Many microorganisms are harmful and adversely affect not only humans but also animals and plants as they cause disease in them. Such disease-causing microorganisms are known as pathogens. A specific disease is caused by a specific pathogen.
Disease causing Microorganisms in Humans:
Pathogens enter our body through the air, water, food, carrier (like mosquitoes) and direct contact with infected person. Microbial diseases that can spread person to person by means of air, water, food or physical contact are called communicable diseases. Some common human diseases, causative microorganisms, mode of transmission and general preventive measures are in the table below:
| Human Disease | Causative Microorganism | Mode of Transmission | Preventive Measures |
| Common Cold | Rhinovirus | Air | Keep the patient in complete isolation.
Keep the personal belongings of the patient away from those of the others.
Vaccination to be given at suitable age. |
| Influenza | Influenza virus | Air | |
| Chicken Pox | Varicella-zoster virus | Air/contact | |
| Mumps | Paramyxovirus | Air | |
| Measles | Measles morbillivirus | Air | |
| Tuberculosis (TB) | Mycobacterium tuberculosis
(a bacterium) |
Air | |
| Polio | Polio virus | Air/water | Vaccination to be given at suitable age. |
| Cholera | Vibrio cholerae bacteria | Water | Drink boiled drinking water.
Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination |
| Typhoid | Salmonella Typhi bacteria | Water | |
| Amoebiasis | Entamoeba histolytica
(a protozoan) |
Water | |
| Hepatitis A | Hepatitis A virus | Water | |
| Malaria | Plasmodium
(a protozoan) |
Female Anopheles mosquito | Use mosquito net and repellents.
Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings. |
| Dengue | Dengue virus | Female Ades mosquito |
Disease causing Microorganisms in Animals:
Several microorganisms cause diseases in animals. Some animals disease, causative microbes and preventive measures are as following:
| Animal Disease | Causative Microorganism | Preventive Measures |
| Anthrax | Bacillus anthracis | Sudden death happens in this disease but early treatment can cure anthrax.
Regular annual vaccination of animals. Isolation of infected animal. Inform to veterinary doctor. Proper disposal of left-over feed of the animal |
| Foot and mouth disease | Picornavirus | |
| Pox |
Capripoxvirus |
Disease causing Microorganisms in Plants:
Many microorganisms cause diseases in plants and reduce the yield of crops. Some common plant diseases are as following:
| Plant diseases | Causative Microorganism | Treatment |
| Leaf Curl | Fungus | Controlled by applying sulphur or copper-based fungicides |
| Yellow Vein Mosaic | Virus | There is no cure for viral diseases.
Remove and destroy all infected plants. Garden tools must be disinfected. |
| Potato Scab | Bacteria | Controlled irrigation. |
| Rust | Fungi | Use of fungicide id effective.
Remove and destroy all infected plants. |
| Citrus Canker | Bacteria | There is no cure for this disease.
Remove and destroy all infected plants. |