Parasitic Infections

Strongyloides stercoralis and Toxoplasma gondii warrant special attention because of the distinctive features of these pathogens and the potential for severe infection in organ transplant recipients.

Strongyloides stercorales

Overview

Strongyloidiasis is a helminthic infection endemic to tropical and subtropical areas of the world, including Southeast Asia, the Caribbean, and West Africa. Rural areas of Kentucky, Tennessee, and Louisiana are the endemic foci within the United States. Infection results in a diarrheal illness with peripheral eosinophilia, but the organism can be maintained in the gastrointestinal tract asymptomatically for decades. The lifecycle of S. stercoralis is complex and unique in that autoinfection of the host occurs; larvae transform into an infectious form in the intestine and invade the intestinal mucosa and perianal skin. This process maintains the infection by constant re-introduction of infectious forms into the hosts. In immunocompromised patients, autoinfection may result in the hyperinfection syndrome, a form of disseminated strongyloidiasis in which an accelerated lifecycle and excessive helminth burden occur. The mortality rate of hyperinfection syndrome approaches 70%. A complication of this syndrome is gram-negative bacteremias and shock caused by the disruption of normal intestinal barriers during invasion of the gut mucosa by larvae.

Clinical Presentation

In patients harboring S. stercoralis, symptoms develop in the first six months after transplantation. The intestinal form presents as abdominal pain, diarrhea, nausea, and vomiting. Hyperinfection syndrome presents with tachypnea, respiratory distress, cough, hemoptysis, and enterocolitis. Fever and rash may also be present. The chest radiograph demonstrates alveolar or interstitial infiltrates. On laboratory data, eosinophilia, if present, is helpful.

The definitive diagnosis is made by examining stool specimens for the presence of larvae. The sensitivity of this method is improved by the examination of multiple specimens and concentration techniques. Sputum and duodenal aspirates may be examined for the presence of larvae. Serologic testing is also available.

Treatment

The treatment options for strongyloidiasis include ivermectin, 200 mcg/kg/day for two days; albendazole, 400 mg/day for three days; or thiabendazole, 25 mg/kg for two days. The hyperinfection syndrome requires seven to ten days of therapy. Secondary bacteremias are treated with antimicrobial agents.

Prevention

Prevention is aimed at candidates who have resided or traveled extensively to endemic areas. Prior to transplantation, candidates are screened for the presence of this infection, either serologically or by examination of multiple stool speci mens for larvae. Established infection is treated before transplant. Interestingly, cyclosporine A (CsA) has activity against S. stercoralis; recipients treated with CsA are less likely to develop the hyperinfection syndrome.

Toxoplasma gondii

Overview

Toxoplasmosis after transplantation is most frequently caused by reactivation of latent disease. Seronegative heart transplant recipients are at the greatest risk for developing this disease when receiving an organ from a seropositive donor; in such cases, the risk of primary infection is 50% if prophylaxis is not administered. This infection is also potentially transmitted by other organs, such as liver, and blood products.

Clinical Presentation

Most infections occur during the first two months after transplantation. Primary infection manifests as fever, malaise, and generalized lymphadenopathy. Other presentations include meningo-encephalitis, pneumonitis, pericarditis, myocarditis, and retinitis.

The definitive diagnosis is made by the histologic demonstration of trophozoites surrounded by inflammatory reaction. Serologic testing is not very helpful for the diagnosis of infection.

Treatment

The options for therapy are one of the following: pyrimethamine and sulfadi-azine or pyrimethamine plus clindamycin. Folinic acid is administered with either regimen to prevent myelotoxicity. Treatment is continued for two to three weeks after resolution of the acute infection.

Prevention

After transplantation, toxoplasmosis is prevented by the use of TMP/SMX in the same doses used for PCP prophylaxis for at least six months. Pyrimethamine is an alternative agent for sulfa-intolerant patients. All heart transplant candidates and donors require serologic screening to determine the post-transplant risk of toxoplasmosis.

0 0

Post a comment