Infection and Immunity

Question 1

What organism causes Q fever? What is the source of infection?

Answer 1

Coxiella burnetii, a rickettsia. The source of infection is typically an abattoir, cattle/sheep or it may be inhaled from infected dust

Question 2

What are the features of Q fever?

Answer 2

• typically prodrome: fever, malaise
• causes pyrexia of unknown origin
• transaminitis
• atypical pneumonia
• endocarditis (culture-negative)

Question 3

What is the management of Q fever?

Answer 3

Doxycycline

Question 4

What is malaria and what are the organisms that cause it?

Answer 4

Malaria is a disease caused by Plasmodium protozoa which is spread by the female Anopheles mosquito. There are four different species which cause disease in man:
* Plasmodium falciparum
* Plasmodium vivax
* Plasmodium ovale
* Plasmodium malariae

Question 5

What are protective factors against malaria?

Answer 5

The protection from malaria that sickle-cell trait offers is well documented. Other protective factors include
* G6PD deficiency
* HLA-B53
* absence of Duffy antigens

Question 6

What is the most common organism causing malaria?

Answer 6

Plasmodium falciparum - also most severe

Question 7

What are features of infection with plasmodium falciparum?

Answer 7

• schizonts on a blood film
• parasitaemia > 2%
• hypoglycaemia
• acidosis
• temperature > 39 °C
• severe anaemia
• complications as below

Question 8

What are the complications of infection with plasmodium falciparum?

Answer 8

• cerebral malaria: seizures, coma
• acute renal failure: blackwater fever, secondary to intravascular haemolysis, mechanism unknown
• acute respiratory distress syndrome (ARDS)
• hypoglycaemia
• disseminated intravascular coagulation (DIC)

Question 9

What is the management of uncomplicated falciparum malaria?

Answer 9

• strains resistant to chloroquine are prevalent in certain areas of Asia and Africa
• the 2010 WHO guidelines recommend artemisinin-based combination therapies (ACTs) as first-line therapy
• examples include artemether plus lumefantrine, artesunate plus amodiaquine, artesunate plus mefloquine, artesunate plus sulfadoxine-pyrimethamine, dihydroartemisinin plus piperaquine

Question 10

What is the management of severe falciparum malaria?

Answer 10

• a parasite counts of more than 2% will usually need parenteral treatment irrespective of clinical state
• intravenous artesunate is now recommended by WHO in preference to intravenous quinine
• if parasite count > 10% then exchange transfusion should be considered
• shock may indicate coexistent bacterial septicaemia - malaria rarely causes haemodynamic collapse

Question 11

What is the most common cause of non-falciparum malaria? Where is it found?

Answer 11

• The most common cause of non-falciparum malaria is Plasmodium vivax.
• Plasmodium vivax is often found in Central America and the Indian Subcontinent

Question 12

Where is plasmodium ovale and knowlesi found?

Answer 12

ovale - Africa
knowlesi - South East Asia

Question 13

How does non-falciparum malaria present? What are plasmodium ovale, vivax and malariae associated with?

Answer 13

• General features of malaria: fever, headache, splenomegaly
• Plasmodium vivax/ovale: cyclical fever every 48 hours.
• Plasmodium malariae: cyclical fever every 72 hours
• Plasmodium malariae: is associated with nephrotic syndrome.

Question 14

How do we treat non-falciparum malaria?

Answer 14

Ovale and vivax malaria have a hypnozoite stage and may therefore relapse following treatment.

Treatment
* in areas which are known to be chloroquine-sensitive then WHO recommend either an artemisinin-based combination therapy (ACT) or chloroquine
* in areas which are known to be chloroquine-resistant an ACT should be used
* ACTs should be avoided in pregnant women
* patients with ovale or vivax malaria should be given primaquine following acute treatment with chloroquine to destroy liver hypnozoites and prevent relapse