Infectious agents

Question 1

what are the main types of infectious agent causing disease in humans?

Answer 1

• virus
• bacteria
• fungi
• helminth parasites

Question 2

give a brief outline of what a virus is, including an example and the disease it causes

Answer 2

viruses are not cells, they are obligate parasites (require a host cell’s nuclear machinery to replicate)

E.g. Ebola virus causing Ebola

Question 3

give a brief outline of what bacteria are, including an example and the disease it causes

Answer 3

bacteria are prokaryotes

E.g. Neisseria meningitidis causing Meningitis

Question 4

give a brief outline of what fungi are, including an example and the disease it causes

Answer 4

fungi are single cell eukaryotes

E.g. Pneumocystis jirovecii causing Pneumocystis pneumonia

Question 5

give a brief outline of what helminth parasites are, including an example and the disease it causes

Answer 5

helminth parasites are multicellular eukaryotes

E.g. Roundworms causing Lymphatic filariasis (elephantiasis)

Question 6

what are the key differences between prokaryotes and eukaryotes?

Answer 6

• prokaryotes don’t have membrane-bound organelles
• prokaryotes only have a single copy of chromosomes (haploid)
• prokaryotic cell walls contain peptidoglycan
• prokaryotes are smaller
• prokaryotes don’t have a well defined cytoskeleton

Question 7

what are protozoa and how do they replicate?

Answer 7

protozoa are eukaryotic and unicellular and infection is acquired by actions of a vector (E.g. Plasmodium causing Malaria and transmitted by mosquitos)

Protozoa replicate by binary fission in host cells