Follow up of specifically treated patients
Tests that follow up of specifically treated patients (serology for cure and parasitological tests for failure) have revealed that specific treatment is effective in nearly all infected by congenital route, in 60—80% of acute phase patients, children, and early chronic phase, and in 25—30% of those treated during the chronic phase.145,146 Treatment is mandatory for first two groups and optional for the last. The follow-up of treated patients to know if they were cured is performed through serological and parasitological tests, though the latter is not essential. Cure is attained when antibodies, formerly present, disappear. Parasitological tests are useful only when positive and indicate treatment failure.48
In Chagas disease, antibodies demand different amounts of time to disappear, related to the phase of the disease and to the type of T. cruzi. In congenital infection, nearly all treated are cured, and 1 year follow-up is enough. Acute and chronically infected individuals with less than 10 years of evolution (mainly children) are cured at a lower rate (60—80%) and the antibodies may take 2—10 years to disappear.146 It has been recently demonstrated that the type of parasite present is of utmost importance.147 In those countries where T. cruzi I predominates (Mexico, Central America, Colombia, and Venezuela), the antibody responses vanish by 16 months in children. Where T. cruzi II predominates, as in Brazil, the same group of patients takes more than 5 and often 10 years to be free of antibodies.147
Those treated during the chronic phase usually take longer: no studies with large series of adults are available from T. cruzi I region, but below the equator line (T. cruzi II) it usually takes 15—30 years to obtain a negative serology and the number cured is no higher than 30%. This long time is probably due to the time the immune memory would forget a parasite which was in circulation for decades.148
Antibody response should be measured by conventional tests as described. The use of recombinant antigens may yield equivocal results. In some already cured, the responses to recombinant antigens is still high when there are no more anti-T. cruzi antibodies found by ELISA, IIF, and HA. A number of nonconventional tests show that antibodies measured by these systems could indeed have a quicker shift and decrease after shorter periods of time.149,150
