⭕ Important definitions in infective epidemiology:

🔹Infectivity = Number infected / Number exposed

🔹Pathogenicity = Number diseased / Number infected

🔹Virulence = Number of serious condition & mortality / Number diseased

🔹Reservoir - It is the environment where the infectious agent lives or multiplies and from where it can be transmitted to susceptible host
Eg : Soil, humans, animals, water


Host
💥Definitive host / primary host
- Where a parasite passes through its sexual phase or attains maturity

💥Intermediate host / secondary host
Where parasite exist in larval or asexual state

💥Transport host
A host in which the organism remains alive but no develpoment occurs.

💥Obligate host
Where the organism (human, animal or plant) is the only host to the parasite

👾Case👾

🌷Index case
First case of the disease that comes to the notice of an investigator or physician

🌷Primary case
First case of the communicable disease introduced into the population unit

🌷Secondary case
One that develops after contact with primary case.

🌷Suspect case
A case which has all the clinical features of the disease but has not been diagnosed with it.


👾Carriers👾
Carriers are those who don't show the symptoms but transmit the disease

🔸Incubatory carriers
Carriers shed the organism during the incubation period of the disease, especially during later parts of it
Eg : measles, mumps, polio, pertussis, influenza, diphtheria and hep B.

🔸Chronic carriers
Shed or excrete the organisms for indefinite period
Eg : Typhoid, Hep B, dysentry, malaria, gonorrhea.

🔸Healthy carriers
Those that suffer from subclinical infections who develop a carrier state without developing the overt disease but continue to shed the organism
Eg : Polio, cholera, meningococcal meningitis, salmonellosis, diphtheria.

🔸Convalescent carrier
Those that shed the organism during recovery or convalescence
Eg : Typhoid, dysentry, cholera, pertussis, diphetheria

🔸Pseudo carriers
Carriers of avirulent organisms

🔸 Paradoxical carriers
Carriers who got infection from another carrier.

📌Infection
- Entry and development or multiplication of an infective agent in host's body

📌Infestation
Lodgement, development and reproduction of arthopods on the surface

📌Contamination
Presence of a disease agent on the body surface like clothes, toys etc. and also in substances like food and water

📌Contagion
Communication of a disease from one person to another by close contact