Trypanosoma cruzi and the United States Blood Supply: Should We Be Testing All Donors?

By Mary-Louise Scully, MD

Synopsis: Insuring that the blood supply is free of transmissible pathogens remains a challenge. Since 1987, 7 cases of transfusion-transmitted Trypanosoma cruzi infections have occurred in the United States/Canada. The chronic nature of Chagas disease and the increasing number of immigrants from endemic countries may warrant the need to institute universal testing for this parasite.

Source: Leiby DA. Epidemiologic aspects of Trypanosoma cruzi in United States blood donors. ASTMH annual meeting. Philadelphia, Pa: December 5, 2003.

Trypanosoma cruzi, the agent of Chagas disease, is a protozoan parasite that can cause lifelong, often untreatable, infection. Patients in the acute stage of illness, which is recognized in only 1-2% of infected patients, have demonstrable parasitemia, and IgM antibodies predominate. During latent/indeterminate and chronic stages of infection, patients have low levels of parasitemia and elevated IgG levels. It is estimated that there are 50,000-100,000 T cruzi-infected immigrants residing in the United States. Most infected patients are asymptomatic, and at this time there is no screening performed to identify T cruzi-infected blood donors.

Since 1987, a total of 7 US/Canadian transfusion cases of T cruzi have occurred. In 1999, a multiple myeloma patient was transfused with a platelet unit from a Chilean donor that was later confirmed as seropositive. Both the donor and recipient were parasitemic and serologically positive. Both were asymptomatic. Of note, the donor had emigrated from Chile 33 years earlier. The most recent transfusion case of T cruzi, from a Bolivian donor, occurred in Rhode Island in 2002.

Leiby and colleagues have looked at the effect of evolving donor demographics on the seroprevalence of T cruzi in Los Angeles and Miami.1 From May 1994 to September 1998, blood donors in Los Angeles and Miami were queried regarding birth or time spent in a T cruzi-endemic country and then tested for T cruzi antibodies by radioimmunoprecipitation assay (RIPA). Seropositive rates were 1 in 7500 for donors in Los Angeles and 1 in 9000 in Miami. In addition, the seroprevalence rates in Los Angeles increased from 1996 to 1998, most likely secondary to minority donor recruitment efforts. The seroprevalence in directed donation was even higher, at 1 in 2400. Perhaps of greater concern are data suggesting congenital transmission of T cruzi across several generations.2 Therefore, asymptomatic, yet transmissible, infection may be present not only in the immigrants from T cruzi-endemic countries, but also in their children and their children’s children. Clearly, this enlarges the spectrum of the problem.

Chagas disease following solid organ transplantation has occurred in Latin America where T cruzi is endemic, but the first reported US case occurred in 2001. A 37-year-old woman who had received cadaveric kidney and pancreas transplants had a febrile illness, and T cruzi trypomastigotes were found on her peripheral blood smear.3 Subsequently, the 2 other patients who had received organs from the same donor were culture positive for T cruzi as well. The donor had been an immigrant from Central America.

Another study looked at seroprevalence of T cruzi in more than 11,000 Baltimore/Houston postoperative cardiac surgery patients.4 There were 6 (0.05%) confirmed seropositives, and 5 out of the 6 were Hispanic patients. Four of 6 patients had positive pre-operative serology tests. The other 2 patients were cardiac transplants, and both excised hearts were found to be positive for T cruzi by PCR. Therefore, all 6 patients were infected with T cruzi prior to surgery. Clinicians should consider the possibility of Chagas disease in patients from endemic areas, especially patients with cardiac conditions that could be consistent with chronic Chagas disease.

Strategies to alleviate this problem are being developed. Unlike many pathogens for which nucleic acid testing is best for donor screening, T cruzi serology is actually more useful because not everyone infected with T cruzi has detectable circulating parasites. The parasite can survive irradiation of blood products, and even leukoreduction fails to remove all T cruzi parasites. It is estimated that even if all blood donors were questioned for T cruzi risk factors, up to 4% of seropositive donors might still be missed.

Therefore, the path of the future may be the need for universal, serologic screening of blood donors for T cruzi. This would result in substantial cost, perhaps as high as an additional $50 million per year. However, since infection with this parasite is often chronic and generally untreatable, the long-term benefits may justify the expense.


1. Leiby DA, et al. Trypanosoma cruzi in Los Angeles and Miami blood donors: Impact of evolving demographics on seroprevalence and implications for transfusion transmission. Transfusion. 2002;42:549-555.

2. Leiby DA, et al. Trypanosoma cruzi in a low to moderate risk blood donor population: Seroprevalence and possible congenital transmission. Transfusion. 1999;39:310-315.

3. CDC. Chagas disease after organ transplantation—United States, 2001. MMWR Morb Mortal Wkly Rep. 2002;51:210-212.

4. Leiby DA, et al. Evidence of Trypanosoma cruzi infection among patients undergoing cardiac surgery. Circulation. 2000;102:2978-2982.