Histidine rich protein ii and lactate dehydrogenase levels in saliva and blood in acute malaria cases in Kisumu, western Kenya

Abstract

Globally, malaria is the leading cause of death and economic burden. Diagnosis currently relies on microscopy and blood-based rapid diagnostic tests (RDTs). However, both methods are invasive, which increases the risk of accidental infection and is painful. Non-invasive approaches are thus required. Plasmodium falciparum Histidine Rich Protein-2 (Pf.HRP-2) and Plasmodium falciparum Lactate Dehydrogenase (Pf.LDH) are parasite enzymes released into the host blood during clinical malaria infection and have been demonstrated in saliva though with inconsistent results. This may be because most of these studies have been performed in low malaria endemic zone. This study seeks to determine the levels of these antigens in blood and saliva in a high malaria endemic zone and determine their relationship with parasite density. On the other hand, the performance of blood-based RDTs is dependent on parasite density, which in turn decreases with age. The present study determined the performance and efficiency of detection of P. falciparum antigens levels in saliva and blood as potential biomarkers in the diagnosis of malaria infection using blood-based RDT and saliva-based ELISA assay across ages. Specifically, the study determined the relationship between levels of P. falciparum antigens in saliva and blood, and parasite densities, clinical malaria and age in individuals of varying ages with acute malaria: The correlation between the antigen levels in blood and saliva and the sensitivity, specificity, positive and negative predictive values for detection of P. falciparum antigens. This was a cross- sectional study involving participants presenting with clinical malaria at Chulaimbo Sub- County hospital. Levels of P. falciparum antigens in saliva and blood were measured using ELISA. Generalized linear model was done to assess the relationship between the levels of P. falciparum antigens to parasite densities, clinical malaria and age. Correlation between levels of Pf. HRP-2 and Pf.LDH in blood and saliva were evaluated using Pearson’s correlation. Sensitivity/specificity of the blood-based rapid diagnostic tests as well as blood and saliva-based Elisa assay were calculated. Parasite density did not predict Pf.HRP-2 in plasma and saliva (p=0.974) and (p=0.635) respectively. Also, parasite density did not predict Pf.LDH in plasma and saliva (p=0.570) and (p=0.315) respectively. In addition, clinical malaria did not predict Pf.HRP-2 in plasma and saliva (p=0.179) and (p=0.895) respectively. Equally, clinical malaria did not predict Pf.LDH in plasma and saliva (p=0.291) and (p=0.272) respectively. In contrast, age significantly predicted Pf.HRP-2 levels in plasma (p=0.00) but not in saliva (p=0.580). On the other hand, age did not significantly predict Pf.LDH levels in both plasma and saliva (p=0.406) and (p=0.764) respectively. Moreover, there was no significant relationship in the levels of Pf.HRP-2 and Pf.LDH in plasma and saliva (r=-0.235, p=0.104) and (r=-0.0235, p=0.104) respectively. Sensitivity of detection using blood-based RDTs in children and adults was found to be (98%) and (100%) respectively. Specificity was (28%) in children and (83%) in adults. Sensitivity of Pf.HRP-2 detection in children by ELISA was 78% in plasma and 13% in saliva. Pf.LDH in children was detected at a sensitivity of 15% in plasma and 7% in the saliva. In adults, Pf.HRP-2 had a sensitivity of 75% in plasma and 50% in saliva. Specificity of Pf.HRP-2 was 40% in plasma and 95% in saliva of children. Pf.LDH was detected at 100% specificity in both plasma and saliva of children and adults. Measurement of Pf.HRP-2 and Pf.LDH in plasma and saliva may not be a good proxy measure of infection and clinical disease in populations exposed to endemic malaria, However, Pf.HRP-2 can be used to measure cumulative exposure. Measurement of Pf.HRP-2 and Pf.LDH in saliva cannot substitute for the measurement in plasma hence plasma-based assays are more reliable. The lower sensitivity of Pf.HRP-2 in both plasma and saliva in holoendemic areas may not be improved using saliva samples prompting the need for further research.