There are several ways through which infection can be transferred from one person to another person. Few main are discussed here:
Contact is one of the main mode of transmission of disease. This may be direct or indirect based on the type of infection. Some sexually transmitted diseases like syphilis and gonorrhea spread by direct contact. Indirect contact involved used cloths, bath towel, handkerchief etc. which may be contaminated by infected person.
Respiratory infection such as influenza and tuberculosis are transmitted by inhalation of the pathogen. Such microbrews are shed into the environment by the patient in the form of secretion of nose or through,
Small droplets, under 0.1 mm in diameter, evaporate immediately to become minute particles or droplet nuclei (usually 1 – 10 micrometer in diameter) which remain suspended in the air for long period, acting as sources of infection.
Intestinal infections are seems to acquire generally by the ingestion of food or drink contaminated by pathogens. Infection transmitted by ingestion may be waterborne (cholera), food borne (food poisoning) or hand borne (dysentery).
In some cases pathogen directly reaches to the host tissue. Tetanus spores, rabies virus, HIV are some of the example of such infection. Blood transfusion, contaminated syringes and needles may add up in such infections.
Some pathogens can cross the placental barrier and infect the fetus in utero. This is know as vertical transmission. This may result in abortion, miscarriage or stillbirth. Live infants may be born with manifestations of disease, as in congenital syphilis.
TextBook Of Microbiology