High dose artesunate in combination with mefloquine: pharmacovigilance in the Venezuelan Amazon.

Forty-six patients in a remote health post of Amazonas, Venezuela, accidentally received artesunate in a dose of 10 mg/kg/day combined with mefloquine. This corresponds to the upper limit of the therapeutic range recommended by the WHO (2-10 mg/kg/day). Side effects were retrospectively investigated and a pharmacovigilance report was written. The main side effects were vomiting and diarrhea. Four patients developed complications with signs of dehydration. It is suggested to re-assess the therapeutic range of artesunate when given in combination with mefloquine and to establish a worldwide centralized antimalarial toxicity reporting system.

Assessment of routine malaria diagnosis in the Venezuelan Amazon.

The quality of routine malaria diagnosis is a crucial topic of malaria control. The aim of this assessment was to monitor and evaluate the quality of routine malaria diagnosis in Amazonas (Venezuela) and to improve the quality control system. The traditional non-blinded quality control system was found to be overburdened with diagnostic samples. A modified sampling system with fewer samples to be tested was proposed. Expert microscopists blindly double-checked 1000 slides and 550 rapid diagnostic tests (RDT) (OptiMAL-IT) from health posts (HP). For Plasmodium vivax, HP microscopy and OptiMAL-IT showed sensitivies of 86% and 63%, respectively. For P. falciparum, HP microscopy and OptiMAL-IT showed sensitivities of 68% and 89%, respectively. Both methods lost accuracy when fewer parasites occurred in the sample. HP microscopists from different municipalities displayed significant differences in diagnostic quality. Overall, quality of routine malaria diagnosis in the Venezuelan Amazon is good but not optimal. The change from the traditional non-blinded quality control system to blinded cross-checking of a minimal selection of samples is - comparatively - a low cost intervention with possibly high impact on the quality of routine malaria diagnosis. The introduction of RDTs should be discussed carefully in order not to displace an existing network of HP microscopists.

Anaemia and malaria in Yanomami communities with differing access to healthcare.

Inequitable access to healthcare has a profound impact on the health of marginalised groups that typically suffer an excess burden of infectious disease morbidity and mortality. The Yanomami are traditionally semi-nomadic people living in widely dispersed communities in Amazonian Venezuela and Brazil. Only communities living in the vicinity of a health post have relatively constant access to healthcare. To monitor the improvement in the development of Yanomami healthcare a cross-sectional survey of 183 individuals was conducted to investigate malaria and anaemia prevalence in communities with constant and intermittent access to healthcare. Demographic and clinical data were collected. Malaria was diagnosed by microscopy and haemoglobin concentration by HemoCue. Prevalence of malaria, anaemia, splenomegaly, fever and diarrhoea were all significantly higher in communities with intermittent access to healthcare (anaemia 80.8% vs. 53.6%, P<0.001; malaria 18.2% vs. 6.0%, P=0.013; splenomegaly 85.4% vs.12.5%, P<0.001; fever 50.5% vs. 28.6%, P=0.003; diarrhoea 30.3% vs.10.7% P=0.001). Haemoglobin level (10.0 g/dl vs. 11.5 g/dl) was significantly associated with access to healthcare when controlling for age, sex, malaria and splenomegaly (P=0.01). These findings indicate a heavy burden of anaemia in both areas and the need for interventions against anaemia and malaria, along with more frequent medical visits to remote areas.

Malaria diagnosis under field conditions in the Venezuelan Amazon.

To improve practical, accurate diagnosis of malaria in the Amazon rainforest of Venezuela, two rapid diagnostic tests (RDT) (OptiMAL-IT) and FalciVax) and a laboratory light microscope, used in the field with a battery-operated head lamp as an external light source, were evaluated against the standard laboratory microscope procedure for malaria detection. One hundred and thirty-six Yanomami patients were studied for the presence of malaria parasites. Thirty-three patients (24%) were positive for malaria (Plasmodium falciparum, P. vivax, P. malariae). Twenty-one (64%) of the positive patients had <100 parasites/microl. Both RDTs showed poor sensitivity (24.2% for OptiMAL-IT) and 36.4% for FalciVax) but good specificity (99% both for OptiMAL-IT) and FalciVax). Field and laboratory microscopy showed sensitivities of 94% and 91%, respectively. The kappa coefficient was 0.90, indicating a high agreement between field and laboratory microscopy. We conclude that (i) adequate slide reading cannot be substituted by either of the two RDTs in the Venezuelan Amazon and (ii) the use of a light source such as that described above makes slide reading more feasible than hitherto in remote areas without electricity.

