamiento masivo reiterado. MÉTODOS: La población estuvo compuesta por 909 niños de uno u otro sexo, con edades entre 2 y 13 años, que vivían en dos comunidades marginales de la ciudad: Las Lomas y El Abasto, Santa Fe, Argentina. Se realizó un trabajo prospectivo longitudinal, cuasiexperimental, de comunidades. Durante los 22 meses del estudio se llevaron a cabo 5 controles parasitológicos, evaluados desde el punto de vista cualitativo y cuantitativo, y se dispensaron tratamientos antihelmínticos después de los controles 0, 2, 3 y 4. En Las Lomas se aplicó el tratamiento selectivo a los casos con diagnóstico parasitológico positivo que integraban la muestra A (n = 55) y en El Abasto, tratamiento masivo a todos los niños, incluidos los integrantes de la muestra B (n = 50). Ambas muestras fueron escogidas para realizar los controles. RESULTADOS: Se comprobó una prevalencia e intensidad de la infección por Ascaris lumbricoides significativamente mayor en El Abasto. No se detectaron diferencias para Trichuris trichiura. Al comparar las prevalencias y cargas parasitarias de A. lumbricoides entre los controles realizados dentro de una misma comunidad (inicio y final del estudio) no se observaron diferencias significativas en la muestra A, aunque sí en la muestra B. En cuanto a T. trichiura, se detectaron diferencias significativas entre ambos controles en las dos muestras. CONCLUSIONES: Solo el tratamiento masivo y reiterado logró disminuir eficaz y significativamente la prevalencia y la carga parasitaria de A. lumbricoides durante el período estudiado

Efficacy of multiple dose mebendazole against trichuriasis in Thai and Karen patients.

Treatment of trichuriasis with mebendazole 500 mg for three days, and 100 mg twice daily for three days, yielded cure rates of 93.9 and 88.9% in Thai patients, while the cure rates in Karen patients were 96.2 and 95.5% respectively. The total number of Thai and Karen trichuriasis patients were 60 and 48, when tested by modified cellophane thick smear Kato-Katz technique. There were no significant differences among the two groups of patients and doses of treatment (p > 0.05).

Prevalence of enterobiasis and its incidence after blanket chemotherapy in a male orphanage.

A prospective observational study was conducted in a male orphanage to find out the prevalence of enterobiasis and its incidence after blanket chemotherapy using mebendazole. We found that the prevalence of enterobiasis was 28.9%. The incidence density of enterobiasis after blanket chemotherapy was 379.82 per 1,000 person-years which was quite high. We suggest that blanket chemotherapy should be repeated at every 6 months interval to control enterobiasis in orphanages.

Comparative studies on the efficacy of three anthelminthics on treatment of human strongyloidiasis in Okinawa, Japan.

A study was undertaken to compare the efficacy of three drugs in the treatment of uncomplicated strongyloidiasis in Okinawa, Japan. Two hundred and eleven patients with confirmed Strongyloides stercoralis infection were given either ivermectin, 6 mg in a single dose, albendazole, 400 mg/day for 3 days or pyrvinium pamoate, 5 mg/kg/day for 3 days. For each treatment, the same regimen was repeated once 2 weeks later. Efficacy was evaluated at 2 weeks, 6 months and 12 months after the second course of treatment. Each follow-up examination included a parasitological examination of z stool specimens, using the agar-plate culture method. Coprological cure was obtained in 65 of the 67 patients treated with ivermectin (97.0%), in 65 of the 84 patients treated with albendazole (77.4%) and only in 14 of the 60 patients who were given pyrvinium pamoate (23.3%). The cure rates were lower in males and in the patients with concurrent HTLV-1 infection. An epidemiological feature of Strongyloides infection in recent Okinawa might allow workers to evaluate the exact efficacy of the treatment for an extended period, over a year, without the possibility of reinfection from the environment.

Tratamento de ratos, experimentalmente infectados pelo Strongyloides venezuelensis, através da ivermectina administrada por via oral / The treatment of rats experimentally infected with Strongyloides venezuelensis by orally administered ivermectin

Em modelo experimental, baseado na infecção de ratos pelo Strongyloides venezuelensis, foi avaliada a atividade terapêutica de duas preparações de ivermectina, para usos veterinário e humano. Houve interesse em verificar a efetividade em relação a vermes adultos e formas larvárias. A administração dos fármacos ocorreu sempre por via oral e a posologia correspondeu à dose única de 0,2mg/kg. Considerados os vermes adultos e as formas larvárias, o produto para emprego veterinário propiciou eliminações expressas pelas porcentagens de 98,0% e 84,2%; quanto à outra preparação, as taxas situaram-se em 59,3% e 73,0%, respectivamente. O estudo revelou, então, utilidade do anti-helmíntico quando usada a via oral e, também, mostrou significativa ação sobre as formas larvárias, certamente valiosa quando vigente a modalidade disseminada da estrongiloidíase.

Strongyloides venezuelensis experimental infection in rats was treated by two different oral preparations of ivermectin, 0.2 mg/kg. One was a human formula used by WHO in the treatment of onchocerciasis; the other was a veterinary preparation. Adult worms and larvae were evaluated. The human formulation cleared both forms in 59.3% (adult worms) and 73.0% (larvae), whereas the veterinary one cleared 98.0% and 84.2%, respectively. The antilarval action is very useful when treating systemic strongyloidiasis.

Minimum effective doses of mebendazole in treatment of soil-transmitted helminths.

Three hundred and fifteen primary school children infected with soil-transmitted helminths were divided into 5 groups. Three groups were treated with 25, 50 and 75 mg mebendazole (MBZ) single dose. One group was given MBZ conventional dose of 100 mg twice daily for 3 days and another group was given albendazole (ABZ) standard dose of 400 mg single dose. Every trial lower MBZ dose 75 mg, 50 mg and 25 mg regimen were highly effective against Ascaris lumbricoides but only moderately effective against Trichuris trichiura and Necator americanus.

