Mosquitoes deliver malaria 'vaccine' through bites

Jul 29, 2009 By MARILYNN MARCHIONE , AP Medical Writer

In a daring experiment in Europe, scientists used mosquitoes as flying needles to deliver a "vaccine" of live malaria parasites through their bites. The results were astounding: Everyone in the vaccine group acquired immunity to malaria; everyone in a non-vaccinated comparison group did not, and developed malaria when exposed to the parasites later.

The study was only a small proof-of-principle test, and its approach is not practical on a large scale. However, it shows that scientists may finally be on the right track to developing an effective vaccine against one of mankind's top killers. A vaccine that uses modified live parasites just entered human testing.

"Malaria vaccines are moving from the laboratory into the real world," Dr. Carlos Campbell wrote in an editorial accompanying the study in Thursday's . He works for PATH, the Program for Appropriate Technology in Health, a Seattle-based global health foundation.

The new study "reminds us that the whole malaria parasite is the most potent immunizing" agent, even though it is harder to develop a vaccine this way and other leading candidates take a different approach, he wrote.

Malaria kills nearly a million people each year, mostly children under 5 and especially in Africa. Infected mosquitoes inject immature malaria parasites into the skin when they bite; these travel to the liver where they mature and multiply. From there, they enter the and attack - the phase that makes people sick.

People can develop immunity to malaria if exposed to it many times. The drug chloroquine can kill parasites in the final bloodstream phase, when they are most dangerous.

Scientists tried to take advantage of these two factors, by using chloroquine to protect people while gradually exposing them to malaria parasites and letting immunity develop.

They assigned 10 volunteers to a "vaccine" group and five others to a comparison group. All were given chloroquine for three months, and exposed once a month to about a dozen mosquitoes - malaria-infected ones in the vaccine group and non-infected mosquitoes in the comparison group.

That was to allow the "vaccine" effect to develop. Next came a test to see if it was working.

All 15 stopped taking chloroquine. Two months later, all were bitten by malaria-infected mosquitoes. None of the 10 in the vaccine group developed parasites in their bloodstreams; all five in the comparison group did.

The study was done in a lab at Radboud University in Nijmegen, the Netherlands, and was funded by two foundations and a French government grant.

"This is not a vaccine" as in a commercial product, but a way to show how whole parasites can be used like a vaccine to protect against disease, said one of the Dutch researchers, Dr. Robert Sauerwein.

"It's more of an in-depth study of the immune factors that might be able to generate a very protective type of response," said Dr. John Treanor, a vaccine specialist at the University of Rochester Medical Center in Rochester, N.Y., who had no role in the study.

The concept already is in commercial development. A company in Rockville, Md. - Sanaria Inc. - is testing a vaccine using whole parasites that have been irradiated to weaken them, hopefully keeping them in an immature stage in the liver to generate immunity but not cause illness.

Two other reports in the New England Journal show that resistance is growing to artemisinin, the main drug used against malaria in the many areas where chloroquine is no longer effective. Studies in Thailand and Cambodia found the is less susceptible to artemisinin, underscoring the urgent need to develop a vaccine.

---

On the Net:

New England Journal: www.nejm.org

WHO report: apps.who.int/malaria/wmr2008/malaria2008.pdf

©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Explore further: Scientists find new calorie-burning switch in brown fat

add to favorites email to friend print save as pdf

Related Stories

Malaria vaccine trials begin using 'chimpanzee virus'

Feb 01, 2008

Trials are underway, funded by the Wellcome Trust, for a new vaccine to combat the most deadly form of malaria. For the first time ever, researchers will use a virus found in chimpanzees to boost the efficacy of the vaccine. ...

Gates: $258 million for malaria research

Oct 31, 2005

The Bill and Melinda Gates Foundation has given $258 million in malaria research grants. The foundation says malaria kills an estimated 2,000 African children each day and takes the lives of more than 1 million people wor ...

Early promising results in malaria vaccine trial in Mali

Jan 23, 2008

A small clinical trial conducted by an international team of researchers in Mali has found that a candidate malaria vaccine was safe and elicited strong immune responses in the 40 Malian adults who received it.

Recommended for you

Clues to curbing obesity found in neuronal 'sweet spot'

1 hour ago

Preventing weight gain, obesity, and ultimately diabetes could be as simple as keeping a nuclear receptor from being activated in a small part of the brain, according to a new study by Yale School of Medicine ...

Small RNAs in blood may reveal heart injury

11 hours ago

(Medical Xpress)—Like clues to a crime, specific molecules in the body can hint at exposure to toxins, infectious agents or even trauma, and so help doctors determine whether and how to treat a patient. ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

fixer
3 / 5 (1) Jul 29, 2009
Good.
This will free up more Artemisinin for CANCER therapy.
poi
4.5 / 5 (2) Jul 30, 2009
"This is not a vaccine" as in a commercial product, but a way to show how whole parasites can be used ...

then...
The concept already is in commercial development. A company in Rockville, Md. - Sanaria Inc. - is testing a vaccine using whole parasites ...

Hmm... a little too quick a turn, isn't it?
Sauvignon
not rated yet Jul 30, 2009
They volunteered for malaria? Where did they find these people?