Low transmission of Wuchereria bancrofti in cross-border districts of Côte d'Ivoire: A great step towards lymphatic filariasis elimination in West Africa

Ghana's path towards eliminating lymphatic filariasis

Lymphatic filariasis, also known as elephantiasis, is a debilitating parasitic disease that has been prevalent in various parts of the world, including China and Ghana. This paper explores the historical context of lymphatic filariasis in Ghana and China, as well as the fights towards eliminating the disease in both countries. The review also covered the strategies employed by the Chinese government to eliminate lymphatic filariasis and the key lessons that Ghana can learn from China's success. The discussion highlights the importance of political commitment, multisectoral collaboration, tailoring control strategies to local contexts, adopting a comprehensive approach, and emphasising health education and community mobilisation. By adopting these lessons and fostering a robust national strategy, engaging diverse stakeholders, and ensuring active community involvement, Ghana can work towards achieving lymphatic filariasis elimination, improving public health, and fostering sustainable development.

The impact of mosquito sampling strategies on molecular xenomonitoring prevalence for filariasis: a systematic review

Objective

To explore the impact of mosquito collection methods, sampling intensity and target genus on molecular xenomonitoring detection of parasites causing lymphatic filariasis.

Methods

We systematically searched five databases for studies that used two or more collection strategies for sampling wild mosquitoes, and employed molecular methods to assess the molecular xenomonitoring prevalence of parasites responsible for lymphatic filariasis. We performed generic inverse variance meta-analyses and explored sources of heterogeneity using subgroup analyses. We assessed methodological quality and certainty of evidence.

Findings

We identified 25 eligible studies, with 172 083 mosquitoes analysed. We observed significantly higher molecular xenomonitoring prevalence with collection methods that target bloodfed mosquitoes compared to methods that target unfed mosquitoes (prevalence ratio: 3.53; 95% confidence interval, CI: 1.52-8.24), but no significant difference compared with gravid collection methods (prevalence ratio: 1.54; 95% CI: 0.46-5.16). Regarding genus, we observed significantly higher molecular xenomonitoring prevalence for anopheline mosquitoes compared to culicine mosquitoes in areas where Anopheles species are the primary vector (prevalence ratio: 6.91; 95% CI: 1.73-27.52). One study provided evidence that reducing the number of sampling sites did not significantly affect molecular xenomonitoring prevalence. Evidence of differences in molecular xenomonitoring prevalence between sampling strategies was considered to be of low certainty, due partly to inherent limitations of observational studies that were not explicitly designed for these comparisons.

Conclusion

The choice of sampling strategy can significantly affect molecular xenomonitoring results. Further research is needed to inform the optimum strategy in light of logistical constraints and epidemiological contexts.

Population pharmacokinetics of ivermectin after mass drug administration in lymphatic filariasis endemic communities of Tanzania

Ivermectin (IVM) is a drug of choice used with albendazole for mass drug administration (MDA) to halt transmission of lymphatic filariasis. We investigated IVM pharmacokinetic (PK) variability for its dose optimization during MDA. PK samples were collected at 0, 2, 4, and 6 h from individuals weighing greater than 15 kg (n = 468) receiving IVM (3-, 6-, 9-, or 12 mg) and ALB (400 mg) during an MDA campaign in Tanzania. Individual characteristics, including demographics, laboratory/clinical parameters, and pharmacogenetic variations were assessed. IVM plasma concentrations were quantified by liquid-chromatography tandem mass spectrometry and analyzed using population-(PopPK) modeling. A two-compartment model with transit absorption kinetics, and allometrically scaled oral clearance (CL/F) and central volume (Vc /F) was adapted. Fitting of the model to the data identified 48% higher bioavailability for the 3 mg dose compared to higher doses and identified a subpopulation with 97% higher mean transit time (MTT). The final estimates for CL/F, Vc /F, intercompartment clearance, peripheral volume, MTT, and absorption rate constant for a 70 kg person (on dose other than 3 mg) were 7.7 L/h, 147 L, 20.4 L/h, 207 L, 1.5 h, and 0.71/h, respectively. Monte-Carlo simulations indicated that weight-based dosing provides comparable exposure across weight bands, but height-based dosing with capping IVM dose at 12 mg for individuals with height greater than 160 cm underdoses those weighing greater than 70 kg. Variability in IVM PKs is partly explained by body weight and dose. The established PopPK model can be used for IVM dose optimization. Height-based pole dosing results in varying IVM exposure in different weight bands, hence using weighing scales for IVM dosing during MDA is recommended.

First evaluation of antibody responses to Culex quinquefasciatus salivary antigens as a serological biomarker of human exposure to Culex bites: A pilot study in Côte d'Ivoire

Background

Culex mosquitoes are vectors for a variety of pathogens of public health concern. New indicators of exposure to Culex bites are needed to evaluate the risk of transmission of associated pathogens and to assess the efficacy of vector control strategies. An alternative to entomological indices is the serological measure of antibodies specific to mosquito salivary antigens. This study investigated whether the human IgG response to both the salivary gland extract and the 30 kDa salivary protein of Culex quinquefasciatus may represent a proxy of human exposure to Culex bites.

