How Can Onchocerciasis Elimination in Africa Be Accelerated? Modeling the Impact of Increased Ivermectin Treatment Frequency and Complementary Vector Control.

Background: Great strides have been made toward onchocerciasis elimination by mass drug administration (MDA) of ivermectin. Focusing on MDA-eligible areas, we investigated where the elimination goal can be achieved by 2025 by continuation of current practice (annual MDA with ivermectin) and where intensification or additional vector control is required. We did not consider areas hypoendemic for onchocerciasis with loiasis coendemicity where MDA is contraindicated. Methods: We used 2 previously published mathematical models, ONCHOSIM and EPIONCHO, to simulate future trends in microfilarial prevalence for 80 different settings (defined by precontrol endemicity and past MDA frequency and coverage) under different future treatment scenarios (annual, biannual, or quarterly MDA with different treatment coverage through 2025, with or without vector control strategies), assessing for each strategy whether it eventually leads to elimination. Results: Areas with 40%-50% precontrol microfilarial prevalence and ≥10 years of annual MDA may achieve elimination with a further 7 years of annual MDA, if not achieved already, according to both models. For most areas with 70%-80% precontrol prevalence, ONCHOSIM predicts that either annual or biannual MDA is sufficient to achieve elimination by 2025, whereas EPIONCHO predicts that elimination will not be achieved even with complementary vector control. Conclusions: Whether elimination will be reached by 2025 depends on precontrol endemicity, control history, and strategies chosen from now until 2025. Biannual or quarterly MDA will accelerate progress toward elimination but cannot guarantee it by 2025 in high-endemicity areas. Long-term concomitant MDA and vector control for high-endemicity areas might be useful.

Identification of semiochemicals attractive to Simulium vittatum (IS-7).

Many blackfly species (Diptera: Simuliidae) are economically important insect pests, both as nuisance biters and as vectors of pathogens of medical and veterinary relevance. Among the important blackfly pest species in North America is Simulium vittatum Zetterstedt sensu lato. The objective of this study was to identify compounds excreted by mammalian hosts that are attractive to host-seeking S. vittatum females. The attractiveness of putative compounds to colonized S. vittatum was tested through electrophysiological (electroantennography; n = 58 compounds) and behavioural (Y-tube assays; n = 7 compounds in three concentrations) bioassays. Five compounds were significantly attractive to host-seeking S. vittatum females: 1-octen-3-ol; 2-heptanone; acetophenone; 1-octanol, and naphthalene. These candidate compounds might be useful as attractants in traps that could be developed for use in alternative or complementary management tactics in programmes to suppress nuisance blackfly populations, or for the collection of samples in which to study the transmission ecology of pathogens transmitted by blackflies of the S. vittatum complex.

Vector abundance determines Trypanosoma prevalence in nestling blue tits.

The effect of insect vectors on avian exposure to infection by pathogens remains poorly studied. Here, we used an insect repellent treatment to reduce the number of blood-sucking flying insects in blue tit Cyanistes caeruleus nests and examined its effect on nestling health status measured as body mass, nestling phytohaemagglutinin (PHA) response and blood parasite prevalence. We found that (i) the insect repellent treatment significantly reduced the number of blood-sucking flying insects in nests and (ii) the number of blood-sucking flying insects had a significant effect on the prevalence of the blood parasite Trypanosoma independently of the treatment. In addition, we found support for an adverse effect of parasite infections on nestling PHA response. Nestlings infected by Trypanosoma mounted a weaker response against PHA than non-parasitized ones. In addition, the number of blowflies in the nest was negatively associated with nestling PHA response. Overall, we found support for the hypothesis that blood-sucking flying insects attacking nestlings increase their exposure to parasite infections. Our results further substantiate the adverse effect of parasites on nestling condition.

Evolution of insecticide resistance in non-target black flies (Diptera: Simuliidae) from Argentina.

