Carrier is defined as -
Ans. is 'c' i.e., Infected person harbouring infectious agent without clinical features and acts as source of infection Sources and reservoirs* Source is 'the person, animal, object or substance from which infectious agent passes to host\ i.e. man acquires infection from source.* Reservoir is 'any person, animal, insect, plant, soil or substance in which an infectious agent lives and multiplies'. Infectious agent is dependent on reservoir for survival. From reservoir it can be transmitted to susceptible host. Thus a reservoir may act as a source of infection when a person acquires infection directly from a reservoir.# Source & reservoir are same - Tetanus spores survive in soil (reservoir) and a person acquires infection directly from soil (source). So, soil acts as reservoir as well as source.# Source & reservoir different ->>In typhoid, bacillus survives and multiplies inside human cases or carriers (act as reservoir), but immediate source of infection is feces or urine of patients, or contaminated food, water or milk (act as source).# So, source may or may not be a part of reservoir. In other words reservoir may or may not act as a source.* Reservoir may be: (i) Human, (ii) Animals or bird, or (iii) Non-living things.Human reservoir# Human reservoir is the most important source or reservoir of infection. They can be divided into -1. Cases* A case is a person which is having a particular disease. Cases may be of following types -i) Clinical case# Infected case who develops clinical manifestations.ii) Subclinical case (inapparent/covert/missed/abortive case)# Infected person is asymptomatic. Baring a few e.g. measles and chicken pox, sub-clinicalinfection occurs in most cases.# Important examples are rubella, mumps, polio, hepatitis A & B, influenza, diphtheria and Japanese encephalitis.iii) Latent infection# Infectious agent lie dormant in host without any activity, e.g. Herpes simplex, Brill-zinser diseaes, ankylostomiasis.2. Carriers* A carrier is defined as "an infected person or animal that harbours a specific infectious agent in the absence of clinical disease and serves as a potential source of infection".* As a rule carriers are less infectious than cases, but epidemiologically they are more dangerous than cases because they escape recognition, and continuing as they do to live a normal life among the population or comunity, they readily infect the susceptible individuals over a wider area and longer period of time.* Carrier may be classified as followTemporary carrier* Temporary carriers shed the infectious agent for short period of time.* This category may include -1. Incubatory carriers :Measles, mumps, polio, pertussis (whooping cough), influenza, diphtheria, Hepatitis B.2. Convalescent carriers:Typhoid, cholera, diphtheria, Pertussis (whooping cough), dysentery.3. Healthy carriers:Polio, Cholera, meningococcal meningitis, Salmonellosis, diphtheriaChronic carrier* Chornic carriers excrete the infectious agent for indefinite period.* Examples : Typhoid, hepatitis B, dysentery, malaria, gonorrhoea, cerebrospinal menigitis, Diphtheria.Note: Typhoid, hepatitis B and dysentery may have both temporary as well as chronic carriers.* A carrier who acquires infectious agent from other carrier is called 'paradoxical carrier'* A carrier who acquires infectious agent due to contact with patient is called 'contact carrier'.
Person, animal or object from which infectious agent passes to host
Person, animal or object in which an infectious agent lives and multiplies
Infected person harbouring infectious agent without clinical features and acts as source of infection
A person in which infectious agent lie dormant
Epidemiology