Inflammation of the liver.
Depends on the etiology, many infections can involve the liver, the main ones being viral.
Brucellosis, Cytomegalovirus, Epstein-Barr virus, Hepatitis A, Hepatitis B, Hepatitis C, Hepatitis D, Hepatitis E, Herpes simplex virus, Leptospirosis, Lyme disease, Q fever, Syphilis (esp in HIV), Yellow fever at a minimum, the number of infections that can acutely involve the liver is, well, all of them. Just about.
Depends on the infection.
In HIV patients with unexplained increased ALT, chronic Hepatitis E was found in 2.6%, so it wasn't so unexplained, was it?
Do not forget your damn vaccines. Have you had your A? Your B? No? Moron.