Enteroaggregative Escherichia coli: a public health hazard in Yaounde; Cameroon?

The prevalence of various pathotypes of Escherichia coli was investigated during a case-control study conducted in children diarrhoea in Yaounde. Isolates obtained from the stools samples of children aged 6 months to 5 years were selected on phenotypic basis; and identified by virulence genes detection using polymerase chain reactions. The most prevalent pathotype was enteroaggregative Escherichia coli (25.8). Enteropathogenic Escherichia coli (3.6); enterotoxigenic Escherichia coli (1); and enteroinvasive Escherichia coli (0.2) followed. No shiga toxin-producing Escherichia coli were identified. Enteroaggregative Escherichia coli was not associated with diarrhoea (cases 26.1; controls 25.5; P=0;887); unlike enteropathogenic Escherichia coli (cases 6.7; controls 1; P=0.003). Investigations into documented potentials of enteroaggregative Escherichia coli in causing diarrhoea and other related pathologies indicated that it could be a major public health threat in Cameroon despite the fact that it was not found associated with clinical diarrhoeal cases in this study

Spatial modelling and the prediction of Loa loa risk: decision making under uncertainty.

Health decision-makers working in Africa often need to act for millions of people over large geographical areas on little and uncertain information. Spatial statistical modelling and Bayesian inference have now been used to quantify the uncertainty in the predictions of a regional, environmental risk map for Loa loa (a map that is currently being used as an essential decision tool by the African Programme for Onchocerciasis Control). The methodology allows the expression of the probability that, given the data, a particular location does or does not exceed a predefined high-risk threshold for which a change in strategy for the delivery of the antihelmintic ivermectin is required.

Microfilarial distribution of Loa loa in the human host: population dynamics and epidemiological implications.

Severe adverse events (SAEs) following ivermectin treatment may occur in people harbouring high Loa loa microfilarial (mf) densities. In the context of mass ivermectin distribution for onchocerciasis control in Africa, it is crucial to define precisely the geographical distribution of L. loa in relation to that of Onchocerca volvulus and predict the prevalence of heavy infections. To this end, we analysed the distribution of mf loads in 4183 individuals living in 36 villages of central Cameroon. Mf loads were assessed quantitatively by calibrated blood smears, collected prior to ivermectin distribution. We explored the pattern of L. loa mf aggregation by fitting the (zero-truncated) negative binomial distribution and estimating its overdispersion parameter k by maximum likelihood. The value of k varied around 0.3 independently of mf intensity, host age, village and endemicity level. Based on these results, we developed a semi-empirical model to predict the prevalence of heavy L. loa mf loads in a community given its overall mf prevalence. If validated at the continental scale and linked to predictive spatial models of loiasis distribution, this approach would be particularly useful for optimizing the identification of areas at risk of SAEs and providing estimates of populations at risk in localities where L. loa and O. volvulus are co-endemic.

Co-infection with Onchocerca volvulus and Loa loa microfilariae in central Cameroon: are these two species interacting?

Ivermectin treatment may induce severe adverse reactions in some individuals heavily infected with Loa loa. This hampers the implementation of mass ivermectin treatment against onchocerciasis in areas where Onchocerca volvulus and L. loa are co-endemic. In order to identify factors, including co-infections, which may explain the presence of high L. loa microfilaraemia in some individuals, we analysed data collected in 19 villages of central Cameroon. Two standardized skin snips and 30 mul of blood were obtained from each of 3190 participants and the microfilarial (mf) loads of both O. volvulus and L. loa were quantified. The data were analysed using multivariate hierarchical models. Individual-level variables were: age, sex, mf presence, and mf load; village-related variables included the endemicity levels for each infection. The two species show a certain degree of ecological separation in the study area. However, for a given individual host, the presence of microfilariae of one species was positively associated with the presence of microfilariae of the other (OR=1.79, 95% CI [1.43-2.24]). Among individuals harbouring Loa microfilariae, there was a slight positive relationship between the L. loa and O. volvulus mf loads which corresponded to an 11% increase in L. loa mf load per 100 O. volvulus microfilariae. Co-infection with O. volvulus is not sufficient to explain the very high L. loa mf loads harboured by some individuals.

