Biting on human body parts of Simulium vectors and its implication for the manifestation of Onchocerca nodules along Osun River, southwestern Nigeria

Background: The biting preference of Simulium vectors has been known to influence the distribution ofOnchocerca nodules and microfilariae in human body. There is, however, variation in biting pattern of Simuliumflies in different geographical locations. This study investigates the biting pattern on human parts by Simuliumvectors along Osun river system where Simulium soubrense Beffa form has been implicated as the dominantvector and its possible implication on the distribution of Onchocerca nodules on human body along the river.Methods: Flies were collected by consented fly capturers on exposed human parts namely head/neck region,arms, upper limb and lower limb in Osun Eleja and Osun Budepo along Osun river in the wet season (August–September) and the dry season (November–December) in 2008. The residents of the communities were alsoscreened for palpable Onchocerca nodules.Results: The results showed that number of flies collected below the ankle region was significantly higher thanthe number collected on other exposed parts (p <0.05) while the least was collected on head/neck region in bothseasons. The lower trunk was the most common site (60%) for nodule location at Osun Eleja followed by uppertrunk (40%). Nodules were not found in the head and limb regions. At Osun Budepo, the upper trunk was themost common site of the nodule location (53.8%) followed by the lower trunk (38.5%) and head region (7.7%).Conclusion: Though, most of the flies were caught at the ankle region, the biting of other parts coupled with thepresence of nodules at the head and upper trunk regions showed that Simulium vectors could obtain microfilariaefrom any part of the body, thus increasing the risk of onchocerciasis transmission

Evaluation of a community-based trapping program to collect simulium ochraceum sensu lato for verification of onchocerciasis elimination

Background: Collection of the black fly vectors of onchocerciasis worldwide relies upon human landing collections. Recent studies have suggested that the Esperanza Window Trap baited with a human scent lure and CO2 had the potential to replace human hosts for the collection of Simulium ochraceum sensu lato in Southern Chiapas focus, Mexico. The feasibility of utilizing these traps in a community-based approach for the collection of S. ochraceum s.l. was evaluated. Methodology/Principal findings: Local residents of a formerly endemic extra-sentinel community for onchocerciasis were trained to carry out collections using the traps. The residents operated the traps over a 60-day period and conducted parallel landing collections, resulting in a total of 28,397 vector black flies collected. None of the flies collected were found to contain parasite DNA when tested by a polymerase chain reaction assay targeting a parasite specific sequence, resulting in a point estimate of infection in the vectors of zero, with an upper bound of the 95% confidence interval 0.13 per 2,000. This meets the accepted criterion for demonstrating an interruption of parasite transmission. Conclusions/Significance: These data demonstrate that Esperanza Window Traps may be effectively operated by minimally trained residents of formerly endemic communities, resulting in the collection of sufficient numbers of flies to verify transmission interruption of onchocerciasis. The traps represent a viable alternative to using humans as hosts for the collection of vector flies as part of the verification of onchocerciasis elimination

Identification of human semiochemicals attractive to the major vectors of onchocerciasis

Background: Entomological indicators are considered key metrics to document the interruption of transmission of Onchocerca volvulus, the etiological agent of human onchocerciasis. Human landing collection is the standard employed for collection of the vectors for this parasite. Recent studies reported the development of traps that have the potential for replacing humans for surveillance of O. volvulus in the vector population. However, the key chemical components of human odor that are attractive to vector black flies have not been identified. Methodology/Principal Findings: Human sweat compounds were analyzed using GC-MS analysis and compounds common to three individuals identified. These common compounds, with others previously identified as attractive to other hematophagous arthropods were evaluated for their ability to stimulate and attract the major onchocerciasis vectors in Africa (Simulium damnosum sensu lato) and Latin America (Simulium ochraceum s. l.) using electroantennography and a Y tube binary choice assay. Medium chain length carboxylic acids and aldehydes were neurostimulatory for S. damnosum s.l. while S. ochraceum s.l. was stimulated by short chain aliphatic alcohols and aldehydes. Both species were attracted to ammonium bicarbonate and acetophenone. The compounds were shown to be attractive to the relevant vector species in field studies, when incorporated into a formulation that permitted a continuous release of the compound over time and used in concert with previously developed trap platforms. Conclusions/Significance: The identification of compounds attractive to the major vectors of O. volvulus will permit the development of optimized traps. Such traps may replace the use of human vector collectors for monitoring the effectiveness of onchocerciasis elimination programs and could find use as a contributing component in an integratedvector control/drug program aimed at eliminating river blindness in Africa

Larvicidal efficacies and chemical composition of essential oils of Pinus sylvestris and Syzygium aromaticum against mosquitoes