Geographical patterns of onchocerciasis in southern Venezuela: relationships between environment and infection prevalence.

Onchocerciasis is a chronic filarial infection transmitted by Simulium flies that has a focal geographical distribution in Latin America. The southern Venezuelan focus has a gradient of endemicity that includes the largest number of hyperendemic communities in the continent, many of them in remote forest and mountainous areas, where it is an important public health problem among the Yanomami indigenous population. The recent introduction of Geographical Information Systems (GIS) tools and a landscape epidemiology approach for study of vector borne diseases is helping to understand relationships between environment and transmission dynamics of onchocerciasis. Striking differences in the transmission dynamics of onchocerciasis between different river courses were detected. A significant relationship between onchocerciasis and temperature was also demonstrated. The geologic substrate, kind of landscape and vegetation seemed also to influence the transmission of onchocerciasis. In the Venezuelan Amazon, different kinds of landscapes associated with distinctive vector species, show different intensities of transmission of onchocerciasis. In this sense, landscape analysis aided by GIS, may prove to be a useful tool for better identification of the spatial distribution of onchocerciasis risk in the Orinoco basin.

Diurnal biting periodicity of parous Simulium (Diptera: Simuliidae) vectors in the onchocerciasis Amazonian focus.

We describe the hourly patterns of parous biting activity of the three main simuliid vectors of human onchocerciasis in the Amazonian focus straddling between Venezuela and Brazil, namely, Simulium guianense s.l. Wise; S. incrustatum Lutz, and S. oyapockense s.l. Floch and Abonnenc. Time series of the hourly numbers of host-seeking parous flies caught in five Yanomami villages during dry, rainy, and their transition periods from 1995 to 2001 were investigated using harmonic analysis (assuming an underlying circadian rhythm) and periodic correlation (based on Spearman's r). Parous S guianense s.l. showed a bimodal activity pattern, with a minor peak in mid-morning and a major peak at 16:00 h. S. incrustatum exhibited mainly unimodal activity during either early morning or midday according to locality. S. oyapockense s.l. bit humans throughout the day mainly between 10:00 and 16:00 h but also showed bimodal periodicity in some localities. Superimposed on the endogenous, species-specific daily cycles, parous activity showed variation according to locality, season, air temperature and relative humidity, with biting being promoted by warmer and drier hours during wet seasons/periods and reduced during hotter times in dry seasons or transitions. The results are discussed in terms of their implications for blackfly biology and ecology as well as onchocerciasis epidemiology and control.

Human onchocerciasis in the Amazonian area of southern Venezuela: spatial and temporal variations in biting and parity rates of black fly (Diptera: Simuliidae) vectors.

We investigated some entomological factors underlying altitudinal prevalence variation in the Venezuelan Amazonia human onchocerciasis focus. Spatial and temporal variation in relative abundance, daily biting rate, proportion of parous flies, and monthly parous biting rate were studied for the three main simuliid vectors (based on their vectorial competence: Simulium oyapockense s.l. Floch & Abonnenc approximately = S. incrustatum Lutz << S. guianense s.l. Wise). Yanomami villages were selected among sentinel communities of the ivermectin control program, representing hypo- to hyperendemicity conditions of infection. Spatial variation was explored via increasing village altitude on two river systems (A: Ocamo-Putaco and B: Orinoco-Orinoquito). Temporal variation was studied between 1995 and 1999 by sampling the biting population during dry and rainy mouths. Environmental variables included monthly rainfall and maximum river height. Simuliid species composition itself varied along the altitudinal and prevalence gradient. S. oyapockense s.l. prevailed below 150 m. Above this altitude and up to 240 m, S. incrustatum and S. guianense s.l. became more frequently and evenly collected along A but not along B, where S. incrustatum remained absent. The daily biting rate of S. oyapockense s.l. was higher during the dry season along A, whereas the converse took place along B. Daily biting rate of S. incrustatum was lowest during early rains. By contrast, the daily biting rate of S. guianense s.l. was highest during this period. There was a significant negative cross-correlation between proportion of parous of S. oyapockense s.l. and river height (2 and 3 mo lagged), whereas this variable (1 and 2 mo lagged) was positively correlated with the proportion of parous flies for S. incrustatum. Monthly parous biting rate values suggest that the months contributing most to onchocerciasis transmission in the area are likely to be the dry season and the transition periods between seasons.

