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Common 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

PathogenA disease-causing organism
LymphocytesWhite blood cells with immune functions
InfectionInvasion of the body by pathogens
DiseaseCondition that prevents normal functioning of body
SymptomsFeatures 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.


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.


Important questionsInformation
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


Important questionsInformation
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.


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 questionsInformation
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!
Diagnose the patient 1
A patient enters your clinic with complaints of fever, chills and frequent headaches. There is no sign of congestion or a sore throat, but she has a bad cough and trouble breathing properly.
Which organism do you order a blood test for?
Choose 1 answer:


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.


Important questionsInformation
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 questionsInformation
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, 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.


Important questionsInformation
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.


Important questionsInformation
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


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 .


Important questionsInformation
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.
Diagnose the patient 2
A schoolboy is brought to the hospital by his worried mother, who explains that her son had been complaining of stomach pain and constipation since he returned from a camping trip a few days ago. He does not have a fever or muscular pain, and is not anemic, but says he saw blood in his stool.
For what disease should you test the patient?
Choose 1 answer:

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.
Root cause of these evils
Match the pathogen with the corresponding disease.

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