Infectious Diseases Spread Through Saliva

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If you've ever heard of "mono," then you know of at least one "kissing disease." Mononucleosis, or mono, is probably one of the most well-known infectious diseases among adolescents. While many people know that they can acquire a sexually transmitted disease from intercourse, there are also many infections that can be spread through mere kissing alone.

Infectious Diseases in Saliva

Infectious diseases can be spread through several routes of transmission.

“Oral transmission” refers to spreading of microbes through saliva or shared foods and drinks. When a person accidentally consumes microbe-contaminated items, such as saliva during kissing, the swallowing action of the tongue wipes the microbes against the back of the throat, allowing the microbe to enter the body. Infections, such as mononucleosis, caused by Epstein-Barr virus (EBV), and cytomegalovirus (CMV) are examples of infections spread via oral transmission from virus-containing saliva.

Other infectious microbes that spread through saliva do so by sticking to the inner surface of the cheeks and mouth, the tongue, or teeth. An example is the bacterium Streptococcus, which can cause an array of infections, including gum disease and strep throat.

An important thing to keep in mind is that the surfaces of the respiratory tract (nose, mouth, and throat) are continuous and made up of similar tissues.

As a result, microbes that are found in the saliva can generally be found in other parts of the respiratory tract, including the nose and throat. Therefore, even colds and flu (and other respiratory infections) can potentially be spread through the saliva.

Infectious Diseases From Mouth Sores

Certain infections causing ulcerations in the mouth can also be spread through kissing.

These include cold sores and hand, foot, and mouth disease.

Cold sores are caused by the herpes virus, usually herpes simplex virus-1 (HSV-1). While related, this is different from herpes simplex virus-2 (HSV-2), which is more generally associated with genital herpes. In contrast to infections spread through the saliva, HSV-1 is spread through open cold sores on the lips or near the mouth. Although the infection is contagious through all stages of a cold sore, the infection is most contagious when the sore is open and leaking fluid.

Hand, foot, and mouth disease, caused by Coxsackie virus, is another infectious disease that is spread through open sores in the mouth. This is a type of enterovirus, which is a common infection that has multiple strains that we all often are exposed to. This particular infection is common in kids, especially those in daycare or preschool settings. It spreads primarily via the fecal-oral route.

In contrast to cold sores and coxsackie virus blisters, canker sores have no infectious disease origin and cannot be spread through saliva or kissing.

What About HIV and Hepatitis B?

HIV and hepatitis B virus (HBV) are blood-borne and sexually transmitted infections that have been found in the saliva.

Kissing is, in general, not considered a risk factor for HIV transmission. (It would only be if bleeding occurred or open sores were present). In contrast, transmission of Hepatitis B virus through saliva has been documented, though the infection is usually transmitted through sexual contact or blood.

Meanwhile, other types of hepatitis are not related to kissing. Hepatitis A requires some form of fecal exposure (which would include contaminated water or anilingus) and hepatitis C requires blood exposure. It's, therefore, possible that Hep A or C could be transmitted through kissing if there are open sores or remnant fecal matter in the mouth, but extraordinarily unlikely.

Natural Microbial Defense Mechanisms in the Mouth

Saliva has a natural cleansing role, provided by its flushing activity. Other antimicrobial defenses in the saliva include antibodies and other antimicrobial proteins (e.g., lysozyme), and normal mouth flora (the “good” bacteria that prevents the growth of “bad” bacteria). We also have all sorts of viruses naturally in our bodies at times, including in our mouths.

The spread of infectious microbes through the saliva can occur when natural resistance in the mouth is reduced. For example, gum infections can occur in people with vitamin C deficiencies. Thrush, caused by candida (yeast) infections, is more likely to occur in people who have been taking antibiotics. 

Source:

Aronson MD, Auwaerter PG. Infectious mononucleosis in adults and adolescents. In: UpToDate. Mitty J (Ed.) 2017.

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