Loiasis is a filarial infection endemic in the rainforest zone of west and central Africa particularly in Cameroon, Gabon, Republic of Congo, and Democratic Republic of the Congo. Repeated treatments with ivermectin have been delivered using the annual community directed treatment with ivermectin (CDTI) approach for several years to control onchocerciasis in some Loa loa-Onchocerca volvulus co-endemic areas. The impact of CDTI on loiasis parasitological indicators is not known. We, therefore, designed this cross sectional study to explore the effects of several rounds of CDTI on parasitological indicators of loiasis. The study was conducted in the East, Northwest and Southwest 2 CDTI projects of Cameroon. Individuals who consented to participate were interviewed for ivermectin treatment history and enrolled for parasitological screening using thick smears. Ivermectin treatment history was correlated with loiasis prevalence/intensity. A total of 3,684 individuals were recruited from 36 communities of the 3 CDTI projects and 900 individuals from 9 villages in a non-CDTI district. In the East, loiasis prevalence was 29. 3% (range = 24. 2%–34. 6%) in the non-CDTI district but 16. 0% (3. 3%–26. 6%) in the CDTI district with 10 ivermectin rounds (there were no baseline data for the latter). In the Northwest and Southwest 2 districts, reductions from 30. 5% to 17. 9% (after 9 ivermectin rounds) but from 8. 1% to 7. 8% (not significantly different after 14 rounds) were registered post CDTI, respectively. Similar trends in infection intensity were observed in all sites. There was a negative relationship between adherence to ivermectin treatment and prevalence/intensity of infection in all sites. None of the children (aged 10–14 years) examined in the East CDTI project harboured high (8,000–30,000 mf/ml) or very high (>30,000 mf/ml) microfilarial loads. Individuals who had taken >5 ivermectin treatments were 2. 1 times more likely to present with no microfilaraemia than those with less treatments. In areas where onchocerciasis and loiasis are co-endemic, CDTI reduces the number of, and microfilaraemia in L. loa-infected individuals, and this, in turn, will help to prevent non-neurological and neurological complications post-ivermectin treatment among CDTI adherents.
Loiasis is a filarial infection endemic in the rainforest areas of West and Central Africa, particularly in Cameroon, Gabon, Republic of Congo and Democratic Republic of the Congo (DRC) [1,2], where its distribution is associated with that of its vectors Chrysops silacea and C. dimidiata. The common clinical signs of loiasis are the subconjunctival migration of the adult worm (reported for the first time by Mongin [3], Calabar swellings, pruritus, oedema and arthralgia. Loiasis can also be rarely associated with renal, cardiac, neurologic or chorioretinal complications ([4,5]. In some regions it has been noted that loiasis is the second or third most common reason of medical consultation, after malaria and pulmonary diseases [6]. Chesnais and colleagues revealed that high-grade L loa microfilaraemia was associated with an increased mortality risk, further suggesting that loiasis is not a benign condition and merits more attention because of its effect on onchocerciasis and Lymphatic Filariasis (LF) control strategies [7]. It has been demonstrated that a single oral dose of ivermectin brings about a dramatic decrease in the load of Loa loa microfilariae (mf) and even an improvement in some clinical signs related to the infection [8–15]. The impact of repeated large-scale 3-monthly treatment with ivermectin for over a year on the transmission of loiasis in a forest village in south Cameroon where loiasis was highly endemic, with a prevalence above 30% was investigated by Chippaux and colleagues [16]. The prevalence of loiasis was reduced to less than 10% and the mean microfilaraemia was decreased by 90% over a 2-year period. The infection rate (all stages) in Chrysops was decreased by 75% and the infective rate (percentage of Chrysops harbouring third-stage larvae of L. loa in the head) was decreased by 85% in C. dimidiata and became zero in C. silacea. This pilot study demonstrated that large-scale treatment with ivermectin could be a potential effective method for the control of L. loa. Since the early 1990s, it was observed that ivermectin, the drug of choice for onchocerciasis and LF control in Africa, can induce Severe Adverse Events (SAEs) in individuals harbouring high densities of Loa mf in the blood [13,17]. The condition consists of a potentially fatal encephalopathy occurring within 2–3 days after treatment [18,19]. In non-fatal cases, long-term neurologic sequelae may occur. Since 1991, more than 400 cases of such neurologic SAEs have been reported from Central Africa, mainly from Cameroon and DRC. For this reason, the use of ivermectin on a large-scale basis for the control of LF in loiasis-endemic areas has not been promoted and it has been considered unethical for many areas where the disease is endemic. However, since ivermectin has a direct beneficial effect on the clinical manifestations of onchocerciasis, and these benefits outweigh the risk of central nervous system adverse events (particularly in highly onchocerciasis endemic areas), mass ivermectin distribution for the control of Onchocerca volvulus has been approved in Loa endemic areas where onchocerciasis co-occurs and where the prevalence of Onchocerca nodules exceeds 20% in the adult population (indicating meso- to hyperendemicity). This is done provided that an efficient surveillance system is put in place to promptly identify and manage SAE cases [20]. A significant proportion of Community Directed Treatment with Ivermectin (CDTI) projects of the African Programme for Onchocerciasis Control (APOC) is situated in areas where onchocerciasis and loiasis are co-endemic. This is the case in countries such as Nigeria, Cameroon, DRC and Angola. In Cameroon, amongst the 15 CDTI projects, 13 are partially or entirely situated in areas of onchocerciasis-loiasis co-endemicity. For those Cameroon CDTI projects situated in areas of co-endemicity, eight of them have been distributing ivermectin for more than 10 rounds (11–13) and 5 of them for less than 10 rounds (6–8). Also important is the fact that some of the CDTI projects situated in areas of co-endemicity have historical data and even more recent data on the endemicity of loiasis before the introduction of CDTI. We, therefore, hypothesized that long-term ivermectin treatment areas of onchocerciasis-loiasis co-endemicity might have led to marked reductions in the clinical and parasitological indices of loiasis, together with significant reductions in the risk of developing SAEs in treated communities. This would surely constitute an added value to the primary goal of APOC, which was the control of onchocerciasis. This study was, therefore, designed to assess in selected populations: (i) the changes in the parasitological indices of loiasis (infection prevalence and intensity) that might have occurred under Mass Drug Administration (MDA) with ivermectin; (ii) the relationship between adherence to treatment and the prevalence/intensity of L. loa microfilaraemia; (iii) the impact of ivermectin MDA on the reduction of potential risk of developing SAEs; (iv) the relationship between adherence to treatment and the reduction in potential risk of developing SAEs. As a fifth objective, we also sought to evaluate L. loa infection in children in the East and Northwest CDTI projects of Cameroon, with the ultimate goal of estimating the protective effect of ivermectin MDA in preventing high microfilarial loads, hence minimising the risk of SAEs in children.
This cross-sectional study was designed to evaluate the impact of CDTI on L. loa endemicity in four areas of co-endemicity with onchocerciasis in Cameroon (Fig 1). Three CDTI project sites were selected based on pre-control information on loiasis endemicity and these were the East, Northwest and Southwest 2 projects [21,22]. However, there were no baseline data available for the East CDTI project. Therefore, a non-CDTI health district, also from the East and adjacent to one of the East CDTI sites, was selected. Although no formal comparison is truly possible between the CDTI and the non-CDTI areas in the East, inclusion of the latter provides useful information of the loiasis endemicity situation in an area of geographical proximity (Fig 1). A total of 36 and 9 geo-referenced communities were selected, respectively, from the three CDTI project sites and the non-CDTI health district. In each surveyed community, at least 80 adults (aged ≥15 years) and 20 children (aged 10-14years) of both sexes were screened. In each community, ivermectin mass treatment was documented at the individual level and this information was obtained from oral declarations of participants following an interview on the number of times they had received ivermectin. We relied on oral information due to inconsistency on the availability of treatment registers in study communities [23]. Each individual who consented to participate (see below) was tested for blood mf using a thick blood film. The following parasitological indicators of L. loa were