Germs that cause disease

The idea

Disease-causing organisms, such as bacteria, viruses, fungi, worms and protozoa, are called pathogens.

Good microbes, bad microbes

In Chapter 2 you met bacteria, viruses, fungi and protozoa. Some bacteria turn milk into curd. Do all of them make us ill?

Do all microorganisms cause disease?

• No, only some do
• Yes, all of them
• No, none of them

Pathogen or helper?

Sort each organism: does it cause disease (a pathogen) or help us?

Pathogens

Disease-causing organisms, such as bacteria, viruses, fungi, worms and protozoa, are called pathogens.

Not every microorganism is a pathogen. Many help us.

• Kind of pathogen | Disease it can cause
• Bacteria | Typhoid, cholera, tuberculosis
• Viruses | Chickenpox, measles, dengue
• Protozoa | Malaria
• Worms | Ascariasis (roundworms)
• Fungi | Fungi can cause disease too

Notes

Pathogens are disease-causing organisms: bacteria, viruses, fungi, worms and protozoa. Not all microorganisms are pathogens.

• Pathogen group | Example disease
• Bacteria | Typhoid
• Viruses | Chickenpox
• Protozoa | Malaria
• Worms | Ascariasis

Check yourself

What are disease-causing organisms called?

Which of these is a pathogen?

Which group includes pathogens?

• Pathogens — correct. Yes. A pathogen causes disease.
• Vectors. Vectors are insects that carry pathogens. They are not the disease-causing organisms.
• Nutrients. Nutrients are parts of food, not organisms.
• Protozoa that cause malaria — correct. Yes. They cause a disease.
• Bacteria that turn milk into curd. They help us. They do not cause disease.
• Rhizobium in a bean root. It helps the plant. It does not cause disease.
• Bacteria, viruses, fungi, worms and protozoa — correct. Yes. Pathogens come from all these groups.
• Only bacteria. Viruses, fungi, worms and protozoa can also be pathogens.
• Only worms. Bacteria, viruses, fungi and protozoa can also be pathogens.