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J Remme

Publications and source records attributed to J Remme.

At least 37 records · Page 2Linked to original sources
PubMed1992

Ocular onchocerciasis and the intensity of infection in the community. IV. The degraded forest of Sierra Leone.

To assess the pattern of onchocercal ocular disease and blindness in south Sierra Leone, ophthalmological surveys were carried out in 13 highly infected villages located in various river basins. The most important finding was the blinding potential of onchocerciasis in the degraded forest area where the prevalence of onchocercal blindness reached levels of up to 6%. This is remarkable since previous studies have claimed onchocerciasis in the forest to cause little blindness. Ocular onchocerciasis undoubtedly constitutes a problem of public health importance in south Sierra Leone. The rates of onchocercal ocular disease and blindness, however, were significantly lower than those found in savanna villages with similar levels of endemicity. The community pattern of ocular onchocerciasis was not significantly different from the classical pattern in the forest but this could be explained by the low endemicity levels in the forest villages studied. It is therefore not possible to deduce from this study whether the pattern of ocular onchocerciasis in south Sierra Leone is of the forest type, or a pattern on its own.

Adolescent↗
PubMed1991

The reproductive lifespan of Onchocerca volvulus in West African savanna.

The epidemiological model ONCHOSIM--a model and computer simulation program for the transmission and control of onchocerciasis--has been used to determine the range of plausible values for the reproductive lifespan of Onchocerca volvulus. Model predictions based on different lifespan quantifications were compared with the results of longitudinal skin-snip surveys undertaken in 4 reference villages during 13 to 14 years of successful vector control in the Onchocerciasis Control Programme in West Africa. Good fits between predicted and observed trends in skin microfilarial loads could be obtained for all villages. It is concluded that the reproductive lifespan of the savanna strain of O. volvulus lies between 9 and 11 years, and that 95% of the parasites reach the end of reproduction before the age of 13 to 14 years.

Africa, Western↗
PubMed1991

Detailed epidemiological mapping of three onchocerciasis foci in West Africa.

Detailed epidemiological mapping of three isolated foci of hyperendemic blinding onchocerciasis was undertaken in three West African countries as part of community trials of ivermectin, a new microfilaricide for the treatment of human onchocerciasis. The results show that the geographical distribution of the prevalence and intensity of onchocerciasis infection in the community can be very different from what was expected on the basis of demographic and entomological information. The technique of detailed epidemiological mapping is an important tool for the identification of target populations for large scale ivermectin treatment of onchocerciasis. It is being used extensively in the Onchocerciasis Control Programme in West Africa.

Africa, Western↗
PubMed1991

Importance of migrants infected with Onchocerca volvulus in west African river valleys protected by 14 to 15 years of Simulium control.

A study was done to determine the importance of human migration from non-controlled endemic onchocerciasis foci to the river valleys that have been protected for the past 14 to 15 years by the vector control operations of the Onchocerciasis Control Programme in West Africa. The aim of the study was to assess the contribution of migrants to the prevalence and intensity of infection in villages from 5 major river valleys and their potential role in causing relapse of transmission once the vector is allowed to return. In Burkina Faso the migrant population varied from 0.0% to 18.1% of the village population, and averaged 4.9%. Migrants accounted only for 0.6% of the population in Ghanaian and Ivorian villages along the Black Volta river. The prevalence of infection was significantly higher in migrants (8.2%) than in non migrants (1.1%) in the surveyed villages in Burkina Faso, and 1.5% of migrants had infections with more than 16 microfilariae per snip as against 0.2% of non migrants. Nearly all infected migrants came from the south of the Côte d'Ivoire. The study shows that human migration has caused the importation of Onchocerca volvulus from non-controlled areas. However, the epidemiological importance of this phenomenon is limited because of the very small number of infected migrants per village while two-third of the infected migrants are believed to be infected with the less pathogenic forest strain of the parasite. Because migration patterns changes geographically and over time similar studies will be continued on a regular basis.

Animals↗
PubMed1991

Onchocerciasis distribution and severity in five West African countries.