generated: mf prevalence, mf intensity, prevalence of low to moderate mf loads (1–8,000 mf/ml), prevalence of high mf loads (8,001–30,000 mf/ml) and prevalence of very high mf loads (>30,000 mf/ml). Indicators generated within CDTI projects were compared to pre-control indicators when baseline data were available (Northwest and Southwest 2 projects). Data on adults only were used in these comparisons. To further evaluate the impact of mass ivermectin treatment on loiasis, an association was investigated between adherence to the drug and the prevalence and intensity of mf infection. Adherence in this study was assessed using oral declaration and expressed as the number of times an individual had taken treatment since the inception of CDTI in his/her community. The reduction of potential SAE risk was estimated by comparing the proportion of individuals with high and very high L. loa mf loads (as defined above) before and under CDTI in the different study sites. The relationship between the adherence profiles to ivermectin treatment of community members and their risk of developing SAEs as anticipated by their L. loa microfilarial load was explored. SAEs were described as either individuals at risk of neurologic (in individuals harbouring >30000mf/ml of blood) or non neurologic complications (in individuals harbouring mf loads between 8001-30000mf/ml of blood) [19,24]. The study was carried out in the East, Northwest and Southwest 2 CDTI project sites of Cameroon between March and October 2014 (Fig 1). The Southwest 2 CDTI project, situated in an area of L. loa mild endemicity, had started in the year 2000 and by the time of the study had been under CDTI for 14 years [25]. The East and Northwest CDTI projects, situated in areas of high L. loa endemicity, started much later (in 2004 and 2005 respectively) and so had, respectively, been under CDTI for 10 and 9 years prior to the study [21,22,26]. The East CDTI project consists of two sites, with one of them around the locality of Bertoua, the capital of the East Region of Cameroon (Fig 1). A fourth site, the CDTI-naïve health district in the East region was also surveyed. The climate in the southwest and northwest is tropical with two seasons, one wet season of about 9 months, lasting from March to November and a short dry season from mid-November to mid-March. The mean annual rainfall in these areas varies from 2,500 to 4,000 mm. Ambient temperature ranges from 20°C to 40°C depending on the seasons. The climate of the east region is a Type A wet equatorial climate [27], with average temperatures of about 24°C with four seasons (a long dry season from December to May, a light wet season from May to June, a short dry season from July to October, and a heavy wet season from October to November). Humidity and cloud cover are relatively high, and precipitation averages 1,500–2,000 mm per year except in the extreme eastern and northern parts of the region, where it is slightly less. Eligible individuals were individuals of both sexes that must have resided in the communities for at least 5 years and who accepted to participate in the study by signing the consent or assent forms provided by the research team. Prior to recruitment, the nature, objectives, benefits and potential risks of the study were explained to potential participants and those who agreed to take part in the study signed a consent form. Since some study participants were minors, their parents/guardians provided informed consent on their behalf. Recruitment was done based on the approach described previously by Kengne-Ouafo et al. [28]. The study protocol received ethical approval from the Cameroon National Ethics Committee, and the Research Ethics Review Committee of the Regional Office for Africa of the World Health Organization (WHO/AFRO). Questions were asked as to whether individuals had ever taken ivermectin, the number of times and the last time he/she had taken the drug. Comparison of the records of the oral declarations with the records of the treatment registers of the Community Drug Distributors (CDDs) was not done because the latter were incomplete and, therefore, considered unreliable. Eligible participants were categorised by the number of times they had taken the drug ([0], [1–2], [3–4], [5–6], [7–8], [9–10], [11+] times), and underwent a parasitological (thick blood smear) examination. The correlation between the parasitological results thus obtained and the participants’ treatment profiles was investigated. Only participants who had not taken any filaricide medication for the past one year were enrolled in the study to avoid the situation in which a reduction in mf load could be due to the effect of a recently administered drug. Recruitment of the study participants was, therefore, carried out before the routine large-scale annual distribution of ivermectin in the villages of the CDTI projects. Data were entered in a template created in EPI Info version 3. 