Viral infection	Causative organism	Clinical features	Neuropsychiatric manifestations	Diagnosis
Herpes simplex virus (HSV) infection	HSV-1 HSV-2	Herpetic stomatitis, herpes labialis, keratoconjunctivitis and encephalitis. Genital herpes, systemic infections in immunocompromised host.	Hypomania, personality changes, dysarthria, seizures, autonomic dysfunction, ataxia, delirium, and psychosis. Rarely; Kulver-Bucy syndrome	Detection of HSV DNA by polymerase chain reaction.
Epstein-Barr Virus infection	EBV (one of the herpes viruses)	Acute febrile illness known as infectious mononucleosis (glandular fever), headache, malaise, sore throat, cervical lymphadenopathy, slenomegaly, mild hepatitis.	Depression, chronic fatigue syndrome,	Atypical mononuclear cells in peripheral film. Positive Paul-Bunnel reaction detecting heterophile antibodies (IgM).
Cytomegalovirus infection	CMV (one of the herpes viruses)	Usually asymptomatic (>50% of the adult population has evidence for latent infection). Symptoms identical to infectious mononucleosis. Fever, hepatitis with or without jaundice, occasionally lymphocytosis with atypical lymphocytes.	Encephalitis in immunocompromised patients, depression, dementia.	Serological test: Latent (IgG) or primary (IgM) infection. Polymerase chain reaction. Direct immunofluorescence: characteristic intracellular “owl-eye” inclusions. Negative Paul-Bunnell test.
Measles	Paramyxo viruses	Incubation period: 8 - 14 days. Two distinct phases: The pre-eruptive and catarrhal stage, the eruptive or exanthematous stage.	Post infectious encephalomyelitis, subacute measles encephalitis, and subacutesclerosingpanencephalitis which occurs 7 - 10 years following measles (cognitive dysfunction, behavior change, headache, myoclonic jerks).	Most cases diagnosed clinically
Flaviviruses infections (a group of 6o viruses)	Dengue	Incubation period is 5 - 6 days. Asymptomatic or mild infections are common. Can occur in two clinical forms: 1.calssic dengue fever, 2. Dengue haemorrhagic fever.	encephalitis, delirium, confusion and seizures	Tissue culture in sera obtained the first few days of infection is diagnostic. ELISA, Complement-fixing antibodies. Leucopenia, thrombocytopenia.
Flaviviruses infections (a group of 6o viruses)	West Nile Virus	Can be symptomless. Mild febrile illness. Severe symptoms may include meningitis and encephalitis.	Difficulty with memory and word-finding, fatigue, extremity weakness, headache, personality changes, irritability and aggression.