How dangerous is the kissing bug?

Infectious mononucleosis, also known as Pfeiffer’s disease, mono (in the United States of America) and more commonly known as glandular fever in other English-speaking countries. It occurs most commonly in adolescents and young adults, where it is characterized by fever, sore throat, muscle soreness, and fatigue. Infectious mononucleosis typically produces a mild illness and is often asymptomatic. Mononucleosis is predominantly caused by the Epstein-Barr virus (EBV), which infects B cells (B-lymphocytes), producing a reactive lymphocytosis predominantly consisting of atypical lymphocytes, a specific type of T-cell that gives the disease its name.

The name “kissing disease” is often applied to mono in casual speech, as in developed countries it is most common at the same age when adolescents and young adults are initiating romantic behavior. This co-occurrence is not apparent in undeveloped countries, where poor sanitation and close living arrangements cause the causative virus to be spread at a much earlier age, when the disease is mild and seldom diagnosed: http://www.webmd.com/a-to-z-guides/infectious-mononucleosis-topic-overview