Short- and long-term action of multiple doses of ivermectin on loiasis microfilaremia.

One hundred nine Gabonese patients infected with Loa loa microfilariae were treated with ivermectin (200 microg/kg of body weight) at the Parasitology, Mycology and Tropical Medicine Department (Faculte de Medecine et des Sciences de la Sante, Libreville, Gabon). Each was given one dose per month for six consecutive months. The peripheral blood microfilaria (mf) count before and after each dose showed an average decrease in the microfilaremia of 87.3% (short-term-single dose). An annual single-dose mass treatment with 200 microg/kg of ivermectin was sufficient to control the parasite in populations with low (< 400/ml) L. loa mf counts. One month after the sixth dose (short-term-multiple doses), the average microfilaremia rate had decreased by 99.2% compared with the initial infection (35 patients). Samples were taken from 28 patients one month after the first dose and one month after the sixth dose. The average mf count decreased by 96.4% after the first dose and by 99.6% after the sixth dose (average residual mf counts = 13.7 and 1.5 mf/ml, respectively). The mf count after the sixth dose was only 11.2% of the count after the first dose. The low mf count persisted for more than six months after the sixth treatment (long-term-multiple doses). Thus, mass treatment with multiple doses is more appropriate for areas where the blood mf count is very high. These results show that the number of the annual treatments used in mass chemotherapy with ivermectin can be adapted to each population to provide efficient protection.

Detection of circulating antigens in Gabonese patients with Loa loa filariasis.

Circulating antigens were detected in sera of Gabonese patients with Loa loa filarial infection by co-electrosyneresis (Co-ES). The serum samples selected for this study were exposed to rabbit hyperimmune antifilarial antisera and human immune antisera: specific arcs were observed in 35/60 filarial patients, of whom 24/47 were microfilaraemic and 11/13 amicofilaraemic. The identity of rabbit hyperimmune antisera and loiasial immune sera was confirmed by the continuity of precipitation arcs. These preliminary studies were carried out to develop diagnostic tools for loiasis and to study the physiopathology of immune complexes.

Evaluation of Onchocerca volvulus-specific IgG4 subclass serology as an index of onchocerciasis transmission potential of three Gabonese villages.

The major objective of this study was to evaluate the usefulness of IgG4 ELISA and Western blot analysis, using a crude extract of Onchocerca volvulus adult worms as antigens, for diagnosing onchocerciasis in a Gabonese paediatric population with mixed filarial infections. The subjects had loaisis, streptocercosis or mansonellosis in addition to onchocerciasis. Control sera from loaisis or mansonellosis subjects residing outside the endemic zone were used to provide the cut-off point for positive results. The IgG4 ELISA had a specificity of 96% but a lower sensitivity of 78.7%. It detected 25 onchocerciasis cases out of 65 individuals who were negative on parasitological examination. Furthermore, the ELISA provided a more accurate picture of onchocerciasis transmission in a village with very low skin microfilarial load. A 27.5-kD antigen was identified on Western blots as a marker of onchocerciasis. The paediatric population provided a reliable window for assessing the parasitologic and serologic parameters in the three villages with disparate levels of onchocerciasis transmission.

[Evaluation of 3 tests applied in the immunological diagnosis of hepatic amebiasis in Gabon]. / Evaluation de trois tests appliqués au diagnostic immunologique de l'amibiase hépatique au Gabon.

The diagnosis of hepatic amoebiasis is not always easy. In case of suspicion of hepatic amoebiasis in an endemic area, the patient is immediately treated with a 5-nitroimidazole. Immunological diagnosis is indispensable. After a comparative study of BLA, IHA and IFA reactions, the BLA test has shown to be well adapted to the context of a country with insufficient sanitary infrastructure. The BLA test is easily performed and enables rapid detection of antibodies. The result obtained in about 5 minutes allows to adjust the therapeutic conduct.

Elevated antifilarial IgG4 antibody levels in microfilaremic and microfilaridermic Gabonese adults and children.

