Malaria Flashcards
What is malaria
Systemic tropical parasitic infection of red blood cells caused by plasmodium spp and transmitted by the female anopheles mosquitos
Name the 5 protozoal species of genus plasmodium and if they cause complicated or uncomplicated malaria
- Plasmodium falciparum (most common, complicated)
- Plasmodium vivax (uncomplicated; relapsing)
- Plasmodium ovale (uncomplicated; relapsing)
- Plasmodium malariae (uncomplicated, doesn’t relapse)
- Plasmodium knowlesi (zoonotic malaria (Macaques); restricted to certain parts in SE Asia
What is the most common type of protozoal species
Plasmodium falciparum (most common, complicated)
Where is plasmodium falciparum from
africa
How does transmission of malaria happen
- Bite of infected female Anopheles mosquito
- congenital - transmission through pregnant mother
- blood transfusion
When does the female anopheles mosquito feed
- Dusk to Dawn
What is the incubation period for malaria
Incubation period: 7-30 days (shorter for P. falciparum, longer for P. malariae)
describe an area of stable transmission of malaria
- Populations continuously exposed to malaria
- High background immunity – mainly adults
- Young children suffer acute illness and high parasite densities
- Epidemics less likely
- sub-Saharan Africa and parts of Oceania
Describe an area of unstable transmission of malaria
- Fluctuating rates of malaria
- Low background immunity
- Both adults and children suffer acute malaria and its complications
- epidemics likely to occur due to sudden increase in mosquito vector densities
- Asia and Latin America
Who suffers in stable transmission areas of malaria
- children - lack of immunity
Who suffers in unstable transmission areas of malaria
Both adults and children suffer acute malaria and its complications as children don’t have immunity by the time they are adults
How many countries are endemic from malaria
100 tropical countries and some subtropical regions
Where are the greatest number of deaths from malaria
90% of these deaths were in children in sub-Saharan Africa
Those living in the most economically deprived areas
what is the main risk for acquiring malaria in travellers
Failure to take effective prophylaxis is the main risk for acquiring malaria in tropical travellers
Who has higher risk of complications when getting malaria
Older people (>65 years) have higher rates of complications
who accounts for 65% of all cases of malaria in the UK
People who travelled to visit friends and families account for 65% of all cases of malaria in the UK
What is airport malaria
Airport malaria”: mosquitos stowed away in aircrafts or luggage infect people who haven’t travelled abroad
Describe the lifecycle of malaria in the mosquito
- When a female mosquito bites a human who is infected it is the gametocytes that take up the infected malaria
- the gametocytes are ingested into the mosqutios stomach
- they emerge from the infected blood cells and become gametes
- the male and female gametes fuse and produce a zygote
- the zygotes elongate into ookinetes which move through the stomach wall
- ookinetes develop into oocytes
- the oocysts grow and rupture releasing sporozoites
- the sporozoites migrate to the salivary glands and a ready to be inject into an uncontaminated human and renew the cycle
describe how the malaria transmits and has its lifecycle in human
- female mosquito that is infected bits an uninfected human,
Liver cell phase (2 weeks)
- the sporozoites go to the liver cell and infect the liver cell
- in the liver cell they form schizonts or they can remain dormant
- schizonts are large number of merozoites
- when the liver cell ruptures after about 2 weeks they releases the merozoites into the blood stream
Blood cell phase (2-3 day cycles)
- the merozoites infect red blood cells
- the parasite forms a ring called a trophozoite - this becomes larger and can mutiply
- then becomes a schizont
- once the schizont rupture to release multiple merozoites into the blood stream again this stage is associated with high temperature, body aches, and a big cytokine response
- some red blood cells will develop into gametocytes and this will continue the transmission cycle to other people
do you see schizonts on the bloodstream of someone with malaria
not often but, If you do see schizonts on the blood film that patient may deteriorate as you see more schizonts on the blood stream and more parasite is released
- this is an indication for IV use
What species of plasmodium can cause relapse of malaria
P. vivax and Plasmodium ovale only: some sporozoites enter a dormancy stage “hypnozoites” and may cause relapses weeks, months or years later
all types of malaria cause
intervascular hameolysis
What does the infected erythrocytes adhering to host endothelium cause in P.Falciparum
- Microvascular occlusion
- Metabolic derangement and acidosis
- Intravascular haemolysis
What can a schizont rupture evoke
Microvascular occlusion
Metabolic derangement and acidosis
Intravascular haemolysis
Why does P.Falciparum lead to complicated malaria
- leads to move complicated infection due to cytoadherence of the red blood cells by PfEMP1
- this causes the infected red blood cells to adhere to the endothelium and obstruct them causing
- Microvascular occlusion
- Metabolic derangement and acidosis
- Intravascular haemolysis
this can eventually lead to end organ damage
Why does P.falciparum lead to death
- Higher number of red blood cells infected, leads to greater parasitaemias
- infects red blood cells at all ages of the cell
- cause sequestration
- therefore majority of deaths are due to falciparum malaria
what plasmodium does not really cause death from malaria
Vivax and knowlesi can rarely cause severe and fatal malaria - but far less likely
What is the gold stand for malaria diagnosis
- Light Microscopy
- Parasites may be visualized on both thick and thin blood smears stained with Giemsa stains
What is the difference between thick and thin blood film for light microscopy
Thick blood film:
- sensitive
- allows examination of a greater volume of RBCs
- concentrates parasites as RBCs are lysed
Thin blood film:
- useful for species identification and determination of level of parasitaemia
- less sensitive than thick film
How does a thick blood film work
- Large drop of blood in a small part of the slide
- fixed to the slide
- can see if there is any gimesa stain parasites there
- doenst tell us the species that is present
How do you identify a specieis of malaria from a blood film
Thin blood film
How does a thin blood film work
- Spread thinly out over a larger area and see the morphology - smaller number of parasites
Describe what P.falciparum looks like on a blood film
- Numerous fine ring forms.