Amazonian onchocerciasis: parasitological profiles by host-age, sex, and endemicity in southern Venezuela.

This paper describes, for the human onchocerciasis focus of southern Venezuela, the age profiles of Onchocerca volvulus microfilarial (mf) and nodule prevalence, mf intensity, and mf aggregation for the whole examined population (836 Yanomami people) living in 20 villages, and for these communities classified according to endemicity levels (hypoendemic: < or = 20 %; mesoendemic: 21-59 %; hyperendemic: < or = 60 % infected). Mf prevalence and intensity increased with age, particularly in the hyperendemic areas, and there were no marked differences between the sexes. The prevalence of nodules followed the same age pattern. Fifty percent mf prevalence was reached in the 15-19 year age-class when the population was taken as a whole; nearly in the 10 to 14-year-olds for the hyperendemic level, in those aged 20-29 years in mesoendemic areas, and not reached at all in hypoendemic villages. The degree of mf aggregation was measured by the k value of the negative binomial distribution and by the variance to mean ratio (VMR). The relationship between the standard deviation (S.D.) of mf counts and the mean mf density was also explored. These 3 indices (k, VMR, and S.D.) showed a tendency to increase with both mean mf load and host age. Since infection intensity and host age were themselves positively related, it was not possible to draw definite conclusions about age-specific changes of parasite aggregation. There was not a significant decrease of mf intensity after an earlier peak neither was there a shift towards younger ages of the maximum no. of mf/mg reached as the endemicity level increased. These results are discussed in relation to detection of density dependence in the human host, selection of an indicator age-group for rapid epidemiological assessment (REA) methods, and strategies of ivermectin distribution in the Amazonian focus. It is recommended that, for the Amazonian onchocerciasis focus, the indicator group for REA consists of all those aged 15 years and over.

Parasitological indicators of onchocerciasis relevant to ivermectin control programmes in the Amazonian focus of Southern Venezuela.

In the previous paper it was concluded that those aged > or = 15 years of both sexes could comprise the indicator group for rapid epidemiological assessment (REA) of onchocerciasis in the Amazonian focus. This paper explores relationships between community microfilarial (mf) prevalence, intensity, and nodule prevalence in 20 Yanomami communities, that would allow identification of REA methods in the region. The mean nodule ratio (prevalence of nodules/prevalence of mf) was 0.54 when onchocercomata in the indicator group were considered. The Spearman correlation coefficient between mf and nodule prevalence was 0.686 (P = 0.001). Palpation of nodules had 92 % specificity and 32 % sensitivity when compared to skin-snipping for the diagnosis of onchocerciasis. The predictive value positive increased from 75 % to 81 % when the indicator group was used. A microfilarial prevalence > 75 % in this group would be indicative of hyperendemic status in the village, between 30 and 75 % of mesoendemicity, and < 30 % of hypoendemicity. For the assessment of infection intensity, biopsies may be taken from the iliac crest for all endemicity levels. Five of the hyperendemic villages surveyed in this work had a community microfilarial load (CMFL) greater than 10 mf/skin snip; the remaining 5 had a CMFL between 5 and 9. These levels of infection merit high priority ivermectin treatment. In Latin America, communities at both moderate and severe risk are included in mass chemotherapy programmes (i.e. when mf prevalence is over 20 %). Roughly, a nodule prevalence in the indicator group > 10 % would suggest a community mf prevalence > 20 % with a sensitivity of 85 % and a specificity of 71 %. A multiple linear regression model of the arc-sine transformed mf prevalence in the village (all ages) on nodule prevalence in those aged > or = 15 years and altitude of the village explained 72 % of the variance. The model combining nodule and altitudinal information had a sensitivity of 92 % and a specificity of 71 % in comparison to an estimated mf prevalence of 21 % or more. It is suggested that the usefulness of the REA methods proposed be assessed in other areas of the Amazonian onchocerciasis focus.