Genetic polymorphism of the beta-tubulin gene of Onchocerca volvulus in ivermectin naïve patients from Cameroon, and its relationship with fertility of the worms.

Observations of low response of patients infected with Onchocerca volvulus to ivermectin suggest that the parasite may be under a selection process toward potential resistance. To limit the extension of this phenomenon, it is crucial to characterize the genes of O. volvulus that are involved. For this, O. volvulus adult worms collected before the introduction of ivermectin in an onchocerciasis endemic area of central Cameroon were genotyped for beta-tubulin. To derive a baseline to investigate the selective pressure of ivermectin, we analysed (1) the frequency distribution of the beta-tubulin alleles, and (2) the relationship between the different beta-tubulin related genotypes and the fertility status of the female worms. The frequency of allele b of the beta-tubulin gene was very low, as it was observed in West Africa. We observed a deficit of heterozygous female worms leading to Hardy Weinberg disequilibrium, which might be explained by a shorter life-span of these worms compared to the homozygous worms. Unexpectedly, our results also show that the heterozygous female worms were much less fertile than the homozygotes: more than two thirds of the homozygotes were fertile, whereas only 37% of the heterozygotes were fertile. These results will be further considered when analysing post-treatment data.

Structure of the microfilarial reservoir of Loa loa in the human host and its implications for monitoring the progr,ammes of Community-Directed Treatment with Ivermectin carried out in Africa.

This paper describes the structure of the microfilarial reservoir of Loa loa in an endemic population of central Cameroon. The possible effects of age and sex on the prevalence and intensity of microfilaraemia have been explored. Logistic analysis showed that the prevalence of microfilaraemia increased significantly with age, reaching 60 % in the oldest males. This result suggests that the figure commonly reported, according to which only one third of the infected individuals were microfilaraemic, should be reconsidered; in addition, as part of surveys of loiasis, crude microfilaraemia prevalence values should be replaced by adjusted ones. The intensity of infection did not show any age-specific change. As a result, even if the oldest members of the male population are clearly the most at risk of developing post-ivermectin serious adverse reactions, especially Loa-encephalopathy, the other members of the population are not risk-free. Therefore, in those areas where the African Programme for Onchocerciasis Control is undertaking regular mass distributions of ivermectin for onchocerciasis control, and where loiasis is co-endemic, no subpopulation should be excluded from surveillance and monitoring during community directed treatments with ivermectin.

Cytokine response profiles predict species-specific infection patterns in human GI nematodes.

This study investigated associations between pre-treatment cytokine expression and infection patterns, before and after de-worming, in humans exposed to two gastrointestinal nematode species. Quantitative measures of Ascaris lumbricoides and Trichuris trichiura infection (based on faecal egg counts) were estimated immediately before and 8-9 months after treatment in a Cameroonian population. Whole blood cytokine responses to parasite-derived antigens were assayed immediately pre-treatment. An overall measure of the tendency towards species-specific infection (increasing with A. lumbricoides faecal egg counts and decreasing with T. trichiura faecal egg counts) was significantly positively related to IL-10 levels in older (14-57 year) hosts. There was a significant negative influence of IL-5 on reinfection probability in T. trichiura but not A. lumbricoides. This effect coincided with reduced reinfection success in T. trichiura compared to A. lumbricoides. T(H)2 cytokine expression by younger hosts (4-13 year) was negatively associated with contemporary A. lumbricoides faecal egg counts before treatment. Following treatment, the pre-treatment T(H)2 cytokine expression data for younger hosts (now reflecting responsiveness 8-9 months in the past) were negatively associated with T. trichiura faecal egg counts. Taken together, these observations suggest a successional interaction between T(H)2-driven immune responses and species infection over time. However, any differential effects of the measured immune responses on species-specific recruitment, maturation and mortality were superimposed upon (and outweighed by) the effects of other factors favouring coinfection.

Neoplastic change in Onchocerca volvulus and its relation to ivermectin treatment.