Objective: To assess the chemical composition and mosquito larvicidal potentials of essential oils of locally sourced Pinus sylvestris (P. sylvestris) and Syzygium aromaticum (S. aromaticum) against Aedes aegypti (A. aegypti) and Culex quinquefasciatus (C. quinquefasciatus). Methods: The chemical composition of the essential oils of both plants was determined using GC-MS while the larvicidal bioassay was carried out using different concentrations of the oils against the larvae of A. aegypti and C. quinquefasciatus in accordance with the standard protocol. Results: The results as determined by GC-MS showed that oil of S. aromaticum has eugenol (80.5%) as its principal constituent while P. sylvestris has 3-Cyclohexene-1-methanol, .alpha., .alpha.4-trimethyl (27.1%) as its dominant constituent. Both oils achieved over 85% larval mortality within 24 h. The larvae of A. aegypti were more susceptible to the oils [LC50 (S. aromaticum)=92.56 mg/L, LC50(P. sylvestris)=100.39 mg/L] than C. quinquefasciatus [LC50(S. aromaticum)=124.42 mg/L; LC50(P. sylvestris)=128.00 mg/L]. S. aromaticum oil was more toxic to the mosquito larvae than oil of P. sylvestris but the difference in lethal concentrations was insignificant (P>0.05). Conclusion: The results justify the larvicidal potentials of both essential oils and the need to incorporate them in vector management and control

Co-endemicity of Loiasis and Onchocerciasis in Rain Forest Communities in Southwestern Nigeria

<div><p>Background</p><p>Loiasis is currently receiving attention as a disease of public health importance because of the possibility of increased risk of developing neurologic serious adverse event following mass ivermectin treatment against onchocerciasis in individual co-infected with <i>Onchocerca volvulus</i> and <i>Loa loa</i>.</p><p>Methodology/Principal Findings</p><p>Rapid assessment procedure for loiasis (RAPLOA) was conducted in 12 communities covering the 3 senatorial districts of Osun State, Nigeria. A total of 960 people were interviewed for history of eye worm using the WHO guidelines for rapid assessment. The survey confirmed the presence of loiasis in all the 12 communities with 4 in Osun East/Ife south senatorial district being at high risk with a prevalence of over 40%. Based on the RAPLOA results, communities within Osun East/Ife south senatorial district were selected for microfilaraemic assessment of <i>L</i>. <i>loa</i> and <i>O</i>. <i>volvulus</i>. A total of 1115 and 1091 individuals were screened for <i>L</i>. <i>loa</i> and <i>O</i>. <i>volvulus</i> microfilaria worms respectively. 160 (14.3%) had <i>L</i>. <i>loa</i> microfilaria detected in their blood with 8 (5.0%) individuals having <i>L</i>. <i>loa</i> loads above 8000 mf/ml. 166 (15.2%) subjects had <i>O</i>. <i>volvulus</i> microfilaria (range 4-504 mf/ml) detected in their skin snip. 30 (2.69%) subjects were co-infected with both <i>L</i>. <i>loa</i> and <i>O</i>. <i>volvulus</i>. There was a significant variation in the prevalence (2.1% to 33.3%) of onchocerciasis in the communities studied (p = 0.001). Five (41.7%) of the studied communities had a prevalence that is equal to or greater than 20%.</p><p>Conclusions/Significance</p><p>Low prevalence of onchocerciasis and loiasis co-infection in this study suggests that loiasis may not pose a serious epidemiological threat to the continuous distribution and sustainability of ivermectin for the treatment of onchocerciasis. Evaluation of the interruption of onchocerciasis transmissions in this region using all the indicators set forth by WHO is therefore suggested.</p></div

Development of a novel trap for the collection of black flies of the Simulium ochraceum complex.

BACKGROUND:Human landing collections are currently the standard method for collecting onchocerciasis vectors in Africa and Latin America. As part of the efforts to develop a trap to replace human landing collections for the monitoring and surveillance of onchocerciasis transmission, comprehensive evaluations of several trap types were conducted to assess their ability to collect Simulium ochraceum sensu lato, one of the principal vectors of Onchocerca volvulus in Latin America. METHODOLOGY/PRINCIPAL FINDINGS:Diverse trap designs with numerous modifications and bait variations were evaluated for their abilities to collect S. Ochraceum s.l. females. These traps targeted mostly host seeking flies. A novel trap dubbed the "Esperanza window trap" showed particular promise over other designs. When baited with CO2 and BG-lure (a synthetic blend of human odor components) a pair of Esperanza window traps collected numbers of S. Ochraceum s.l. females similar to those collected by a team of vector collectors. CONCLUSIONS/SIGNIFICANCE:The Esperanza window trap, when baited with chemical lures and CO2 can be used to collect epidemiologically significant numbers of Simulium ochraceum s.l., potentially serving as a replacement for human landing collections for evaluation of the transmission of O. volvulus

Distribution of <i>Loa loa</i> microfilaraemia and <i>O</i>.<i>volvulus</i> by age and sex.

<p>Distribution of <i>Loa loa</i> microfilaraemia and <i>O</i>.<i>volvulus</i> by age and sex.</p

The prevalence of loiasis and onchocerciasis in the selected rural communities in Osun State.

<p>The prevalence of loiasis and onchocerciasis in the selected rural communities in Osun State.</p

Clinical spectrum observed from filarial infected members of the surveyed population.

<p>Clinical spectrum observed from filarial infected members of the surveyed population.</p

Map of Osun State showing the three senatorial districts and the communities within the districts that were selected for the study.

<p>Map of Osun State showing the three senatorial districts and the communities within the districts that were selected for the study.</p