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Saliva Biofluid: Transmission Source and Potential Diagnostic Specimens for Covid-19 – A Review

Covid-19 was first reported in Wuhan, China, due to the case of pneumonia. This virus spread through droplets from humans with or without symptoms. Angiotensin-converting enzyme 2 (ACE-2), the receptor for Covid-19, facilitates the viral spike (S) protein entry to the target cells. This virus is reported to accumulate in nasal, oral, and oropharyngeal and will further accumulate in the lungs. The number of ACE-2 receptors in salivary glands is higher than those expressed in the lungs. It was suggested that the salivary gland is a reservoir for Covid-19, especially in asymptomatic patients. ACE-2 receptors are also highly enriched on the tongue, gingiva, and the floor of the mouth. Viral RNA was also detected in saliva at high titers. The diagnosis of Covid-19 was proved using a nasopharyngeal and oropharyngeal swab. Sampling specimens requires direct contact between medical personnel and patients;thereby, it can facilitate healthcare-associated infections. Specimens collected from this area causes discomfort for the patient and may cause a risk of bleeding. In addition, those swab specimens are not desirable for monitoring the viral load of Covid-19. In contrast, taking saliva specimens is easier to carry out by patients, as well as more comfortable and non-invasive. Thereby, it can potentially reduce the risk of transmission to medical personnel. Collected information suggested that saliva is a great potential candidate for Covid-19 diagnosis and monitoring. This review aims to collect information on the potential of saliva as a diagnostic tool for Covid-19 and the impact of its transmission.