Without Worms Within

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Science  26 Jul 2013:
Vol. 341, Issue 6144, pp. 319
DOI: 10.1126/science.341.6144.319-b

Some humans share several characteristics with pigs, including very similar parasitic worms. Ascaris spp. roundworms are large, pungent, and can occur in sufficient numbers to block the gut, pierce the peritoneum, and invade the bile duct. In children, the morbidity caused by a heavy worm infection can have lifelong consequences. Surprisingly perhaps, roundworms can be killed by a Bacillus thuringiensis (Bt) toxin a bacterium more usually encountered in crop pest control. Urban et al. have been exploring the potential of one Bt toxin, Cry5B, as an anthelmintic (a deworming drug), using young pigs as a human substitute. Experiments on the mode of action in the classic worm model Caenorhabditis elegans showed that Cry5B binds to galactose-containing glycolipid receptors found only in invertebrates, and this was confirmed to be the case in Ascaris, too. Cry5B was given by gavage to groups of five piglets as spore crystal lysate in two doses (20 mg/kg) at 10 and 12 days after infection, when the penultimate larval worm stage emerges into the gut (unfortunately, there are severe practical constraints on testing the limited-availability Bt toxin on the slow-growing adult worms), and 6 days later, 97% of these larvae were dead and the remainder disabled. The natural product Cry5B could thus be a valuable addition to the anthelmintic roster, especially as resistance is emerging to the standard drugs.

PLoS Negl. Trop. Dis. 7, e2263 (2013).

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