Black flies, a non-target species of the insecticides used in fruit production, represent a severe medical and veterinary problem. Large increases in the level of resistance to the pyrethroids fenvalerate (more than 355-fold) and deltamethrin (162-fold) and a small increase in resistance to the organophosphate azinphos methyl (2-fold) were observed between 1996-2008 in black fly larvae under insecticide pressure. Eventually, no change or a slight variation in insecticide resistance was followed by a subsequent increase in resistance. The evolution of pesticide resistance in a field population is a complex and stepwise process that is influenced by several factors, the most significant of which is the insecticide selection pressure, such as the dose and frequency of application. The variation in insecticide susceptibility within a black fly population in the productive area may be related to changes in fruit-pest control. The frequency of individuals with esterase activities higher than the maximum value determined in the susceptible population increased consistently over the sampling period. However, the insecticide resistance was not attributed to glutathione S-transferase activity. In conclusion, esterase activity in black flies from the productive area is one mechanism underlying the high levels of resistance to pyrethroids, which have been recently used infrequently. These enzymes may be reselected by currently used pesticides and enhance the resistance to these insecticides.

Repellent activity of some essential oils against Simulium species in India.

Use of repellents seems to be most reliable method of personal protection against annoyance and infections associated with haematophagous insects. We have investigated the biting activity of Simulium and tested the repellency of five essential oils extracted from Homalomena aromatica Schott (Alismatales: Araceae), Pogostemon heyneanus Bentham (Lamiales: Lamiaceae), Citrus aurantifolia Swingle (Sapindales: Rutaceae), Vitex negundo L. (Lamiales: Lamiaceae), and Ageratum conzoides L. (Asterales: Asteraceae) on the human volunteers against Simulium (blackflies) in three locations of Arunachal Pradesh, India. Blackflies preferred biting legs (> 79%) as compared to hand and face with profound biting activity during 1000-1100 h (> 23%) and 1500 - 1600 h (> 28%). The essential oil extracted from Homalomena aromatica, Vitex negundo and Ageratum conizoides provided > 2 h protection at 5% concentration and > 5 h protection at 10% concentration in all the three testing locations. The repellency of Homalomena aromatica, Vitex negundo and Ageratum conizoides essential oils after 6 h application was > 50% at 5% concentration and > 90% at 10% concentration. The study provides evidence for the potential of these essential oils in developing new repellents against blackflies.

Spinosad toxicity to Simulium spp. larvae and associated aquatic biota in a coffee-growing region of Veracruz State, Mexico.

Spinosad is a naturally derived insecticide that has shown potential as a mosquito larvicide. To determine the activity of spinosad against blackflies, late-instar larvae from a community comprising Simulium triittatum (63.6%) and seven other species, including three known vectors of onchocerciasis in Mexico (S. metallicum, S. ochraceum, and S. callidum), were subjected to concentration-mortality laboratory bioassays following World Health Organization guidelines. Cephalic capsule measurements confirmed the relatively homogeneous distribution of experimental larvae. The 50% lethal concentration of spinosad was estimated at 1.48 ppm spinosad (95% confidence interval: 1.07-2.33) for a 10-min exposure period, whereas larvae treated with 0.05 ppm of the organophosphate temephos experienced 61% mortality. Immature aquatic insects were identified to genus and tested for their susceptibility to spinosad in the laboratory. After exposure to 12 ppm spinosad for 10 min, ephemeropterans, odonates, trichopterans, and hemipterans did not experience significantly increased mortality over that of untreated controls, whereas a significant increase in mortality was observed in spinosad-treated Plecoptera (P < 0.001). Tilapia and trout fry exposed to 12 ppm spinosad for 10 min did not experience increased mortality at 24-h postexposure over that of the controls. We conclude that spinosad is less toxic than temephos to these blackfly species, but is likely to have a low impact on nontarget members of the aquatic community.

Onchocerca volvulus transmission in the Mbam valley of Cameroon following 16 years of annual community-directed treatment with ivermectin, and the description of a new cytotype of Simulium squamosum.

