Inadequate vaccines can help breed more vicious malaria strains.

2004 JUL 7 - (NewsRx.com & NewsRx.net) -- Vaccination programs could create conditions that promote the evolution of virulent strains of the disease, according to a laboratory-based study of the malarial parasite Plasmodium in mice.

The findings, published online in the open-access journal, PLoS Biology, are likely to spark debate among public health groups seeking to curb the disease, which claims up to 2 million lives each year and accounts for one child death every 30 seconds in Africa.

Vaccines are designed to protect people by boosting the immune system to kill parasites but, unless a malaria vaccine leads to the death of every single parasite, the ones that survive are likely to be the nastiest. The new research by Dr. Margaret Mackinnon and Professor Andrew Read, of the University of Edinburgh's Institute of Cell, Animal & Population Biology, sought to investigate how vaccination can, in fact, lead to the evolution of more virulent strains of the disease.

Initially, the Edinburgh researchers directly injected two groups of mice with infectious parasites - "immunized" mice, which had been exposed to Plasmodium and then treated with the antimalarial drug, mefloquine, and "naive" mice, which had not. They then transferred parasites via a syringe from host to host 20 times. The parasites thus evolved in the immune or nonimmune environments. The parasites that evolved in the immunized mice were more virulent than parasites evolved in the naive mice.

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