concept of host parasite relationship and immunity

Gnotobionts:

Animals which are free of normal flora or which live in association with one or more known normal flora are called gnotobionts. When compared with animals having normal flora gnotobionts have poor disease resistance capacity and are more suceptical to disease. Gnotobiotic animals are germ-free and they are used to study the effect of normal flora on the host.

Concept of host parasite interaction:

• Pathogenicity: Ability of microorganisms to cause disease is called pathogenicity. microorganisms which cause disease are called pathogens, not all microorganisms are pathogens.
• Virulence: Degree of pathogenicity of microorganisms is called virulence. Different pathogenic microorganisms differ in their virulencei.e some are highly virulence while other are less.
• Infection: Pathological condition due to lodgements and multiplication of microorganisms is called infection. Disease caused by infection is called infectious disease. IN order to cause infectious disease, pathogens must complete the following steps:

1. It must enter into the host.
2. It must metabolize and multiply in the host tissue.
3. It must resist host defence mechanism.
4. It must damage the host cell.

Not all diseases are infectious.eg, food poisoining caused by Clostridium botalium is the noninfectious disease. It is not caused by the growth and multiplication of Clostridium botalium in the body, rather it is caused by ingestion of performed toxin in food.

• Virulence factors: Virulence factors arevarious structure and components of microorganisms required for pathogenesis. These are microbial weapons that can combact defence mechanism of the host. Microorganisms possess different type of virulence factor, some of which are;

1. Anti-pathogenic factor: it prevents the killing of microorganism by phagocytosis of the host. WBC best anti-phagocytic factor of many bacterial cell capsule.
2. Attachment of adherence factor: Microorganism posses various structure that helps the organisms to attach to the host cell. eg, many organisms to attach to the host cell they use oili, some prganism attach with the help of capsule etc.
3. Spreading factor: Microorganism produces many enzymes which help the bacteria to spread into the host tissue. Some example streptokinase produced by Streptococcus dissolve the blood clot and helps the bacteria to spread.
4. Toxin: Some bacteria produce the poisionous substance known as the toxin. Toxin are divide into two categories they are;

• Attenuation and attenuated culture: Process of decreasing virulence of rganisms is called attenuation. it decreases the virulence but retains the immunogenic property of organisms. The bacterium whose virulence has been decreased is called attenuated bacteria or attenuated culture. There are different techniques of decrease virulence eg, aging by culture, by drying etc.The attenuated culture of bacteria and virus are used for profuction of live attenuated vaccines like BCG, Sabin's polio vaccines etc.

Immunity:

every individual possessThe some type of ressistance mechanism to protect them from disease caused by the pathogenic microorganism. This condition of resistance shown by the host to disease causing microorganisms is called immunity. The word immunity os derived froma latin word called 'immunis' which means free from burden. There are two types of immunity;

1. Innate or natural immunity: This type of immunity is present from birth and last for life. Innate immunity is provided by several components such as skin , mucus membrane, chemicals, phagocytic cel and physiological condition of the body such as body temperature. Innate immunity is usually nonspecific.
2. Acquired or adaptive immunity: This type of immunity is developed after the entry of pathogens into the host. It is provided by the antibody, this type of immunity is specific. eg, antibody produced against one organism kills only that organisms.

Antigen:

It is a protein or carbohydrate, which when introduced into vertebrate animal cause production of antibody by the host. Antigen combines with the specific antibody. To become antigenic substance it must be foreign to the host.

Antibody:

Antibody are special serum proteins which are produced when antigens enter into the host. Antibody combines specifically with antigen and removes it from blood circulation. Antibodies are serum protein globulin type. Therefore, they are also called immunoglobin. There are 5 types of antibodies i.e, Ig-A, Ig-D, Ig-E, Ig-G and Ig-M

Functions of antibody:

1. Antibody combines with antigenand removes it from the body.
2. sometimes readymade antibodies are injected into the patient to cure the particular disease.
3. Serum level of antibody is used in diagnosing of the particular disease.

References:

C.H.Collins. (1995). Microbiological Methods. Oxford Univ Press.

D.Greemwood, R. S. (2002). Medical Microbiology. London: Churchill Livingstone.

M.J.Pelezar. (1993). Microbiology. Tata McGraw hill.

M.T.Madigan, J. a. (1997). Biology of microorganisms. London: Prentice hall International Inc.

R.N.Atlas. (1984). Fundamentals and Applications. NewYork: MacMiHiam Publishing Co.