viral infection causing chronic disease. hepatitis viruses, influenza virus h1n1, flu, cell infect organism, aids

abstract aids background bacteria bacterium biology blood blue body cancer causing cell chronic disease epidemic fever flu genetic germ h1n1 health healthcare hepatitis hiv human illness illustration immune infect infection infectious influenza life macro medical medicine microbe microbiology microorganism microscope microscopic molecule organic organism outbreak pandemic research retrovirus science scientific sickness viral virus viruses