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

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

“Cross-border collaboration in onchocerciasis elimination in Uganda: progress, challenges and opportunities from 2008 to 2013”

Abstract Background Until recently onchocerciasis was prevalent in 37 out of 112 districts of Uganda with at least 3.8 million people at risk of contracting the disease, but following the launching of community-directed treatment with ivermectin (CDTI) in 1996 and the adoption of an onchocerciasis elimination policy in 2007, the country has made significant progress in combating the disease. By 2015, interruption of transmission had been achieved in ten of the 17 onchocerciasis foci, but cross-border foci remained particularly problematic, and therefore within the onchocerciasis elimination framework, Uganda embarked upon addressing these issues with its neighbouring countries, namely the Democratic Republic of Congo (DRC) and South Sudan. This paper summarises the experience of Uganda in addressing cross-border issues on onchocerciasis elimination with DRC. Main achievements and lessons learned The key achievements comprise of the adoption of an elimination policy by the Government of Uganda, cross-border meetings, training DRC technical staff and entomological/ epidemiological surveys. The first strategy meeting was held in Kampala in 2008, but the second strategy meeting was not held in Kinshasa until 2013. The involvement of the high-level officials from the Ministry of Health of DRC was critical for the success of the second strategy meeting, and was precipitated by collaboration to control an outbreak of Ebola Virus. Both meetings demonstrated the political commitment of endemic countries and allowed the implementation of a joint action plan. Important steps in establishing a mutually respected elimination targets was agreed on during cross border meetings. The African Programme for Onchocerciasis Control facilitated and funded these initial meetings, thus overcoming some political and financial challenges faced by both countries. This highlighted the need for multilateral organisations such as the Expanded Special Project for the Elimination of Neglected Tropical Diseases in cross-border activities for other Neglected Tropical Diseases. The collaboration between both countries facilitated the training of technical staff from DRC in entomology which facilitated joint cross-border activities to update the epidemiological understanding of onchocerciasis in Beni and Mahagi districts in North Kivu and Ituri Provinces respectively. In Nebbi district, Uganda, 23.7% of crabs were infested by the vector Simulium neavei compared with 6.3% in Mahagi district, DRC. Rapid Epidemiological Assessment (REA) revealed nodule prevalence of 3.2% and onchodermatitis at 26.4% from five villages in DRC. Conclusion Political commitment of both countries and the support from APOC allowed two cross-border meetings which were critical for the implementation of initial cross border activities for onchocerciasis elimination

Validation of the rapid assessment procedure for loiasis (RAPLOA) in the democratic republic of CongoS

Background: A simple method called RAPLOA, to rapidly assess what proportion of people in a community are infected with L. loa and hence which communities are at high risk of severe adverse reactions following ivermectin treatment, was developed in Cameroon and Nigeria. The method needed further validation in other geographical and cultural contexts before its application in all endemic countries. The present study was designed to validate RAPLOA in two regions in the North East and South West of the Democratic Republic of Congo. Methods: In each study region, villages were selected from different bio-ecological zones in order to cover a wide range of loiasis endemicity. In each selected community, 80 people above the age of 15 years were interviewed for a history of eye worm (migration of adult L. loa under the conjunctiva of the eye) and parasitologically examined for the presence and intensity of L. loa infection. In total, 8100 individuals from 99 villages were enrolled into the study. Results: The results confirmed the findings of the original RAPLOA study: i) the eye worm phenomenon was well-known in all endemic areas, ii) there was a clear relationship between the prevalence of eye worm history and the prevalence and intensity of L. loa microfilaraemia, and iii) using a threshold of 40%, the prevalence of eye worm history was a sensitive and specific indicator of high-risk communities. Conclusion: Following this successful validation, RAPLOA was recommended for the assessment of loiasis endemicity in areas targeted for ivermectin treatment by lymphatic filariasis and onchocerciasis control programmes

Log-likelihood-ratio statistic <i>D</i> = 2(<i>L</i>_<i>w</i> − <i>L</i>_<i>g</i>), for 156 villages where <i>L</i>_<i>w</i> and <i>L</i>_<i>g</i> denote maximised log-likelihoods for Weibull and Gamma fits, respectively.

<p>Log-likelihood-ratio statistic <i>D</i> = 2(<i>L</i>_<i>w</i> − <i>L</i>_<i>g</i>), for 156 villages where <i>L</i>_<i>w</i> and <i>L</i>_<i>g</i> denote maximised log-likelihoods for Weibull and Gamma fits, respectively.</p

Empirical (coloured lines and dots) and fitted (black lines) cumulative distributions of parasite levels for the five randomly selected villages shown in Fig 3.

<p>Empirical (coloured lines and dots) and fitted (black lines) cumulative distributions of parasite levels for the five randomly selected villages shown in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005157#pntd.0005157.g003" target="_blank">Fig 3</a>.</p

Log-likelihood-ratio statistics, D, degrees of freedom, df, and p-values, p, for candidate covariates in univariable analysis.

<p>Log-likelihood-ratio statistics, D, degrees of freedom, df, and p-values, p, for candidate covariates in univariable analysis.</p

Map showing the locations of the 222 villages for which data are available.

<p>Map showing the locations of the 222 villages for which data are available.</p

Correction: Dusabimana et al. Surveillance for Onchocerciasis-Associated Epilepsy and Ov16 IgG4 Testing of Children 6&ndash;10 Years Old Should Be Used to Identify Areas Where Onchocerciasis Elimination Programs Need Strengthening. Pathogens 2022, 11, 281

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