Viruses vs Bacteria
Both can make us sick, but bacteria and viruses are very different. Bacteria are small and single-celled, they are living organisms that do not depend on a host cell to reproduce.
A virus is an tiny, infectious particle that can reproduce only by infecting a host cell.
Because of these differences, bacterial and viral infections are treated very differently and which is why antibiotics only work against bacteria, not viruses.
The main viral diseases transmitted by respiratory secretions (sneezes, coughing) and by saliva drops are the flu, the mumps, smallpox (variola, already considered eradicated), rubella, measles, and SARS. The main viral diseases transmitted through blood or sexual contact are AIDS, hepatitis B, hepatitis C, HPV, and Ebola hemorrhagic fever. The main viral diseases transmitted by animal vectors are rabies, dengue fever, and yellow fever. Some viral diseases transmitted by the fecal-oral route, including contaminated food, are hepatitis A, and poliomyelitis (a disease almost eradicated in many parts of the world).
The main human bacterial infections transmitted by respiratory secretions (sneezes, coughing) and saliva are bacterial pneumonia, tuberculosis, whooping cough (pertussis), diphtheria, and bacterial meningitis. The main bacterial diseases transmitted by blood or sexual contact are: gonorrhea and syphilis. The main bacterial diseases transmitted by animal vectors are the bubonic plague, endemic typhus, and leptospirosis. Some bacterial diseases transmitted through the fecal-oral route and contaminated food are cholera and typhoid fever. Other important bacterial infections are: Hansen's disease, possibly transmitted by saliva and contact with injured skin and mucosae; trachoma, an eye disease transmitted by ocular secretions; and tetanus, which is transmitted when the etiological agent enters the body through skin wounds.