Abstract:
Background: 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 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.
Methods: Matched 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.
Results: One-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].
Conclusion: The 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.