5. 3 and analyzed with the Statistical Package for the Social Sciences (SPSS 20. 0. 0). Examined individuals were grouped as either males or females, children (10–14 years of age) or adults (15+ years of age) and classified according to the number of times they had taken ivermectin. The different treatment classes were: [0], [1–2], [3–4], [5–6], [7–8], [9–10] and [11+]. The microfilarial prevalence was computed as the proportion of individuals, among those examined, harbouring mf in the blood (after microscopy). Microfilarial intensity was calculated as the arithmetic mean number of mf per ml of blood among those examined (i. e. including mf-positive and mf-negative individuals). Prevalence categories of mf load were calculated as: i) the proportion of individuals with low to moderate microfilaraemia (those with 1–8,000 mf/ml among examined); ii) the proportion of those with high mf load (individuals harbouring 8,001–30,000 mf/ml); and the proportion of individuals with very high mf loads (individuals harbouring > 30,000 mf/ml) as described in the Rapid Assessment Procedure for Loiasis (RAPLOA) report of 2001 [32]. Box-and-whiskers plots were used to summarize the overall mf prevalence and the prevalence of categories of mf load among the different CDTI projects according to the number of years under CDTI. This type of plot, enables visual inspection of the distribution of the data, with the box spanning the interquartile range, the horizontal line inside the box representing the median, and the whiskers extending to the lowest (minimum) and highest (maximum) observations. Based on the fact that prevalence data are binomially distributed, the (baseline and post-CDTI) study periods were independent of each other, and the participants at the two study periods were different (not a longitudinal cohort but a cross-sectional study), differences between baseline and post-CDTI data in the proportions of mf positives, or of positives for each prevalence of mf load category, were analysed by the 2-sample z-test to compare sample proportions when this was an appropriate test (i. e. z times p-values >5) or a chi-square test applied to a 2×2 contingency table (without continuity correction as sample sizes were large) when the normal approximation of the binomial distribution could not be applied (i. e. sample size times the proportion (or 1 minus the proportion) < 5). The exact (Clopper-Pearson) 95% confidence intervals (95% CI) accompanying the calculated prevalence values are also provided. The (non-parametric) Mann-Whitney U test was used to compare average loiasis infection intensities given that mf loads are typically over dispersed and therefore do not follow a normal (Gaussian) distribution. The Spearman correlation coefficient (rs) was calculated to quantify the relationship between treatment history indicators and indicators of loiasis endemicity. Contingency tables, with chi-square tests, and the chi-square test for trends, were used to assess the association between the frequency of individuals in the different ivermectin treatment groups and age/sex. The mixed effects logistic regression model was used to explore whether ivermectin intake was a significant factor in L. loa mf prevalence and the risk of harbouring high/very high mf intensities. The CDTI projects were considered random effects while fixed effects were the covariates: age (children or adults, categorical), sex (males or females, categorical), ivermectin treatment (never, 1–5 times or > 5 times, categorical). The outcome variables were either the proportion of individuals with zero mf or the proportion of individuals with mf below 8000mf/ml or the proportion of individuals with mf load between 8001-30000mf/ml or proportion of individuals with >30,000 mf/ml. Reference categories for our fixed effects were: adults, females and individuals who had never taken ivermectin respectively. The Odd Ratios (ORs) indicated the magnitude and direction of the ivermectin treatment, age or sex effect for the various ivermectin treatment history/age/sex groups. If ivermectin intake, age and sex demonstrated a protective effect against harbouring mf, or high or very high mf loads or no mf, the ORs was less than 1 and statistically significant. All the statistical tests were performed at a 5% significance level.
