Methods of transmission of infections.

                      

1. Contact Transmission

Contact transmission include direct contact or indirect contact.

Direct contact

Person-to-person transmission is a form of direct contact transmission. Here the agent is transmitted by physical contact between two individuals through actions such as touching, kissing, sexual intercourse, or droplet sprays. Contact transmission may also be site-specific; for example, some diseases can be transmitted by sexual contact but not by other forms of contact. eg. syphilis, gonorrhea

Indirect contact

 Indirect contact transmission involves inanimate objects called fomites -clothes, beddings, towels etc., that become contaminated by pathogens from an infected individual or reservoir . For example, an individual with the common cold may sneeze, causing droplets to land on a fomite such as a tablecloth or carpet, or the individual may wipe her nose and then transfer mucus to a fomite such as a doorknob or towel.

2. Inhalation (Air-borne transmission)

Respiratory infections such as influenza, tuberculosis may be spread by inhalation of droplets (airborne droplet nuclei) containing microorganisms generated during coughing, sneezing and talking. These microorganisms land on another person, entering through  conjunctivae, nasal mucosa or mouth. 

 3. Inoculation

Vector-borne transmission and infections due to animal bites like rabies are transmitted by inoculation . Vectors  that are capable of transmitting diseases are flies, mites, fleas, ticks, rats, and dogs. The most common vector for disease is the mosquito. Mosquitoes are vectors for malaria, West Nile virus, dengue fever, and yellow fever. Tetanus spores implanted in deep wounds following soil contamination is another example.

 4. Ingestion

Intsetinal infections are generally by fecal-oral route transmission where microorganisms enter the body through ingestion of contaminated food (food-borne) and water (water-borne). Unclean hands can also lead to such infections. In the intestine, these microorganisms multiply and are shed from the body in feces. In the absence of proper hygienic and sanitation practices, the microorganisms in the feces may contaminate the water supply through inadequate sewage treatment and water filtration. Diseases caused by fecal-oral transmission include diarrhea, typhoid, cholera, polio and hepatitis.

5. Congenital transmission (Perinatal Mother-to-Child Transmission (PMTCT; Vertical Transmission)

Pathogens which cross the placental barrier, infect the fetus in utero. This is also called vertical transmission. Cytomegalovirus is the most common,  Rubella virus, HIV, Syphilis, Gonorrhea  is also transmitted vertically. If it causes malformations in the fetus, such diseases are termed teratogenic infections. Rubella, cytomegalovirus, varicella, herpes simplex, toxoplasma, syphilis, etc. are teratogenic infections.

6. Iatrogenic transmission

Infections caused by medical intervention or iatrogenic infections are mostly  by inoculation. There are many organisms that can be transmitted to health care workers in a clinical setting, then it is occupational threat.

• Using unsterile syringes/equipment
• Transfusion of infected blood, use of contaminated syringes, needles etc.
• Exchange transfusion, dialysis, organ transplant surgery- increased possibilities of cases of iatrogenic Hepatitis B and C
• Laboratory personnel handling infectious material (anthrax, plague, tuberculosis)