BACKGROUND: The onchocerciasis focus surrounding the lower Mbam and Sanaga rivers, where Onchocerca volvulus is transmitted by Simulium damnosum s.l. (Diptera: Simuliidae), was historically the largest in the southern regions of Cameroon. Annual community-directed treatment with ivermectin (CDTI) has been taking place since 2000, but recent studies have shown that new infections are occurring in children. We aimed to investigate blackfly biting and O. volvulus transmission rates along the lower Mbam river 16 years after the formal onset of annual CDTI. METHODS: Black flies were collected for three consecutive days each month between July 2016 and June 2017 at two riverside villages and two inland sites situated 4.9 km and 7.9 km from the riverside. Specimens collected at each site were dissected on one of the three collection days each month to estimate parity rates and O. volvulus infection rates, while the remaining samples were preserved for pool screening. RESULTS: In total, 93,573 S. damnosum s.l. black flies were recorded biting humans and 9281 were dissected. Annual biting rates of up to 606,370 were estimated at the riverside, decreasing to 20,540 at 7.9 km, while, based on dissections, annual transmission potentials of up to 4488 were estimated at the riverside, decreasing to 102 and 0 at 4.9 km and 7.9 km, respectively. However, pool screening showed evidence of infection in black flies at the furthest distance from the river. Results of both methods demonstrated the percentage of infective flies to be relatively low (0.10-0.36%), but above the WHO threshold for interruption of transmission. In addition, a small number of larvae collected during the dry season revealed the presence of Simulium squamosum E. This is the first time S. squamosum E has been found east of Lake Volta in Ghana, but our material was chromosomally distinctive, and we call it S. squamosum E2. CONCLUSIONS: Relatively low O. volvulus infection rates appear to be offset by extremely high densities of biting black flies which are sustaining transmission along the banks of the lower Mbam river.

Assessment of the toxicological interaction of sertraline with cholinesterase inhibiting insecticides in aquatic insects using the black fly, Simulium vittatum IS-7.

Sertraline is a selective serotonin reuptake inhibitor (SSRI) prescribed as an antidepressant. Although SSRIs are known to block serotonin reuptake sites on cell membranes, they also have been shown to inhibit acetylcholinesterase (AChE) activity. Thus, the interaction of these chemicals with other AChE inhibitors, namely, organophosphate and carbamate insecticides, is of interest. In addition, these insecticides have been shown to interact with serotonergic neuronal pathways creating questions as to how these chemicals might interact. In this study, the interactive effect of sertraline (SSRI) in binary combinations with carbaryl (carbamate insecticide) and diazinon (organophosphate insecticide) was assessed using a 48-h acute toxicity test with black fly larvae, Simulium vittatum IS-7. Results showed that observed mortality was bracketed by the independent action model and concentration addition model with the independent action model slightly underestimating mortality and the concentration addition model slightly overestimating mortality. Varying the concentration of the chemicals in the mixture did not indicate that sertraline was interacting with the insecticides to make them more toxic or vice versa. These results indicate that sertraline and the insecticides are likely eliciting toxicity at separate neuronal pathways since no interaction was observed.

Testing the use of a citronella-based repellent as an effective method to reduce the prevalence and abundance of biting flies in avian nests.

Here, we validate the use of a citronella (natural oil) based repellent to reduce the abundance of flying blood-sucking insects in avian nests. These insects are important parasites of birds affecting them as blood feeders and as vectors of a diversity of pathogens. When nestling were 10 days old, we assigned wild great tit Parus major nests to one of two treatments, control and fumigated nests. The abundance of biting midges and blackflies captured during 3 days following the treatment application were lower in fumigated nests with respect to control ones. By contrast, the abundance of blowfly pupae measured when nestlings left their nests was not affected by the treatment. Although many experimental studies modify the abundance of nest-dweller ectoparasites, to our knowledge, this is the first one describing an easy, safe, and effective method, reducing the total abundance of both biting midges and blackflies in wild avian nests. Our results could be used in future conservation projects and experimental studies on host-parasite evolution affecting the abundance of flying blood-feeder insects under natural conditions.

Evaluation of Larval Medium in the Controlled Current Toxicity Test.

