Therapeutic Use of Helminths

Most of the therapeutic helminth trials to date have used Trichuris suit, the porcine whipworm (Fig. 2). T. suit is closely related to T. trichiura (human whipworm) and can briefly colonize people. Trichuris spp. have unique features that make them good candidates for clinical use. Ingesting microscopic embryonated parasite eggs initiates the colonization. Once ingested each e releases one larva that matures into an adult worm. The larvae and adults do not migrate beyond the intestines. They do not multiply within their host. Freshly deposited ova require incubation in moist soil for one to two months to mature and become infective. Thus, normal hygienic practices preclude transmission of this agent from host to host. 

Trichuris suit has additional characteristics that make it an attractive candidate. Human whipworms T. trichiura) can be obtained only from colonized primates. 77 suis is obtained from pigs raised in a specific pathogen-free environment. For the published studies, adult worms were collected from the colon, washed and cultured in vitro to collect freshly deposited ova. These ova were washed extensively and incubated for months to allow embryonation. This removed the risk of contaminating the T suis ova with other infectious agents. Since T. suis is present in many pig herds, farmers must be exposed to 77 suis and this organism has not been documented to cause human disease. This suggests that any risk from using this helminth is likely to be small. 

Initially, the effect of 77 suis colonization was studied in a small trial of 7 patients with IBD (4 Crohn s disease, 3 ulcerative colitis) under conditions where the patients and their care givers knew that they had received helminths ( open-label ). The patients ingested 2500 embryonated ova and were observed. All had improvement in their symptoms. A second study tested repeated dosing of T. suis in 29 patients with active Crohn s disease. The patients received 2500 77 suis ova every 3 weeks for 24 weeks. At week 24, 79% had responded with a significant reduction in symptoms. A third study was a double blind placebo-controlled trial of 77 suis in 54 patients 

Hie therapeutic application of helminths is not without controversy. At least a third of the world s population is actively infected with helminths and eradication programs stru le for resources. Some helminths can cause significant disease. This leads people to ask Isn t this dangerous or Will patients actually want to have worms  

We typically use medications with significant toxicides and side-effects to treat immune-me-diated diseases. Most of these chronic life-threatening diseases require immune suppression mediated by glucocorticoids (e.g., prednisolone, hydrocortisone), anti-metabolites (e.g., methotrexate. 

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