Haematology (Blood borne parasites) Flashcards
What is parasitism?
A form of symbiosis where the parasite benefits form the relationship at the expense of the host
What are the main groups of endoparasites that affect humans?
Protozoa and helminth worms
What is malaria? What is it transmitted by?
- A potentially fatal infectious disease
- May be transmitted by female mosquitoes of the genus Anopheles
Other than through mosquitoes, how may malaria be passed on?
Transfusion
Transplanation of infected bone marrow
Placental transmission (congenital malaria)
Where is malaria common?
Tropical and sub-tropical areas
How many deaths are there each year from malaria?
1-3 million
mainly of yound children in sub-saharan africa
Infection with what parasite causes 80% of cases?
P. falciparum
What is the receptor for P. falciparum?
Glycophorin A/B/C
Describe the process of red cell invasion by malarial merozoite
1) Merozoite in the blood attach to receptors on RBC surface
2) Merozoite re-orientates so that the apical pole is directed towards the RBC surface
3) Tight junction forms between merozoite and RBC surface accompanied by initial deformation of RBC membrane
4) Entry of merozoite coinciding with formation of parasitophorous vacuole
5) Closure of RBC and parasitophorous vacuole membranes
6) Junction between RBC membrane and parasitophorous vacuole severed releasing merozoite into cell where it transforms into young trophozoite
Describe what happens after the merozoite becomes the trophozoite?
- ‘Feeding stage’
- Ingests 80% of haemoglobin and other contents of the RBC
Name some other forms of malaria forming parasites
P. falciparum
P. vivax
P. ovale
P. malariae
What is the incubation period between infection and onset of clinical symptoms for P. flaciparum?
7-14 days
What are the common symptoms in all species?
- Fever
- Sweating
- Headache
- Weakness
- Dizziness
- Nausea
- Anaemia
What are some symptoms unique to P. falciparum?
- Neurological imbalances
- Muscle spasms
- Pulmonary oedema
- Jaundice/liver failure
- Hypoglycemia
- Diarrhoea
- Circulatory collapse
What is a potentially life threatening consequence of malaria?
Haemolytic anaemia
How are RBCs destroyed during malaria?
1) The reiculoendothelial system removes parasitised RBCs by extravascular phogocytosis
2) Red cell parasites removed in spleen by ‘pitting’
- Pitting is removal of parasite and part of the red cell membrane
- Reduces lifespan of RBCs
What happens to the spleen as the result of this increased activity?
Splenomegaly
Name some other things that happen to RBCs due to malaria
1) Release of pro-inflammatory cytokines by immune system (e.g TNF-alpha) can result in dyserythropoiesis (abnormal RBC development)
2) Erythropoiesis suppressed by formation of haemozoin (heme that has converted by parasite)
What is blackwater fever?
A complication of malaria infection in which red blood cells burst in the bloodstream (hemolysis), releasing hemoglobin directly into the blood vessels and into the urine, frequently leading to kidney failure.
What can occur to WBCs as a result of malaria?
- Neutrophilia
- Eosinophilia or eosinopenia
- Atypical lymphocyte morphology
Can be see in the recovery phase
What commonly occurs to platelets during malaria?
- Increased activation
- Increased clearance by spleen
- Reduced lifespan
Results in thrombocytopenia
By what 3 mechanisms may blood coagulation occur in malaria?
1) Cytokine storm in response to infection activating clotting mechanisms
2) Alterations to the membranes of infected cells reveal coagulation promoting phospholipids
3) Adherence of parasitised cells to deep tissue capilary endothelium
Reduced synthesis and increased activation of coagulation factors have what effect on prothrombin time and activated partial thromboplastin time?
Mild elevations in PTT and APTT
What is the most common lab detection method for malaria?
Light microscopy of Romanowski-stained blood films
What are the 2 types of Romanowski-stained blood films?
Thick and thin
How is the thick film created and what is the purpose?
A drop of blood is spread in a circular motion over an area of approx 1cm diameter
- Larger volume of blood increases the chance of identifying parasites in a small infection
How is a thin film prepared and what is its purpose?
Spread more thinly, stains of pH 7.2 recommended
- Allows detection of characteristics that assist in assigning the species of the parasite
What are Schuffners dots?
Multiple small brick red dots inside RBCs infected with P. vivax or P. ovale
- formed from invaginations of the cell membrane
What are Jame’s dots?
Darker dots seen in P. ovale infection
- can be used to specify species
How are estimates of parasitaemia calculated?
% of parasitised cells calculated by examining a minimum of 1000 cells
- Can be problematic as parasite density can be as low as 1 per 100,000 cells
What are lateral-flow immunochromatographic techniques?
Early techniques for detecting malaria including dipsticks, strips, cards, wells and cassettes
What are the problems with lateral-flow immunochromatographic techniques?
They are prone to false positives due to:
- persistent malarial antigens in the blood after infection is cleared
- cross-reacting antibodies
Give the main advantage and disadvantage of the quantitative buffy coat method?
Gives quantititive data
Results five no information on species
What are the advantages and disadvantages of PCR-based assays?
Gives info about the species of the parasite
Doesn’t give info on parasitaemia
How is immunochromatography used for detection of malarial antigens?
1) Blood is lysed, releasing P. falciparum specific antigen PfHRP-2 and pLDH which is common in all species
2) Lytic buffer contains anitbodies to PfHRP-2 and pLDH labelled with colloidal gold which complexes with respective antigens
3) Complexes forced to migrate by capillary action along the test strip until they encounter separate regions of capture antibodies (antibodies fixed to strip) that bind different epitope of antigen
How is the quantitative buffy coat technique performed?
1) Blood drawn into a glass haematocrit tube containing acridine orange to stain the parasite DNA and potassium oxalate (anticoagulant)
2) Cylindrical float inserted
- Tube is centrifuged so that cells separate
- Float forces cells to periphery, increasing their thickness and visibility
3) RBSc do not contain DNA but parasite infected ones do - these fluoresce under UV light
