Main content
Class 12 Biology (India)
Course: Class 12 Biology (India) > Unit 8
Lesson 1: Common Diseases in Human BeingsCommon diseases in humans
Overview of common diseases in humans and the pathogens that cause them.
This article offers a review of the following concepts:
- types of pathogens,
- details of common diseases caused by these pathogens (including symptoms and route of infection), and
- how to prevent and control the spread of disease
Key terms
| Term | Meaning |
|---|---|
| Pathogen | A disease-causing organism |
| Lymphocytes | White blood cells with immune functions |
| Infection | Invasion of the body by pathogens |
| Disease | Condition that prevents normal functioning of body |
| Symptoms | Features that indicate a disease or condition |
What is a pathogen?
Have you ever fell unwell after eating some dodgy food, or sharing space with someone who was coughing, or maybe mysteriously, right before school on a Monday?
When we "catch a bug", or "spread germs", we're actually talking about pathogens. A pathogen is an infectious organism that causes disease when it enters our bodies. They can be of many types, the most common of which are - bacteria, viruses, protozoa, worms, and fungi.
Let's take a look at some common diseases these organisms can cause.
Bacteria
There are tens of thousands of known species of bacteria (and still counting!), some of which are harmless or even useful to us. However, pathogenic bacteria can cause serious illnesses in humans, a few of which are listed below.
Typhoid
| Important questions | Information |
|---|---|
| What causes it? | Salmonella typhi |
| How can you get it? | Contaminated food or water |
| How do you check if you have it? | Widal test |
| What does it affect? | Small intestine at first, other organs later |
| What are the symptoms? | Sustained high fever (102-104 °F), weakness, stomach pain, constipation, headache, loss of appetite. |
| How bad can it get? | Intestinal perforation and death |
Pneumonia
| Important questions | Information |
|---|---|
| What causes it? | Streptococcus pneumoniae and Haemophilus influenzae |
| How can you get it? | Inhaling droplets/aerosol, sharing contaminated utensils |
| What does it affect? | Alveoli in lungs |
| What are the symptoms? | Fever, chills, cough, headache, liquid-filled alveoli in lungs |
| How bad can it get? | Gray/bluish nails and lips, respiratory distress |
Other common bacterial diseases include dysentery, diphtheria, and the plague.
Viruses
Viral infections can range from mild to very serious illnesses. In late 2019, the SARS-CoV-2 virus brought the world to a stand-still with the COVID-19 pandemic. A few other common viral diseases are listed below.
Common cold
| Important questions | Information |
|---|---|
| What causes it? | Rhino viruses |
| How can you get it? | Inhalation of infected droplets/contact with contaminated objects |
| What does it affect? | Nose and respiratory passage |
| What are the symptoms? | Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness (lasts between 3-7 days.) |
Other examples of viral diseases include dengue and chikungunya, which are spread by the bite of female Aedes mosquitoes.
Let's play doctor!
Protozoa
There are harmless protozoa that live happily in the sea (until a blue whale gobbles them up for lunch), and there are deadly ones that can really harm us.
Malaria
| Important questions | Information |
|---|---|
| What causes it? | Plasmodium vivax, Plasmodium malaria, Plasmodium falciparum |
| How can you get it? | Bite of female Anopheles mosquito |
| What does it affect? | Liver and red blood cells |
| What are the symptoms? | Recurring high fever and chills (every 3-4 days) |
Amoebiasis/Amoebic dysentery
| Important questions | Information |
|---|---|
| What causes it? | Entamoeba histolytica |
| How can you get it? | Food/water contaminated by houseflies transmitting parasites from infected fecal matter |
| What does it affect? | Large intestine |
| What are the symptoms? | Constipation, abdominal pain and cramps, excess mucus and blood clots in the stool. |
Helminths
Helminths, or parasitic worms, are some of the most common and largest pathogens known to us (adults are usually visible to the naked eye). Many helminths can live free of hosts, but others can infect humans with the diseases listed below.
Ascariasis
| Important questions | Information |
|---|---|
| What causes it? | Ascaris (roundworm) |
| How can you get it? | Water/vegetables/fruits contaminated with eggs excreted by infected person |
| What does it affect? | Intestine |
| What are the symptoms? | Internal bleeding, muscular pain, fever, anemia and blockage of the intestinal passage. |
Elephantiasis/Filariasis
| Important questions | Information |
|---|---|
| What causes it? | Wuchereria bancrofti, Wuchereria malayi (filarial worms) |
| How can you get it? | Bite of female mosquito vectors |
| What does it affect? | Lymphatic vessels of lower limbs, genital organs |
| What are the symptoms? | Chronic inflammation of infected organs, deformities of genitals |
Fungi
The term fungi brings to mind delightful things like mushrooms and truffles. Maybe it reminds you of less tasty, but important things like decomposition of organic matter. Perhaps the least delightful, are the fungi that can cause discomfort and skin lesions .
Ringworm
| Important questions | Information |
|---|---|
| What causes it? | Microsporum, Trichophyton, Epidermophyton |
| How can you get it? | Contaminated soil, sharing towels, clothes or combs of infected persons |
| What does it affect? | Skin (especially warm and moist regions such as folds of groin/toes), nails, scalp |
| What are the symptoms? | Appearance of dry, scaly lesions, intense itching |
Doctor, your services are needed again. Please report to the clinic.
Prevention and control
- Practising good personal and public hygiene are good ways to prevent the spread of disease.
- Proper cleaning of food items, periodic disposal of waste and disinfection of water bodies can help eradicate pathogens.
- Avoiding stagnation of water, along with the use of mosquito mesh and nets will reduce the breeding of insect vectors.
- If it's possible, don't hesitate to vaccinate!
Let's run a quick refresher before we leave the clinic for the day.
Want to join the conversation?
what are the most common 25 diseases and their effects on the human body?(4 votes)
of all the diseases listed above are any of them fatal to animals or do they only affect humans?
if only to humans, then is there any particular defense that an animals body uses that a human does not posses?(0 votes)
Bacteriophage isn't a pathogen.(0 votes)