Retrospective Evaluation of P. vivax Antibodies

Antibodies against the P. vivax blood stage can last for months or years in exposed patients. However, antibody titres fade out more rapidly in treated patients [29 (link)–31 (link)]. To reveal P. vivax re-exposure, with and without clinical symptoms and/or low parasitaemia in recurrent blood infections, retrospective research was conducted at the end of the 12-month follow-up period to look for native P. vivax blood-stage proteins in preserved blood samples by using ELISA, as previously reported [32 (link)]. Briefly, the blood samples that had been taken from each patient and smeared on filter paper were eluted in PBS and tested at 1:500 dilutions in an indirect ELISA. The reaction was revealed using goat anti-human IgG (H + L)-HRP (Pierce, Rockford, IL, USA) diluted 1:5000 and ABTS (2,2′-Azinobis [3-ethylbenzothiazoline-6-sulfonic acid]-diammonium salt) as substrate for 60 min, and then OD values were recorded in a spectrophotometer (Biotek^® model EL312) at 405 nm. Cut-off values were previously determined using unexposed individuals as the mean and 2SD as 0.25 OD values (95 % confidence). The ELISA-OD values were plotted according to time point per patient.