Pathogens; typhoid, pneumonia and common cold
Disease-causing organisms are pathogens. Typhoid and pneumonia are bacterial; the common cold is viral and stays in the nose and airways, not the lungs.
Pathogens and parasites
Good health depends on our genes, on infections, and on lifestyle such as food, exercise and habits. Pathogens are organisms that cause disease: bacteria, viruses, fungi, protozoans and helminths (worms). Most parasites are pathogens, because they harm the host they live in or on. A pathogen enters the body, multiplies, and damages the structure and working of organs. It must be adapted to life in the host; for example, a gut pathogen must survive the low pH of the stomach and resist digestive enzymes.
Three diseases at a glance
| Disease | Pathogen | How it spreads | Symptoms |
|---|---|---|---|
| Typhoid | Salmonella typhi (bacterium) | Contaminated food and water; enters the small intestine, then spreads through blood | Sustained high fever (39 to 40 °C), weakness, stomach pain, constipation, headache, loss of appetite; intestinal perforation and death in severe cases |
| Pneumonia | Streptococcus pneumoniae and Haemophilus influenzae (bacteria) | Inhaling droplets or aerosols from an infected person; sharing glasses and utensils | Fever, chills, cough, headache; alveoli fill with fluid; in severe cases lips and fingernails turn grey to bluish |
| Common cold | Rhino viruses | Inhaling droplets from coughs and sneezes; touching contaminated objects such as pens, books, cups, doorknobs, keyboards | Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness; lasts 3 to 7 days |
Pneumonia vs common cold
Carriers: the story of Typhoid Mary
A carrier has a pathogen in the body and can pass it on but shows no symptoms of the disease. Mary Mallon, a cook nicknamed Typhoid Mary, was a typhoid carrier. For several years she spread typhoid through the food she prepared. This shows why food handlers must be screened and must follow strict hygiene.
Street food and pani puri made with unsafe water are common routes for typhoid in Indian cities. Drinking boiled or purified water, washing hands before eating, and covering coughs with a handkerchief cut the spread of typhoid, pneumonia and colds.
2 marks: “Name the pathogen that causes typhoid and the test used to confirm it. How does it enter the body?” Salmonella typhi; Widal test. It enters through contaminated food and water, reaches the small intestine, then spreads to other organs through blood.
3 marks: “Differentiate between pneumonia and common cold on the basis of pathogen, organ affected and two symptoms.” Pneumonia: Streptococcus pneumoniae or Haemophilus influenzae; alveoli of lungs; fever, chills, bluish lips. Common cold: rhino viruses; nose and respiratory passage, not lungs; nasal discharge, sore throat.
Salmonella = Street food fever (typhoid, Widal). Pneumonia fills the alveoli; a cold never reaches the lungs.