Abstract
Visceral leishmaniasis (VL) is a potentially lethal, sand fly-borne disease caused by protozoan parasites belonging to the Leishmania donovani species complex. There are several adequate methods for diagnosing VL, but the majority of infected individuals remain asymptomatic, comprising potential parasite reservoirs for transmission of the disease. The gold standard for assessing host infectiousness to biting vector insects is xenodiagnosis (i.e. scoring infection rates among insectary-reared insects that had fed on humans suspected of being infected). However, when it comes to sand flies and leishmaniasis, xenodiagnosis is an intricate operation burdened by logistical hurdles and ethical concerns that prevent its effective application for mass screening of widely dispersed communities, particularly in rural regions of underdeveloped countries. Minimally invasive microbiopsy (MB) devices were designed to penetrate the skin to a depth of ∼200µm and absorb blood as well as skin cell lysates, mimicking the mode by which phlebotomine sand flies acquire blood meals, as well as their composition. MBs taken from 137 of 262 volunteers, living in endemic VL foci in Ethiopia, detected Leishmania parasites that could potentially be imbibed by feeding sand flies. Although the volume of MBs was 10-fold smaller than finger-prick blood samples, Leishmania DNA detection rates from MBs were significantly higher, implying that skin, more often than blood, was the source of parasites. Volunteers with histories of VL were almost as likely as healthy volunteers to test positive by MBs (southern Ethiopian focus: 95% CI: 0.35–2.59, P=1.0. northern Ethiopian focus 0.87: 95% CI: 0.22–3.76, P=1), suggesting the importance of asymptomatic patients as reservoirs of L. donovani. Minimally invasive, painless MBs should be considered for reliably and efficiently evaluating both L. donovani infection rates among large numbers of asymptomatic carriers and their infectiousness to blood-feeding sand flies.
Highlights
Visceral leishmaniasis (VL) is caused by disseminated infections with eukaryotic Leishmania donovani parasites
Ten consenting patients were sampled; seven of them were diagnosed less than 24 h prior to sampling and had not been treated; one patient was diagnosed with post-kala azar dermal leishmaniasis (PKDL), a chronic form of cutaneous leishmaniasis (CL) that develops after treatment and resolution of VL; one patient was co-infected with the human immunodeficiency virus (HIV) and L. donovani; and one was a case of CL caused by Leishmania aethiopica (Table 1)
Several studies have shown that L. donovani (DNA) is found in the blood of clinical VL cases (Murray et al, 2005)
Summary
Visceral leishmaniasis (VL) is caused by disseminated infections with eukaryotic Leishmania donovani (complex) parasites. Sand flies induce minute superficial hemorrhages by macerating skin cells and cutting dermal capillaries with their serrated mouthparts They imbibe blood that drains into the resultant hematomas together with skin cell lysates (pool-feeding or telmophagous). Leishmania parasites are not blood-borne parasites per se, pool-feeding makes sand flies likely to ingest Leishmania amastigotes inhabiting resident dermal macrophages, despite the small volume of their blood meals (e.g. 0.59 ml on average for Phlebotomus orientalis, a vector of VL in Sudan and Ethiopia) (Seblova et al, 2013). We used absorbent microbiopsy (MB) devices that painlessly collect minute skin/ blood samples similar in composition to sand fly blood meals These MB devices were developed by two of the authors Similar MBs can potentially serve for the xenodiagnosis of other vector-borne diseases caused by skin-dwelling parasites such as onchocerciasis (river blindness)
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