Infectious Diseases: 

Sanyam Jain, Academic Content Writer

1. Organ & tissue-specific manifestation of infectious diseases

• Organ of disease manifestation

1. Target organ linked to point of entry–

• Air-borne pathogen enters through nose and infects lungs e.g. TB

• Microbe brought via food/water into mouth stay in gut e.g. typhoid

2. Target organ different from point of entry–

• HIV enters through genitals but infects lymph nodes 

• Malarial parasite enters via mosquito bite goes to liver and then attacks RBCs

• Brain fever virus enters through mosquito bite but infects brain

•  Signs & symptoms 

1. Symptoms linked to target organs (tissue-specific effects)

• Breathlessness- lungs

• Jaundice- liver

• Headaches, vomiting, fits or unconsciousness- brain

2. Immune system linked responses (common effects)

• Inflammation– recruitment of immune cells to affected site causing 

1. Local effects such as swelling and pain

2. General effects such as fever

3. HIV-AIDS: special case

• Tissue-specificity of infection produces general-seeming effects

• Minor infections become fatal due to immune function loss

• Examples: common cold becomes pneumonia, gut infection becomes major diarrhoea

• Other infections kill people suffering from HIV-AIDS

• Factors determining severity of disease manifestation

1.  Number of pathogens in the body

2. Strength of immune system of the body

3. Toxicity of pathogens entering the body

2. Principles of treatment

• Two ways to treat an infectious disease–

1. Reduce the effects of the disease 

• Symptom-directed treatment

• Do not eliminate the disease

• Provide relief to the body

• Examples: taking medicines to bring down fever or reduce pain, bed-rest to conserve energy

2. Kill the cause of disease

• Taking drugs that kill the pathogens (e.g. antibiotics)

•  Antiviral drugs are hard to make-

1. Viruses use the host cell machinery 

2. Viruses have few biochemical mechanisms of their own

• Three limitations of treatment-

1. Damage to bodily functions of patients

2. Loss of working days of patients

3. Patients act as a source of infections

3. Principles of prevention

• “Prevention is better than cure’’

• Two ways to prevent an infectious disease–

1. General for all diseases

• No exposure to pathogens by maintaining public hygiene 

1. Air-borne diseases- Avoid overcrowdedness 

2. Vector-borne infections- Live in clean environments

3. Water-borne microbes- Provide safe drinking water

• Strengthening immunity by taking proper and sufficient food 

2. Specific to each disease

• Principle of immunisation- re-exposure of pathogens to immune system results in its quick elimination

• Immune system develops memory of infection

• Vaccination– disease-specific means of prevention