The Controlled Current Toxicity Test (CCTT) is a protocol used by the University of Georgia Black Fly Rearing and Bioassay Laboratory to evaluate the efficacy of larvicides based on Bacillus thuringiensis subsp. israelensis (Bti) against Simulium vittatum larvae. A standard CCTT provides a larval medium with suspended organic nutrients, a sustained current, and a clean surface for black fly larval attachment in each exposure vessel. In an effort to streamline the CCTT and eliminate a potential source of variability, 3 types of larval medium were evaluated: deionized water, distilled water, and moderately hard water, which were compared to the currently used protocol. A statistical significance in mean lethal concentration (LC50) rates was observed between the CCTT (deionized water with suspended organic nutrients) medium and the other 3 experimental media. The presence of suspended organic nutrients in the CCTT significantly improved the efficacy of the Bti-based larvicide. The interaction of the suspended organic nutrient particles and the Bti-based particles in the larvicide appears to produce a mixture that is more efficiently captured and ingested by the black fly larvae than the larvicide formulation particles alone.

Repellency of hydrogenated catmint oil formulations to black flies and mosquitoes in the field.

The essential oil of catmint, Nepeta cataria L., was hydrogenated to yield an oil enriched in dihydronepetalactone (DHN) diastereomers, termed. This material was used for the preparation of liquid alcohol-based and lotion formulations. The efficacy of these formulations as repellents was tested after application to human test subjects at two locations in the United States: Maine and Florida. In Maine, data on repellency of the hydrogenated catmint oil formulations toward black flies (Simulium decorum Walker) and mosquitoes (primarily Aedes intrudens Dyar) were obtained. In these tests, protection from black flies was conferred for 6 h or more with all formulations, and both liquid and lotion formulations at 15 wt% active ingredient gave complete protection for 7.5 h. All formulations conferred protection from mosquitoes for >4 h, with the best (15 wt% lotion) giving >8 h of complete protection. In Florida, data on repellency toward a mixed population of mosquitoes indicated that all formulations conferred protection for >4 h, with the 15 wt% lotion giving >6 h complete protection from bites.

Resistance of black soldier fly (Diptera: Stratiomyidae) larvae to combined heavy metals and potential application in municipal sewage sludge treatment.

Treating municipal sewage sludge (MSS) sustainably and economically in China remains a challenge because of risks associated with the heavy metals it contains. In this study, black solider fly larvae (BSFL) were used for MSS treatment. The resistance of larvae to combined heavy metals and their potential use in conversion of MSS were investigated. The results indicated that seven MSS samples contained large amounts of heavy metals, with the lead and nickel contents of several samples exceeding Chinese national discharge standards. BSFL were highly tolerant to an artificial diet spiked with combined heavy metals. Principal component analysis revealed that high concentrations of lead, nickel, boron, and mercury potentially interfered with larval weight gain, while zinc, copper, chromium, cadmium, and mercury slightly reduced larval survival. The addition of chicken manure and wheat bran as co-substrates improved the conversion process, which was influenced by the nature and amount of added co-substrate and especially the quantity of nitrogen added. With the amended substrate, the BSFL accumulated heavy metals into their bodies but not into extracted larval oil. The heavy metal content of the treatment residue was lower than that considered safe for organic-inorganic compound fertilizers standards in China and the harvested larvae could be used as a source of oil for industrial application.

Modelling the impact of larviciding on the population dynamics and biting rates of Simulium damnosum (s.l.): implications for vector control as a complementary strategy for onchocerciasis elimination in Africa.