- Double chromatin dots
- Multiple parasitization of cells
- Schizonts rare in peripheral blood
- Red cells are not enlarged
What does P.Vivax look like on a blood film
- Developing and thick (signet) ring forms
- Trophozoites have an amoeboid appearance
- Enlarged red cells
Describe what P. Ovale looks like on a blood film
- Oval-shaped trophozoite
- Comet-like red cells.
- Enlarged red cells
Describe what P.Malariae looks like on a blood film
- Broad band form of plasmodium.
- Red cells not enlarged.
Describe what P.Knowlesi look like
- Ring stages resemble P. falciparum
- Mature stages indistinguishable from P. malariae
- Molecular methods needed to confirm diagnosis
name another way to diagnose malaria
Antigen detection
What antigens are used to diagnose malaria
- detection of an antigen (histidine rich protein-2, HRP-2) associated with P. falciparum
- detection of a plasmodium-associated lactate dehydrogenase (pLDH)
Name the antigen associated with P. falciparum
histidine rich protein-2, HRP-2
Describe how antigen detection works
Detection of antigens or enzymatic activities associated with the malaria parasites
Methods are often packaged as individual test kits called rapid diagnostic tests or RDTs
What is the clinical presentation of malaria
- Fever (temperature may be normal at the time of assessment)
- Headache,
- muscle aches,
- diarrhoea
- vomiting
- cough and SOB if pulmonary oedema
- seizures
- changes in the urine if renal involvement
what should you look for in a foreign history
- When: last 12 month for falciparum (longer for other types of malaria)
- Where: likely risk of malaria, Plasmodium spp, resistance, etc
- Malaria prophylaxis (drugs, duration, compliance)
What prediposes you to more severe malaria
Pregnancy status (high risk for complications)
Immunocompetence status (HIV, cancer, transplant recipients)
Describe how you should examine a patient with malaria
A - airway B - breathing C - circulation D - disability E - exposure F- fluids G - glucose
What are the signs of severe malaria
- Impaired consciousness or seizures.
- Renal impairment (oliguria <0.4 ml/kg bodyweight per hour or creatinine >265 mmol/l)
- Acidosis (pH < 7.3)
- Hypoglycemia (<2.2 mmol/l)
- Pulmonary oedema or acute respiratory distress syndrome (ARDS)
- Haemoglobin less than 80 g/L
- Spontaneous bleeding/disseminated intravascular coagulation
- Shock
- Haemoglobinuria (without G6PD deficiency)
- Parasitaemia >10%
What severe signs of malaria are more common in children
- Severe anaemia
- hypoglycaemia
- seizures
What severe signs of malaria are more common in adults
- renal failure
- parasite count greater than 2%
Name a sign of severe malaria
severe opisthotonic (extensor) posturing
How do you manage severe malaria
- Seek expert advice
- Anti-pyretic therapy as appropriate
- Careful rehydration if indicated (risk of pulmonary oedema)
- Other supportive measures as appropriate
- May require nursing on HDU/ITU ward
- Non-falciparum malaria cases may be managed in outpatients
- Notify your local Public Health Team
What is the drug treatment for uncomplicated P.falciparum
Oral therapy with either
- Malarone (Atovaquone-Proguanil)
- Riamet (Artemether-lumefantrine; artemesinin combination therapy – ACT)
- Quinine & Doxy / Clinda
What is the drug treatment for non facliparum malaria
Chloroquine followed by primaquine - check G6PD status (primaquine can lead to haemolysis if G6PD deficient)
How do you treat severe and complicated P.Falciparum
- IV Artesunate (preferred) OR
- IV Quinine (cardiac & blood glucose monitoring)
- Oral therapy as for uncomplicated once improved
- check blood film daily
What is indications for IV therapy
- Parasitaemia >2% or presence of schizonts
- Vomiting
- Pregnancy (get specialist advice)
How do you prevent malaria
A - awareness of the risk
B - bite prevention
C - chemoprophylaxis
D - prompt Diagnosis and treatment
What personal protective measures can you use
DEET-based insect repellents
Bed nets: Insecticide-treated nets
Clothing
What chemoprophylaxis can you use for malaria
Travel clinics
Follow evidence-based guidelines
Different regimes for different countries depending on malaria species + anti-malarial resistance patterns
No regime is 100% protective: need to use a combination of protective measures
describe what vector control you can have to prevent malaria
Insecticide-treated nets (ITNs)
- Effective public health intervention for communities suffering malaria
- Issues around cost, logistics, and insecticide resistance
- Long-term effects on background population immunity
Indoor residual spray (IRS)
How long does the fever last with each malaria type
- 24hrs – P. knowlesi
- 48hrs – P. vivax/ovale/falciparum
- 72hrs – P. malariae
