Blackflies in the ointment: O. volvulus vector biting can be significantly reduced by the skin-application of mineral oil during human landing catches

Filarial disease in the Brazilian Amazon and emerging opportunities for treatment and control

Following the successful eradication of Wuchereria bancrofti, there are now just three species of conventional microfilaremic human filarial parasites endemic to the Brazilian Amazon region: Mansonella ozzardi, Mansonella perstans and Onchocerca volvulus. The zoonotic filarial parasite Dirofilaria immitis is also found in the Amazon region as are several sylvatic filarial parasites, some of which have been recorded causing zoonoses and some of which have never been recorded outside the region. Onchocerca volvulus is only found in the Amazonia onchocerciasis focus in the Brazilian state of Roraima where it affects the people of the Yanomami tribe living around the densely forested Venezuela border region. Mansonella ozzardi is by far the most common filarial parasite in Brazil and has a broad but patchy distribution throughout the western Amazon region. Recorded in the Brazilian states of Acre, Roraima, Matto Grosso, and within almost every municipality of Amazonas state, it is believed that pollution of the urban stream and river systems prevents the development of the simuliid vectors of M. ozzardi and explains the parasite's reduced distribution within urban areas and an absence of recent reports from the state capital Manaus. Decades of WHO-led periodic ivermectin treatment of Yanomami tribe's people have resulted in the partial suppression of O. volvulus transmission in this focus and has also probably affected the transmission of M. ozzardi in the region. Mansonella perstans, O. volvulus and very probably M. ozzardi infections can all be treated and most likely cured with a 4-6-week treatment course of doxycycline. The Brazilian Ministry of Health does not, however, presently recommend any treatment for mansonellosis infections and thus parasitic infections outside the Amazonia focus are typically left untreated. While the long treatment courses required for doxycycline-based mansonellosis therapies preclude their use in control programmes, new fast-acting filarial drug treatments are likely to soon become available for the treatment of both onchocerciasis and mansonellosis in the Amazon region. Filarial disease management in the Brazilian Amazon is thus likely to become dramatically more viable at a time when the public health importance of these diseases is increasingly being recognized.

Molecular circumscription of the blackfly Simulium oyapockense from South America

Problems related to the identity of Simuliidae species are impediments to effective disease control in Amazonia. Some of these species, such as Simulium oyapockense Floch & Abonnenc, 1946 (Diptera: Simuliidae), are vectors of the organisms that cause onchocerciasis and mansonellosis diseases. This blackfly species has a wide distribution in South America, and it is suspected of being a complex of cryptic species. The aim of this study is to characterize the nominal species S. oyapockense using partial COI gene sequences. Seven populations of S. oyapockense (morphologically identified) were analysed, including one from its type-locality. The other six populations were collected in Brazil and in Argentina. A taxon collected in Amazonas state, Brazil, with adults similar to S. oyapockense but with distinct pupae, was also included in the analysis (Simulium 'S'). The nominal species S. oyapockense is circumscribed, and its geographical distribution is restricted to areas north of the Amazon River. Populations of S. oyapockense s.l. collected south of the Amazon River comprise a species complex that needs to be evaluated using integrative taxonomy. Simulium 'S' represents a species with unique morphological and molecular characteristics. Distinguishing cryptic species is a prerequisite for reducing the taxonomic impediment, especially in medically important taxa.

Molecular detection of Mansonella mariae incriminates Simulium oyapockense as a potentially important bridge vector for Amazon-region zoonoses

OBJECTIVE

To assess the emergent zoonotic disease risk posed by the voracious human-biting blackfly species Simulium oyapockense in the peripheral regions of an expanding urban centre situated deep in the Brazilian Amazon rainforest.

METHODS

We performed nine human landing catches at three periurban sites surrounding the Brazilian Amazon town of São Gabriel da Cachoeira. Using the detection of non-human primate filarial parasites as an indicator of the zoonotic disease threat posed by a biting insect, we screened 3328 S. oyapockense blackflies for the presence of zoonotic filarial DNA with an ITS-1 PCR assay and Sanger sequencing.

RESULTS

Between 98 and 100% of the biting insects captured during our nine collections were identified as S. oyapockense; at our three collection sites and during our three seasonally-distinct collections this species was captured at rates between 28 and 294 blackflies per hour. PCR screening of the march-collected S. oyapockense detected infectious-stage (L3) Mansonella mariae parasites (which are only known to infect non-human primates) in >0.15% of the tested head samples.

CONCLUSIONS

Our results show that residents of the periurban regions of São Gabriel da Cachoeira are routinely exposed to the bites of S. oyapockense blackflies which have previously fed on non-human primates.

An Overview of the Management of Mansonellosis

Mansonellosis is caused by three filarial parasite species from the genus Mansonella that commonly produce chronic human microfilaraemias: M. ozzardi, M. perstans and M. streptocerca. The disease is widespread in Africa, the Caribbean and South and Central America, and although it is typically asymptomatic it has been associated with mild pathologies including leg-chills, joint-pains, headaches, fevers, and corneal lesions. No robust mansonellosis disease burden estimates have yet been made and the impact the disease has on blood bank stocks and the monitoring of other filarial diseases is not thought to be of sufficient public health importance to justify dedicated disease management interventions. Mansonellosis´s Ceratopogonidae and Simuliidae vectors are not targeted by other control programmes and because of their small size and out-door biting habits are unlikely to be affected by interventions targeting other disease vectors like mosquitoes. The ivermectin and mebendazole-based mass drug administration (iMDA and mMDA) treatment regimens deployed by the WHO´s Elimination of Neglected Tropical Diseases (ESPEN) programme and its forerunners have, however, likely impacted significantly on the mansonellosis disease burden, principally by reducing the transmission of M. streptocerca in Africa. The increasingly popular plan of using iMDA to control malaria could also affect M. ozzardi parasite prevalence and transmission in Latin America in the future. However, a potentially far greater mansonellosis disease burden impact is likely to come from short-course curative anti-Wolbachia therapeutics, which are presently being developed for onchocerciasis and lymphatic filariasis treatment. Even if the WHO´s ESPEN programme does not choose to deploy these drugs in MDA interventions, they have the potential to dramatically increase the financial and logistical feasibility of effective mansonellosis management. There is, thus, now a fresh and urgent need to better characterise the disease burden and eco-epidemiology of mansonellosis so that effective management programmes can be designed, advocated for and implemented.