Onchocerciasis hyperendemic in the Unturán Mountains: the value of recombinant antigens in describing a new transmission area in southern Venezuela.

A recently described hyperendemic onchocerciasis area, located in the Unturán Mountains (between the Siapa and Orinoco basins) of southern Venezuela was studied using a cocktail of 3 low molecular weight onchocercal recombinant antigens (OvMBP/10, OvMBP/11, and OvMBP/29). The resulting seroepidemiological data were compared with those from a hypoendemic community (Altamira) situated in the northern coastal mountain range. Parasitological (skin biopsy) and serological (enzyme-linked immunosorbent assay, ELISA) methods for the specific diagnosis of Onchocerca volvulus in these 2 very different endemic areas were, respectively, 88% and 96% sensitive in Unturán, and 57% and 91% sensitive in Altamira. The mean microfilarial load, the mean optical density (OD), and the seropositivity rates all increased significantly with age in both communities. The serological variables (mean OD and prevalence of anti-O. volvulus antibodies) were both significantly higher in Unturán than in Altamira for children and young adults (aged < 25 years), although above this age no differences between communities were detected. Seroprevalence had already reached 50% in the under 15 year-olds examined at Unturán but was just 5% at Altamira for the same age-class. The prevalence of specific antibodies (mainly a marker of exposure to risk of infection) exceeded 85% in the remaining age-categories at the hyperendemic area. This is in agreement with the high community microfilarial load recorded in Unturán (> 20 mf/mg) and the presence of sclerosing keratitis and hanging groin, suggesting that onchocerciasis is a public health problem in this community. The ELISA test used here, based on a cocktail of 3 low molecular weight onchocercal recombinant antigens, appears, therefore, to constitute a practical tool for the description of endemicity levels in remote areas, particularly given the fact that finger-prick blood samples are routinely taken from children in the Upper Orinoco region for surveys of malaria incidence. Such studies could aid in defining the true extent of the Amazon focus (still unknown) and providing priority indicators for the selection of communities where onchocerciasis control programmes should be implemented.

Onchocerciasis in the Amazonian focus of southern Venezuela: altitude and blackfly species composition as predictors of endemicity to select communities for ivermectin control programmes.

In preparation for an ivermectin distribution programme, the prevalence and intensity of infection due to Onchocerca volvulus as well as the species composition and abundance of Simulium vectors were investigated in 22 Yanomami communities situated along 2 altitudinal transects in the southern Venezuelan onchocerciasis focus. These transects corresponded to the Ocamo-Putaco and Orinoco-Orinoquito river systems, covering a range of elevation between 50 m and 740 m above sea level (asl). A total of 831 people underwent parasitological examination in this survey and an additional 196 patients from a previous study, at an altitude of 950 m, were included in the analysis. A total of 92,659 man-biting blackflies were collected and identified to morphospecies. S. oyapockense s.l. was the predominant simuliid up to 150 m asl, whereas S. guianense s.l. and S. incrustatum s.l. prevailed above 150 m. Communities located below 150 m were found to range from hypo- to mesoendemic; all villages above 150 m proved to be hyperendemic (> 60% microfilarial prevalence) and mass ivermectin treatment should be implemented. Age above 10-14 years, altitude of the village and biting rate of S. guianense s.l. up to 200 m asl were found to be statistically significant independent predictors of infection by multivariate logistic regression using a spline model. There were no differences in infection status according to sex. Above 200 m, microfilarial rate and density remained approximately constant, prevalence averaging 79% regardless of blackfly abundance. For the implementation of ivermectin-based onchocerciasis control programmes in the Amazonian focus, altitude and species composition of the blackfly population might be adopted as useful indicators aiding selection of the most affected communities. However, below 200 m additional parasitological indicators may also be necessary. As a direct result of this study, regular mass-ivermectin delivery to meso- and hyperendemic communities is now in progress.