Saliva and infectious disease

Definition

Saliva, a derivative of blood plasma that is necessary for optimal chewing, swallowing, and speaking, can carry microbes such as streptococci, cytomegalovirus, and hepatitis types A, B, and C. Thus, infectious diseases can be transferred from one person to another in saliva.

Saliva normally keeps the tissues of the oral cavity moistened and cleared of food particles. Although saliva is 98 percent water, it also contains mucus, enzymes, electrolytes, and antibacterial agents that keep natural oral flora in check.

Causes

Saliva can spread an infectious disease by many means, including through spit, bites, kisses, sneezes, coughs, and sharing food, beverages, and personal items.

Spit. The forcible ejection of saliva is called spitting. A person may spit to remove phlegm, or they may spit to show contempt. Depending on weather conditions, spit that lands on a sidewalk, paved streets or other outdoor surfaces may sustain live pathogens for six to eight hours, creating a public health hazard. Countries such as Australia, Brazil, China, and India have addressed this health issue.

When saliva containing bacteria or viruses makes contact with another person, the microorganisms can enter the recipient’s body through wounds in the skin or through the mucous membranes of the mouth, nose, and eyes. Diseases such as tuberculosis, influenza, and hepatitis may be passed this way. To deter spitting and biting and, thus, to reduce the risk of getting infected, police and other law enforcement officers are now placing mesh hoods over the heads of combative detainees, arrestees, and prisoners as protection. Also, contemptuous spitters, in some locales, may face a criminal charge of felonious assault.

Bites. When a person’s teeth create a wound in another person’s skin, the biter’s saliva also enters that wound. There are two forms of contact: striking a person with a clenched fist that hits that person’s mouth and catches on that person’s teeth and biting another person hard enough to break their skin and draw blood. Of these wounds, 10 to 15 percent become infected; the pathogens may be aerobic or anaerobic. Diseases that may result from this transference of saliva include tetanus, tuberculosis, syphilis, and hepatitis types B and C.

Kisses. Saliva is exchanged during kissing, which can lead to diseases such as infectious mononucleosis and meningococcal disease, both of which are transmitted through the oral mucous membranes.

Sneezes and coughs. Droplets of saliva containing influenza virus or other microbes are ejected from a person’s mouth during sneezing and coughing. Another person standing within three feet of the sick person is at risk of inhaling these droplets or receiving the spray on the skin. Even if the sick person covers their sneeze or cough with their hands, the microbe-containing saliva will be transferred to whatever surface is subsequently touched, including doorknobs, writing implements, and money. Some kinds of microbes live longer than others on these surfaces and may be picked up by the next person to come in contact. Public health officials urge persons to cover their sneezes and coughs with a tissue or with their own elbow.

With the outbreak of coronavirus during the 2019 and 2020 COVID-19 pandemic, the ability of saliva to transmit certain illnesses received global attention from health officials. The knowledge of the presence of coronavirus in saliva led to the formulation of effective measures to prevent the spread of the virus, including wearing masks.

Sharing beverages. Saliva and infectious diseases can be passed by sharing beverages. Bacteria, viruses, and fungi that live in the mucous lining of the mouth, tongue, and throat may be shed in saliva that is washed back into a beverage after drinking, thus contaminating it for the next drinker. For this reason, beverages that come in containers should be poured into individual cups or glasses when serving more than one person.

Sharing food. The microorganisms in saliva may contaminate food if a utensil or piece of food (such as a carrot stick or potato chip) that has had contact with saliva or has been in the mouth is returned to a shared food supply, such as a container of dip. For this reason, one should use a spoon to place dip or sauce onto a plate for personal consumption and should not eat from a shared serving utensil.

Alaskan Natives have a cultural practice of chewing solid foods before feeding them to infants, incidentally transmitting cavity-causing bacteria and other oral pathogens to infants. To prevent the transmission of disease-causing bacteria and other pathogens, one should use a chlorhexidine mouthwash before each feeding.

Sharing personal items. Saliva is left behind on items such as eating utensils, toothbrushes, drinking glasses, and oral thermometers. When these items are put into another person’s mouth without cleaning, the pathogens in the saliva may be transferred. Dental caries, or cavities, and other microbes may be transmitted from an adult to a child when the adult puts a pacifier in their mouth to clean or moisten it before giving it to the child.

Impact

Saliva has important physiological functions, including the cleansing, moisturizing, and buffering of mucous membranes in the mouth, pharynx, and esophagus. The measurement of enzyme levels in saliva is the basis of new diagnostic tools for many diseases, including type 2 diabetes and hormone deficiencies. However, one milliliter of saliva may contain 100 billion microorganisms of 190 different types. Researchers are studying the addition of antimicrobial agents to toothpastes, mouthwashes, and artificial saliva solutions to determine their protective effects in the mouth and the rest of the body. They are also studying the preventive effects of these agents in the propagation of microbes and infectious diseases.

Bibliography

“Does Saliva Have Health Risks? 3 Ways Germs Can Spread.” Cleveland Clinic Health Essentials, 7 Apr. 2020, health.clevelandclinic.org/does-saliva-have-health-risks-3-ways-germs-can-spread/. Accessed 6 Mar. 2023

Gorbach, Sherwood L., John G. Bartlett, and Neil R. Blacklow, eds. Infectious Diseases. 3d ed. Philadelphia: W. B. Saunders, 2004.

Koo, Ingrid. "Infectious Diseases That Spread Through Saliva." VeryWellHealth, 23 Jan. 2025, www.verywellhealth.com/kiss-of-deathor-diseases-1958924. Accessed 4 Feb. 2025.

Mandell, Gerald L., John E. Bennett, and Raphael Dolin, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. New York: Churchill Livingstone/Elsevier, 2010.

Pretty, Iain, et al. “Human Bites and the Risk of Human Immunodeficiency Virus Transmission.” American Journal of Forensic and Medical Pathology 20, no. 3 (1999): 232-239.

Tenovuo, Jorma. “Antimicrobial Agents in Saliva: Protection for the Whole Body.” Journal of Dental Research 81, no. 12 (2002): 807-809.