Veterans Affairs

Leishmaniasis diagnostic test

Rapid, and relatively inexpensive means of detecting, quantifying, and determining the species of Leishmania in clinical or epidemiologic samples

Medical & Biotechnology

Sandflies such as this P. papatasi, are responsible for the spread of the vector-borne parasitic disease leishmaniasis, which is caused by the obligate intracellular protozoa of the genus Leishmania. US CDC.

The global burden of leishmaniasis is high and visceral leishmaniasis has reached epidemic proportions in three regions (Bangladesh/Nepal/Bihar State, India; southern Sudan-Ethiopia/Afghanistan; and Brazil).

Drug resistance has further augmented the disease burden in northern India, and the HIV epidemic has led to new patterns of visceral leishmaniasis in Spain and Portugal. Across the ocean, urbanization has caused the spread of visceral leishmaniasis in northeastern and southern Brazil. Cutaneous leishmaniasis is highest in the Middle East, Syria, Brazil, and Peru, but imported cutaneous leishmaniasis is becoming problematic in the United States, particularly in military personnel. Leishmaniasis in the blood supply is becoming a concern, and an outbreak of Leishmania (L.) infantum infection affecting foxhounds has introduced a possible reservoir into the United States. All of this combined makes leishmaniasis a disease of concern with both human and veterinary importance.

The spectrum of symptomatic human leishmaniasis is wide, and the most important factor determining the clinical outcome of infection seems to be the species of Leishmania. Yet, diagnostic testing for leishmaniasis is less than optimal. Clinical presentation and a positive test of immune response to the parasite can be suggestive, but definitive diagnosis requires parasite identification. The latter can be in the form of microscopic examination of tissue biopsy specimens, bone marrow or splenic aspirates (a very rarely performed procedure), or cultivation of live organisms from clinical tissue specimens. The sensitivity and riskiness of each procedure are positively correlated – splenic aspiration has >95% sensitivity, bone marrow aspiration is lower at 52 to 69%; microscopic identification and culture from biopsied cutaneous lesions is less sensitive and very dependent on the disease form, with parasites isolated from only 30 to 50% of ulcers and rarely isolated from lesions of mucosal or disseminated leishmaniasis. The species of Leishmania is most commonly determined by electrophoretic mobility assay of isoenzymes from cultured promastigotes, a lengthy method that is only feasible if parasites are isolated in culture.

Addressing the above deficiencies, researchers at the Department of Veterans Affairs have developed a serial nucleic acid amplification-based method for the diagnosis and species determination of Leishmania parasites in human or animal-derived tissues. The VA team has created a set of primers and probes for serial qPCR* assays. These assays have potential applications for diagnosis and species discrimination, as well as novel approaches to determining parasite load and post-treatment response in infected humans.

The qPCR serial testing strategy requires a reference laboratory with the technical capacity to perform qPCR. This technology is becoming available in many countries and could be developed in a central diagnostic laboratory in countries where leishmaniasis is endemic.

*Polymerase chain reaction (PCR) is a relatively simple and widely used molecular biology technique to amplify and detect DNA and RNA sequences. The technique is highly sensitive and fast. In dye-based qPCR (typically green), fluorescent labeling allows the quantification of the amplified DNA molecules by employing the use of a dsDNA binding dye.

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