3. Mechanism of disease transmission: There are 3 actions (step) for disease transmission: 1. Escape of the agent from the source or reservoir 2. Conveyance of the agent to a susceptible host. 3. Entry through appropriate entry point There are 2 ways of conveyance of agent to susceptible host A.)Direct, immediate, where no vectors is involved from person to person through actual physical contact i.e. transmission through direct contact between susceptible host and reservoir (infected person, e.g. gonorrhea, syphilis.

4. B.) indirect: involve the use of vector as: 1.) Animate (living e.g. blood sucking arthropod), transmission occur after incubation period during which agent multiplies in the arthropod vector. 2.) Inanimate (non- living) which facilitate indirect transmission e.g. personal articles as keys, pens.

5. Portal of entry: The path by which infectious agent enter the susceptible host e.g. respiratory, gastrointestinal. Portal of exit: This is the pathway through which infectious agent leaves the reservoir. e.g. respiratory : (coughing, sneezing, talking) -- genitourinary: (Foley catheter, sexual transmitted disease) - skin, mucus membrane :( wounds, skin breaks, needle sticks, blood transfusion). - vertical e.g. :( transplacental transmission).

6. infectios exit Mode of transmission Site of entry Type of disease respiratoty secration inhalation of by Droplets of infectious agent respiratory tract Cold measles common Blood Intravenous (I.V) or subcutaneous inoculation skin serum hepatits Blood mosquito sucking infected skin broken by insect bite malaria infected exudates Person sexual intercourse ot person genital mucous membrane gonorrhea syphilis (stool) faece s By ingestion of infected water, foodG.I.T Typhoid fever respiratory secration Person To person by inhalation of infected droplets Upper respiratory tract Diphtheria tuberculosis (T.B)

7. Person to person or serial transfer transmission: * Def: the spread of a disease agent through contact between infection and susceptible persons. Examples of disease: measles, syphilis, gonorrhea. *mode of transmission The mechanism of transfer of an infective agent from the reservoir to a susceptible host. 1. Air –born. (Droplet infection) respiratory system. Organism contained within droplet nuclei or dust particles. (Droplet nuclei of tuberculosis). For example if the agents viral in origin affecting the respiratory tract, e.g. measles, rubella, whooping cough, mumps If the agent is bacteria in origin e.g. tuberculosis, diphtheria, sore throat (streptococcus)

8. 2. faeco-oral (gastrointestinal) transmission: The source is usually contaminated food (milk, water).flies and fingers are potent routes for transmission. Agent is mostly bacterial in origin e.g. typhoid fever, cholera, bacillary dysentery. It may also be protozoa or amoebic e.g. amoebic dysentery. 3. Sexually transmitted (venereal) disease (STDS): It occurs by closely body contact because agent is usually killed outside the body e.g. gonorrhea, syphilis, AIDS. 4. Contact transmission (other than STDs): this occur through direct contact through skin or mucus membrane. Examples: 1) some dermatological disorders (tenea vercicolor, herpes simplex by kissing) 2) Eye infection e.g. trachoma by flies or contaminated finger or towels

9. 5. animal transmitted diseases (zoonoses): Where an animal is the mode of transmission. Example: intestinal T.B. by ingestion of row milk contaminated by bovine T.B. 6. Insect – borne disease (vector- born): Examples: 1.) Malaria is protozoa diseases where the parasite multiplies inside the body of the mosquito to be mosquito bite. 2.) Yellow fever viruses.external vector- born transmission by mechanical transfer on external appendages (feet of flies), so the insect play an essential role in disease transmission.

10. 7. Vertical transmission: It occur by transmission of infectious disease from mother (one generation )to an infant (next generation). During: A) Pregnancy (through transplacental way e.g. rubella in the first three months of pregnancy) B.)Delivery (through infection e.g. toxoplasmosis, cytomegalovirus) C.) Breast feeding *transmission of HIV from mother passes to the baby: 1. during pregnancy through placenta. 2. during delivery through process contact. 3. after delivery through breast feeding

11. Transmitted disease bacteria Transmitted infection viral chlamidia HIV gonrrheaHepatits B vaginitus bacterial Genital herps trichomoniasis Genital warts syphilis Rubella Cytomegalovirus *person to person _disease agent is transmitted through contact between infected and susceptible person. _can spread by means of respiratory, anal, oral, genital routes.