A pleomorphic neoplasm (PN) is described from sections of Onchocerca volvulus worms in nodules excised from Cameroonian patients. PN is confined to older, non-fecund, female worms, and those classed as moribund/dead. It is mainly composed of small, roundish, basophilic cells of diverse sizes, often forming a 'rosette' pattern around amorphous eosinophilic centres. The cells have a high nuclear/cytoplasmic ratio and up to 2-3 mitoses/high-power field; some become grossly enlarged, highly polymorphic and contain large, irregular blocks of chromatin. The eukaryotic PN cells first appear posteriorly in the pseudocoelom, probably from ovarian cells; they spread anteriorly, invading or compressing the uteri. Ivermectin treatment increased the prevalence PN from 3.7% of 1422 female worms in 637 patients before treatment to 17.5% of 1134 worms in 511 patients after 3 years treatment. Ivermectin at 400-800 microg/kg annually, or at 150 microg/kg or 400-800 microg/kg 3-monthly, over 3 years, did not increase the PN prevalence significantly, as compared with standard doses of 150 microg/kg annually. In other small series of African patients, PN prevalence increased in worms 2, 4, 6 and 10 months after ivermectin treatment; but there was no increase after treatment with amocarzine, albendazole or diethylcarbamazine and suramin. PN may partly account for the increased macrofilaricidal action of ivermectin on female O. volvulus in patients treated for 3 years at 3-monthly intervals.

Relationship between onchocerciasis and epilepsy: a matched case-control study in the Mbam Valley, Republic of Cameroon.

Studies conducted during the past 10 years to investigate the possible relationship between onchocerciasis and epilepsy have led to contradictory results. In 1991-92 and 2001 we investigated 14 villages in central Cameroon to evaluate the relationship, at the community level, between the prevalence of epilepsy and the endemicity level of onchocerciasis. A case-control study compared the microfilarial loads of 72 epileptic and 72 non-epileptic individuals, matched according to sex, age, and village of residence. The prevalence of epilepsy and the community microfilarial load (CMFL) were closely related (P < 0.02), and the case-control study demonstrated that the microfilarial loads (microfilariae per snip) in the epileptic group (arithmetic mean = 288, median = 216) were significantly higher (P < 10(-4)) than in the control group (arithmetic mean = 141, median = 63). The results strongly support the existence of a link between onchocerciasis and epilepsy. The fact that such a relationship has not been found recently in some other West and Central African areas is probably due to the lowered endemicity of onchocerciasis following vector- and ivermectin-related control measures applied over the past 5-25 years. The socio-economic and demographic impact of onchocerciasis-related epilepsy should be evaluated, and taken into account as part of all onchocerciasis control programmes.

Efficacy of repeated doses of ivermectin against Mansonella perstans.

Treatment of Mansonella perstans infection, although seldom necessary, is difficult. In a 3 year's trial of normal and high-dose annual and 3-monthly ivermectin treatment against Onchocerca volvulus, the effects on M. perstans were recorded and related to the cumulative dose received. The World Health Organization's African Programme for Onchocerciasis Control may thus reduce the endemicity of M. perstans.

Excess mortality associated with blindness in the onchocerciasis focus of the Mbam Valley, Cameroon.

The association between blindness, mortality and nutritional status was investigated in a retrospective cohort study in villages of central Cameroon where onchocerciasis is hyper-endemic. Overall, 101 blind subjects and 101 non-blind controls matched with the blind for age, sex and (generally) village of residence were followed for 10 years. Blindness gave rise to a significant increase in mortality (relative risk = 2.3; P = 0.012), the life expectancy of the blind adults being reduced by 4 years compared with that of their controls. For a given age, excess mortality was found to be associated with a late onset of blindness. The causes of death were similar for the blind and the controls but blind subjects had relatively low body mass indices, which may lead to relatively early fatal disease outcomes. These results are similar to those obtained in other parts of Africa and emphasise, once more, the demographic impact of blindness in developing countries.

Effect of a single dose (600 mg) of albendazole on Loa loa microfilaraemia.

The problem of Loa-encephalopathy, which may occur after ivermectin treatment of patients harbouring high Loa microfilarial loads, might be solved if one could find a treatment regimen bringing about a significant but progressive decrease in the Loa microfilaraemia. A trial was performed in Central Cameroon, whose aim was to follow up for 10 months, and to compare the changes in the Loa microfilarial loads in two groups of patients, one treated with a single dose (600 mg) of albendazole (Alben, SmithKline Beecham) given with fatty food, and the other treated with mebendazole (100 mg, twice a day, generic tablets) at a fasting state. The microfilarial loads remained stable in the mebendazole group, whereas a significant decrease in microfilaraemia was recorded in the albendazole group (initial median load: 230 microfilariae per 50 microliters; median load ten months after: 84 microfilariae per 50 microliters). This should encourage further trials to evaluate the effects and the safety of two- or three-day albendazole regimens in patients infected with Loa loa.