The Onchocerciasis Control Programme in West Africa recently extended its operation to Guinea, Guinea-Bissau, the western part of Mali, Senegal and Sierra Leone. To estimate the number of people infected and blinded by the disease and to determine its distribution and severity in the extension area, 215 villages were selected, using a stratified random sampling procedure, and surveyed. All the relevant entomological information available at the time was used in the sampling procedure and in the selection of 92 non-representative villages that were surveyed to confirm the findings. In addition, the populations of 608 villages were examined to map out in detail the distribution of onchocerciasis in the areas at a high risk of onchocercal blindness. The study estimated that 1,475,367 people were infected and 23,728 were blinded from onchocerciasis out of a rural population of 4,464,183. The northern and western part of the study area and the lower Niger basin presented a low or no risk of onchocercal blindness. The upper Niger basin, the south-central part of Sierra Leone, and three small foci in the Gambia, Bakoye, and lower Niger river basins were areas with a high risk of onchocercal blindness. The other parts of the study area presented a medium risk of onchocercal blindness. By detecting the communities at risk of onchocercal disease this study permits the selection of populations for disease control based on mass distribution of ivermectin, a microfilaricide.

Gambia↗
PubMed1991

The risk and dynamics of onchocerciasis recrudescence after cessation of vector control.

Using a computer simulation study, we have investigated the risk and dynamics of onchocerciasis recrudescence after stopping vector control, in order to provide guidelines for operational decision-making in the Onchocerciasis Control Programme in West Africa (OCP). For this purpose, we used the microsimulation model ONCHOSIM to predict for periods of 9-15 years of vector control the ensuing risk and dynamics of recrudescence in an onchocerciasis focus. The model was quantified and validated using OCP evaluation and field research data. A range of plausible values was determined for important confounding parameters, i.e., vector biting rate, variation in exposure between individuals, parasite life span, and the relation between skin microfilarial load and vector infection. Different model quantifications were used in order to take account of the possible confounding effect of these parameters on the prediction of recrudescence. In the absence of immigration of infected humans or invasion by infected flies, the model predicts that 14 years of full-scale vector control are required to reduce the risk of recrudescence to less than 1%. The risk depends, in particular, on the vector biting rate, and this has implications for the planning of post-larviciding surveillance. Recrudescence will be a relatively slow process, and its rate will depend on the duration of vector control. Even if vector control were stopped too early, i.e., after 12-13 years in a highly endemic area, it would take more than 20 years before the intensity of infection in the community would reach levels of public health importance.

Africa, Western↗
PubMed1990

ONCHOSIM: a model and computer simulation program for the transmission and control of onchocerciasis.

ONCHOSIM is a computer program for modelling the transmission and control of the tropical parasitic disease onchocerciasis, or river blindness. It is developed in collaboration with the Onchocerciasis Control Programme in West Africa (OCP), and is used as a tool in the evaluation and planning of control operations. The model comprises a detailed description of the life history of the parasite Onchocerca volvulus and of its transmission from person to person by Simulium flies. The effects of different control strategies, based on larvicide application and chemotherapy (ivermectin), on the transmission and on the disease symptoms can be evaluated and predicted. In the program two simulation techniques are mixed. Stochastic microsimulation is used to calculate the life events of individual persons and inhabitant parasites, while the dynamics of the Simulium population and the development of the parasite in the flies are simulated deterministically. Output of ONCHOSIM conforms to the format in which data collected by the OCP are reported. This enables detailed checking of model specifications against empirical data. Output can also consist of summarizing key indices for the intensity of onchocerciasis infection, which is especially useful for comparing the effectivity of control strategies.

Animals↗
PubMed1990

The predicted and observed decline in onchocerciasis infection during 14 years of successful control of Simulium spp. in west Africa.

In 55 villages from the well-protected central area of the Onchocerciasis Control Programme in West Africa (OCP), skin snip surveys have been carried out at regular intervals since the programme started, and the latest round of surveys was undertaken after 12-14 years of successful vector control. The observed trends in the prevalence and intensity of onchocerciasis infection in cohorts of adults were compared with the trends predicted using a host-parasite model. After 12-14 years of control the community microfilarial load (CMFL) was close to zero in all villages. During the last few years of control, the prevalence of infection declined at an accelerated rate, and this was predicted by the model. There was generally good agreement between observed and predicted trends. The predictions were based on an estimated average duration of infection of 10.4 years, which corresponds to a mean reproductive lifespan for Onchocerca volvulus of 9-9.5 years, and an upper limit of 15 years for 95% of the infections. Differences between the observed and predicted data included the trend in CMFL between the first and second surveys, which in 18 villages did not show the predicted decline. Furthermore, the observed final decline in prevalence was faster than predicted in the north-eastern part of the central OCP area. After 14 years of vector control, the level of onchocerciasis has fallen to such a low level that consideration is being given to ending larviciding.

