● A wide range of organisms belonging to `color{Violet}"bacteria"`, `color{Violet}"viruses"`, `color{Violet}"fungi"`, `color{Violet}"protozoans"`, `color{Violet}"helminths"`, etc., could cause diseases in man.

● Such `color{Violet}"disease causing"` organisms are called `color{Violet}"pathogens"`.

● All `color{Violet}"parasites"` are therefore `color{Violet}"pathogens"` as they cause `color{Violet}"harm to the host"` by living in (or on) them.

● The `color{Violet}"pathogens"` can enter our body by various means, multiply and interfere with normal vital activities, resulting in `color{Violet}"morphological"` and `color{Violet}"functional damage"`.

● Pathogens have to `color{Violet}"adapt to life"` within the environment of the host.

● `color{brown}"For example"`, the pathogens that `color{Violet}"enter the gut"` must know a way of surviving in the stomach at `color{Violet}"low pH"` and resisting the various `color{Violet}"digestive enzymes"`.

● `color{brown}"𝘚𝘢𝘭𝘮𝘰𝘯𝘦𝘭𝘭𝘢 𝘵𝘺𝘱𝘩𝘪"` is a pathogenic bacterium which causes `color{Violet}"typhoid fever"` in human beings.

● These pathogens generally enter the `color{Violet}"small intestine"` through `color{Violet}"food and water"` contaminated with them and migrate to other organs through `color{Violet}"blood"`.

● `color{Violet}"Sustained high fever"` (39° to 40°C), `color{Violet}"weakness"`, `color{Violet}"stomach pain"`, `color{Violet}"constipation"`, `color{Violet}"headache"` and `color{Violet}"loss of appetite"` are some of the common symptoms of this disease.

● `color{Violet}"Intestinal perforation"` and `color{Violet}"death"` may occur in severe cases.



● Typhoid fever could be confirmed by `color{Violet}"Widal test"`.

● A classic case in medicine, that of `color{Violet}"Mary Mallon"` nicknamed `color{Violet}"Typhoid Mary"`, is worth mentioning here.

● She was a `color{Violet}"cook by profession"` and was a `color{Violet}"typhoid carrier"` who continued to `color{Violet}"spread typhoid"` for several years through the food she prepared.

● Bacteria like `color{brown}"𝘚𝘵𝘳𝘦𝘱𝘵𝘰𝘤𝘰𝘤𝘤𝘶𝘴 𝘱𝘯𝘦𝘶𝘮𝘰𝘯𝘪𝘢𝘦"` and `color{brown}"𝘏𝘢𝘦𝘮𝘰𝘱𝘩𝘪𝘭𝘶𝘴 𝘪𝘯𝘧𝘭𝘶𝘦𝘯𝘻𝘢𝘦"` are responsible for the disease `color{violet}"pneumonia"` in humans.

● Here the organisms infect the `color{violet}"alveoli (air filled sacs)"` of the lungs.

● As a result of the infection, the alveoli get `color{violet}"filled with fluid"` leading to severe `color{violet}"problems in respiration"`.



● The symptoms of pneumonia include `color{violet}"fever"`, `color{violet}"chills"`, `color{violet}"cough"` and `color{violet}"headache"`.

● In severe cases, the `color{violet}"lips and finger nails"` may turn `color{violet}"gray to bluish"` in colour.

● A healthy person acquires the infection by `color{violet}"inhaling the droplets"`/`color{violet}"aerosols"` released by an infected person or even by `color{violet}"sharing glasses"` `color{violet}"and utensils"` with an infected person.

● `color{violet}"Dysentery"`, `color{violet}"plague"`, `color{violet}"diphtheria"`, etc., are some of the other bacterial diseases in man.

● Many `color{violet}"viruses"` also cause `color{violet}"diseases"` in human beings.

●`color{brown}"Rhino viruses"` represent one such group of viruses which cause one of the most infectious human ailments – the `color{violet}"common cold"`.

● They infect the `color{violet}"nose and"` `color{violet}"respiratory passage"` but not the lungs.

● The common cold is characterised by `color{violet}"nasal congestion"` and `color{violet}"discharge"`, `color{violet}"sore throat"`, `color{violet}"hoarseness"`, `color{violet}"cough"`, `color{violet}"headache"`, `color{violet}"tiredness"`, etc., which usually last for `color{violet}"3-7 days"`.

● `color{violet}"Droplets"` resulting from `color{violet}"cough or sneezes"` of an infected person are either inhaled directly or transmitted through `color{violet}"contaminated objects"` such as pens, books, cups, doorknobs, computer keyboard or mouse, etc., and `color{violet}"cause infection"` in a healthy person.