INFECTION AND INFECTIOUS DISEASE
Each of us is colonized with huge numbers of micro-organism ( bacteria plus viruses ,fungi , protozoa , and worms ) with which we coexist .The relationship with some of these organism is symbolic ,in which both partners benefit ,while others are commensals , living on the host without causing harm .Infection and illness may be due to these normally harmless commensals and symbiotes evading the body's defences and penetrating into abnormal sites.Alternatively ,disease may be caused by exposure to exogenous pathogenic organism which are not part of our normal flora.
The symptoms and signs of infection are a result of the interaction between host and pathogen .in some cases ,such as the early stages of influenza ,symptoms are almost entirely due to killing of host cells by the invading organism .Usually ,however ,the harmful effects of infection are due to a combination of direct microbial pathogenicity ,and the body's response to infection .In meningococcal septicemia ,for example ,much of the tissue damage is caused by cytokines released in an attempt to fight the bacteria .In a few instances , such as chronic South American trypanosomiasis ( Chaga's disease ) ,mortality is almost entirely immunological ,with the parasite itself having little effect once the inflammatory process has been triggered .
SOURCES OF INFECTION
The endogenous skin and bowel commensals can cause disease in the host ,either because they have been transferred to an inappropriate site ( e.g bowel coliforms causing urinary tract infection ) ,or because host immunity has been attenuated ( e.g candidiasis in an immune compromised host ) .Many infections are acquired from other people ,who may be symptomatic themselves or be asymptomatic carriers .Some bacteria ,like the meningococcus ,are common transient commensals ,but cause invasive disease in a small minority of those colonized .Infection with other organisms ,such as the hepatitis B virus ,can be followed in some cases by an asymptomatic but potentially infectious carrier state.
Zoonoses are infections that can be trasmitted from wild or domestic animals to man .Infections can be acquired in a number of ways : direct contact with the animal ,ingestion of meat or animal products , contact with animal urine or faeces ,aerosol inhalation ,via an arthropod vector ,or by inoculation of saliva in a bite person to person .
Most microorganisms do not have a vertebrate or arthropod host but are free-living in the environment . The vast majority of these environmental organisms are non-pathogenic ,but a few can cause human disease.Person to person transmission of these infections is rare .Some parasites may have a stage of their life cycle which is environmental ( for example the free-living larval stage of Strongyloides stercoralis and the hookworms ) even though the adult worm requires a vertebrate host.Other pathogens can survive for periods in water or soil and may be transmitted from host to host via this route ,these should not be confused with true environmental organisms.
World -wide mortality from infectious disease such as :
ORGANISM INTERACTION AND SOURCES OF INFECTION
HOST / ORGANISM INTERACTIONS
Each of us is colonized with huge numbers of micro-organism ( bacteria plus viruses ,fungi , protozoa , and worms ) with which we coexist .The relationship with some of these organism is symbolic ,in which both partners benefit ,while others are commensals , living on the host without causing harm .Infection and illness may be due to these normally harmless commensals and symbiotes evading the body's defences and penetrating into abnormal sites.Alternatively ,disease may be caused by exposure to exogenous pathogenic organism which are not part of our normal flora.
The symptoms and signs of infection are a result of the interaction between host and pathogen .in some cases ,such as the early stages of influenza ,symptoms are almost entirely due to killing of host cells by the invading organism .Usually ,however ,the harmful effects of infection are due to a combination of direct microbial pathogenicity ,and the body's response to infection .In meningococcal septicemia ,for example ,much of the tissue damage is caused by cytokines released in an attempt to fight the bacteria .In a few instances , such as chronic South American trypanosomiasis ( Chaga's disease ) ,mortality is almost entirely immunological ,with the parasite itself having little effect once the inflammatory process has been triggered .
SOURCES OF INFECTION
The endogenous skin and bowel commensals can cause disease in the host ,either because they have been transferred to an inappropriate site ( e.g bowel coliforms causing urinary tract infection ) ,or because host immunity has been attenuated ( e.g candidiasis in an immune compromised host ) .Many infections are acquired from other people ,who may be symptomatic themselves or be asymptomatic carriers .Some bacteria ,like the meningococcus ,are common transient commensals ,but cause invasive disease in a small minority of those colonized .Infection with other organisms ,such as the hepatitis B virus ,can be followed in some cases by an asymptomatic but potentially infectious carrier state.
Zoonoses are infections that can be trasmitted from wild or domestic animals to man .Infections can be acquired in a number of ways : direct contact with the animal ,ingestion of meat or animal products , contact with animal urine or faeces ,aerosol inhalation ,via an arthropod vector ,or by inoculation of saliva in a bite person to person .
Most microorganisms do not have a vertebrate or arthropod host but are free-living in the environment . The vast majority of these environmental organisms are non-pathogenic ,but a few can cause human disease.Person to person transmission of these infections is rare .Some parasites may have a stage of their life cycle which is environmental ( for example the free-living larval stage of Strongyloides stercoralis and the hookworms ) even though the adult worm requires a vertebrate host.Other pathogens can survive for periods in water or soil and may be transmitted from host to host via this route ,these should not be confused with true environmental organisms.
World -wide mortality from infectious disease such as :
- Acute lower respiratory infections
- HIV/AIDS.
- Diarrheal disease.
- Tuberculosis.
- Malaria.
- Measels.
- Tetanus.
- Whooping cough.
- Meningitis.
- Leishmaniasis.
No comments:
Post a Comment