Mode of Transmission

Subject: Community Health Nursing I

Overview

Modes of Disease Transmission

Depending on the host infecting agents, portal of entry, and local ecological conditions, communicable diseases may be transmitted from the reservoir or source of infection to a in different ways.

Classification of Modes of Transmission

  • Direct Transmission
    • Direct Contact
    • Droplet Infection
    • Contact with Contaminated Soil
    • Inoculation into Skin or Mucosa
    • Transplacental (vertical)
  • Indirect Transmission
    • Food
    • Water
    • Blood
    • Organ Transplant
    • Vehicle Borne Transmission
    • Vector Borne Transmission
      • Mechanical Transmission
      • Biological Transmission
    • Air borne Transmission
      • Droplet Nuclei
      • Infected Dust
      • Air Pollution
    • Fomite Borne Transmission
      • Unclean Hand/Fingers

                                                                                               

Direct Transmission

Direct transmission occurs when the disease agent contacts a vulnerable host directly, without the need of an intermediary host, objects, or substance.

  • Direct Contact
    • The infection may be transmitted by direct contact from skin to skin, mucosa to mucosa or mucosa to skin of a person like in touching, kissing, sexual intercourse etc. Example: STDs, HIV/AIDS, scabies, skin and eye infections
  • Droplet Infection
    • This is the direct projection of a spray of droplets of saliva and nasopharyngeal secretions during coughing, sneezing, speaking or spitting. The expelled droplets may impinge or stick directly upon conjunctiva or respiratory mucosa or skin of close contact. The droplet spread is usually limited to a distance of 30 to 60 cm between the service and the host. Example: TB, diphtheria, whooping cough, common cold etc.
  • Inoculation
    • The disease agent may be inoculated directly into skin or mucosa/ mucus membrane.Example: rabies virus by dog bites, hepatitis B through contaminated needles and syringes.
  • Contact with Contaminated Soil
    • The disease may be acquired by direct exposure of susceptible tissue to the disease agent in soil, compost or decaying vegetable matter (saprophytic existence). Example: hookworm larvae, tetanus, mycosis (fungal infection).
  • Transplacental or Vertical Transmission
    • Disease transmitted through placenta from mother to fetus is transplacental transmission. Example: Hepatitis, B, AIDS, Syphilis, TORCH (Toxoplasmosis, Rubella, Cytomegalovirus, Herpes virus). Some non living agents like thalidomide can be transmitted vertically causing malformations of embryo. Transplacental immunization is immunization of fetus through the mother. For example, two doses of tetanus toxoid to the pregnant mother immunize the fetus against neonatal tetanus.

Indirect Transmission

Among the 5Fs in indirect transmission are:

  • Flies
  • Fingers
  • Fomites
  • Food
  • Fluids

Infections spread indirectly through indirect methods. The ability of the infectious agents to survive outside of the human host in the external environment and maintain their fundamental pathogenesis and virulence characteristics until they find a new host is a crucial need for indirect transmission.

Vehicle Borne Transmission

It suggests that disease agents are spread through

  • Staphylococcal food poisoning can be brought on by food, including raw fruits and vegetables, milk, and milk products.
  • Typhoid, cholera, typhoid fever, polio, and Hepatitis A can all be brought on by water.
  • Hepatitis B and syphilis are transmitted through blood.
  • Cytomegalovirus can be brought on by kidney transplant.

Vector Borne Transmission

The term "vector" refers to any arthropod or live carrier, such as a mosquito, sand fly, fly, mouse, etc., that transmits an infectious agent to a susceptible individual.

classification of vector-borne diseases

Using a vector-involvement approach

  • Mechanical Transmission
    • A crawling or flying arthropod mechanically transmits the agent by soiling its foot or proboscis with dirty materials, passing through the GI tract, then passively excreting it. In the host, there is no multiplication or development. For instance, mosquitoes and houseflies can spread diseases like giardiasis and amoebiasis.
  • Biological Transmission
    • In the vector, the infectious agent either replicates, develops, or does both. Prior to transmission, there must be an incubation period for the vector. Three types of biological transmission exist.
  • Propagative
    • The agent doesn't change in form; it only multiplies in vector. example: plague bacilli in rat fleas.
  • Cyclo-Propagative
    • The agent multiplies and changes shape. For instance, malarial parasites in mosquitoes.
  • Cyclo Development
    • The disease agent just develops; it does not multiply. Consider a mosquito or a microfilarial parasite.

By vector

  • Invertebrate
    • Acarina: Ticks and mites, Copepoda: Cyclops, Orthoptera: Cockroaches, and Flies and Mosquitoes
  • Vertebrate
    • Disease brought on by mice, rats, and bats

By Transmission Chain

  • Man And a Non-Vertebrate Host
    • Malaria, the man-arthropod cycle Schstosomiasis, man-small-man
  • Man, Another Vertebrate Host And a Non Vertebrate Host
    • Bird - arthropod - man encephalitis and mammal - arthropod - plague
  • Man and Two Intermediate Hosts
    • Cyclops, fish, man, and tape worm Clonorchis sinesis, the man-snail-fish-man,

Others

  • Pathogens are bitten and intravenously inoculated. such as ticks, fleas, and mosquitoes.
  • Defecation
    • The feces were being rubbed into the skin abrasions. For instance, epidemic typhus and trench disease are spread via infected louse excrement.
  • When an infected arthropod is crushed, its body fluid can contaminate the host's damaged skin. For instance, when an infected louse is crushed in the scalp, relapsing fever can spread.

Air Borne Transmission

When bacteria or viruses travel on dust particles or on tiny respiratory droplets that may become aerosolized when people sneeze, cough, laugh, or exhale, this is known as airborne transmission. Three agents are used in airborne transmission to spread disease.

  • Droplet Nuclei
    • Smaller than 5u in diameter, the contaminated droplets will be floating in the air as they exit the reservoir through the mouth or nose. In the meantime, the moisture content evaporates, leaving only a mass of viruses as residue. These infections are then dispersed by the air current to various locations, causing epidemics and pandemics. As an illustration, consider influenza, SARS, measles, tuberculosis, etc.
  • Infected Dust
    • The spread of cross-infections in the wards is facilitated by the infected droplets, larger than 10 in diameter, which will settle on the floor and become a part of the floor, bed-making, or whenever wind blows, the dust is expelled into the atmosphere. For instance, staphylococcal and streptococcal infections, pulmonary tuberculosis, etc.
  • Air Pollution
    • For instance, the Bhopal gas tragedy, bronchitis, bronchial asthma, hay fever, pneumoconiosis, allergic respiratory diseases, etc.

 

Fomite Borne Transmission

Fomites are inanimate objects or substances—other than water or food—that have been contaminated by an infected patient's discharge. Fomites are things like filthy towels, linen, handkerchiefs, mugs, spoons, and clothing. For instance: eye and skin infections, Hepatitis A, Diphtheria, Typhoid, etc.

  • Unclean Hands and Fingers

Lack of personal hygiene is demonstrated by dirty hands and fingers. The most frequent method for transferring pathogenic agents into the body from the skin, nose, and gut is through the hands. Both directly (hand to mouth) and indirectly are involved in the transmission. For instance, typhoid fever, diarrhea, streptococcal infections, etc.)

 
Things to remember

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