BACKGROUND: In 2012, the World Health Organization set goals for the elimination of onchocerciasis transmission by 2020 in selected African countries. Epidemiological data and mathematical modelling have indicated that elimination may not be achieved with annual ivermectin distribution in all endemic foci. Complementary and alternative treatment strategies (ATS), including vector control, will be necessary. Implementation of vector control will require that the ecology and population dynamics of Simulium damnosum (sensu lato) be carefully considered. METHODS: We adapted our previous SIMuliid POPulation dynamics (SIMPOP) model to explore the impact of larvicidal insecticides on S. damnosum (s.l.) biting rates in different ecological contexts and to identify how frequently and for how long vector control should be continued to sustain substantive reductions in vector biting. SIMPOP was fitted to data from large-scale aerial larviciding trials in savannah sites (Ghana) and small-scale ground larviciding trials in forest areas (Cameroon). The model was validated against independent data from Burkina Faso/Côte d'Ivoire (savannah) and Bioko (forest). Scenario analysis explored the effects of ecological and programmatic factors such as pre-control daily biting rate (DBR) and larviciding scheme design on reductions and resurgences in biting rates. RESULTS: The estimated efficacy of large-scale aerial larviciding in the savannah was greater than that of ground-based larviciding in the forest. Small changes in larvicidal efficacy can have large impacts on intervention success. At 93% larvicidal efficacy (a realistic value based on field trials), 10 consecutive weekly larvicidal treatments would reduce DBRs by 96% (e.g. from 400 to 16 bites/person/day). At 70% efficacy, and for 10 weekly applications, the DBR would decrease by 67% (e.g. from 400 to 132 bites/person/day). Larviciding is more likely to succeed in areas with lower water temperatures and where blackfly species have longer gonotrophic cycles. CONCLUSIONS: Focal vector control can reduce vector biting rates in settings where a high larvicidal efficacy can be achieved and an appropriate duration and frequency of larviciding can be ensured. Future work linking SIMPOP with onchocerciasis transmission models will permit evaluation of the impact of combined anti-vectorial and anti-parasitic interventions on accelerating elimination of the disease.

Comparative larvicidal property of leaf extract of Chromolaena odorata L (Composidae) and Chlopyrifos (organophosphorus compound) on Simulium larvae.

OBJECTIVE: To assess the phytochemical properties of Chromoleana odorata in the control of blackflies to help check the problem of environmental pollution from the use of chemical insecticides. METHODS: Dried pulverized leaves of Chromolaena odorata (100 g) were soaked in distilled water for 24 hours and the extract was filtered, marc pressed and evaporated over water bath. Stock solution of the dried mass (1 g) was concentrated by dissolving in 100 mL of water. Serial dilutions (100 mg/mL, 10 mg/mL, 1 mg/mL, 0.1 mg/mL, 0.01 mg/L, and 0.001 mg/mL) of both the extract and Chlopyrifos (organo phosphorus) were prepared and toxicity was tested on the larvae of Simulium species. RESULTS: The chemical compound recorded 100% larval mortality at all concentrations while the plant extract recorded 100% larval mortality in three (100, 10, and 1 mg/mL) of its diluent concentration. The percentage of larval mortality by chemical compound and plant extract was statistically insignificant (t=0.2456, P>0.05), but the mortality rate was significant within 30 min interval of exposure time (t=3.756, P<0.05). The LC50 of the plant extract was determined at about 0.001 mg/mL concentration. This showed that the plant extract had an appreciable larvicidal property close to that of the chemical compound. CONCLUSION: This result indicates the usefulness of plant materials in the control of obnoxious insect vectors of mn. It also opens additional approach to the management of environment from toxic chemicals that are non-biodegradable and cause environmental imbalance in the ecosystem.

Influences of chromium and cadmium on the development of black soldier fly larvae.

The black soldier fly Hermetia illucens is a good candidate for waste management. The harvested insects are rich in protein and have the potential to be used in animal feed. However, people are wary about heavy metals in waste. Therefore, it is necessary to understand how the uptake of heavy metals could affect H. illucens and where and to what extent metals are accumulated by the black soldier fly. Based on these considerations, developmental parameters were investigated in the different life stages of H. illucens fed an increasing concentration gradient of cadmium (Cd) and chromium (Cr); additionally, Cd and Cr distribution in the body parts of H. illucens at the different life stages was monitored. We found that Cd and Cr have no effects on larvae survival and eclosion rate, but they do have effects on larvae duration and pupation rate. Both Cd and Cr were transferred into larvae, prepupae, and pupae. While the concentrations of Cd in larvae and prepupae were much higher than that in their diets, the opposite case was observed with Cr. The concentrations of Cd and Cr in H. illucens decreased in later development stages. In individual larva and prepupa, Cd and Cr were mainly included in the body and not in the integument. In the pupa, the puparium contained higher Cd and Cr concentrations than the pupa body. The distribution of Cd and Cr in the different life stages and body parts may present a potential strategy for how H. illucens tolerate and remove heavy metal stress.

