Classification of Infections & Disease, Host, Reservoir & Carriers of Infectious agents

Important Term & Definition

A.    Infectious agent:  a microorganism which is capable of producing an infection. (bacteria, virus,   fungi, parasite and prion)

B.     Infection:  Invasion of the body tissue of a host by an infectious agent whether or not it causes disease

Pathogenicity:  refer to the ability of microbial species to produce disease  
Virulence is the ability of the strain of microorganisms to cause disease. M.  Tuberculosis contain a strain of a varying degree of virulence. Eg. The vaccine contains avirulent strain. Virulence of a strain is not constant and may undergo  variations   
Exaltation:  enhancement of virulence of the strain of Microorganisms   
Attenuation:  reduction of virulence of a strain.
Invasiveness: the ability of an organism to spread within the host tissue after establishing infection.
Type of infection:
Primary infection:  initial infection   
Reinfection:  subsequent infection with the same parasite in the same host   
Secondary infection:  when the body resistance is lower by preexisting infectious disease, a new parasite set up an infection secondary infectiono   
Cross infection:  when a patient already suffering from a disease acquires a new infection from another host for another external source. Ex Nosocominal infection   
Iatrogenic infection:  Physician induced infection resulting from drug therapy or an investigative procedure(infection like AIDS and Hepatitis B may sometimes transmit during a procedure such as injection, blood transfusion, dialysis and surgery)
Subclinical infection:  when clinical symptoms of infection are not Apparent   
Latent infection:  following infection,  some parasites  may remain in a latent  for hidden from in host tissue and they proliferate and produce disease when the resistance of the host is loweredv  
Atypical infection:  Atypical or characteristic clinical  manifestations of the  infectious disease are not present.

C.     Infectious disease: a disorder caused by  an infectious agent/organism

D.    Infestation :  invasion of insect and worm that causes a disease to the host. Eg.  Mites,  ticks, flea, lice & worm

a.      Ectoparasites:  on the surface of  host

b.      Endoparasite:   inside the host/  lumen of host

E.     Contagious disease:  diseases which are transmitted from one person to another person either by direct contact or by casual contact with their secretion / object touched by them

F.     Communicable diseases:  disease which are transmitted by direct and indirect (disease is spread from one person to another through a variety of ways)

G.    Endemic (स्थानिक):  

    a  disease that exist  in a particular/ restricted reason/ area for population with relative Ni low level throughout the year

H.    Epidemic (महामारी):  quick and Rapid breathing of infectious disease on a mass scale

I.      Pandemic:  

        Global disease outbreak/ several countries/worldwide

J.      Exotic: a disease which is introduced from a foreign land

K.    Nosocomial infection:  infection acquired in Healthcare facility including Hospital biomedical intervention are called nosocomial infection or Healthcare-associated infection (HAI) { acquired as clinical setting}

Example urinary tract infection &upper respiratory tract infection

L.     Host (get the disease):  

a person or other(but on the living)  organism that is susceptible to or harbors an infectious agent under natural condition

a.      Primary host:  the host in which parasite residues  to sexual maturity/  primary host provides food shelter etc

b.      Intermediate host:  parasite friends only part of its life cycle or does not reach sexual maturity

M.   Reservoir 

(may be living or non-living):  Reservoir of an infectious agent is the habitat in which agents normally live, grows and multiplies to persist over a long period of time &May or may not show effect of illness

Eg:  environment (water, Soil,  plant),  human and animal

N.    Carriers:  an individual capable of transmitting pathogen/  agent without display symptoms is referred to as a carrier:

a.      Passive carriers: contaminated with agent & can mechanically transmit it to other post (the passive carrier is not infected)

b.      Active carriers: infected individual who can transmits disease to others

                                                    i.     Incubatory: who can transmit the agent during the incubation before clinical illness begins

                                                   ii.     Convalescent:  record from their illness but remain capable of transmitting to others

                                                 iii.     Chronic: who continue to herbers agent/pathogen surcharge hepatitis B &Salmonella typhi

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