Current Inadequate Therapy for Intestinal Roundworms:
There are currently two classes of drugs approved by the World Health Organization for treating intestinal roundworm infections like hookworms, whipworms, and giant roundworms1. Of these two, the best and most practical for use is the benzimidazole class (mebendazole and albendazole). Mebendazole has, unfortunately already “failed” and has poor efficacy against hookworm treatment (average cure rates 15%)2. Its efficacy against whipworms is also low (cure rate 36%)1. Mebendazole is a classic case where repetitive use of a single drug led to its reduced efficacy in places like Tanzania3 and Mali4, most likely because the parasites became resistant to it.
So that leaves just one drug to treat the large populations of infected children, albendazole. Albendazole has average single-dose cure rates of 88% against giant roundworms, 72% against hookworms (variable efficacy that is sometimes worse, see below), and (a very poor) 28% against whipworms2. Albendazole can have side effects such as abdominal pain, dizziness, headache, fever, nausea, and vomiting and is not recommended for use in pregnant women (another group severely impacted by intestinal roundworms).
There are also growing reports of albendazole failures against intestinal roundworms, showing worrying low cure rates in Tanzania perhaps as a consequence of repeated usage5, likely resistance in hookworm populations in Ghana6, and very low cure rates and possible resistance in hookworms in Lao PDR7. In summary, none of the drugs work well against whipworms, their efficacy against hookworms is dicey, and resistant parasites appear to be on the way. The one, very imperfect drug we have is inadequate.
Resistance to all these classes of anti-roundworm drugs is already rampant in veterinary medicine8 and, based on available evidence, growing in human medicine. If we wait until large-scale resistance is a reality, it will be too late. We will have no good drugs left in our arsenal to clear worm infections and help the children and women. We have been down this road before, for example, with drug-resistant malaria, tuberculosis, and bacterial infections. The tragedy is this—if we do nothing we will eventually have nothing to give these children.
What’s surprising on top of this is that all of the drugs used to treat humans were developed to treat farm animals for parasites different that the ones in humans. We treat the hundreds of millions children with intestinal roundworms in the world with farm animal drugs. Intestinal roundworms are only disease in the world where we do that.
Can we do better? Can we find drugs that work much better than the drugs we have now? Can we find ways to ensure that the parasites don’t develop resistance?
2 Keiser and Utzinger, Adv. Parasitol. (2010) 73:197-230.
3 Albonico et al., Bulletin of the World Health Organization (2003) 81: 343-352.
4 De Clercq et al., Annales de la Societe Belge de Medecine Tropicale (1997) 75: 191-199.
5 Stothard et al., Annals of Tropical Medicine & Parasitology (2009) 103:357-360.
6 Humphries et al., American Journal of Tropical Medicine and Hygeine (2011) 84: 792-800.
7 Soukhathammavong et al., PLoS Neglected Tropical Diseases (2012) 6: e1417.
8 Kaplan, Trends Parasitol (2004) 20: 477-481.