Interruption of the transmission of Onchocerca volvulus in the Kashoya-Kitomi focus, western Uganda by long-term ivermectin treatment and elimination of the vector Simulium neavei by larviciding.

Uganda is the only country in sub-Saharan Africa whose onchocerciasis elimination programme extensively uses vector control and biannual treatment with ivermectin. The purpose of this study was to assess the impact of combined strategies on interrupting onchocerciasis transmission in the Kashoya-Kitomi focus. Mass Drug Administration annually (13 years) followed by biannual treatments (6 years) and ground larviciding (36 cycles in 3 years) with temephos (Abate®, EC500) against Simulium neavei were conducted. Routine fly catches were conducted for over seven years in six catching sites and freshwater crabs Potamonautes aloysiisabaudiae were examined for immature stages of Simulium neavei. Epidemiological assessments by skin snip were performed in 2004 and 2013. Collection of dry blood spots (DBS) from children <10 years for IgG4 antibodies analysis were done in 2010 and 2013. Treatment coverage with ivermectin improved with introduction of biannual treatment strategy. Microfilaria prevalence reduced from 85% in 1991 to 62% in 2004; and to only 0.5% in 2013. Crab infestation reduced from 59% in 2007 to 0% in 2013 following ground larviciding. Comparison of total fly catches before and after ground larviciding revealed a drop from 5334 flies in 2007 to 0 flies in 2009. Serological assays conducted among 1,362 children in 2010 revealed 11 positive cases (0.8%; 95% CI: 0.4%-1.2%). However, assessment conducted on 3246 children in 2013 revealed five positives, giving point prevalence of 0.15%; 95% CI: 0.02%-0.28%. Four of the five children subjected to O-150 PCR proved negative. The data show that transmission of onchocerciasis has been interrupted based on national and WHO Guidelines of 2012 and 2016, respectively.

Protection of horse ears against Simulid parasitism: Efficacy of a mammal semiochemical solution over 10hours.

Hematophagous insects can be vectors of pathogens and cause significant economic loss in zootechnical production. Among biting insects, many dipteran species feed on horse blood. The black fly (Diptera: Simuliidae) group, is responsible for several disorders in horses and inflicts painful bites that lead to undesirable behaviours in horses, particularly when bites occur in sensitive areas such as the inner ear. A field study was conducted in a French equestrian center during which a semiochemical was applied on horses' ears to assess repellent efficacy against simulid infestation. During the first phase of the study, efficacy was evaluated over a one hour period. Then, during the second phase of the study, persistency of the effect was tested at 8, 9 and 10h after application. The results of the study's first phase showed 90% efficacy over one hour, with 121.5 insects found in control ears and 12 insects in treated ears (p=0.001). In the second phase of the study, a total amount of 411 insects were observed on control ears whereas only 2 insects were observed on treated ears (p<0.0001); the treatment remained over 98% effective up to 10hours after application. When using a slow release excipient, this semiochemical may offer at least 10h of protection against simulids. This safe, efficient, and long lasting protection could help horses and their owners to manage simulid parasitism.

Knowledge, attitude and practice of community drug distributors' about onchocerciasis and community directed treatment with ivermectin in Quara district, North Western Ethiopia.

