Biomedical subjects
Publications and source records attributed to N L Nguyen.
Explore the source record for details and available documents.
OBJECTIVES: To describe the prevalence and characteristics of isolates of Neisseria gonorrhoeae grown from urine samples that produced negative results with nucleic acid amplification assays (NAA) targeting the cppB gene. METHODS: An initial cluster of culture positive, but cppB gene based NAA negative, gonococcal infections was recognised. Urine samples and suspensions of gonococci isolated over 9 months in the Northern Territory of Australia were examined using cppB gene based and other non-cppB gene based NAA. The gonococcal isolates were phenotyped by determining the auxotype/serovar (A/S) class and genotyped by pulsed field gel electrophoresis (PFGE). RESULTS: 14 (9.8%) of 143 gonococci isolated were of A/S class Pro(-/)Brpyut, indistinguishable on PFGE and negative in cppB gene based, but not other, NAA. CONCLUSIONS: This cluster represents a temporal and geographic expansion of a gonococcal subtype lacking the cppB gene with consequent loss of sensitivity of NAA dependent on amplification of this target. Gonococci lacking the cppB gene have in the past been more commonly associated with the PAU-/PCU- auxotype, a gonococcal subtype hitherto infrequently encountered in Australia. NAA based on the cppB gene as a target may produce false positive as well as false negative NAA. This suggests that unless there is continuing comparison with culture to show their utility, cppB gene based NAA should be regarded as suboptimal for use either as a diagnostic or supplemental assay for diagnosis of gonorrhoea, and NAA with alternative amplification targets should be substituted.
Semi-annual mass DEC chemotherapy combined with vector control at the beginning of the programme, has been administered on the remote island of Maupiti (French Polynesia) since 1955 (except two periods in 1960-67 and 1970-74). The results of two surveys in 1985 and 1989, reporting 0% microfilaraemia, led to the hope that the eradication of lymphatic filariasis had been achieved. We combined parasitological criteria (microfilaraemia by membrane filtration), immunological (antigenaemia and serum levels of specific IgG antibodies) and molecular (PCR-based evaluation of infection in mosquitoes) techniques and found only good control of the parasite: We found residual microfilaraemia in 0.4% of the sample (mean level in carriers: 101.2 mf/ml), antigenaemia in 4.6% (mean level in positive persons: 714.4 units/ml) and specific IgG in 21.6% (including in one very young child). In addition, an infection rate of 1.4% was calculated in the Aedes polynesiensis vector population. These data, obtained in 1997 just before a hurricane, were partially confirmed in 1999 (0.1% of infection rate in the vector). Together with the possibility of some resistance to DEC, various epidemiological factors critical for the eradication of lymphatic filariasis are discussed.
Two rapid immunodiagnostic tests (ICT Filariasis test), developed for the quick diagnosis of Wuchereria bancrofti infection, have been validated in laboratory and field situation. The aim of this study was to assess the performance and usefulness of this antigen capture assay as a diagnostic method in three foci of lymphatic filariasis, located in the South Pacific (Society archipelago, French Polynesia), with different levels of endemicity. A sample of 1,595 patients was tested with this assay in parallel with a reference Og4C3 antigen capture assay and microfilariae detection. A second-generation ICT test, available for whole blood analysis, was also tested in parallel with the first generation test, developed for serum analysis, on a sample of 50 reference cases. The correspondence between the results obtained with the two rapid tests was excellent, without any influence of rheumatoid factors, but the sensitivity was in both cases slightly inferior to the one obtained with the ELISA reference test. This seems particularly true in epidemiological situation where a high proportion of amicrofilaraemic, adult worm carriers are observed.
Explore the source record for details and available documents.
In March 1991, a study on Wuchereria bancrofti (Cobbold, 1887) infection rates in its vector, Aedes polynesiensis Marks, was carried out in a village of French Polynesia. Our data were collected 10 yr after the suspension of human mass chemoprophylaxis and served as a baseline for pending ivermectin treatment scheduled in 1991-1993. In total, 1,789 biting females were collected, of which 1,740 were dissected and 1,183 (68%) were parous. Among these, 106 (8.96%) were infected with W. bancrofti and 34 (2.87%) harbored infective L3 larvae. The mean number of larvae per infected mosquito was 2.69, and the mean number of L3 larvae per L3 positive mosquito was 1.44. The Ae. polynesiensis biting index was 4.7 bites per 15 min, but varied significantly among habitats. The highest parous biting rates occurred in fields and peridomestic gardens and the lowest was close to houses. The proportion of parous infected and infective mosquitoes was higher in peridomestic habitats (0.25 infective bites per 15 min) than in domestic habitats (0.09) or in fields (0.11).
