Unclear association between levels of Plasmodium falciparum lactate dehydrogenase (PfLDH) in saliva of malaria patients and blood parasitaemia: diagnostic implications?

Stephen Kaniaru,Francis Kimani,Eva A Nambati,Wallace Bulimo,James H Kimotho,Janice Limson,William C Kiarie,Edwin Too,Maureen S Otinga

doi:10.1186/s12936-017-2151-y

Abstract

BackgroundThe use of saliva in diagnosis of infectious diseases is an attractive alternative to procedures that involve blood drawing. It promises to reduce risks associated with accidental needle pricks and improve patient compliance particularly in malaria survey and drug efficacy studies. Quantification of parasitaemia is useful in establishing severity of disease and in assessing individual patient response to treatment. In current practice, microscopy is the recommended technique, despite its limitations. This study measured the levels of Plasmodium falciparum lactate dehydrogenase (PfLDH) in saliva of malaria patients and investigated the relationship with blood parasitaemia.MethodsMatched pre-treatment blood and saliva samples were collected from patients at Msambweni District Hospital, Kenya. Parasitaemia was determined and only those confirmed to be Plasmodium falciparum mono-infected were recruited. PfLDH was quantified in saliva using a commercial ELISA kit. A total of 175 samples were collected. Relationship between blood parasitaemia and concentration of PfLDH in saliva was determined using Pearson correlation statistics. F test was used to determine whether there is a significant difference between levels of PfLDH in saliva of patients with moderate to high parasitaemia and those with low parasitaemia.ResultsOne-hundred and seventy-five patient samples were positive for malaria by microscopy. Of these, 62 (35%) tested positive for PfLDH in saliva, 113 (65%) were false negatives. For those that tested positive, (53) 85% were from patients with moderate to high parasitaemia while 9 (15%) were from patients with low parasitaemia. A correlation co-efficient of 0.18 indicated a weak positive relationship between the concentration of PfLDH in saliva and blood parasitaemia. There was a marginal difference between levels of PfLDH in saliva of patients with moderate to high parasitaemia and those with low parasitaemia [F (1, 59) = 1.83, p = 0.1807].ConclusionThe results indicate that there is a weak correlation between levels of PfLDH in saliva and blood parasitaemia. This is weak association could be as a result of low sensitivity of the assay used as well as presence of inhibitors and proteases in saliva. Further studies should be focused towards reducing the number of false negatives and developing a customised assay that is specific for detection of PfLDH in saliva.

Highlights

The use of saliva in diagnosis of infectious diseases is an attractive alternative to procedures that involve blood drawing
Thirty-five per cent of the patients recruited into study tested positive for Plasmodium falciparum lactate dehydrogenase (PfLDH) ELISA in saliva
This can be attributed partly to the fact that the target analytes are usually present in Statistical analysis The F test was used to determine whether there is a significant difference between levels of PfLDH in saliva of patients with moderate to high parasitaemia > 1000 parasite/μl and those with low parasitaemia < 1000 parasites/

Summary

Introduction

The use of saliva in diagnosis of infectious diseases is an attractive alternative to procedures that involve blood drawing It promises to reduce risks associated with accidental needle pricks and improve patient compliance in malaria survey and drug efficacy studies. Lack of diagnostic support in field and resource-limited settings has led to over-reliance on clinical assessment This practice has led to over-diagnosis of populations at risk posing a risk of rapid development of anti-malarial drug resistance [4, 5]. The technique is limited due to infrastructural and technical requirements that are not always available in resource-limited settings In such settings, the adoption of malaria rapid diagnostic test (MRDT) has greatly improved access to diagnosis. A positive correlation would provide a useful non-invasive assay that can be used to predict parasite load in malaria surveys of healthy populations, population-wide monitoring of the impact of anti-malarial interventions as well as in drug efficacy studies where repeated sampling of study cohorts is required

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