Indirect Transmission of diseases

Various methods of transmission of diseases indirectly are depicted in the slide along with their epidemiology and distribution.

1. Indirect transmission of diseases Mohsi n Ahmed Ansari II MBBS

2. Infectious agent must be capable of surviving outside the human host in the external environment and retain its basic properties of pathogenesis and virulence till it finds a new host. Viability of the agent depends upon: Characteristics of agent The inanimate object Environmental factors (temp, humidity) Drug resistance.

3. I n a nutshell Flies Fluids Foods

4. Transmission

5. 1. Vehicle borne transmission Transmission through the agency of water, food (including raw vegetables, fruits, milk and milk products), ice, blood and other biological products. Pathogen may develop within the vehicle (S. aureus in food) or may passively be transmitted (hepatitis A virus in water)

6. Epidemiology of vehicle borne diseases Heavy dose of contamination: outbraeak may be explosive (cholera and hepatitis A) Confined to those on exposure to the contaminated vehicle. Primary casers my be obscured when secondary cases occur Can be widespread (eg: outbreaks of food poisoning) May not be aleways possible to isolate the pathogen in the incriminated vehicle (typhoid bacilli in contaminated water) When the vehivel is controlled / whotdrowan the epidemic subsides ( epidemics of cholera) The common sources of infection os often traceable.

7. 2. Vector borne transmission Vectors are defined as an arthropod or any living carrier (eg: snail) that transport an infectious agent to a susceptible individual. Transmission maybe mechanical or biological

8. Epidemiological classification of vector borne diseases: Transovarian transmission : Transmission of the infected agent from infected female to her progeny in the vector Transstadial transmission : transmission of the agent from one stage of the life cycle to another as for example nymph to adult Factors influencing vector borne transmission: Host feeding preferences Infectivity Susceptibility Survival rate Domesticity Suitable environmental factors

9. 3. Air borne transmisson Droplet nuclei: Tiny particles (1-10 microns) Formed by evaporation, aerosols, accidentally (lab facilities, etc.) Disseminated by air currents Particles less than 5 microns are liable to infect the alveoli of the lungs (eg: tuberculosis, influenza, chickenpox, measles, Q fever etc.) Dust: Larger droplets that settles down on the floor, carpets, furniture, clothes etc. Spread during act of sweeping, dusting, bed making, etc. also blown though wind from the soil. Eg: Coccidioidomycosis Dust may also settle on uncovered food and milk – Nosocomial infection in hospitals

10. Fomite borne transmission Definition: inanimate articles or substances other than water or food contaminated by the infectious discharges from a patient and capable of harbouring and transferring the infectious agent to a healthy person. Include soiled clothes, towels, linen, handkerchiefs, cups, spoons, pencils, books, toys, drinking glasses, door handles, etc. Disease like diphtheria, typhoid fever, bacillary dysentery, hepatitis A, eye and skin infections are known to be transmitted via fomites.

11. Survival of microbes on hard inanimate surfaces

12. 5. Unclean hands and fingers Most common medium of transmission by which pathogens are transferred to food from the skin, nose, bowel etc. as well as from other foods. May be both directly (hand to mouth) or indirectly Eg: staphylococcal and streptococcal infections, typhoid fever, dysentery, hepatitis A & intestinal parasites. Unclean hands and fingers indicates lack of personal hygiene which maybe coupled with poor sanitation favouring person to person transmission of infections. (Eg: 1984 dysentery epidemic in India

13. references Park’s textbook of Preventive & Social medicine Survival of pathogens on inanimate objects https :// bmcinfectdis.biomedcentral.com/articles/10.1186/1471-2334-6-130 www.bing.com/images

14. Group members Pranshu Dwivedi – Roll no. 11 Siddharth Gurung – Roll no. 12 Mohsin Ahmed Ansari – Roll no. 13 Gemin Langkam – Roll no. 14 Radhe Nampi – Roll no. 15 Yanu Kodak – Roll no. 16 Nani Kuru – Roll no. 17 Marjum Haji – Roll no. 18 Tilling Rema – Roll no. 19 Tadar Matma – Roll no. 20