Lecture 23- Malaria Flashcards
1
Q
Malaria definition
A
- obligate intracellular protozoa of the genus Plasmodium
- natural hosts are human
- produces acute or chronic infection, most commonly characterised by paroxysms of fever, anaemia and splenomegaly
- transmitted by Anopheles mosquitoes
2
Q
- Classification
A
- P. Falciparum
- P. Vivax
- P. Ovale
- P. Malaria
- P. Knowlesi
3
Q
Epidemiology
A
- 100 countries world wide with 2 billion people at risk
- 300-500 million incidence with an annual mortality of 1 million
- P malaria exists in Africa, haiti and the dominican republic
- P vivax and P falciparum are both present in mexico, central and south america, the indian subcontinent, southeast asia and oceania
- P vivax is rare in africa while falciparum is common in africa
- P ovale is found almost exclusively in africa
4
Q
Pathogenesis
A
- genetic factors involving surface proteins of erythrocytes have evolved in human societies by selective pressures
- heterozygous sickle cell trait is protective of P falciparum infection
- the absence of Duffy A and B blood group determinants is protective against P vivax
- cytoadherance and sequestration are the critical parasite-host interactions responsible for severe disease
- P falciparum sequesters in the microcirculation
- disruption of the microcirculation
- probable RBC receptors are ICAM1, CD36, VCAM1
5
Q
PApathophysiology
A
- gametophytes are the infected RBC - infect mosquitoes but do not cause the disease
- manifestations are a consequence asexual forms and their interactions in the blood compartment
6
Q
Disease may be a consequence of:
A
- haemolysis of parasites and normal cells
- haemoglobinuria and ARF
- hypoglycaemia secondary to parasite consumption of glucose and/or inadequate hepatic gluconeogenesis
- Acidosis, SIADH, hyponatremia
7
Q
Pathophysiology
A
- density of parasitemia is dependent on the proportion of susceptible erythrocytes
- reticulocutes are rpeferentially infected with Ovale and Vivax
- older erythrocytes are infected in Malariae infestations
- all erythrocytes are susceptible in falciparum infections
8
Q
Clinical features
A
- fever in the returned traveller
- prodrome 2-3 days
- paroxysm with rigors
- frequently have headache, myalgia, back pain, fatigue
- GI symptoms or resp symptoms may confuse the picture
- fever, pallor, jaundice, hepatosplenomegaly
- anemia, thrombocytopenia, leukopenia
- hyperbilirubinemia and non-specifically elevated transaminases are frequent
- hyponatremia and hypoglycemia may occur
9
Q
Clinical features of vivax/ovale
A
- incubation usually 12-18 days
- terrain malariae: febrile paroxysms are separated by intervals of 48 hr
- replapses usually occur within 6 months
- splenomgaly usually occurs within 2 weeks
- after 5-7 days may develop classing benign tertian periodicity
- good prognosis
10
Q
Clinical features: malariae malaria
A
- mildest form of malaria, produces chronic low level parasitemia
- incubation is usually >18 days
- diagnosis may be difficult, requiring multiple blood films
- recrudescence may occur decades later
- Quartan malaria: febrile paroxysms are separated by intervals of 72 hours
- good prognosis
11
Q
- Clinical features falciparum malaria
A
- should be considered a medical emergency in non-immune individuals
- incubation shortest: 10-14 days
- paroxysms often irregular
- clinical findings are similar to other forms of malaria byt mroe severe and acute
- more often more severe anemia and multisystem involvement
- prognosis: mortality up to 25% in non-immune individuals
12
Q
Clinica features of severe/complicated malaria
A
- parasitemia
- cerebral malaria
- shock
- Pulmonary oedema
- DIC
- macroscopic hemoglobulinuria
- renal failure: serum creatinine >265 umol/L
- severe anemia
- hypoglycemia
- academia
13
Q
Clinical features of cerebral malaria
A
- unrousable coma not attributable to other cause in a patient with falciparum malaria
- mortality 15-25%, neurological sequelea uncommon
- most common severe complication of falciparum malaria in children
- neurological findings are variable: raised ICP, focal gaze abnormalities, seizures
- rapid recovery in survivors
14
Q
Diagnosis: microscopy
A
- gold standard
- capillary rich blood, fresh EDTA/heparinised sample
- uses classing stains
- takes an hour
15
Q
Thick vs thin film
A
- thick film improves sensitivity by superimposing 202-30 layers. Measures parasite density +/- speciation, essential for low level parasitemia
- thin film: a fixed monolayer to permit speciation by preservation of parasite and RBC morphology