Strongyloides
Infection with Strongyloides stercoralis occurs when the larvae penetrate the skin of persons walking in soil contaminated with feces and typically occurs in people from rural agricultural areas, especially if poor sanitation exists. Autoinfection is an important source of prolonged carriage and adult worms can live for up to 5 years, allowing for ongoing infection even when the donor is no longer living in the endemic area. Consequently, individuals may remain chronically infected and able to transmit infection throughout their lives via organ donation. Individuals infected with Strongyloides are often asymptomatic; symptomatic infection occurs more commonly in immunocompromised hosts. Manifestations may be variable and involve the gastrointestinal and/or pulmonary tracts, sepsis syndromes, gram-negative bloodstream infections, and/or meningitis (especially with gram-negative organisms). The most severe manifestation is hyperinfection syndrome.
The precise prevalence of chronic infection is unknown. The disease occurs throughout the world and infection rates are highest in tropical or subtropical regions, exceeding 80% in some locations. In the United States, rates as high as 3.8% have been measured in Appalachia and southeastern states. The last community-based survey was conducted in 1982, and current rates are unknown.
Which Living Donor Candidates Should Be Screened for Strongyloides?
Strongyloidiasis typically occurs only in the setting of specific environmental exposures; thus, screening all potential live donors is not indicated. Screening is justified for the following potential organ donors:
Persons who were born in or lived in tropical or subtropical countries where sanitation conditions are substandard. This includes candidates with prior military service in endemic areas. Strongyloidiasis has occurred in most countries with the exception of Canada, Japan and Northern Europe.
Persons with unexplained eosinophilia and travel to endemic area.
Those born in the United States who have significant exposure to soil in Appalachia or the southeastern United States.
Persons reporting a prior history of Strongyloides infection.
How Should Donor Candidates Be Screened for Strongyloides?
Strongyloides IgG antibody testing is readily available in many reference labs (Table 1). Currently, these ELISA assays (which correlate with antibody to filariform larvae) are not specifically approved by the Food and Drug Administration (FDA) for donor testing. Test sensitivities vary and false-negative results have occurred, including in early infection and immunocompromised hosts. Indirect immunofluorescence assays have improved sensitivity; however, they are generally only available through research laboratories. There is no standard commercially available confirmatory testing for antibody positive specimens; false-positive tests are uncommon. Individuals with a history of treatment for Strongyloides infection may have persistent antibody; consequently, those donors should undergo further evaluation by an expert in infectious diseases. Serology is the preferred screening test for Strongyloides infection, as the sensitivity of stool testing is limited and multiple stool screening tests may be negative in asymptomatic chronic infection. Fecal examination for Strongyloides larvae may sometimes identify additional infected individuals who are newly infected and can be requested at the time of the initial evaluation. Because the methodology used to identify Strongyloides differs from that for routine ova and parasite examinations, it is important to specify the organism when ordering the test. Multiple stool specimens should be obtained to increase the yield; the optimal number is unknown but reports note that seven consecutive daily specimens may increase the sensitivity to nearly 100%. Given that transplant candidates may share similar epidemiological risk factors for Strongyloides infection, potential recipients with similar geographic exposures should also be considered for screening and treatment should be administered if found to be positive.
Eosinophilia is commonly seen in patients with active Strongyloides infection. Thus, those individuals with potential environmental exposures and unexplained eosinophilia should undergo serological testing and fecal examination for Strongyloides. However, since eosinophilia is not universally noted in patients with chronic strongyloidiasis, it should not be used as the only determinant for which individuals are screened with serologic testing. The optimal timing of live donor testing has not been established. However, unless the donor will resume residence in an environment where new exposures are likely, it is reasonable to test at the time of donor identification.
Can Infected Donors Be Considered for Transplantation?
Donor-derived strongyloidiasis has been rarely reported in the setting of deceased kidney donation, typically related to the use of donors from endemic areas. It has been suggested that the risk of donor-derived strongyloidiasis is enhanced due to predonation conditioning with high-dose corticosteroids. Consequently, it is unclear if live donors will pose the same risk for transmission as noted with deceased donors. Nevertheless, given the availability of effective treatment options for Strongyloides infection, infected individuals can be considered for live donation. Ideally, infected donors should be treated with a minimum of two doses of ivermectin prior to donation (200 μg/kg orally daily on 2 consecutive days). Because of the potential for persistence of migrating larvae and eggs in the tissues, some experts recommend repeating this treatment 2 weeks later to cover an autoinfection cycle. Following treatment, there is no need for follow-up laboratory testing of the donor prior to donation for confirmation of cure, unless re-exposure has occurred.
How Should the Recipients of Strongyloides-Positive Donor Organs Be Managed Posttransplant?
If the donor is treated prior to donation, no specific treatment or monitoring of the recipient is required as the likelihood of transmission is probably extremely low.
If the donor cannot be treated prior to donation or receives only a single course of treatment, then the recipient should be treated with the same regimen as outlined for the donor (considering two courses of two doses of ivermectin separated by 2 weeks as the most conservative approach) as soon as possible after the transplant has occurred. There are no significant drug interactions and the medication is typically well tolerated with no requirement for dose adjustment based on either renal or hepatic function. All recipients of organs from donors with Strongyloides infection should be monitored clinically; no additional serological or microbiological studies are indicated in the absence of symptoms. If recipients develop signs and symptoms consistent with Strongyloides infection or eosinophilia, expert consultation should be obtained. Serological diagnosis is unreliable in patients receiving immunosuppressive medications; therefore, appropriate samples (e.g. stool, respiratory samples) should be obtained for direct examination for Strongyloides larvae. Because eosinophilia is not always present, its absence cannot exclude the diagnosis. Recipients with posttransplant Strongyloides infection should be treated with ivermectin; the dose and duration may vary with the specific clinical syndrome and expert consultation should be solicited.