. C OMMON D ISEASES IN H UMANS A wide range of organisms belonging to bacteria, viruses, fungi, protozoans, helminths, etc., could cause diseases in man. Such disease- causing organisms are called pathogens . Most parasites are therefore pathogens as they cause harm to the host by living in (or on) them.
The pathogens can enter our body by various means, multiply and interfere with normal vital activities, resulting in morphological and functional damage. Pathogens have to adapt to life within the environment of the host. For example, the pathogens that enter the gut must know a way of surviving in the stomach at low pH and resisting the various digestive enzymes. A few representative members from different groups of pathogenic organisms are discussed here alongwith the diseases caused by them.
Preventive and control measures against these diseases in general, are also briefly described. Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings. These pathogens generally enter the small intestine through food and water contaminated with them and migrate to other organs through blood. Sustained high fever ( ° to °C), weakness, stomach pain, constipation, headache and loss of appetite are some of the common symptoms of this disease.
Intestinal perforation and death may occur in severe cases. Typhoid fever could be confirmed by