BACKGROUND: Onchocerciasis is one of the most important public health problems over large areas of tropical Africa countries including Ethiopia. The African Program for Onchocerciasis Control (APOC) has been working with ultimate goal of reducing the public health and socio-economic problems of onchocerciasis through administration of the tablet for continuous 12-15 years using the strategy of yearly community-directed treatment with ivermectin (CDTI) in endemic areas of Africa to kill the microfilariae that invade the eyes and are present in the skin to be transported to another victim by the black fly. The objective of this study was to assess knowledge, attitude and practice of community drug distributors (CDDs) towards onchocerciasis and CDTI in Quara district. RESULT: Of all the study participating CDD 11.4% (9/79) said that they knew about the etiology of the disease, 35.4% (28/79) had good level of knowledge, 19 (24.1%) had good level of positive attitude and 18 (22.8%) had good level of positive practice about onchocerciasis. Similarly, 45.6% (36/79), 81.0% (64/79) and 29.1% (23/79) had good level of knowledge, attitude and practice about CDTIP, respectively. Being a female CDD (adjusted OR 7.246, P = 0.035, 95% CI 1.147, 45.455) and being older than 35 years (adjusted OR 8.435, P = 0.001, 95% CI 4.53, 9.003) were significantly associated with the likelihood of having good level of knowledge about the disease. CONCLUSION: Although onchocerciasis is endemic in Quara district, large proportion of the CDDs had misconceptions about its causation, transmission and prevention. Therefore, CDTIP for onchocerciasis control need to be supported by proper and continuous training, and health education about different aspects of the disease.

Ongoing Transmission of Onchocerca volvulus after 25 Years of Annual Ivermectin Mass Treatments in the Vina du Nord River Valley, in North Cameroon.

BACKGROUND: Recent reports of transmission interruption of Onchocerca volvulus, the causing agent of river blindness, in former endemic foci in the Americas, and more recently in West and East Africa, raise the question whether elimination of this debilitating disease is underway after long-term treatment of the population at risk with ivermectin. The situation in Central Africa has not yet been clearly assessed. METHODS AND FINDINGS: Entomologic data from two former endemic river basins in North Cameroon were generated over a period of 43 and 48 months to follow-up transmission levels in areas under prolonged ivermectin control. Moreover, epidemiologic parameters of animal-borne Onchocerca spp. transmitted by the same local black fly vectors of the Simulium damnosum complex were recorded and their impact on O. volvulus transmission success evaluated. With mitochondrial DNA markers we unambiguously confirmed the presence of infective O. volvulus larvae in vectors from the Sudan savannah region (mean Annual Transmission Potential 2009-2012: 98, range 47-221), but not from the Adamawa highland region. Transmission rates of O. ochengi, a parasite of Zebu cattle, were high in both foci. CONCLUSIONS/SIGNIFICANCE: The high cattle livestock density in conjunction with the high transmission rates of the bovine filaria O. ochengi prevents the transmission of O. volvulus on the Adamawa plateau, whereas transmission in a former hyperendemic focus was markedly reduced, but not completely interrupted after 25 years of ivermectin control. This study may be helpful to gauge the impact of the presence of animal-filariae for O. volvulus transmission in terms of the growing human and livestock populations in sub-Saharan countries.

Status of forest onchocerciasis in the Lower Cross River basin, Nigeria: entomologic profile after five years of ivermectin intervention.

In the Lower Cross River basin in Nigeria, no pre-control entomologic profile of Onchocerca volvulus infection in the local Simulium damnosum population was available prior to the initiation of an ivermectin control program in 1995. A longitudinal entomologic study was therefore carried out over a 12-month period (January-December 2001) at the Agbokim waterfalls and Afi River, which are breeding sites of S. damnosum in the river basin. A total of 9,287 adult S. damnosum were caught on human bait; 9,048 (97.43%) were dissected, of which 313 (3.46%) were infected. Annual biting rates (ABRs) of 42,419 and 28,346 bites per persons per year were recorded at the Agbokim Waterfalls and Afi River, respectively. The annual transmission potential (ATP) was 419 infective larvae per person per year at the Agbokim Waterfalls and 427 at the Afi River. Monthly biting rate and monthly transmission potential varied significantly (P < 0.05) at the two sites. Transmission was highly seasonal from April to September, corresponding to the peak biting period of the vector. The high ATP and ABR values are a measure of the mesoendemicity of onchocerciasis in the river basin. There was a significant F(0).05 (1, 10) (P < 0.05) variation in the relative fly abundance from both sites. It was observed that human activities such as farming, fishing, timber cutting, and hunting are done in the early morning and late afternoon, which corresponds to the peak diurnal biting period of the vector. Changes in these practices and attitudes may markedly affect the disease intensity and transmission.