Antibiotics offer 'vaccine-like' immunity to malaria
23 July 2010
Researchers from the KEMRI-Wellcome Trust Research Programme in Kenya and colleagues found that if mice were infected with malaria parasites and given preventative antibiotics, they developed immunity against reinfection.
If proved to work in human clinical trials, this could help to control or eliminate malaria in high-risk populations, particularly young children, says Dr Steffen Borrmann from Heidelberg University School of Medicine, who led the research.
The use of antibiotics, administered regularly in combination with currently used antimalarial drugs, would form a valuable additional tool in resource-poor settings, he adds.
There is no effective malaria vaccine, but current approaches to develop one use irradiated malaria parasites. Traditional vaccines work by injecting dead or weakened forms of a pathogen into the body, allowing it to mount an effective immune response that is primed to react should the body be infected again.
Conversely, antibiotics are normally taken as a drug treatment to fight an infection already underway. They are established as a safe and affordable way to deal with acute malaria infection, particularly in combination with other antimalarial drugs.
In regions where malaria transmission is moderate to high, humans are repeatedly bitten by mosquitoes infected with the malaria parasite. If the body can survive the first infection, it can develop its own immune response.
In the study, the researchers showed that two antibiotics - clindamycin and azithromycin - caused a defect in the malaria parasites when they entered the liver. The defect didn't prevent the parasites multiplying, but it did stop them from changing into the disease-causing form that enters the bloodstream.
Stopping the parasites in the liver then buys the immune system time to mount a defence. The study found that this immune response was robust enough to protect against subsequent infections 40 days after the 'immunisation' - even without the presence of antibiotics.
"Our 'needle-free' approach banks on naturally occurring transmission of the 'vaccine dose' by mosquito bites, whereas the more conventional vaccine approaches currently being tested use irradiated malaria parasites," says Dr Borrmann.
He says an advantage of this approach is that it does not require the "technically and logistically challenging" production and delivery of weakened parasites to a population. However, the reliance on 'natural delivery' means they cannot predict the exact effect, as the number of mosquito bites varies from individual to individual.
The antibiotics used are no more expensive than the treatments currently used in the field, such as artemisinin combination therapies. Dr Borrmann suggests that azithromycin-chloroquine, currently being developed by Pfizer with support from the Medicines for Malaria Venture, would be a good candidate for the first proof-of-concept studies of this method in humans.
Image: Sporozoite on liver. Credit: Volker Brinkmann
Reference
Friesen J et al. Natural immunization against malaria: causal prophylaxis with antibiotics. Sci Transl Med 2010;2(40):40-9.
