Abstract
BackgroundMetagenomic studies have revealed the presence of a filarial nematode in Ixodes scapularis. The phylogeny of this agent, and its potential for human infection, are unknown.MethodsWe used existing metagenomic data from I. scapularis to determine the phylogeny of this tick-associated nematode and employed quantitative PCR to determine if the presence of this agent had an effect on the burden of Borrelia burgdorferi. We also developed a Luciferase Immunoprecipitation System assay using the Av33 antigen as a target to investigate the presence of antibodies against this nematode in 128 serum specimens from patients with Lyme disease and babesiosis. To demonstrate assay utility, we used 15 sera from patients with onchocerciasis as controls.ResultsWe show that this agent is a new species in the genus Monanema and its presence in vector ticks does not impact the burden of B. burgdorferi. We did not detect IgG antibodies to this agent in 127 of 128 sera from patients with Lyme disease or babesiosis. One sample had reactivity above the threshold, but at the low-level equivalent to the least reactive onchocerciasis sera. This low positive signal could be a result of cross-reacting antibodies, antibodies from a previous infection with a filarial nematode, or, less likely, a exposure to the Ixodes scapularis-associated nematode.ConclusionsWe found no evidence that this nematode contributes to the spectrum of human tick-borne infections.
Highlights
Metagenomic studies have revealed the presence of a filarial nematode in Ixodes scapularis
Monanema martini is a filarial nematode identified in Africa that infects at least two species of African rodents, the typical striped grass mouse (Lemniscomys striatus), and the African grass rat (Arvicanthis niloticus) with Hyalomma and Rhipicephalus ticks implicated as vectors [7, 8]
The Ixodes scapularisassociated nematode (ISN) sequences were homologous to the sequences reported from I. scapularis from Connecticut in 2014, and were clustered with nematode sequences previously identified in Amblyomma americanum ticks in Virginia and Maryland (92%) and M. martini (88%) [9] (Fig. 1)
Summary
Metagenomic studies have revealed the presence of a filarial nematode in Ixodes scapularis. The phylogeny of this agent, and its potential for human infection, are unknown. In 1982, Burgdorfer and colleagues identified Ixodes scapularis as a vector of Borrelia burgdorferi, the agent of Lyme disease [1]. Along with this discovery, the group noted the presence of motile microfilariae in approximately 1% of adult ticks they examined [2]. The group noted the presence of motile microfilariae in approximately 1% of adult ticks they examined [2] After this initial report, the identity of this agent remained obscure for the three decades. Because filarial nematodes are implicated in veterinary and human disease and there is a high degree of human contact with I. scapularis, we sought to genetically characterize this nematode (tentatively named Ixodes scapularis-associated nematode, or ISN) and determine the level of human exposure
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