Dynamics of disease  transmission  

High yield chapter -so much MCQ.

Dr Abhijit Vinodrao Boratne  

MBBS, MD, PGDHPE, ACME, MIPHA  

Additional Professor  Dept. of Community & Family Medicine  AIlMS, Deoghar  

Source and reservoir of infection  

‣ Source - The person, animal, object or substance from which an infectious agent passes through or is disseminated to the host. 

‣ Reservoir - Any person animal, arthropod plant, soil or substance in which infectious agent lives and multiplies on which it depends primarily for survival & where it reproduces itself in such a manner that can be transmitted to a susceptible host.  

Reservoirs & Sources  

‣ Hookworm - reservoir man, source - soil  

‣ Tetanus - reservoir & source - soil  

‣ Typhoid - reservoir - case or carrier ,  source- faeces, urine, milk  

‣ Homologous - man(Victim) eg. V. cholera  

‣ Heterologous - animals sources eg.  salmonella  

Types of reservoir  

1. Human reservoir - 

A. cases - a person in the population or study group identified as having the particular disease or health disorder or condition under investigation 

‣ Spectrum of disease ⁃ clinical, subclinical and latent 

Viva Qn

‣ Primary case - first case 

‣ Index case - first noted by an investigator 

 ‣ Secondary case -infected by primary case  

Q) opposite of word case → control

case - person having that disease

control → having no ds.

‣ B. Carriers - an infected person or animal that harbours specific infectious agent in the absence of clinical disease & serves as potential source of infection.  

Typhoid Mary  
Classification of carriers  

A. Type 

a) Incubatory 

b) Convalescent- he became alright, but yet can transmit ds to other 

c) Healthy 

 B. Duration 

 a)Temporary 

 b) Chronic 

 C. Portal of exit 

a)  Urinary eg. E. coli,

b) Intestinal 

c) Respiratory

d) others  

MCQ

Type  

‣ Incubatory carriers -measles, polio, pertusis 

‣ Convalescent - typhoid fever, dysentery 

‣ Healthy carrier - polio, cholera, meningococcal meningitis 

‣ Temporary - incubatory, convalescent & healthy 

‣ Chronic -typhoid & hepatitis 

‣ Portal of exit- urinary, intestinal, respiratory & nasal  

2. Animal reservoir  

‣ Zoonosis - Rabies, Yellow fever, Influenza  

‣ Ornithosis and arboviruses - birds-  histoplasmosis, mosquito borne encephalitis  

3. Reservoir in non living things  

Soil and inanimate matter - tetanus, anthrax,  mycetoma  

Modes of transmission  

1. Direct 

1. Direct 

2. Droplet 

3. Contact with soil 

4. Inoculation in to skin or mucosa 

5. Trans-placental (vertical)  

2. Indirect 

1. Vehicle borne 

2. Vector borne Mechanical a. Biological b. 3.Air borne a. Droplet nuclei b. ust 4. Fomite borne 5.Unclean hands and fingers  

Direct transmission  

‣ Direct contact - skin to skin, mucosa to mucosa Eg: STD, AIDS & Leprosy ‣ Droplet infection -droplets of saliva or nasopharyngeal secretions (overcrowding, lack of ventilation) <5mm Eg: Tuberculosis, Diphtheria & Meningococcal meningitis  

‣ Contact with soil - Hookworm, Tetanus, Mycosis ‣ Inoculation in to skin or mucosa- Rabies by saliva, Hepatitis B by syringes and needles ‣ Trans-placental (vertical)- TORCH, syphilis  

B. Indirect transmission - 5F's - Food, Flies Fingers, Fluids, Faeces  

1. Vehicle borne - water, food, fruits vegetables, ice, blood, S. aureus in food, Hepatitis A with water organ transplacentation - CMV 

2.  Vector borne - an arthropod that transmits infectious agent to a susceptible individual  

Epidemiological classification of vector borne diseases 

 1.By Vector ‣ Invertebrate type -flies, mosquitoes, ticks, mites, Cyclops ‣ Vertebrate type-Mice, rodents 

 2.By transmission chain ‣ Man & non-vertebrate man-arthropod-man- malaria ‣ Man, non vertebrate and vertebrate man- arthropod-man -plague ‣ Man & 2 intermediate hosts-man-cyclops- fish-man-fish tape worm  

3. By methods vector transmit 

 ‣ Biting Regurgitation 

 ‣ Scratching 

 ‣ Contamination with fluids 

 4.By methods vectors are involved in transmission 

 ‣ Mechanical -soiled proboscis or feet-typhoid 

 ‣ Biological  

Biological transmission  

Infectious agent - multiplies or develop within IP ‣ Propagative -multiplies -Plague in rat flea ‣ Cyclo-Propagative -multiplies & develops- malaria in mosquito ‣ Cyclo-developmental -develops-Microfilaria in man ‣ Trans-ovarian - Dengue ‣ Trans-stadial -Ticks-Tyhus, Paralysis Encephalitis  

Airborne  

‣ Droplet nuclei-1-10microns -dried residue of droplets ‣ Evaporation of droplets -sneezing &coughing ‣ Generated automated devices ‣ Accidently in lab ‣ Tuberculosis ,Influenza, Measles & resp infections ‣ Dust -Streptococci, Fungal spores- Coccidiodomycosis, fever  

Fomite- borne  

‣ Inanimate objects -other than food & water- towel, hand kerchief, spoon, instruments, toys -Diptheria, skin & eye infections Typhoid & Hepatitis A ‣ Unclean hands & fingers - hand to mouth - intestinal parasites Hepatitis A