Infectious diseases: Pathology - Protozoa

Question 1

What kind of organism is Cryptosporidium parvum?

Answer 1

Protozoan parasite

Question 2

What infective syndromes are caused by Cryptosporidium parvum in immunocompetent vs immunodeficient hosts?

Answer 2

Immunocompetent hosts: transient watery diarrhoea
In AIDS patients: chronic debilitating diarrhoea

Question 3

What kind of organism is Toxoplasma gondii?

Answer 3

Obligate intracellular protozoa

Question 4

What infective syndromes are caused by Toxoplasma gondii in immunocompetent vs immunodeficient hosts?

Answer 4

Immunocompetent: mild lymphadenopathy
In foetus: destroys developing head, brain, lung tissues
In AIDS patients: space-occupying CNS lesions

Question 5

How is Toxoplasma gondii transmitted?

Answer 5

Ingestion of oocytes in cat faeces
Ingestion of incompletely cooked contaminated pork/lamb

Question 6

What is a unique property of Toxoplasma gondii?

Answer 6

Penetrates any type of host cell

Question 7

What organism causes malaria?

Answer 7

Plasmodium

Question 8

What are the four different types of Plasmodium? Which cause severe malaria and which cause mild disease? What are the symptoms of each?

Answer 8

P. falciparum: causes severe malaria (severe anaemia, cerebral symptoms, renal failure, pulmonary oedema, death)
P. ovale, vivax, malariae: mild anaemia, may cause splenic rupture and nephrotic syndrome

Question 9

How is malaria transmitted?

Answer 9

By female anopheles mosquitoes

Question 10

Describe the life cycle of Plasmodium

Answer 10

1. Sporozoites released into blood when host bitten by mosquito
2. Sporozoites invade liver cells within minutes
3. Parasites multiple rapidly in hepatocytes and are released into blood as merozoites (asexual form)
4. Merozoites bind and enter red blood cells
5. Develop in red blood cells to trophozoites, then schizonts, then either to merozoites (which are then released upon cell lysis to infect other red blood cells) or small numbers of gametocytes (which infect other mosquitoes when host is bitten)

Question 11

What is cerebral malaria and what causes it?

Answer 11

Complication of severe malaria and main cause of death in children with malaria
Due to clumping of infected red blood cells resulting in vessel plugging and ischaemic -> produces ring haemorrhages

Question 12

Two mechanisms of host resistance to malaria

Answer 12

1. Inherited alterations in red blood cells: e.g. in heterozygous HbS and HbC, lack of Duffy antigen
2. Immune-mediated resistance with repeat infections: largely due to specific antibody and T cells responses (although limited due to antigenic variation in P. falciparum)