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Og4C3 circulating filarial antigen was detected in the sera of 94.5% (259/274) of microfilaremic patients, 32% (239/751) of persons with presumption of filariasis, and 23% (11/48) of chronic filariasis patients. The antigen level was correlated with the microfilariae (Mf) density and patient age (P < .01). It remained stable in patients treated with microfilaricidal drugs. Og4C3 antigen, undetectable in Mf culture media, was demonstrated to be a rare somatic Mf antigen. It appears to be an excreted or secreted antigen from adult filaria. It could be used as a marker of infection and an indicator of adult worm burden.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
In April 1991 supervised mass prophylaxis of lymphatic filariasis with a single dose of ivermectin, 100 micrograms/kg, was carried out in a Polynesian village with a high infection rate of Wuchereria bancrofti in humans and active transmission by the vector mosquito, Aedes polynesiensis. Of 876 inhabitants aged 3 years or more (pregnant women excluded), 864 (98.6%) were treated. Simultaneously, venous blood samples were collected from 577 (97.5%) of the 595 inhabitants aged 15 years or more, of whom 122 (21.4%) were found to be microfilaria (mf) carriers (86 males and 36 females). The geometric mean microfilariae (GMM) count was 358.7 mf/ml for the whole group, 387 mf/ml for males (range 1-8160 mf/ml) and 280 mf/ml for females (range 1-7769 mf/ml). Following treatment, 33 (3.8%) of the 864 persons treated experienced some adverse reactions (21 with grade 1 and 12 with grade 2). Of the 33 with reactions, 29 were among the 122 (23.8%) mf carriers and 4 among the 831 (0.5%) non-microfilaraemic persons. Six months later, 123 (21.1%) of 584 inhabitants sampled were microfilaraemic: the GMM count for the whole group was 106 mf/ml (1-8177), with 29 mf/ml (1-3740) in 35 female and 177 mf/ml (1-8177) in 88 male carriers. Of these 123, 15 (whose GMM count was 4.5 mf/ml; range 1-204) were amicrofilaraemic 6 months before, and 19 had a microfilaraemia level higher than that 6 months earlier, before treatment. 117 of the 122 carriers identified in April were resampled: comparison of their GMM counts before and 6 months after mass treatment indicated that treatment with a single dose of 100 micrograms/kg ivermectin resulted in a reduction of microfilaraemia by 69%.
In 1991, a study on Wuchereria bancrofti microfilariae (mf) and infection rates was carried out in the human and mosquito populations of a Polynesian village where, 10 years before, the mf prevalence rate was 6.4% and twice-yearly mass treatment with 3 mg/kg of diethylcarbamazine (DEC) was interrupted. Venous blood samples were collected from 575 (97%) individuals aged 15 years or more, of whom 122 (21.4%) were mf positive. The mf carrier prevalence rate was 27.4% in males, significantly higher than that of 14% in females; it increased from 7-12% in the youngest age group (15-19 years) to 40-50% in the oldest (> or = 60 years) for both males and females. 387 mosquito collections were performed and 1748 female Aedes polynesiensis were dissected, of which 1176 were parous. Among the latter, 114 (9.7%) were infected with Wuchereria bancrofti larvae at L1, L2 or L3 stages. The mean number of larvae per mosquito was 2.46 (range 1-15). Of the 114 infected mosquitoes, 30 harboured L3 larvae, giving a 2.55% infective rate; the mean number of L3 larvae per mosquito was 1.15 (range 1-2). Such findings indicate that the interruption of systematic twice-yearly mass treatment with DEC (3 mg/kg) has resulted, after 10 years, in a substantial increase of microfilarial prevalence in humans, and in high infection rates in mosquitoes.
In April and October in 1991-1993, 5 supervised single doses of ivermectin were given to inhabitants aged > or = 3 years in a Polynesian district: the first 3 treatments were with 100 micrograms/kg and the 2 latter with 400 micrograms/kg. At each treatment, about 97% of the eligible population (899) were treated and blood samples were collected just before treatment from 96% of the 613 inhabitants aged > or = 15 years. Following the 5 successive treatments, adverse reactions were observed in, respectively, 23.8, 13, 6.2, 13.6 and 7.9% of the microfilariae (mf) carriers, and in less than 1% of amicrofilaraemic subjects. Neither the frequency nor the intensity of adverse reactions was significantly different between single doses of 100 micrograms/kg and 400 micrograms/kg. Although the geometric mean microfilaraemia (GMM) was reduced, the mf carrier prevalence remained unchanged before and after 3 mass treatments with 100 micrograms/kg (21.4 and 20.7% respectively), and the mf recurrence rate 6 months after each dose of 100 micrograms/kg was roughly stable (respectively, 34.3%, 21.6% and 31.2% of the initial GMM). In contrast, after one dose round of 400 micrograms/kg, the mf carrier prevalence decreased significantly to 14.9% (P < 10(-6)), and the mf recurrence rate dropped to 9.9% (P < 10(-3)) of the initial GMM. These results confirm the safety and the effectiveness of 400 micrograms/kg of ivermectin for lymphatic filariasis control.
Community treatment with ivermectin was implemented in Opoa, French Polynesia from April 1991 to October 1993. All consenting inhabitants aged 3 years or more were treated with twice-yearly single doses of ivermectin, pregnant women excepted. A dosage of 100 microgram/kg was used for the 3 first treatments and then abandoned because it did not reduce the prevalence of microfilariae (mf) carriers. With a dosage of 400 micrograms/kg dosage, this prevalence decreased dramatically from 21% to 7%, and the mf level in carriers dropped to only 0.5% of its initial value after 3 treatments. The 400 micrograms/kg dosage was well tolerated and compliance was excellent. The twice-yearly single dose strategy with ivermectin at 400 micrograms/kg is safe and highly effective for filariasis control in an endemic area.