On the basis of overall malaria antibody prevalence (17.4%) in blood donors, our region can be categorized as meso-endemic for malaria. In a study done by Choudhry et al
. in North Indian blood donors more than a decade ago, malaria antibody was detected in 12.39% and 19.37% of subjects by Indirect Fluorescence Antibody test (IFAT) and in-house ELISA, respectively.[10
] Our results compare well with their study, as at that time the history-based donor deferral for malaria was not followed. summarizes the malaria antibody prevalence in blood donors reported from various endemic and non-endemic countries and strategies adopted to prevent TTM, for comparison. As seen in , malaria antibody screening of blood donors is a routine method to prevent TTM in non-endemic countries. However, since malaria antibody prevalence in our donor population is high, discarding of blood on the basis of malaria antibody positive result is not a feasible option. In a study done by Oh et al
. malaria antibody ELISA was found to have a clinical specificity of 94.0% for P. vivax
with polymerase chain reaction (PCR) as reference method.[20
] Thus, it would be prudent to evaluate and adopt additional strategies to make these units non infectious.
Malaria antibody and antigen prevalence in blood donors from India and other countries
The statistically insignificant higher seroprevalence of malaria antibody in donors having history of fever within the last 3 months (22%) as compared with that in normal donors (16.9%) does not provide enough evidence at this stage to prove or disprove usefulness of such criteria, and results need to be confirmed on a larger sample size study to prevent unnecessary donor deferrals. Except for rural residence (33% vs. 15.2% in urban) no other donor characteristics studied, i.e., age, gender, or type of donor, had any bearing on malaria antibody prevalence. This is in concurrence with reported findings and is closely related to the agricultural practices and habits such as sleeping out of the doors and not using measures of personal protection.[21
None of the donors was found to be positive for malaria by microscopy or RDT expect one deferred donor (0.09%) who tested positive with RDT, while in a study done by Bahadur et al
. recently, 0.03% out of 11,736 units of donated blood were positive for malaria by RDT.[22
] Therefore, blood donor screening for malaria by microscopy may not be an acceptable method as more sensitive malaria screening methods like RDT and malaria antigen testing by ELISA are now available.
Malaria antibody prevalence in multi-transfused patients was not greater than in blood donors. Therefore, no conclusion can be made as to whether malaria exposure through transfusion is a significant risk factor. Rather, the prevalence of malaria antibody in thalassemia patients (6%) was considerably lower as compared with that in donor population (17.4%), though not statistically significant. The difference could be because of lesser duration of exposure to community-acquired vector borne malaria, as majority of the thalassemia patients (90%) were less than 18 years of age whereas all the donors were above 18 years. Other studies have reported malaria incidence of 6.4%[6
] and 6.9%[23
] in thalassemia patients. In contrast, patients with Hb E- β Thalassemia disease at the National Thalassemia Center in Kurunegala, Sri Lanka, a region of low malarial transmission, have been found to have high frequencies of antibodies to P. vivax
(>60%) and to a lesser degree to P. falciparum
(>30%) from the early years of life, and the levels are significantly higher than those of age-matched controls from the same region, suggesting increased susceptibility.[24
] The same study also reported significantly higher malaria antibody prevalence in thalassemics with splenomegaly or those who have undergone splenectomy. This finding was also not confirmed in our study, and the issue needs further investigation by comparing antibody prevalence in healthy non-transfused and transfused age-matched controls.
Malaria antibody prevalence in other multi-transfused group of patients in our study was 15%, which was not significantly different from the normal healthy donors acquiring malaria by vector. In comparison, in a study done by Ali et al
. in 2004, post transfusion malaria incidence of 4.9% has been reported for multi-transfused patients.[25
As with other transfusion-transmitted infections, suspected TTM was difficult to prove to be transmitted by transfusion, as implicated donors did not report for follow-up despite repeated requests.
In conclusion, the existing strategy of donor deferral for fever in preceding 3 months can be combined with anti-malaria antibody screening by commercially available ELISA. Anti-malaria antibody positive units may then undergo pathogen inactivation to render them non-infectious before transfusion or anti-malaria chemoprophylaxis can be given to recipients of anti-malaria antibody reactive units as targeted intervention. The ideal approach, however, would be to screen all donations for malaria by PCR which is currently the most sensitive technique (~
5 parasites/ uL).[26
] A recently available technique based on detection of hemozoin pigment in the neutrophils and monocytes by automated hematology cell counters should also be evaluated as it is a convenient, less costly, and objective method.[27
] The usefulness of each, however, has to be evaluated in terms of TTM cases prevented and the additional costs incurred.