Introduction: Infectious mononucleosis (Mono), also known as a “the kissing disease” is mainly caused by Epstein-Barr virus (90%), Cytomegalovirus (5%), Toxoplasma gondii, adenovirus, hepatitis viruses, HIV. Mono is a contagious illness, it’s very common in teens and young adults, often spread by contact way with infected saliva, blood or other body fluids. Most common symptoms include; intoxication syndrome (fever, headache, easy fatigue), cervical lymphadenopathy, adenotonsillitis, hepato- and splenomegaly, specific CBC changes. ELISA test is usually used now to confirm the etiology.

Case report: A 14 year old girl, was admitted at the infectious department of the pediatrics hospital, Ternopil. Her complaints on admission were pain in the throat which increases with swallowing, increased body temperature (38-39.3℃), easy tiredness. Anamnesis: Illness started three days before admission with a gradually onset with a headache and an increase in temperature on the first day; on the second day, there was pain in the throat which progressed on the third day. She was brought to the hospital on the third day and was admitted for further investigation. At physical examination: She was moderately grave. Tonsils were enlarged to the 3^rd degree, reddened and coated with whitish exudates, firmly connected with their surface. Lymph nodes at the anterior cervical-2cm, posterior cervical-1cm and, occipital-0.5cm, were enlarged, a bit painfull, thickened, elastic and movable. Liver was +1.5cm, painless, spleen was non-palpable. Laboratory investigation: CBC: RBC-4.3*10¹²/l, Hb-130 g/l, WBC-12*10⁹/l, eosinophil-1%, bands-10%, segmented-29%, lymphocytes-48%, monocytes-12%, ESR-6mm/hr. Biochemical blood: AST-90 U/L, ALT-92 U/L, bilirubin-13.2mmol/l. ELISA: Ig for EBV capsid antigen: IgM-0.4, IgG-1.0; Ig for CMV: IgM-4.3, IgG-1.0. Throat culture: streptococcus viridans with an intensive growth of culture and Pseudomonas aeruginosa. Ultrasound: liver +2 cm, homogeneous, spleen +1.5cm. Clinical diagnosis: Infectious mononucleosis, typical form, caused by CMV, severe course. Treatment: Clarithromycin and Ceftazidime for 7days, Dexamethasone IV for 1week, IV desintoxication, fever control. Patient’s temperature normalized on the 9^th day, lymph nodes decreased, tonsils became clean on the 11^th day.

Conclusion: Patient had a typical infectious mononucleosis caused by cytomegalovirus, complicated with a secondary bacterial infection. Course was severe and prolonged, need differentiation with diphtheria. Signs of tonsillitis were primary and adenoiditis with lymphadenopathy appeared 2-3 days of staying in the hospital. Severe complicated course of the disease demanded so long IV infusion of dexamethasone (1week) and combination of antibiotics.