SPREAD OR TRANSMISSION
OF INFECTION
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Pathogenic organisms
can spread from one host to another by various ways.
Inhalation
Most infections are
transmitted by the respiratory route by aerosolization of respiratory
secretions when inhaled by others: Spread of infection depends on the size of
aerosol droplets. Droplets are vary in size, in still air, a particle of 100mm
in diameter requires seconds to falls down but a 10pm particle remain airborne
for about 20 minutes, small particle even longer. When droplet particles with a
diameter of 6um or greater are usually trapped by the mucosa of the nasal
turbinates, where as particle of 0.6 to 5.0 um attach to mucous sites at
various levels along the upper and lower respiratory tract and may initiate
infection. Respiratory secretions are often transferred on hands or inanimate
objects (fomites) and may reach the respiratory tract. Clothing, handkerchiefs,
bedding, floors, furniture and household articles become contaminated with
secretions and act as reservoir of infection.
Ingestion (fecal-oral
spread)
Fecal-oral spread
involves direct or finger-to-mouth spread, the use of human feces as a
fertilizer or fecal contamination of food or water. Food handlers who are
infected with an organism transmissible by this route, when their personal
hygienic practices are very poor.
Contact
Infection may be
acquired by direct or indirect contact with the parasites. Sexually transmitted
diseases are acquired by direct contact, usually termed as contagious disease.
E.g. syphilis, gonorrhoea, and AIDS.
Blood borne transmission
Insect vectors are
responsible for bloodborn transmission. E.g. mosquito and the malarial
parasite. Presently, direct transmission from human to human through blood are
increased by the use of blood transfusions and blood products and the increased
self-administration of illicit drugs by intravenous or subcutaneous routes,
using shared nonsterile equipment. E.g. Hepatitis B and C viruses as well as
HIV are frequently transmitted in this method.
Vertical transmission
Organisms such as
rubella virus can spread from the mother to the fetus through the placental
barrier is known as vertical transmission. Other form of transmission from
mother to infant occurs by contact during birth with organisms such as group B
Streptococci, C. trachomatis and N.gonorrhoeae which colonize the vagina. The
third way of transmission is transmitted by breast milk. E.g. CMV.
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