A total of 3,684 individuals (54% female) were recruited from 36 communities of the 3 CDTI project sites, while 900 (48% female) came from the 9 non-CDTI communities (Table 1). Age varied from 10–95 years (Fig 2). In the East study sites, the prevalence of individuals with high microfilaraemia (among adults), after 10 years of CDTI, ranged from 0 to 4%, with a general prevalence of 1. 2% (n = 1130; 95% CI = 0. 7–2. 1%). This was markedly lower than the prevalence obtained from non-CDTI communities (6. 2%; n = 710; 95% CI = 4. 5–8. 2%), where it ranged from 1. 4 to 12. 5% (Fig 3D). In the Northwest site, and after 9 years of CDTI, the overall prevalence of individuals with high mf loads was 2. 3% (n = 1,089; 95% CI = 1. 6–3. 4%) and ranged from 0. 7% to 11. 6% between the villages of this project. This was statistically significantly lower than the overall pre-control value of 7. 7% (n = 1,028; 95% CI = 6. 1–9. 5%), ranging from 0% to 18. 7% among the communities (X2 = 31. 115, p <0. 0001, (Fig 3E). In the Southwest 2 project site, the overall prevalence of high mf load carriers post 14 years of CDTI was 0. 7% (n = 733; 95% CI = 0. 2–1. 6%), with villages ranging from 0% to 3. 1%, not experiencing significant change from the pre-control value of 0. 8% (n = 1,458; 95% CI = 0. 4–1. 4%), with range from 0% to 2. 8% (X2 = 0. 126, P = 0. 723, (Fig 3F). In the East study sites, the prevalence of individuals with very high microfilaraemia (among adults), after 10 years of CDTI, ranged from 0 to 2. 2%, with a general value of 0. 62% (n = 1,130; 95% CI = 0. 25–1. 3%). This was not different from the prevalence obtained from non-CDTI communities (1%; n = 710; 95% CI = 0. 4–2%), where it ranged from 0 to 3. 3%, z-value = 0. 9, p-value (two-tailed test) = 0. 375 (Fig 3G). In the Northwest site, and after 9 years of CDTI, the overall prevalence of individuals with very high mf loads was 0. 8% (n = 1,089; 95% CI = 0. 4–1. 6%) and ranged from 0% to 3. 5% between the villages of this project. This was statistically significantly lower than the overall pre-control value of 3. 3% (n = 1,028; 95% CI = 2. 3–4. 6%), ranging from 0% to 11% among the communities; z-value = 4, p-value (one-tailed test) < 0. 0001 (Fig 3H). In the Southwest 2 project site, the overall prevalence of very high mf load carriers post 14 years of CDTI was 0. 11% (n = 932; 95% CI = 0–0. 6%) in the general population, with villages ranging from 0% to 1%, not changing significantly from the pre-control value of 0. 2% (n = 1,458; 95% CI = 0. 04–0. 6%), with range from 0% to 1. 9%; chi-squared = 0. 003 (1 DF), p-value = 0. 954 (Fig 3I). Treatment coverage was ascertained in all 36 surveyed CDTI communities based on questionnaires. Treated individuals were able to recall the number of times they had taken ivermectin, which ranged from 1 to > 10 times. The study results indicated that over 80% of adult respondents interviewed had participated in the ivermectin MDA at least once, although >50% of these individuals were low compliers (had taken ivermectin < 5 times). In the East, Northwest and Southwest project sites, 21%, 29% and 17% of the adult population, respectively, declared to have never taken ivermectin treatment. In the East study sites, there was a significant difference across the different treatment groups in adults and children and between adult males and females. The same trend was observed in the Northwest and Southwest project sites except for the fact that there was no significant difference in treatment intake between adult males and females (Table 2). Taking the three CDTI projects as a whole, most treated adult individuals declared to have taken ivermectin 1–2 times (27. 3%), while relatively few (6. 3%) were treated more than 10 times. (The duration of the CDTI project since inception till the time of the study ranged from 9 to 14 years; see above.) The proportions of high mf load carriers were significantly reduced in the Northwest and Southwest sites and different in the East while those of the very high mf load carriers were significantly reduced in the Northwest and different in the East. In the Southwest site, no difference was observed between the two study periods as observed in Table 3. The proportion of high mf load carriers was reduced by 73. 6%, 59. 7% and 20% in the East, Northwest and Southwest sites respectively while the proportion of very high mf load carriers was reduced by 40%, 75. 8% and 50% in the respective sites. Amongst children of the East region, there were none with high or very high mf load following 10 years of ivermectin treatment (nonCDTI n = 190, CDTI n = 293, Table 4). Logistic regression analysis revealed that individuals who had taken ivermectin 5 times or more had an OR of 2. 1. This means that they are close to two times more likely to have no mf compared to the zero ivermectin intake group (95% CI [1. 5–2. 9], p < 0. 0011; Table 5). Individuals in the general population who had undergone at least 5 treatment rounds had significantly reduced the risks of getting either low (1-8000mf/ml), high (8001-30000mf/ml) or very high (>30000mf/ml) mf loads (Table 5). Furthermore, age and sex were significant factors which could predict zero or low mf loads as adults and males were those with higher odds of having zero and low mf loads. Surprisingly, age and sex were no longer significant predictors of high and very high mf loads while only ivermectin intake remained the most significant predictor to high and very high mf loads (Table 5). A total of 922 children were screened during this study and the results indicated that the Northwest had the highest L. loa mf prevalence with 5. 4% while the East non CDTI, East CDTI and Southwest respectively recorded 5. 3%, 3. 4% and 1. 0%. Important to note is that almost three quarters (71. 5%) of the children had either never taken the drug or had taken it less than 3 times during the previous MDAs (Table 2). High and very high mf load carriers were registered only in the non-CDTI site while in the areas under MDA, no child was found to have a high or very high mf load (Table 6).