Immunologic analyses of sera from 47 selected individuals living in a mixed filariasis transmission zone in Gabon were carried out. Onchocerca volvulus, Loa loa, Mansonella streptocerca, and M. perstans are transmitted in this region. Based on parasitologic findings and age, the 47 individuals were stratified into four groups: microfilaria negative (Mf-) children (3-15 years old), Mf- adults (> 15 years old), microfilaria positive (Mf+) children and Mf+ adults. For descriptive purposes, the term microfilaria positive refers to individuals with skin and blood microfilariae. Antifilarial antibody titers were determined using an enzyme-linked immunosorbent assay with Dipetalonema viteae antigens. In general, children had higher titers of IgG antibodies than adults. For the IgG1, IgG2, and IgG3 subclass responses, both age and microfilarial status appeared to be important variables since Mf- children consistently had the highest titers whereas Mf- adults had the lowest titers. For the IgG4 antifilarial response, only the microfilarial status was an important variable. All Mf+ individuals had significantly higher levels of IgG4 antibody than Mf- individuals. Pooled sera of Mf- and Mf+ individuals reacted with similar O. volvulus antigens on Western blots. Control sera of individuals who did not reside in the study area, but who had single infections with L. loa or M. perstans, did not react with any O. volvulus antigens.

Ivermectin in loiasis and concomitant O. volvulus and M. perstans infections.

Two clinical studies were carried out in Gabon, Africa to evaluate the efficacy, safety, and tolerability of ivermectin in the treatment of patients with Loa loa infection. In the first study, 35 patients received single oral doses of ivermectin, 5-200 mcg/kg body weight. Blood microfilariae levels did not decrease after a single oral 5, 10, 30, or 50 mcg/kg dose of ivermectin, but levels did decrease after doses of 100, 150, and 200 mcg/kg. The most efficacious dose was 200 mcg/kg; mean blood microfilariae levels decreased to 12% of mean pretreatment values by day 15 and remained decreased for 28 days. A second study evaluated the safety and efficacy of ivermectin in patients with multifilarial infections. All 17 patients had concomitant Loa loa and O. volvulus infection. M. perstans affected 5 of the patients. Sixteen patients also had infections due to intestinal nematodes. The patients each received single oral doses of 200 mcg/kg ivermectin. Ten days later, the mean Loa loa blood microfilariae level had decreased to 20% of the mean pretreatment level. O. volvulus dermal microfilariae densities were reduced to 2% of the pretreatment levels. A minimal increase in blood microfilaria levels was observed on day 28. In contrast, dermal microfilariae levels remained near zero for the duration of the study. Intestinal infection due to Ascaris was eradicated in all of the affected patients by day 23; efficacy against Trichuris and hookworm infections, however, was poor. All patients tolerated ivermectin well including those with multiple infections.

[Malaria in Gabon. 2. Evaluation of the qualitative and quantitative prevalence of parasites in the total school and preschool population of the country]. / Le paludisme au gabon. 2. Evaluation des prévalences parasitaires qualitatives et quantitatives sur l'ensemble du pays en milieu scolaire et préscolaire.

The distribution of carriers of hematozoa in the pre-school and school age group in Gabon has been established with the help of systematic enquiry. The plasmodial indexes vary between 11 and 32% in the savanna zones of the south-east, they rise to 64.9% in the forest regions of the north of the country, and in the urban zones (Libreville, Franceville, Lambarene) 6 to 18% of the school children are gametocyte carriers. In Libreville, amongst the febrile children seen in pediatric consultation, the prevalence reached 30%. Boys and girls are equally affected. The most important prevalence is observed in the group of children from 5 to 10 years of age. P. falciparum is found in 96.4% of the cases, P. malariae in 5.3% and P. ovale in 2.4%. The study of the parasitic load revealed that 56% of the positive subjects had less than 10,000 asexual forms/mm3, 44% more than 10,000 hematozoa/mm3. These results are similar to those of the neighbouring countries of equatorial Africa.