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

Pion, S. D. S.; Filipe, J. A. N.; Kamgno, Joseph; Gardon, Jacques; Basáñez, María‐Gloria; Boussinesq, Michel

doi:10.1017/s0031182006000035

Cited by 24 publications

(20 citation statements)

References 50 publications

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“…This relationship has been explained by suggesting that the degree of parasite overdispersion among hosts (probably driven by heterogeneous exposure to infection) decreases as mean infection intensity rises, allowing for infection prevalence to reach high values (nearly 100%) when intensity is high. Interestingly, previous studies have suggested that the degree of L. loa overdispersion across communities is severe and does not change with mean infection intensity [69], an observation that could lead to the lower levels (50-60%) of saturating microfilarial prevalence that have been reported.…”

Section: Prevalence and Intensity Of Infection In Human Populationsmentioning

confidence: 90%

The Population Biology and Transmission Dynamics of Loa loa

Whittaker

Walker

Pion

et al. 2018

Trends in Parasitology

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African eye worm (caused by the filarial nematode Loa loa) -affects more than 10 million people. Despite causing ocular and systemic symptoms, it has typically been considered a benign condition, only of public health relevance because it impedes mass drug administration-based interventions against onchocerciasis and lymphatic filariasis in co-endemic areas. Recent research has challenged this conception, demonstrating excess mortality associated with high levels of infection, implying that loiasis warrants attention as an intrinsic public health problem. This review summarises available information on the key parasitological, entomological, and epidemiological characteristics of the infection and argues for the mobilisation of resources to control the disease, and the development of a mathematical transmission model to guide deployment of interventions.

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Section: Prevalence and Intensity Of Infection In Human Populationsmentioning

confidence: 90%

The Population Biology and Transmission Dynamics of Loa loa

Whittaker

Walker

Pion

et al. 2018

Trends in Parasitology

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“…For randomly distributed microfilariae, a Poisson distribution would be appropriate. However, it is likely that there is ' clumping ' of microfilariae in the skin (Kershaw, Duke and Budden, 1954), leading to an excess of zeros in comparison with the Poisson distribution (Grenfell et al 1990 ;Pion et al 2006). We have chosen to model the observed distribution of microfilariae with a zero-inflated Poisson distribution.…”

Section: Expected Microfilarial Load Within An Individual Hostmentioning

confidence: 99%

Rates of microfilarial production by Onchocerca volvulus are not cumulatively reduced by multiple ivermectin treatments

Bottomley

Isham

Collins³

et al. 2008

Parasitology

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Bottomley, C; Isham, V; Collins, RC; Bas??ez, MG (2008) Rates of microfilarial production by Onchocerca volvulus are not cumulatively reduced by multiple ivermectin treatments. Parasitology, 135 (13 Regular distribution of ivermectin reduces onchocerciasis transmission and morbidity by killing, within humans, the microfilarial stage of the parasite (microfilaricidal effect). In addition, ivermectin exerts a so-called embryostatic effect by which microfilarial production by the adult female worm becomes suppressed during a number of weeks after treatment. To assess the overall effect of ivermectin on onchocerciasis transmission and evaluate the likelihood of local elimination of the infection it is important to estimate the magnitude of the anti-fertility effect over the course of a treatment programme. Estimates of the effect of repeated drug treatments on the production of microfilariae by adult Onchocerca volvulus were obtained by developing a model that was fitted to data collected from three hyperendemic communities in Guatemala, where eligible residents received ivermectin twice per year for two and a half years. The data consist of microfilarial load measurements in the skin, collected just before each six-monthly treatment during the programme. The model that is developed describes the dynamics of an individual host's expected microfilarial load over the 30-month study period. We adopt a Bayesian approach and use Markov chain Monte Carlo (McMC) techniques to fit the model to the data. Combining estimates from the three villages, average microfilarial production in the first six months post-treatment was reduced by y64 % of its pre-treatment level, regardless of values chosen for the pre-ivermectin fertility rate within plausible ranges. Increased adult worm death rate after treatment (to mimic removal of macrofilariae via nodulectomy during the programme) resulted in a smaller estimated magnitude of the embryostatic effect (rate of microfilarial production was reduced by y58 % of pre-ivermectin value). After subsequent treatments, the rate of microfilarial production appeared to be similarly decreased. The data and analyses therefore do not support the hypothesis of a cumulative effect of multiple ivermectin treatments on microfilarial production by female worms.

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“…To address this problem we first develop a model for the variation in parasite count between individuals within a community, and explore how the parameters of this distribution co-vary with each other and with community-level covariates.This study builds on previous work which also looked at the distribution of Loa loa microfilarial loads in communities [11]. In contrast to this earlier work, we allow the relationship between community-level prevalence and mean intensity of infection to vary stochastically between communities.…”

Section: Introductionmentioning

confidence: 99%

Using Community-Level Prevalence of Loa loa Infection to Predict the Proportion of Highly-Infected Individuals: Statistical Modelling to Support Lymphatic Filariasis and Onchocerciasis Elimination Programs

Schlüter

Ndeffo-Mbah

Takougang³

et al. 2016

PLoS Negl Trop Dis

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Lymphatic Filariasis and Onchocerciasis (river blindness) constitute pressing public health issues in tropical regions. Global elimination programs, involving mass drug administration (MDA), have been launched by the World Health Organisation. Although the drugs used are generally well tolerated, individuals who are highly co-infected with Loa loa are at risk of experiencing serious adverse events. Highly infected individuals are more likely to be found in communities with high prevalence. An understanding of the relationship between individual infection and population-level prevalence can therefore inform decisions on whether MDA can be safely administered in an endemic community. Based on Loa loa infection intensity data from individuals in Cameroon, the Republic of the Congo and the Democratic Republic of the Congo we develop a statistical model for the distribution of infection levels in communities. We then use this model to make predictive inferences regarding the proportion of individuals whose parasite count exceeds policy-relevant levels. In particular we show how to exploit the positive correlation between community-level prevalence and intensity of infection in order to predict the proportion of highly infected individuals in a community given only prevalence data from the community in question. The resulting prediction intervals are not substantially wider, and in some cases narrower, than the corresponding binomial confidence intervals obtained from data that include measurements of individual infection levels. Therefore the model developed here facilitates the estimation of the proportion of individuals highly infected with Loa loa using only estimated community level prevalence. It can be used to assess the risk of rolling out MDA in a specific community, or to guide policy decisions.

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

Cited by 24 publications

References 50 publications

The Population Biology and Transmission Dynamics of Loa loa

The Population Biology and Transmission Dynamics of Loa loa

Rates of microfilarial production by Onchocerca volvulus are not cumulatively reduced by multiple ivermectin treatments

Using Community-Level Prevalence of Loa loa Infection to Predict the Proportion of Highly-Infected Individuals: Statistical Modelling to Support Lymphatic Filariasis and Onchocerciasis Elimination Programs

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