Saliva Protection and Transmissible Diseases

Crispian Scully, Jacobo Limeres Posse, Pedro Diz Dios

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128136829
• Topic: Medicine
• Subtopic: Medical Microbiology & Parasitology

Saliva Protection and Transmissible Diseases provides a review of saliva protection, raising debate on micro-organisms potentially transmissible in saliva, and also considering the evidence on diseases that may be transmitted by kissing. Saliva is a complex body fluid essential to health, especially mastication, swallowing and speech, and hyposalivation can lead to dysfunction and even infection. More serious pathogens, such as herpes viruses and papillomaviruses can be conveyed by kissing, as can potentially lethal micro-organisms present in some saliva, such as meningococci, fungal organisms and Ebola viruses.

• Stipulates the defensive roles of saliva, an important topic not previously reviewed in-depth in literature
• Provides awareness that saliva also transmits infectious agents that can produce serious or even lethal diseases
• Gives understanding that kissing may be an at-risk practice

Chapter 1

Infection Transmission by Saliva and the Paradoxical Protective Role of Saliva

Abstract

Saliva is produced by both major (parotid and submandibular and sublingual) and minor (located in the mouth) glands, with different constituents and properties between the two groups. In the mouth saliva is a colorless, odorless, tasteless, watery liquid containing 99% water and 1% organic and inorganic substances and dissolved gases, mainly oxygen and carbon dioxide. Salivary constituents can be grouped into proteins (e.g., amylase and lysozyme), organic molecules (e.g., urea, lipids, and glucose mainly), and electrolytes (e.g., sodium, calcium, chlorine, and phosphates). Cellular elements such as epithelial cells, leukocytes and various hormones, and vitamins have also been detected. The composition of saliva is modified, depending on factors such as secreted amount, circadian rhythm, duration and nature of stimuli, diet, and medication intake, among others.

Keywords

Saliva; infection; transmission; kissing; protective; agglutinins; defensins; histatins; mucins

1.1 Saliva Composition and Secretion

Saliva is produced by both major (parotid and submandibular and sublingual) and minor (located in the mouth) glands, with different constituents and properties between the two groups. In the mouth saliva is a colorless, odorless, tasteless, watery liquid containing 99% water and 1% organic and inorganic substances and dissolved gases, mainly oxygen and carbon dioxide. Salivary constituents can be grouped into proteins (e.g., amylase and lysozyme), organic molecules (e.g., urea, lipids, and glucose mainly), and electrolytes (e.g., sodium, calcium, chlorine, and phosphates).¹ Cellular elements such as epithelial cells, leucocytes and various hormones, and vitamins have also been detected. The composition of saliva is modified, depending on factors such as secreted amount, circadian rhythm, duration and nature of stimuli, diet, and medication intake, among others.

Despite this heterogeneous composition, from the functional point of view saliva has to be considered as a unique biological fluid, and not as the sum of its biochemical components.^2,3

Salivary secretion and maintenance of a film of saliva on oral surfaces is dependent upon nerve-mediated, reflex salivary gland secretion mainly stimulated by taste. The afferent arm is mainly activated by stimulation of chemoreceptors (located in the taste buds) and mechanoreceptors (located in the periodontal ligament).⁴ Olfaction, mental processes, and stretch of the stomach are weak stimuli. Impulses affecting secretion depending on the emotional state are carried by afferent cranial nerves V, VII, IX, and X to the CNS salivary nuclei (salivation center) in the medulla oblongata. The efferent part of the reflex is mainly parasympathetic. The cranial nerve VII provides control of the submandibular, sublingual, and minor glands, whereas the cranial nerve IX controls the parotid glands. The flow of saliva is enhanced by sympathetic innervation, which promotes contraction of muscle fibers around the salivary ducts.⁵ Autonomic nerves also have an important role in both gland development and function.⁶ A dry mouth is a common experience where there is fear.

