Pathogenicity of Toxoplasma gondii under control of a plant hormone

As diseases caused by tropical parasites become more resistant to drugs, new treatments are urgently being sought. A paper in the recent issue (10 Jan 2008) of Nature reports the surprising discovery that the pathogenicity of a parasite known as Toxoplasma gondii is under the control of a hormone previously found only in plants and some primitive sea creatures - making it a potential target for an inhibiting drug that won't affect the human host.

David Sibley from the Department of Molecular Microbiology, Washington University School of Medicine and his colleagues compared plant and parasite genomes to discover a T. gondii metabolic pathway responsible for synthesising the plant hormone abscisic acid, which turns out to be crucial for the parasite's replication and development. Accordingly, they tested the effect of the herbicide fluridone - which prevents the hormone from working in plants - on laboratory mice infected with T. gondii. Parasite burden in treated animals was significantly reduced.

The malaria parasite Plasmodium falciparum is related to T. gondii and also carries genes implicating abscisic acid in its development. Perhaps the ripples from this unexpected new discovery may extend to a better understanding of malaria infection.