Methodology/Principal findings

A multidisciplinary survey was conducted with children aged 1 to 14 years living in neighborhoods with varying exposure to Culex quinquefasciatus in the city of Bouaké, Côte d’Ivoire. Children living in sites with high exposure to Cx quinquefasciatus had a significantly higher IgG response to both salivary antigens compared with children living in the control site where only very few Culex were recorded. Moreover, children from any Culex-high exposed sites had significantly higher IgG responses only to the salivary gland extract compared with children from the control village, whereas no difference was noted in the anti-30 kDa IgG response. No significant differences were noted in the specific IgG responses between age and gender. Sites and the use of a bed net were associated with the level of IgG response to the salivary gland extract and to the 30 kDa antigen, respectively.

Conclusions/Significance

These findings suggest that the IgG response to Culex salivary gland extracts is suitable as proxy of exposure; however, the specificity to the Culex genus needs further investigation. The lower antigenicity of the 30 kDa recombinant protein represents a limitation to its use. The high specificity of this protein to the Culex genus makes it an attractive candidate and other specific antibody responses might be more relevant as a biomarker of exposure. These epidemiological observations may form a starting point for additional work on developing serological biomarkers of Culex exposure.

The evaluation of exposure to mosquitoes is a key parameter in assessing the risk of transmission of associated pathogens, including zoonoses. Entomological methods represent the gold standard but have several limitations, and efforts are being made to develop new indicators to accurately assess human–Culex contact. This study showed the IgG response to Culex quinquefasciatus salivary gland extract is suitable proxy of exposure to Culex bites. The lower antigenicity of the 30 kDa recombinant protein represents a limitation to its use. The high specificity of this protein to the Culex genus makes it an attractive candidate and other isotypic antibody responses specific to this salivary antigen might be more relevant as a biomarker of exposure.

Evaluating the Diagnostic Test Accuracy of Molecular Xenomonitoring Methods for Characterizing Community Burden of Lymphatic Filariasis

Background

Molecular xenomonitoring (MX), the detection of pathogen DNA in mosquitoes, is a recommended approach to support lymphatic filariasis (LF) elimination efforts. Potential roles of MX include detecting presence of LF in communities and quantifying progress towards elimination of the disease. However, the relationship between MX results and human prevalence is poorly understood.

Methods

We conducted a systematic review and meta-analysis from all previously conducted studies that reported the prevalence of filarial DNA in wild-caught mosquitoes (MX rate) and the corresponding prevalence of microfilaria (mf) in humans. We calculated a pooled estimate of MX sensitivity for detecting positive communities at a range of mf prevalence values and mosquito sample sizes. We conducted a linear regression to evaluate the relationship between mf prevalence and MX rate.

Results

We identified 24 studies comprising 144 study communities. MX had an overall sensitivity of 98.3% (95% confidence interval, 41.5–99.9%) and identified 28 positive communities that were negative in the mf survey. Low sensitivity in some studies was attributed to small mosquito sample sizes (<1000) and very low mf prevalence (<0.25%). Human mf prevalence and mass drug administration status accounted for approximately half of the variation in MX rate (R² = 0.49, P < .001). Data from longitudinal studies showed that, within a given study area, there is a strong linear relationship between MX rate and mf prevalence (R² = 0.78, P < .001).

Conclusions

MX shows clear potential as tool for detecting communities where LF is present and as a predictor of human mf prevalence.

Lymphatic filariasis, infection status in Culex quinquefasciatus and Anopheles species after six rounds of mass drug administration in Masasi District, Tanzania

Background

Lymphatic filariasis (LF) elimination program in Tanzania started in 2000 in response to the Global program for the elimination of LF by 2020. Evidence shows a persistent LF transmission despite more than a decade of mass drug administration (MDA). It is advocated that, regular monitoring should be conducted in endemic areas to evaluate the progress towards elimination and detect resurgence of the disease timely. This study was therefore designed to assess the status of Wuchereria bancrofti infection in Culex quinqefasciatus and Anopheles species after six rounds of MDA in Masasi District, South Eastern Tanzania.

Methods

Mosquitoes were collected between June and July 2019 using Center for Diseases Control (CDC) light traps and gravid traps for indoor and outdoor respectively. The collected mosquitoes were morphologically identified into respective species. Dissections and PCR were carried out to detect W. bancrofti infection. Questionnaire survey and checklist were used to assess vector control interventions and household environment respectively. A Poisson regression model was run to determine the effects of household environment on filarial vector density.

Results

Overall, 12 452 mosquitoes were collected of which 10 545 (84.7%) were filarial vectors. Of these, Anopheles gambiae complex, An. funestus group and Cx. quinquefasciatus accounted for 0.1%, 0.7% and 99.2% respectively. A total of 365 pools of Cx. quinquefasciatus (each with 20 mosquitoes) and 46 individual samples of Anopheles species were analyzed by PCR. For Cx. quinquefasciatus pools, 33 were positive for W. bancrofti, giving an infection rate of 0.5%, while the 46 samples of Anopheles species were all negative. All 1859 dissected mosquitoes analyzed by microscopy were also negative. Households with modern latrines had less mosquitoes than those with pit latrines [odds ratio (OR) = 0.407, P < 0.05]. Houses with unscreened windows had more mosquitoes as compared to those with screened windows (OR = 2.125, P < 0.05). More than 80% of the participants own bednets while 16.5% had no protection.

Conclusions

LF low transmission is still ongoing in Masasi District after six rounds of MDA and vector control interventions. The findings also suggest that molecular tools may be essential for xenomonitoring LF transmission during elimination phase.