Routine use of mebendazole in pregnancy.

INTRODUCTION: The Ministry of Health has recommended the routine administration of a broad spectrum anthelmintic to all pregnant women after completion of the first trimester of pregnancy. OBJECTIVE: To estimate prevalence and intensity of geohelminth infections in pregnant women attending an antenatal clinic in Ragama and determine the use of anthelmintics by them. METHODS: Women on their first visit to antenatal clinics of the University Obstetrics Unit, General Hospital Colombo North, Ragama, during July-August 1995, were recruited for the study. Demographic details, duration of pregnancy and a history of using anthelmintics during the current pregnancy were noted. A stool sample was obtained and examined using modified Kato-Katz technique. RESULTS: 309 pregnant women were studied [mean age 26.6 years (SD 5.3)]. 94 (30.4%) had taken an anthelmintic during the current pregnancy. 78 (25.2%) had taken it in the second trimester, 9 (2.9%) in the third, 6 (1.8%) in the first, and one was uncertain of the timing. Stool samples were obtained from 181 women giving a compliance rate of 58.6%. Prevalence of geohelminth infections were: whipworm 10%, hookworm 2.2%, roundworm 1.1%. The intensities of the infections were mild. 157 (86.7%) did not have any geohelminth infection. Of the 181 women whose stools were examined, 52 had taken an anthelmintic. There was no significant difference in the prevalence of geohelminth infections between this group (6/52; 11.2%) and those who had not taken an anthelmintic (18/129; 13.9%) (Chi-square test). CONCLUSION: It may not be necessary to treat all pregnant women in Sri Lanka with anthelmintics, as some areas have a low prevalence of infection. Routine anthelmintic therapy could-be limited to areas where prevalence rates are known to be high.

Larva migrans visceral: forma mista de apresentaçäo em adulto: aspectos clínicos e laboratoriais / Visceral larva migrans: a mixed form of presentation in adult patient: clinical and laboratorial features

We relate a case of an 18-year-old man, resident of Xapuri (state of Acre, Brazil), with a history of repeated episodes of meningoencephalitis (three in one year), each one was examined by a local doctor. In our service (Emílio Ribas Institute of Infectology) we observed a patient with polyjoint aches, radiological and bronchoscopic pulmonary alterations (without clinical features), meningeal and brain stem manifestations--with normal brain computed tomography and cerebrospinal fluid. Blood eosinophils and serological Toxocara canis test (ELISA) were greatly increased. With the hypothesis of Toxocariasis (visceral larva migrans) we administered thiabendazole that brought complete clinical and laboratory remission. Inspite of a new episode of headache with meningeal manifestation approximately one month later (treated with dexamethasone resulting in a full remission after three days) we have not found other manifestations in approximately three and a half years of ambulatory care.

The efficacy of three anthelmintic drugs given in a single dose.

OBJECTIVE: To compare the efficacy of a single dose mebendazole 500 mg from the original manufacturer and a formulation locally produced by State Pharmaceuticals Manufacturing Corporation of Sri Lanka and albendazole 400 mg in mass treatment of soil-transmitted nematode infections. DESIGN: Randomised trial. SETTING: Government owned plantations in low-country regions of Sri Lanka with poor sanitary facilities. SUBJECTS: 399 children 3 to 15 years of age infected with at least one type soil-transmitted nematode. INTERVENTION: Mebendazole 500 mg or albendazole 400 mg given as single dose treatment. MEASUREMENTS: Cure rates and egg reduction rates calculated from egg counts of pre- and post-treatment stool samples using the quantitative Kato-Katz technique. RESULTS: All three drugs were effective against Ascaris infection with cure rates above 95%. The efficacy against Trichuris trichuria was uniformly poor. For hookworm infection albendazole appeared to be more effective in a single dose with cure rates of 77.9% compared with 28.7% and 35.8% for the two mebendazole formulations; corresponding egg reduction rates were 95.4% compared with 72.0% and 74.5%. CONCLUSION: Albendazole is the drug of choice for mass deworming where hookworm disease is prominent. There was no statistically significant difference between the original and locally produced mebendazole.

Single doses of ivermectin 400 micrograms/kg-1: the most effective dosage in bancroftian filariasis.

Forty-three Wuchereria bancrofti carriers were given four successive semi-annual single doses of ivermectin 100 micrograms.kg-1 (IVER 100). The geometric mean microfilaremia (mf) recurrence percentage as compared to the pre-initial treatment mf level was 35%, 21%, 17% and 17% at 6, 12, 18 and 24 months, respectively. However, the recurrence of mf 6 months after the fourth treatment remained high in several individuals: 15 have been considered as 'bad responders' and 28 as 'good responders' individuals. At month 24 (M 24), they were randomly allocated into 2 groups. A first group was treated with a fifty and a sixth dose of IVER 100, at M24 and M30, respectively; the second one was treated, at the same time, with single doses of IVER 400 micrograms.kg-1 (IVER 400). At M 36, the mf recurrence percentage (mf M36/mf M0) was significantly higher in patients treated with IVER 100 than IVER 400 (11% vs 1%, p < 10(-4). From the group IVER 100, 6 out of the 8 'bad responders' remained 'bad responders' whereas there were none of the 7 in the group IVER 400. Moreover, there were only 2 more patients in the group IVER 100 showing sustained complete zero mf, whereas they were 13 in the group IVER 400. Single doses of IVER 400 were effective on 'bad responders'; IVER 400 must be recommended for semi-annual mass treatment in bancroftian filariasis.