The search for better treatment strategies for mansonellosis: an expert perspective

INTRODUCTION

Four species of the Mansonella genus infect millions of people across sub-Saharan Africa and Central and South America. Most infections are asymptomatic, but mansonellosis can be associated with nonspecific clinical manifestations such as fever, headache, arthralgia, and ocular lesions (M. ozzardi); pruritus, arthralgia, abdominal pain, angioedema, skin rash, and fatigue (M. perstans and perhaps Mansonella sp. 'DEUX'); and pruritic dermatitis and chronic lymphadenitis (M. perstans).

AREAS COVERED

We searched the PubMed and SciELO databases for publications on mansonelliasis in English, Spanish, Portuguese, or French that appeared until 1 May 2023. Literature data show that anthelmintics - single-dose ivermectin for M. ozzardi, repeated doses of mebendazole alone or in combination with diethylcarbamazine (DEC) for M. perstans, and DEC alone for M. streptocerca - are effective against microfilariae. Antibiotics that target Wolbachia endosymbionts, such as doxycycline, are likely to kill adult worms of most, if not all, Mansonella species, but the currently recommended 6-week regimen is relatively impractical. New anthelmintics and shorter antibiotic regimens (e.g. with rifampin) have shown promise in experimental filarial infections and may proceed to clinical trials.

EXPERT OPINION

We recommend that human infections with Mansonella species be treated, regardless of any apparent clinical manifestations. We argue that mansonellosis, despite being widely considered a benign infection, may represent a direct or indirect cause of significant morbidity that remains poorly characterized at present.

Detection of Mansonella ozzardi in peripheral blood in two malaria-endemic areas in Panama

Introduction:

Studies conducted in 1984 demonstrated the presence of Mansonella ozzardi in the Darien and Colon provinces. Since then, there have not been further reports of this parasitic infection in Panama.

Methodology:

We conducted a cross-sectional assessment of peripheral blood samples of individuals across Panama over a 4-year period (2013–2016) as part of malaria surveillance activities.

Results:

We identified microfilaria in 96 cases. Most of these cases were found in East Panama (78%) followed by the Darien region (22%). Mansonella ozzardi was the filarial parasite identified by morphological features in all cases.

Conclusion:

After 36 years of epidemiological silence, we identified human cases of Mansonella ozzardi infection in Panama. This is, however, the first report of this filarial parasite’s presence in the Eastern region of Panama. There is a need for further surveillance efforts to elucidate the epidemiology associated with Mansonella infections in Panama.

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.

Deep Sequencing Reveals Occult Mansonellosis Coinfections in Residents From the Brazilian Amazon Village of São Gabriel da Cachoeira

Mansonella ozzardi and Mansonella perstans infections both cause mansonellosis but are usually treated differently. Using a real-time polymerase chain reaction assay and deep sequencing, we reveal the presence of mansonellosis coinfections that were undetectable by standard diagnostic methods. Our results confirm mansonellosis coinfections and have important implications for the disease's treatment and diagnosis.

High Prevalence of Mansonella ozzardi Infection in the Amazon Region, Ecuador

We reviewed Giemsa-stained thick blood smears, obtained through the national malaria surveillance program in the Amazon region of Ecuador, by light microscopy for Mansonella spp. microfilariae. Of 2,756 slides examined, 566 (20.5%) were positive. Nested PCR confirmed that the microfilariae were those of M. ozzardi nematodes, indicating that this parasite is endemic to this region.

Molecular Verification of New World Mansonella perstans Parasitemias

We obtained ribosomal and mitochondrial DNA sequences from residents of Amazonas state, Brazil, with Mansonella parasitemias. Phylogenetic analysis of these sequences confirm that M. ozzardi and M. perstans parasites occur in sympatry and reveal the close relationship between M. perstans in Africa and Brazil, providing insights into the parasite's New World origins.

Mansonella ozzardi: a neglected New World filarial nematode

Mansonella ozzardi (Nematoda: Onchocercidae) is an understudied filarial nematode, originally described by Patrick Manson in 1897, that can be transmitted by two families of dipteran vectors, biting midges (most of them members of the genus Culicoides) and black flies (genus Simulium). With a patchy geographic distribution from southern Mexico to northwestern Argentina, human infection with M. ozzardi is highly prevalent in some of the Caribbean islands, along riverine communities in the Amazon Basin, and on both sides of the border between Bolivia and Argentina. There is no clinical entity unequivocally associated with M. ozzardi infection, although fever, arthralgia, headache, cold lower extremities, and itchy cutaneous rashes are occasionally mentioned in case report series. More recently, ocular manifestations (especially keratitis) have been associated with mansonelliasis, opening an important area of investigation. Here, we briefly review the biology, epidemiology, pathogenesis, and clinical aspects of M. ozzardi infection and point to some existing knowledge gaps, aiming to stimulate a research agenda to help filling them.

Historic accounts of Mansonella parasitaemias in the South Pacific and their relevance to lymphatic filariasis elimination efforts today

There are two species of filarial parasites with sheathless microfilariae known to commonly cause parasitaemias in humans: Mansonella perstans and Mansonella ozzardi. In most contemporary accounts of the distribution of these parasites, neither is usually considered to occur anywhere in the Eastern Hemisphere. However, Sir Patrick Manson, who first described both parasite species, recorded the existence of sheathless sharp-tailed Mansonella ozzardi-like parasites occurring in the blood of natives from New Guinea in each and every version of his manual for tropical disease that he wrote before his death in 1922. Manson's reports were based on his own identifications and were made from at least two independent blood sample collections that were taken from the island. Pacific region Mansonella perstans parasitaemias were also later (in 1923) reported to occur in New Guinea and once before this (in 1905) in Fiji. Although Mansonella-parasitaemias are generally regarded as benign, they are thought to be of public health importance because they can affect the epidemiological monitoring of other filarial diseases. In this article, we reviewed the historic literature concerning Pacific-origin Mansonella-parasitaemias in an attempt to explain how, despite repeated reports of Pacific-region Mansonella-parasitaemias, by as early as the 1970s, the WHO had arrived at the present-day view that Wuchereria bancrofti is the only cause of filarial parasitaemias in Papua New Guinea. We have also evaluated the evidence supporting the contemporary existence of Pacific-area parasitaemia-causing Mansonella parasites and assessed the relevance such parasites could have for present-day lymphatic filariasis elimination efforts in the region.