Experimental Vaccine for Horrible 'Rose of Jericho' Parasite Works, on Mice

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Paula Gino points at leishmaniasis lesion on her cheek, Tiberias, 2004
Paula Gino points at leishmaniasis lesion on her cheekCredit: Yaron Kaminsky

Israelis are unhappily familiar with the Rose of Jericho, not a gorgeous flower, but an unsightly disease caused by parasites brought to us by bites of the desert sandfly. Known elsewhere as leishmania, the condition is notoriously hard to cure, and there is no vaccine. But there may be soon, if a model vaccine based on a fake virus that worked on mice can be brought to the stage of protecting humans as well.

Leishmania parasites made the news in recent years mainly thanks to Syrian refugees bringing them along as they fled the country, but the panic in Europe was unwarranted. One needs a phlebotomine sandfly to spread the disease, for one thing. For another, leishmania – of which there are no less than 30 strains – is already common worldwide, being found in South America, Africa, the Middle East (and Israel of course), Asia and southern Europe. Moreover, as global warming makes northern climes more comfortable for insects, infections by the parasite are showing up nearer and nearer to the southern United States as well.

Leishmania which are single-cell organisms no bigger than large bacteria, but they are not bacteria, they are proper animals. In this era of easy mass travel, they flourish throughout the Middle East – and have spread throughout much of South America, Africa, Asia and southern Europe as well, wherever the sandfly thrives.

For decades, researchers have worked to find a vaccine against them and similar parasites without success. Now however an experimental vaccine that uses fake viruses to wake up our immune systems has proven to work against the parasite, in mice, reports the team in ACS Central Science.

The fake virus, or virus-like particle, is not infectious, and the body destroys it after use, the scientists explain.

'Flesh-eating disease'

The biggest problem with leishmania, its fatal aspect aside, is how hard it is to cure. Left untreated, the parasites can cause large, weeping lesions on the skin that just invite secondary infection by true bacteria, fungi and what not. External leishmaniasis can become so severe that the nasal tissues and lips may even irreversibly erode.

Worse – leading the World Health Organization to deem leishmania the second-deadliest parasite after malaria – is when certain forms of the parasite get into the bloodstream and reach the internal organs, where they can fatally damage the liver and spleen. This form of visceral leishmaniasis is also known as black fever.

"If you don't treat it, within 20 to 40 days visceral leishmaniasis very often kills the victim," noted Alexandre Marques, parasitology professor at the Universidade Federal de Minas Gerais in Brazil and one of the lead researchers.

Conventional treatment usually works, in time, but some of the parasites survive, which can lead to relapse. Or the patient may act as a carrier.

Now an artificial, proprietary particle developed at the Georgia Institute of Technology has succeeded in immunizing mice, not wild ones, mind you, but mice that were genetically altered to mimic the human immune system.

It bears noting that murine immune systems are not the same as human immune systems, so if the scientists had used wild-type mice (not engineered), and the wild-type mice had proven resistat to leishmania, that would have proved precisely nothing.

Not that immunizing engineered mice is proof, but it's a good indicator that the scientists are moving in the right direction.