9 Malaria, part 1 Flashcards
Remarks on malaria
“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.”
Besides P. falciparum, these species of Plasmodium can also cause fatal disease
P. vivax
P. knowlesi
Resistance of Plasmodium to chloroquine
- Resistance of P. falciparum to chloroquine has been widespread for many years.
- Resistance of P. vivax to chloroquine has also been identified in Southeast Asia (rare)
Anopheles mosquito requires a blood meal every
3 to 4 days
These are injected into the host’s bloodstream during the Anopheles’ blood meal
sporozoites
These are ingested by another feeding Anopheles mosquito from the host’s blood
Gametocytes (sexual forms)
This accounts for the paucity of observed mature parasites in the peripheral smear of patients infected with P. falciparum
Sequestration of mature parasites in the microvasculature of many tissues and organs
Mode of transmission of malaria
- Mosquito bite
- Blood transfusion*
- Needlestick accident*
- Transplacental*
*In these cases, an exoerythrocytic phase is absent, and hypnozoites of P vivax and P ovale cannot develop
Malaria sequelae of glomerulonephritis leading to a nephrotic syndrome is attributed to which Plasmodium
P malariae (without strong evidence)
Incubation of malaria
In the nonimmune, symptoms begin after an incubation period ranging from 7 days to several weeks or more
Remarks on P. faciparum
- 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.
- 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.
The clinical hallmark of malaria
Fever
with a prodrome of malaise, myalgia, headache, and chills
This is the paroxysms in malaria
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.”
Clinical signs that point to a diagnosis other than (or in addition to) malaria include
lymphadenopathy and a maculopapular or petechial rash
The following make a malaria case severe or complicated
- coma with or without seizures (“cerebral malaria”)
- prostration
- severe anemia
- acidosis
- hypoglycemia
- acute renal failure
- ARDS
- pulmonary edema
- jaundice
- intravascular hemolysis
- shock
- DIC
This finding strengthens confidence that malaria is the cause of a syndrome of coma a parasitemia
Presence of a recently identified retinopathy, such as patches of whitening around the fovea and scattered white-centered hemorrhages
3 major questions to be answered by the blood smear in malaria work-up
- Is there evidence of malaria?
- If so, what is the density of parasitemia (correlates with prognosis)?
- What species of malaria is responsible for the infection, and in particular, is P. falciparum present?
Clues to the diagnosis of P. falciparum infection
- small ring forms with double-chromatin dots within the RBC
- Multiple infected rings in individual RBCs
- Paucity (usually absence) of mature trophozoites and schizonts on smear
- Infected RBCs that are not enlarged and that have cytoplasm without basophilic stippling
Remarks on P. knowlesi
- P. knowlesi is usually misdiagnosed as the less aggressive P. malariae, because the two are identical under light microscopy and require PCR for differntiation
- Any patient coming from Asia with a high parasite burden resembling P malariae should be assumed to be harboring P. knowlesi
- Hospital admission is recommended
Significance of a thin smear
- 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
- 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
Remarks on negative smears
- In highly suspicious cases, failure to detect parasitemia is not an indication to withhold therapy.
- If parasites are not seen in the stained thin smear, a thick smear must be done.
- 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
Remarks on rapid antigen tests for malaria
Antigen-detecting rapid tests remain positive for up to a month after a malarial infection, even if the infection has been successfully treated.