Adult↗
PubMed1990

Ocular onchocerciasis and intensity of infection in the community. III. West African rainforest foci of the vector Simulium sanctipauli.

The community pattern of ocular onchocerciasis is described for 11 villages from the forest area in Côte d'Ivoire where S. sanctipauli is the princial vector. An analytical method is applied which relates indices of ocular onchocerciasis with the Community Microfilarial Load (CMFL) and compares the results with the ocular onchocerciasis pattern found in the West African savanna. In spite of high transmission levels as estimated by entomological indices, the CMFLs were relatively low which complicated the characterization of the ocular disease pattern. Nevertheless, it could be shown that ocular onchocerciasis is less severe in the Sanctipauli forest than in the savanna, even after correction for differences in CMFL. The prevalence of onchocercal eye lesions and blindness were low and advanced sclerosing keratitis was completely absent. The differences are explained by presuming strain differences of the parasite Onchocerca volvulus. For given CMFLs the mean microfilarial loads in the eye were significantly lower than in the savanna which suggests that the parasite strain in the Sanctipauli forest is less invasive to the eye. Ocular microfilarial loads were too low to determine if the parasite is also less pathogenic to the eye, as has been concluded previously for foci of S. yahense, but this possibility cannot be excluded.

Animals↗
PubMed1990

Large scale ivermectin distribution and its epidemiological consequences.

Community trials were started to address questions concerning the safety of ivermectin during large scale treatment, its potential for transmission control, its effect in preventing ocular onchocercal disease, its acceptability and the organization of large scale treatment. A summary is presented of the major, latest results on the short-term epidemiological impact of large scale ivermectin treatment, as observed in eight community trials undertaken in the Onchocerciasis Control Programme in West Africa (OCP). Ivermectin treatment resulted in a 96%-99% reduction in the mean load of microfilariae (mf) in the skin in treated patients. The subsequent mf-repopulation of the skin was faster than in the clinical trials and after 12 months the mean loads had returned to more than 40% of the pre-treatment load. Ocular mf loads were also greatly reduced and a post-treatment regression of early lesions of the anterior segment of the eye was observed. The transmission of Onchocerca volvulus was reduced by some 60% during the first year after treatment in one trial but no additional reduction was observed after the second treatment round. These results, and other recent research findings, have been used to quantify an epidemiological model for the transmission and control of onchocerciasis. Preliminary results of computer simulations of the predicted long-term epidemiological impact of large scale ivermectin treatment indicate that ivermectin treatment may play a very important role in disease control but that it is unlikely to become a practical tool for transmission control in endemic foci. Ivermectin treatment appears to be the most appropriate method for control of recrudescence of infection in an area where the parasite reservoir has been virtually eliminated by vector control, such as in the core area of the OCP.

Africa, Western↗
PubMed1990

Epidemiological impact of vector control. I. Incidence and changes in prevalence and intensity of Onchocerca volvulus infection.

Since 1974, the Onchocerciasis Control Programme (OCP) has been engaged in a large scale attempt to control the savanna species of the vector of onchocerciasis in seven West African countries. The effect of the vector control effort has been measured by epidemiological evaluation. For this purpose 474 villages have been examined by means of skin snip surveys between 1975 and 1983 and of these, 184 have been retained to-date for follow-up surveys which have documented over the years the reduction of the parasite population. The latest results of the epidemiological evaluation clearly demonstrate an outstanding success of the vector control campaign. The parasite has been or is close to being eliminated from the hyperendemic foci of the core area of the Programme. Major improvements have been registered in the reinvaded areas located at the Western and Eastern borders of the Programme. A major improvement has been found along the river Marahoué, the only focus of the intermediate area between the savanna and the forest where at the previous survey, the endemic situation was still similar to the pre-control situation. The exceptions to this gratifying picture are foci along the Dienkoa and Kulpawn rivers, both located in the core area, where transmission has relapsed and several more years of an effective vector control will be needed to eliminate the local parasite population.

Adult↗
PubMed1990

Epidemiological impact of vector control. II. Changes in ocular onchocerciasis.

