In a recent report in Science, researchers from Switzerland, Washington University, and the WHO used the hamster model of mucocutaneous leishmanaiasis (MCL) to examine the effects of Leishmania RNA virus 1 (LVR1) burden on Leishmania Vianna parasites.
MCL is typically characterized by a persistent immune response with inflammation and high levels of tumor necrosis factor (TNF-α), CSCL10 and CCL4, among others. This led the researchers to examine the levels of cytokine and chemokine levels after macrophage infection between metastasizing and non-metastasizing parasites. They found a positive correlation for metastasizing parasites wherein macrophages expressed significantly greater amounts of chemokines, cytokines CCL5, CXCL10, TNF-αand IL-6. They went on to characterize this by examining the essential pathways for pro-inflammation, providing evidence that this was dependent on the TLR3-TRIP. With the introduction of LVR1, the immune response was inhibited, promoting the persistence of metastasizing parasites. When examined in vivo, mice and hamsters infected with virally- infected metastasizing parasites had an increased disease pathology. This is one of the first reports of viruses increasing that infection and success of intracellular parasites.