Stages of Disease

Stages of Disease: Incubation Period Time between infection and onset of signs and/or symptoms

         Factors affecting the incubation period:  Virulence of of the pathogen Infective dose ealth of the patient!s immune system "eneration time of the pathogen Site of infection Therefore# incubation periods differ depending on the pathogen involved

         Stages of Infectious Disease:Prodromal Disease:Prodromal Period Short time of generali$ed# mild symptoms preceding illness Symptoms often include malaise and muscle aches %ot all infectious diseases have a prodromal period

         Stages of Infectious Disease:Illness Disease:Illness &ost severe stage of an infectious disease Signs and symptoms are most evident at this time Patient!s immune system has not yet fully responded Pathogen is harming the body and causing disease  ' physician typically typically sees the patient during during this stage

         Stages of Infectious Disease:Decline Disease:Decline (ody gradually returns to a normal state of health Immune response and/or medical treatment begin to affect the growth and survival of the pathogen Signs and symptoms subside The immune response and antibody titers normally pea) during this stage of infectious disease If the patient does not recover# the disease may be fatal

         Stages of Infectious Disease:*onvalescence Disease:*onvalescence This is a period of recovery  Damaged tissues and other body systems are repaired

         Factors affecting the length of the convalescence period:  'mount of damage damage %ature of the pathogen Site of infection +verall health of the patient Depending of the disease# patients may be infectious during any stage of disease including the convalesc convalescence ence period

         Portal of ,-its: Pathogens must leave the body to infect other hosts &any portals of e-it are identical to portals of entry 

         Pathogens often leave the body in:

Secretions ,arwa-# tears# nasal secretions# saliva# sputum# respiratory droplets# blood# genital secretions# and mil)  ,-cretions Feces and urine

         *hain of Infection: .eservoir of Infection &ost pathogens cannot survive for long outside of their host Pathogens encounter a wide variety of stresses in the e-ternal environment Sites were pathogens persist and go on to cause other infections are termed reservoirs of infection

         There are three maor reservoirs of human infection:  'nimal reservoirs uman reservoirs %on0living reservoirs

          'nimal reservoirs &any pathogens that infect domestic or wild animals can also infect humans Diseases that spread from animals to humans are called $oonoses or $oonotic diseases There are currently over 123 $oonotic disease )nown The animals involved serve as a reservoir of the pathogen Pathogens can be spread from animal to human through direct contact with animals and their wastes# by eating meat# and by bloodsuc)ing arthropods umans are often a 4dead0end4 host for $oonotic pathogens owever# diseases transmitted by arthropod vectors can travel from humans to animals

         $oonoses or $oonotic diseases Diseases that spread from animals to humans are called

         uman reservoirs +ther people with active infections are reservoirs of infection if the disease is a communicable disease *arriers can remain asymptomatic and infective for years 5e6g6# syphilis and 'IDS7 Some carriers go through the stages of disease while others may never develop illness at all These healthy carriers presumably have immune systems that protect them from becoming sic)  5e6g6# typhoid &ary7

         %on0living reservoirs Soil# water# and food can all harbor pathogenic microbes The bacteria that cause tetanus and botulism live in soil  8ater can contain many types of pathogens especially if contaminated by feces &eats# vegetables# and mil) can all contain microbes able to survive in such an environment

Pasteuri$ation is a method that uses heat to reduce the number of microorganisms present in li9uids such as mil)