Effects of a 3-day regimen of albendazole (800 mg daily) on Loa loa microfilaraemia.

The encephalopathy that sometimes develops after ivermectin treatment in patients with high Loa microfilaraemias is probably related to a massive effect of the drug on the Loa microfilariae. A trial was therefore conducted to evaluate whether a course of albendazole would bring about a slower decrease in the Loa microfilaraemia, and thus could be used as a mass 'clearing' treatment, before the distribution of ivermectin in areas where onchocerciasis and loiasis are co-endemic. The Loa microfilarial loads were followed monthly for 9 months in two groups of subjects, one treated with albendazole (400 mg twice a day for 3 days), and the other with vitamin (B(1), B(6) and B(12)) tablets. There were no significant between-group differences in the microfilarial loads at any of the examination rounds. During the follow-up period, there was also no significant change in the overall loads among those treated with albendazole, although the counts in those with high initial microfilaraemias (>8000 microfilariae/ml) tended to decrease progressively during the first 3 months. Further trials should now be performed, to evaluate the effects on Loa loa of two courses of albendazole given 2-3 months apart.

Antibody responses in onchocerciasis as a function of age and infection intensity.

Onchocerciasis is caused by the filarial nematode Onchocerca volvulus and is a major public health problem in West and Central Africa. With only partial and long-term treatment currently available, there is a need to develop a suitable vaccine. We analysed the antibody response to infective L3 larvae because this stage is thought to be associated with host protective immunity. In addition, we have related our findings to the age, gender and current infection intensity of our participants: variables that may significantly influence antibody production. Interestingly, whilst 90% of our study group were seropositive for adult specific immunoglobulin (Ig)E, only 23% produced L3 specific IgE. This is in contrast to IgG4 where seropositivity was comparable at 96% and 92%, respectively. Furthermore, IgG levels were significantly affected by age and the intensity of infection but unaffected by host gender. This finding is independent for the IgG subclass (IgG1, IgG2, IgG3 and IgG4) and its specificity (L3 versus adult antigen). In summary, we show that L3 larvae induce little specific IgE and the antibody response shows a different isotype balance than that against adult antigens. Both host and parasite variables can influence antibody production in this disease.

Relationships between the prevalence and intensity of Loa loa infection in the Central province of Cameroon.

Ivermectin treatment may induce marked adverse effects in those harbouring > 8000 Loa microfilariae (mff)/ml of blood, individuals with > 30 000 Loa mff/ml being at risk of developing serious neurological reactions. It is thus necessary to delineate the geographical areas where such responses may occur. To determine if the simple measure of prevalence of Loa microfilaraemia would be appropriate to identify the communities at risk, the relationships between prevalence and intensity of Loa microfilaraemia were investigated in 67 villages in Cameroon. The prevalence recorded in the adult population was found to be closely related to each of the indicators of infection intensity investigated. For example, when the prevalences of Loa microfilaraemia in adults were 20%, 30% and 40%, approximately 5%, 9% and 16% of the adults had microfilarial loads exceeding 8000 mff/ml, respectively; the corresponding percentages of adults with > 30 000 mff/ml were about 1%, 3% and 5%-6%. Thus it seems that, in areas where loiasis is co-endemic, the monitoring procedure during large-scale ivermectin treatments for the control of onchocerciasis only needs to be strengthened in those communities where the prevalence of Loa microfilaraemia in adults exceeds 20%.

Studies on the macrofilarial population of Onchocerca volvulus in hyper-endemic villages of the Central province of Cameroon.