This study has demonstrated that repeated annual treatment with ivermectin for the control of onchocerciasis using Community directed delivery approach has achieved a significant impact on L. loa parasitological indicators. This impact was highly felt on the reduction in the proportion of adult individuals with high and very high microfilarial load and with increase in the proportion of the individuals in the study population with no circulating L. loa microfilariae in their blood. Potentially, the reduction in L. loa microfilarial intensity could contribute to the prevention of potential risk of individuals who better adhere to ivermectin treatment to develop severe adverse events (SAEs) during subsequent ivermectin mass drug administration campaigns. Children born within CDTi projects are also protected from the potential risk of developing SAEs. The study has revealed that the adherence to the Ivermectin repeated annual treatment is a key determinant for its full impact on L. loa parasitological indicators. The non-adherence to ivermectin treatment has been demonstrated to be associated to perceived fear of severe adverse events (SAEs). This constitutes an inbuilt design that may prevent ivermectin to ever have full impact on L. loa transmission in endemic areas. In the areas of co-endemicity L. loa with O. volvulus or Wuchereria bancrofti, ivermectin would likely also have limited impact on both the parasitological and entomological indicators of those filariae. These observations reinforce the urgent need of putting in place alternative strategies to accelerate the elimination of onchocerciasis and LF in areas co-endemic with L. loa. This also calls for a research agenda to develop safe drugs to combat L. loa.
Loa loa (the parasite causing loiasis), also known as African eye worm, is endemic in forest areas of west and central Africa. In several of the endemic areas, it co-exists with onchocerciasis and lymphatic filariasis (LF). Because of the benefit individuals suffering from onchocerciasis could have by taking ivermectin where the disease is severe, despite the risk of developing serious side-effects due to being co-infected with L. loa, mass drug administration (MDA) of ivermectin for the control of onchocerciasis has been ongoing in areas where the two diseases overlap. Ivermectin is also effective against loiasis. It is, therefore, hypothesized that several years of ivermectin MDA against onchocerciasis in those areas may have impacted on parasitological indicators for loiasis. In particular, we assess the impact of annual community directed treatment with ivermectin (CDTI) on loiasis with specific reference to the relationship between adherence to treatment and the risk of developing severe (nervous system) complications following ivermectin treatment. We also discuss the feasibility of eliminating onchocerciasis and/or LF in areas endemic for L. loa with ivermectin as the sole intervention tool.
invertebrates
medicine and health sciences
body fluids
tropical diseases
parasitic diseases
animals
parasitology
nematode infections
seasons
neglected tropical diseases
onchocerciasis
infectious disease control
infectious diseases
loiasis
loa loa
helminth infections
eukaryota
blood
anatomy
physiology
earth sciences
nematoda
biology and life sciences
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Impact of repeated annual community directed treatment with ivermectin on loiasis parasitological indicators in Cameroon: Implications for onchocerciasis and lymphatic filariasis elimination in areas co-endemic with Loa loa in Africa