The impact of 10-11 years of successful vector control on ocular onchocerciasis was evaluated in the population of 13 villages in the central part of the Onchocerciasis Control Programme area. The prevalence of ocular microfilariae was found to have reduced remarkably and loads over 20 microfilariae in the anterior chamber of the eye or the cornea which was rampant before the start of vector control, were rare. Whilst limited change in the age specific prevalence of lesions of the posterior segment of the eye was recorded, significant reduction in the prevalence of lesions of the anterior segment of the eye was found. The small decrease in the age specific prevalence of lesions of the posterior segment of the eye was partly explained by a reduced occurrence of the type of lesions of the anterior segment of the eye which previously obstructed the effective view of the fundus during examination. The prevalence of blindness was found to have reduced by 40% and onchocercal blindness was no longer found below the age of 20 years. It was concluded that 10-11 years of successful vector control has effectively reduced the incidence of onchocercal eye lesions, the deterioration of the existing eye lesions and the risk of developing an onchocercal eye lesion as well as going blind to virtually nil.

Adolescent↗
PubMed1990

Prospective evaluation of onchocerciasis control strategies.

After more than 13 years of aerial larviciding, the Onchocerciasis Control Programme in West-Africa (OCP) is considering the future of its control activities. In the original OCP-area the prevalence of infection has been brought down to very low levels and cessation of larviciding is being contemplated. The introduction of ivermectin has broadened the spectrum of available control measures. Countries outside the OCP are also planning chemotherapy-based onchocerciasis control. The prediction of the epidemiological impact of the different control options is difficult in view of the many factors which affect the dynamics of a chronic infectious disease like onchocerciasis. We developed the computer simulation model ONCHOSIM, which takes these many factors and their interrelationships into account. The program has a broad spectrum of uses of which some examples are given. It is explained how the model is used to simulate endemic situations and epidemiological trends during vector control. These trends can be explained in terms of longevity of the parasite and other model parameters. Secondly, predictions are made about the risk of recrudescence after stopping larviciding. Finally, the possible role of ivermectin to control recrudescence after interruption of vector control and to reduce disease symptoms in an endemic situation is explored. The latter application is also important outside the OCP-area. This shows the usefulness of ONCHOSIM as a means for transferring the OCP-knowledge about onchocerciasis control to other countries. From our experience with ONCHOSIM, it is concluded that model based prospective evaluation of control measures is useful in synthesizing existing knowledge, in steering applied research, in interpreting the results of experimental studies, and last but not least, in aiding the policy-making process.

Africa, Western↗
PubMed1989

The third ribosomal tRNA-binding site, the E site, is occupied in native polysomes.

The nucleic acids of Escherichia coli cells were uniformly labelled with 32P by growing the cells in [32P]orthophosphoric acid for about four generations. The cells were harvested in the logarithmic phase, resuspended in a buffer containing 6 mM Mg2+, 150 mM NH4+ and polyamines and incubated for 3 min at 37 degrees C in the presence of 3H-labelled amino acids. This procedure preferentially labels growing peptidyl chains. Polysomes were isolated, the fraction in the post-translocational state was assessed by a puromycin reaction and the tRNA content/70S ribosome was quantified in comparison to the amount of 5S rRNA determined after separation by gel electrophoresis. The data revealed that at least 75% of post-translocational ribosomes in isolated native polysomes carry a tRNA in their E site. The results are consistent with the allosteric three-site model for the elongation cycle but disagree with the two-site model.

Binding Sites↗
PubMed1989

Ocular onchocerciasis and intensity of infection in the community. II. West African rainforest foci of the vector Simulium yahense.

A novel method of analysis was used to describe community patterns of ocular onchocerciasis in relation to the intensity of infection in West African forest villages where S. yahense is the sole vector. The pattern is completely different from that found in the savanna, even after correction for the intensity of infection as measured by the Community Microfilarial Load (CMFL). Lesions of the anterior segment of the eye as well as onchocercal blindness either do not occur or occur only sporadically with increasing CMFL in the Yahense forest whilst a steep linear relation exists between the prevalence of these lesions and the CMFL in the savanna. Lesions of the posterior segment of the eye are also less common in the Yahense forest. For a given skin microfilarial load, the ocular microfilarial load is lower in the Yahense forest. For a given ocular microfilarial load, a lower prevalence of eye lesions is found in the Yahense forest compared to the savanna. It is concluded that microfilariae of Onchocerca volvulus in the Yahense forest are less eye invasive than microfilariae from the savanna. Furthermore, they appear to be also less pathogenic to the eye. These findings explain why ocular onchocerciasis is relatively mild in the Yahense forest, in spite of the high intensities of O. volvulus infection in the community.

Animals↗