The population structure of Onchocerca volvulus macrofilariae was studied in villages of central Cameroon where onchocerciasis is hyper-endemic. One nodule selected at random was removed from each of 576 adult males, and examined by histology. The numbers of male and female worms/nodule, and the status of the female worms (fecund, non-fecund, or dead) were recorded. The observations were analysed to evaluate whether the mean numbers of worms of each category varied in relation to the patient's age, the level of endemicity in his village, the anatomical localization of the nodule, the weight of the nodule, and the total number of palpable nodules harboured by the patient. The results obtained were very similar to those reported from West Africa. The mean numbers of dead female worms/nodule were relatively high in the villages with the lowest levels of endemicity. The mean numbers of fecund females and of live males were significantly higher in the nodules located around the knees. These results provide information which might be useful in modelling the population dynamics of O. volvulus, and also in the context of trials of any potentially macrofilaricidal drugs.

[Hyperendemic loaiasis in the Tikar plain, shrub savanna region of Cameroon]. / Hyperendémicité de la loase dans la plaine Tikar, région de savane arbustive du Cameroun.

A survey on filariasis was conducted in the south-western part of the Adamaoua Province (Cameroon). In the Bankim district, located in the Tikar plain, the 10 surveyed villages were all hyperendemic for loiasis. The prevalence of microfilaraemia in adults exceeded 50% in four communities, and 5.4% of the adults had microfilarial loads above 30,000 microfilariae per ml blood. In the Banyo district, which is contiguous but located on the Adamaoua Plateau, five of the six villages examined were hypoendemic for loiasis. The considerable levels of endemicity recorded in the Tikar Plain, a region of pre-forest shrub savanna, are probably due to the presence of forest-galleries, favourable to the biology of Chrysops. Regarding onchocerciasis, the most affected villages were located south of the Tikar Plain, near the Mbam River. The low prevalence of hydroceles suggests that lymphatic filariasis is not endemic in this study area.

[Analysis of the prevention of post-ivermectin Loa loa encephalopathy by administration of initial low dose]. / Essai de prévention des encéphalopathies à Loa loa post-ivermectine par l'administration d'une faible dose initiale.

A number of cases of Loa-encephalopathy have been reported following ivermectin (Mectizan) treatment for onchocerciasis in patients with high Loa microfilaraemia. A possible explanation for these severe reactions is the formation of micro-emboli in small brain vessels as a result of massive paralysis of Loa microfilariae in the blood. This suggests that encephalopathy might be prevented by giving an initial low dose of ivermectin to induce a more gradual action on the Loa microfilariae. To test this hypothesis, a trial was conducted on 23 adult patients in Cameroon. Patients were divided into two groups. One group received the recommended dose of 150 micrograms/Kg. The other group received a lower dose of 50 micrograms/Kg (one 3 mg tablet of Mectizan). Blood smears were made daily from day 1 to 7 after treatment and then on days 15 and 30. Results showed no difference in the effect of the dosage level on Loa microfilaraemia. This finding suggests that an initial low dose of 3 mg Mectizan will not prevent encephalopathy following treatment for onchocerciasis.

Three probable cases of Loa loa encephalopathy following ivermectin treatment for onchocerciasis.

Over the past nine years, more than 12 million people exposed to Onchocerca volvulus infection have received at least one dose of ivermectin, almost all without serious adverse reactions. Since 1991, however, several cases with neurologic manifestations, including coma, have been reported after ivermectin treatment of persons infected with O. volvulus who also had concomitant Loa loa infection with very high microfilaremia (> 50,000 microfilariae/ml of blood). In 1995, four criteria were established to define probable cases of Loa encephalopathy temporally related to treatment with ivermectin (PLERI). The present paper describes three PLERI cases recorded in Cameroon and compares them with two others reported previously. Disorders of consciousness began 3-4 days after treatment. The objective neurologic signs were variable. The conditions improved favorably in three patients who benefited from early hospitalization and good nursing; their disorders of consciousness lasted only 2-3 days; the results of clinical examination became normal after one month and electroencephalographic abnormalities disappeared after 5-7 months. Conversely, late diagnosis and delay in proper management in two others probably led to worsening of the condition and to fatal outcome related to the usual complications of coma. In addition to these cases, patients w with high Loa microfilaremia also developed milder neurologic manifestations causing functional impairment lasting for at least one week after treatment. Before launching mass ivermectin distribution programs to control onchocerciasis in central Africa, communities in which the intensity of concomitant L. loa microfilaremia is high need to be identified, and specific educational measures and monitoring strategies should be developed and applied before they are treated.