Source of infection

UG Medical Microbiology, unit 1

1. SOURCE OF INFECTION DR. S. DHIVA ASSISTANT PROFESSOR IN MICROBIOLOGY SREE NARAYANA COLLEGE, ALATHUR, PALAKKAD

2. Definition An object in which the agent of infection lives and propagates. Source can either be a living organisms or an inanimate object, that provides a pathogen an adequate condition for survival and multiplication and an opportunity for transmission Such source is called reservoir of infection Sources may be - human beings, animals, insects, soil, water and food

3. Human body itself Is a reservoir of disease Harbors microorganisms and transmits directly or indirectly to others People with signs and symptoms of disease may transmit the infection to others Some may transmit infection to others without exhibiting sign or symptoms They are called carriers, living reservoir of infection Some carriers have inapparent infection - where no clinical sign and symptoms appears Some carriers have latent infection, carry disease during symptom free stages or during incubation period before symptoms appear or during recovery ( convalescent period) Ex. AIDS, Diptheria , typhoid fever, hepatitis, gonorrhea, amoebic dysentery and streptococcal infections HUMAN RESERVOIR

4. ANIMAL RESERVOIR Both wild and Domestic animals acts as reservoir Diseases that occur primarily in animals can be transmitted to humans are called zoonotic diseases Ex. Rabies, found in bats, skunks, foxes, dogs and cats Lyme disease found in field mice Drinking contaminated cow’s milk leads to tuberculosis and brucellosis Transmission of infection from animals to humans takes place either by direct contact or by contact with their waste such as cleaning of litter box, cage, etc., By contamination of food and water By air from contaminated hides, fur or feathers (inhaling dust contaminated excreta) leads to Q fever, anthrax, etc., By consuming infected animal products, or by insect vectors

5. Non living Reservoirs Air Soil Water Food

6. AIR Infectious dust carrying droplets or droplet nuclei acts as source of infection Dust carrying nasal droplets, excreta, or dried infectious particle remains in the particular environment for a particular period of time Based on the flow of air these infectious particle move to other areas and cause infection to susceptible individuals

7. SOIL Soil harbours pathogens such as fungi , which causes mycosis including ringworm and systemic infection Bacteria such as C l.botulinum which causes botulism and Cl. tetani that causes tetanus, both organisms are found in the intestine of horses, cattles as normal flora These pathogens are commonly found in the places where these faeces are used as fertilizers

8. WATER Water that has been contaminated by the faeces of human and other animal acts as reservoir of several pathogens These pathogens are responsible for gastrointestinal infection or diseases Ex. V. cholera, which causes cholera Salmonella typhii which causes typhoid

9. FOOD Improperly prepared or stored food acts as reservoir for food borne pathogens which leads to food poisoning Ex. Trichimosis , Salmonella, amoebiasis , etc., INSECT VECTORS Spreads organisms from one host or another Ex. Mosquito, ticks, fleas, mites or bitting flies (equine encephalitis and malaria, lyme disease, Rocky Mountain spotted fever, plague, scrub typhus and tularemia