Saliva may be secreted in the absence of exogenous stimuli, then referred to as the resting or unstimulated salivary flow. In the resting state 70% of saliva is secreted by the submandibular and sublingual glands. When stimulated, the parotids provide most of the saliva and flow can increase by up to fivefold. On average, in healthy nonmedicated adults, the unstimulated and chewing-stimulated salivary flow rates are about 0.3 and 1.5 mL/min respectively,¹ but the range is wide and the limits of normality in all age groups and both genders are considerable. The normal daily production of saliva varies from 700 mL to 1.5 L. A decrease in the daily production of saliva below 500 mL/day is termed hyposecretion or hyposialia.⁷ Sialorrhea, hypersialia, hypersalivation, and ptyalism are terms used to describe salivary flow above the limits of the normal.⁸

Saliva plays a central role in oral health monitoring, regulating and maintaining the integrity of the oral hard and soft tissues.¹ It lubricates and cleans the oral cavity, possesses antibacterial, antiviral, and antifungal properties, buffers the pH, helps in chewing, speech, swallowing, and digestion, promotes taste, and contributes to the maintenance and remineralization of teeth.⁹ Moreover, it may be useful in the diagnosis of various diseases.¹⁰ The characterization by proteomic approaches—of more than 1000 salivary proteins and peptides—has allowed the identification of new salivary markers in oncology, salivary gland dysfunction, Sjögren’s syndrome, systemic sclerosis, psychiatric and neurological diseases, and dental and periodontal pathology.^11–13

1.2 Infection Transmission by Saliva and Kissing

The infectivity of microorganisms can depend on the infective load, virulence, with some, such as the notorious norovirus, being extremely contagious and able to survive weeks on surfaces and fomites.¹⁴ The detection and continuous shedding of infectious agents in saliva does not necessarily mean transmission by this route. Factors including the microorganism load, the existence of specific receptors on oral epithelial cells, and host defenses may play an important defensive role.¹⁵ Moreover, blood contamination in saliva—often invisible to the eye—is not uncommon mainly among active smokers¹⁶ and individuals with poor oral health status, those with gingivitis or periodontitis,¹⁷ and those with certain infectious diseases including human immunodeficiency virus (HIV) infection.¹⁸

Saliva contact can cause overt concern when using utensils such as cutlery or oral health devices, or if kissing a person with an infectious disease. However, the apparent absence of obvious disease does not guarantee the absence of infection or infective agents in saliva (or other body fluids): many diseases (especially viral) can be incubating or be subclinical (causing no or nonspecific symptoms or signs). Intimate mucosal contacts, particularly where there are epithelial breaches or substances that may impede salivary defenses (e.g., other body fluids), predispose to infection transmission.

Kissing is not exclusive to humans or primates, though it may have different connotations in different species.¹⁹ Theories to explain kissing behavior consider it to have an origin in social and sexual interactions, premastication of foods for newborns or even the intentional transfer of microorganisms to promote immunity.²⁰ Kissing is seen in most human cultures,²⁰ and often is part of daily behavior, playing important roles in building and maintaining interpersonal relationships^21,22 and in partner selection.²³ There are, however, huge intercultural differences related to kissing; this being considered an acceptable behavior in some cultures but totally offensive in others. For example, social kissing is an accepted form of salutation in the Mediterranean and Latin cultures, in Muslim-majority societies governed by religious law there are strict taboos about whom one can kiss, or people from some areas in Sudan refuse to kiss because they fear having their soul stolen through kissing.²⁴ In general, kissing is considered by many of the public to have few or no serious health implications.

Different types of kissing are evident and the type of kissing may well be relevant with respect to the transmission of microorganisms, as it not only determines the capacity of the kiss to spread infectious diseases,²⁵ but it can also have a bearing on the chemoprophylaxis strategy to be used in “kissing contacts” in certain situations (e.g., during an outbreak of meningococcal disease).²⁶

“Air kissing” is a cheek-to-cheek approximation; “osculum” is when the lips make contact with the body, usually the cheeks; “basium kiss” consists of mutual approximation of the lips with the mouth closed, exercising light pressure; and finally, there is the “saviolum kiss” in which, in addition to lip contact, the tongue is inserted into the opposite person’s mouth (“French kissing,” “passionate kissing,” deep kissing,” “active kissing,” or “intimate kissing”).²⁷ Finally “kiss of life” refers to direct, intense, and recurrent lip contact during mouth-to-mouth resuscitation—the therapy of choice for cardiorespiratory arrest in the community.

Couples may exchange an average of 5 mL of saliva during active kissing,²⁸ making this an activity that could favor the t...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Authors' Biographies
• Preface
• Introduction
• Chapter 1. Infection Transmission by Saliva and the Paradoxical Protective Role of Saliva
• Chapter 2. Oral Bacteria Transmissible by Saliva and Kissing
• Chapter 3. Systemic Bacteria Transmissible by Kissing
• Chapter 4. Viral Diseases Transmissible by Kissing
• Chapter 5. Fungi, Protozoa, Parasites, and Other Infective Agents Transmissible by Kissing