Numerous parasites may cause infestation of the gastrointestinal tract in man. Most cases of intestinal parasitisation occur in areas of poor sanitation and particularly in ‘third world’ countries. With few financial resources for research in third world countries and low market expectations from the development of anti-parasitic therapies by large ‘pharma’ there has been inadequate market pressure to come up with medications to combat even the most common parasites infesting the gastrointestinal tract. Fortunately, outside the ‘third world’ there is a number of parasitic infestations which are common in developed countries yet these are poorly addressed, perhaps because anti-parasite drug development has been more the realm of the ‘third world’. For example malaria parasites, Entamoeba histolytica, Shistosomiasis and similar parasites are rarely detected in developed countries except in incoming visitors to countries such as United States, Australia and regions such as Europe. On the other hand, there has been little recognition by gastroenterologists and general practitioners in developed countries particularly of two parasites common in the developed countries yet poorly addressed and diagnosed with some difficulty. These include various strains of Blastocystis hominis and Dientamoeba fragilis. 
There is emerging compelling literature which suggests that infestation of the bowel flora by parasites can result in symptomatology that is indistinguishable from the very common condition in the west called Irritable Bowel Syndrome (IBS) (Yakoob et al 2004, Am J Trop Med Hyg 70: 383; Borody et al 2002, Gastroenterol Hepatol 17: Suppl A103). Irritable Bowel Syndrome is characterized by changes in bowel habit including diarrhoea, constipation, bloating, pain, cramping, urgency and at times nausea. More recently, this condition which was previously thought to be caused by stress and inadequate diet is now increasingly thought to be caused by ‘overgrowth of the bowel flora’ by infective agents including bacterial agents, and, parasites, many of which are yet to be characterized. Hence, unless one examines the bowel flora in patients with IBS symptoms for common parasites these may be missed and an “IBS” label may be used without giving the patient the opportunity for cure. Such “IBS” then goes on to be misdiagnosed whereas all along it might have been curable by removal of the chronic parasite infection.
In the ‘first world’ common intestinal parasitic infections include Blastocystis hominis, Dientamoeba fragilis and Giardia lamblia. These are perhaps the more common parasitic infections of the gut flora, particularly in such countries as the USA, Australia and the UK. Originally Blastocystis was not thought to be a pathogenic parasite but more recently has been shown—at least with some sub-types [esp. type 3]—to cause symptoms that can be relieved by treatment. D. fragilis is known to be a pathogen albeit it may cause mild symptoms like IBS although and at times colitis has been caused by this parasite. (Skein et al, 1983 Am J Gastroenterol. 78:634).
In this application the inventor identifies the lack of specific first line and second line therapies for these most chronic infections which can cause IBS-like symptoms in developed countries. This situation has left an unmet need and with increasingly more frequent diagnosis of D. fragilis and B. hominis repeated treatment and failure-to-cure is seen when doctors who do not know how to treat the parasites simply use metronidazole which generally has but a minor effect on parasites. This invention will therefore describe first and second line therapies in patients who have infestation with these common parasites D. fragilis or B. hominis or both. Single anti-parasitic agents are generally ineffective against these parasites and so combinations are necessary. Furthermore there may be more extended applications to other parasites that may respond to such combinations.