Virus gives helping hand to leishmaniasis parasites

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A disfiguring form of the parasitic disease leishmaniasis has turned out to be triggered by a virus, raising hopes that it could easily be prevented by drugs or vaccination.

Transmitted by the sandfly, leishmaniasis is widespread across the tropics and has several forms —from the most common, cutaneous leishmaniasis, which causes skin sores, to the most serious, visceral leishmaniasis, which causes fever and is fatal if not treated.

Another form, mucocutaneous leishmaniasis, destroys the soft tissues of the nose and mouth, leaving disfiguring facial scars. It develops in people who had suffered from the cutaneous form, often many years previously.

"Nobody really understood why [one develops from the other]," Nicolas Fasel of the University of Lausanne in Switzerland, a co-author of the study, told SciDev.Net.

Fasel, and colleagues from Washington University and the WHO, already knew that the leishmaniasis parasites, Leishmania braziliensis and Leishmania guyanensis, can themselves be infected with a virus.

Now they have discovered that those parasites responsible for the worst lesions carry the highest loads of this virus. When the parasite enters a human cell, the virus escapes and triggers an excessive amount of inflammation, creating the perfect environment for the parasite to take hold.

Currently mucocutaneous leishmaniasis is treated with the chemical element antimony with studies reporting a variety of success rates of 30–90 per cent.

But Fasel says the new findings, published in Science yesterday (10 February), could improve diagnosis and prevention. For example, cutaneous leishmanaisis patients whose parasites are found to be carrying the virus could be given treatment to prevent mucocutaneous disease developing.

And patients who already have mucocutaneous leishmaniasis could be given anti-inflammatory drugs alongside antimony.

"This makes the response much better," said Fasel, adding that he hopes to begin trials of this combination.

Debbie Smith, a biologist at the UK’s University of York, said there is still some work to be done to verify the relationship. "They need to collect as many samples from patients as they can and confirm that there is a direct correlation between the presence of the virus and the effects they’re seeing," she told SciDev.Net.

She is, however, excited about the findings: "This may open the door for new types of immunotherapy, whether that means anti-inflammatories or vaccination."

However, Jean-Claude Dujardin, head of molecular parasitology at the Institute of Tropical Medicine Antwerp in Belgium, warned of difficulties with drug resistance. "Leishmania is very flexible and a master at subverting the host cell," he said.

Link to full paper in Science


Science 331, 775 (2011)