9 Malaria, part 1

Question 1

Remarks on malaria

Answer 1

“Malaria is perhaps the most significant disease acquired through international travel to the tropics.”

“A diagnosis of malaria must be considered in any person returning from the tropics with an unexplained febrile illness and must be considered in any resident in the tropics who develops a fever.”

Question 2

Besides P. falciparum, these species of Plasmodium can also cause fatal disease

Answer 2

P. vivax
P. knowlesi

Question 3

Resistance of Plasmodium to chloroquine

Answer 3

1. Resistance of P. falciparum to chloroquine has been widespread for many years.
2. Resistance of P. vivax to chloroquine has also been identified in Southeast Asia (rare)

Question 4

Anopheles mosquito requires a blood meal every

Answer 4

3 to 4 days

Question 5

These are injected into the host’s bloodstream during the Anopheles’ blood meal

Answer 5

sporozoites

Question 6

These are ingested by another feeding Anopheles mosquito from the host’s blood

Answer 6

Gametocytes (sexual forms)

Question 7

This accounts for the paucity of observed mature parasites in the peripheral smear of patients infected with P. falciparum

Answer 7

Sequestration of mature parasites in the microvasculature of many tissues and organs

Question 8

Mode of transmission of malaria

Answer 8

1. Mosquito bite
2. Blood transfusion*
3. Needlestick accident*
4. Transplacental*
   *In these cases, an exoerythrocytic phase is absent, and hypnozoites of P vivax and P ovale cannot develop

Question 9

Malaria sequelae of glomerulonephritis leading to a nephrotic syndrome is attributed to which Plasmodium

Answer 9

P malariae (without strong evidence)

Question 10

Incubation of malaria

Answer 10

In the nonimmune, symptoms begin after an incubation period ranging from 7 days to several weeks or more

Question 11

Remarks on P. faciparum

Answer 11

1. Malaria due to P. falciparum is a medical emergencyin a nonimmune host of any age, because the infection, if untreated, is likely to progress and to become life-threatening.
2. Once a P. falciparum infection has reached the stage of severe disease, there is a 5% to 30% risk of a fatal outcome, even if optimal treatment is then begun.

Question 12

The clinical hallmark of malaria

Answer 12

Fever
with a prodrome of malaise, myalgia, headache, and chills

Question 13

This is the paroxysms in malaria

Answer 13

chills and fever followed by diaphoresis

“The paroxysms of malaria are often lacking in malaria due to P falciparum or in persons who received some form of chemoprophylaxis.”

Question 14

Clinical signs that point to a diagnosis other than (or in addition to) malaria include

Answer 14

lymphadenopathy and a maculopapular or petechial rash

Question 15

The following make a malaria case severe or complicated

Answer 15

1. coma with or without seizures (“cerebral malaria”)
2. prostration
3. severe anemia
4. acidosis
5. hypoglycemia
6. acute renal failure
7. ARDS
8. pulmonary edema
9. jaundice
10. intravascular hemolysis
11. shock
12. DIC

Question 16

This finding strengthens confidence that malaria is the cause of a syndrome of coma a parasitemia

Answer 16

Presence of a recently identified retinopathy, such as patches of whitening around the fovea and scattered white-centered hemorrhages

Question 17

3 major questions to be answered by the blood smear in malaria work-up

Answer 17

1. Is there evidence of malaria?
2. If so, what is the density of parasitemia (correlates with prognosis)?
3. What species of malaria is responsible for the infection, and in particular, is P. falciparum present?

Question 18

Clues to the diagnosis of P. falciparum infection

Answer 18

1. small ring forms with double-chromatin dots within the RBC
2. Multiple infected rings in individual RBCs
3. Paucity (usually absence) of mature trophozoites and schizonts on smear
4. Infected RBCs that are not enlarged and that have cytoplasm without basophilic stippling

Question 19

Remarks on P. knowlesi

Answer 19

1. P. knowlesi is usually misdiagnosed as the less aggressive P. malariae, because the two are identical under light microscopy and require PCR for differntiation
2. Any patient coming from Asia with a high parasite burden resembling P malariae should be assumed to be harboring P. knowlesi
3. Hospital admission is recommended

Question 20

Significance of a thin smear

Answer 20

1. Because the red cells are not destroyed, a thin film allows both parasite and red cell morphology to be examined, enabling a more confident identification of the species of plasmodium
2. A thin film may fail to detect a parasitemia with a density below approx 1000/uL, but it is more useful than a thick film for counting very heavy infections

Question 21

Remarks on negative smears

Answer 21

1. In highly suspicious cases, failure to detect parasitemia is not an indication to withhold therapy.
2. If parasites are not seen in the stained thin smear, a thick smear must be done.
3. If parasites are not seen on the first thick film, obtain repeat thick smears at least twice daily for as long as malaria remains a suspected diagnosis or until the patient is better

The first smear is positive in >90% of cases

Question 22

Remarks on rapid antigen tests for malaria

Answer 22

Antigen-detecting rapid tests remain positive for up to a month after a malarial infection, even if the infection has been successfully treated.