Define Infection? describe Host-parasite Relationship.
If the host has upper hand, due to increased host-resistance it remains healthy and the parasite is either driven away or assumes a being relationship with the host.
Conversely, if the host loses the competition, the disease develops. Thus diseases are the result of competition between the host and the parasite. Disease is a malfunctioning processes caused due to continuous irritation by the parasite.
The concept of infection in the host parasite relationship is expressed in the body's normal flora, Normal flora exists on skin, oral cavity, upper respiratory tract, latter part of small intestine and the large intestine. The normal flora undergoes changes in response to the internal environment of the body.
Pathogenicity
It refers to the ability of a parasite to gain entry into host's tissues and bring about a change resulting in a change of health and thus disease. Pathogen city is a function of the invasive nature of the parasite as well as the level of resistance in the host.
Progress of Disease
Progress of Disease
Disease is a dynamic chain of events that articulates the competition between host and parasite. Most diseases follow a certain recognizable pattern of development. The various phases of disease development that appears in sequence are as follows-
1. Incubation Period - This early stage represents the time period between entry of the parasite and the appearance of symptoms. This may be short of 1-3 days as in cholera, a moderate of two weeks as in chickenpox, or as long as 3-6 years as in leprosy.
2. Period of Prodromal Symptoms - Common symptoms like nausea, fever, headache, etc. appear in this phase, indicating that the competition for supremacy has begun.
3. Period of Acme - This is the acute phase when specific symptoms appear. There may be red rashes on the body, lesions on the brain, jaundice, swollen glands in the skin, etc. High fever and chills may occur.
4. Period of Decline or Defervescence - This is the stage during which the symptoms subside.
5. Period of Convalescence - during this time the body systems return to normal.
Mode of Transmission of Disease Causing Microbes
Pathogen causing communicable diseases infect the healthy persons in two ways -
Direct Transmission of Pathogens
1. Incubation Period - This early stage represents the time period between entry of the parasite and the appearance of symptoms. This may be short of 1-3 days as in cholera, a moderate of two weeks as in chickenpox, or as long as 3-6 years as in leprosy.
2. Period of Prodromal Symptoms - Common symptoms like nausea, fever, headache, etc. appear in this phase, indicating that the competition for supremacy has begun.
3. Period of Acme - This is the acute phase when specific symptoms appear. There may be red rashes on the body, lesions on the brain, jaundice, swollen glands in the skin, etc. High fever and chills may occur.
4. Period of Decline or Defervescence - This is the stage during which the symptoms subside.
5. Period of Convalescence - during this time the body systems return to normal.
Mode of Transmission of Disease Causing Microbes
Pathogen causing communicable diseases infect the healthy persons in two ways -
- Direct Transmission of Pathogens
- Indirect Transmission of pathogens
Direct Transmission of Pathogens
Direct transmission of pathogens may occur by -
1. Contact with an infected person, example- viruses of Chickenpox, Measles, Smallpox, etc. These diseases are called contagious diseases.
2. Droplet infection occurs thorugh sneezing, counghing and spitting, e.g.- pathogens of Common cold, Influenza, Tuberculosis, Pneumonia, Diphtheria, etc.
3. Contact with soil transmits bacteria causing tetanus.
4. Through Animal bite such as bite Dog or Monkey transmit Rabies virus.
5. Through Placenta (Transplacental Transmission) - Viruses of Adis, German measles, Syphilis, etc. are transmitted.
Indirect Transmission of pathogens
In indirect transmission, the pathogens of certain diseases enter the body through some intermediate agents by following ways -
1. Through Carries or Vectors - These diseases transmitted by flies in which Housefly is the carrier of Cholera, Typhoid, Dysentery, etc. Human louse spreads Typhus and Mosquito is verctor for yellow fever.
2. Through contaminated Food and Water - Pathogens of some diseases are transmitted through contaminated food and water, e.g. Cholera, Typhoid, Diarrhoea, Hepatitis B.
3. Through Contaminated Blood or Injection Needles - These can introduce AIDS pathogen into the blood of healthy person.
4. Fomite-borne Diseases - Articles that come in contact with the patients are also source of infection. Diseases spread in this mode are called fomite - borne diseases. Patinet's clothes, utensils, currency, crockery and even doors and handles of the cupboards and windows of room may bear pathogens.
Portal of Entry
1. Contact with an infected person, example- viruses of Chickenpox, Measles, Smallpox, etc. These diseases are called contagious diseases.
2. Droplet infection occurs thorugh sneezing, counghing and spitting, e.g.- pathogens of Common cold, Influenza, Tuberculosis, Pneumonia, Diphtheria, etc.
3. Contact with soil transmits bacteria causing tetanus.
4. Through Animal bite such as bite Dog or Monkey transmit Rabies virus.
5. Through Placenta (Transplacental Transmission) - Viruses of Adis, German measles, Syphilis, etc. are transmitted.
Indirect Transmission of pathogens
In indirect transmission, the pathogens of certain diseases enter the body through some intermediate agents by following ways -
1. Through Carries or Vectors - These diseases transmitted by flies in which Housefly is the carrier of Cholera, Typhoid, Dysentery, etc. Human louse spreads Typhus and Mosquito is verctor for yellow fever.
2. Through contaminated Food and Water - Pathogens of some diseases are transmitted through contaminated food and water, e.g. Cholera, Typhoid, Diarrhoea, Hepatitis B.
3. Through Contaminated Blood or Injection Needles - These can introduce AIDS pathogen into the blood of healthy person.
4. Fomite-borne Diseases - Articles that come in contact with the patients are also source of infection. Diseases spread in this mode are called fomite - borne diseases. Patinet's clothes, utensils, currency, crockery and even doors and handles of the cupboards and windows of room may bear pathogens.
Portal of Entry
- Portal of entry represents the path taken by the parasite or infectious agent to enter the host body tissue.
- Its entry may be through one of the following routes: Oral or GI tract, respiratory passage, genitor-urinary tract, respiratory passage, genitor-urinary tract, conjunctiva of eyes and skin.
- Some bacteria can infect and multiply in any part of host body irrespective to the portal of entry.
- While certain bacteria can survive and multiply in specific tissues and only when they enter through optimal route.
Virulence - Virulence is the degree of intensity of pathogen city or the disease caused by a pathogen. It is determined by two characteristics of pathogenic organism invasiveness and toxigenicity. Invasiveness is the ability of the pathogen to enter its host and multiply. Toxigenicity is the ability of pathogen to produce toxins that cause disease or damage the host tissue.
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