Subcutaneous ivermectin use in the treatment of severeStrongyloides stercoralisinfection: two case reports and a discussion of the literature—authors' response

Between 30 and 100 million people are affected by Strongyloides stercoralis infection yearly, with the majority of cases occurring in endemic areas such as South America and South-East Asia. Some cases are seen outside these areas, however, and diagnosis in such cases may be significantly delayed. Tropical infections are understandably lower on the list of differential diagnoses unless a clear history of recent travel is given. As S. stercoralis can complete its life cycle within a single human host, in a process called ‘autoinfection’, infection can persist for many years after the original exposure, and its cause may not be recognized after a superficial travel review. Infection may re-emerge in the form of severe or hyperinfection following immune suppression, an increasingly frequent occurrence in an ageing and medically complex population. Steroid use, human T lymphocyte virus 1 (HTLV-1) infection and organ transplantation are risk factors for hyperinfection—a rapid increase in the reproduction and migration of the Strongyloides larvae, which can lead to life-threatening illness. Delay in diagnosis reduces the efficacy of conventional therapy, and it can lead to treatment failure. The most effective anthelminthic used to treat Strongyloides infection is ivermectin, which paralyses nematodes by increasing membrane permeability to chloride ions. Currently, the only administration route licensed for use in humans is oral; however, in severe Strongyloides infection, there is often extensive smallbowel involvement, so enteral administration is poorly tolerated or not possible. With treatment, the mortality rate of hyperinfection is close to 60%; without effective treatment, it is likely to be around 100%. Rectal administration has been tried, but it appears to have limited efficacy. One case study describes the intravenous use of ivermectin; however, the patient died. There are limited data on the unlicensed subcutaneous use of ivermectin in such patients. Here, we describe our experience of the successful use of subcutaneous ivermectin in two patients with severe and complicated Strongyloides infection where enteral treatment was not possible, and we summarize the published cases to date.