Mononucleosis, nicknamed the "kissing disease," has been found in 90 percent of adults in Mexico, specifically affecting seniors who contracted the disease as young adults.

Once the herpes-like virus is contracted, it remains hidden in the body for life, according to the Mexico news publication La Jornada.

"In an underdeveloped countries like ours, infection usually occurs in the first years of life, usually before age 5, as there is evidence that 50 percent of children in Mexico under 5 suffered from this disease," stated Luis Arturo Eguiza Salomon, professor in the Infectious Diseases Clinic of the School of Medicine at Instituto Politécnico Nacional.

As a result, a large majority of Mexicans are carriers of the disease by the time they are 18 years old.

An analysis of 100 Mexicans younger than 20 years showed they would have a 90 percent rate of infection, compared to 75 percent in the US.

The virus can be contracted at any time and anywhere.

Mono, scientifically named the Epstein-Barr virus, which is in the same family as herpes, can be contracted through an exchange of saliva, or through blood or organ transplant from an infected patient. Once infected, the incubation period is 30-50 days, but when symptoms begin showing up varies.

Some symptoms include fever, fatigue and headaches at first. If these don't subside and increase to include high fever, trouble eating, and inflammation of lymph glands, it is a sign of progression. Worsening symptoms can include jaundice, an enlarged spleen, and pain in the muscles.

The disease is one of the most common in the world, according to the Center for Disease Control. Many may have it, but never show symptoms.

There is no vaccine to prevent it, but drinking lots of fluids and taking over-the-counter medication may help relieve some of the symptoms.