10.2 Malaria Flashcards
What is Malaria, what parasite causes it and how is it transmitted?
Malaria is a biological vector born disease meaning is NEEDS a host in order to be transmitted.
It is caused by the Plasmodium parasite and needs the Female Anopheline mosquitos to be transmitted
Malaria has very high morbidity and mortality
Vector born disease can be mechanical or biological, explain this with examples
Give one another common vector host?
Mechanical:
- eg. the Plague transmitted by fleas
- can pick up infectious agents from the outside of their bodies and transmit them through physical contact
Biological:
- eg. Malarias
- carry pathogens that can multiply within their bodies and be delivered to new hosts, usually by biting
Vectors can also be transmitted through zoonotic hosts (animals): in asian there is a monkey malaria which can also be transmitted to humans
Are vector borne disease transmissible?
HIGH TRANSMISSIBILITY!!
Give 4 vector borne diseases
1) Malaria
2) Zika Virus
3) Lymphatic filariasis
4) Dengue fever
Define DALY
Daily adjusted life years (the number of healthy years of life lost due to premature death and disability)
What is the main compound in the most commonly used anti-malarial drug?
Artemisia
What are the 5 species of plasmodium that can infect humans?
Put the 2 most common at the top and briefly expand on these
1) P.falciparum: most dangeous
- can be fatal, can develop into cerebral malaria (parasites sequester in the brain and cause coma)
- found globally (highest prevelance in sub saharan africa)
- People that carry the Sickle cell gene are resistant
2) P. vivax
- generally not fatal but can be extremly debilitating
- Relapses- parasite incubates in the liver and can re-activate even after treatment
- More temperate
- Duffy negative gene phenotype provides resistant
3) P.malariae: Long-lived infections
4) P.ovale: similar to vivax
5) P.knowlesi: Zoonotic infection (monkey malaria)
What are sporozoites, merozoites, gametocyte and oocysts
1) sporozoites:
- a motile spore-like stage of the plasmodium parasite
- this is the form that is injected into human host
2) merozoites:
- motile stage of the parasite
- this is formed in the liver cells of human host
- can go on to form many more merozoites
3) gametocyte:
- sexual precursor cells of the parasite
- this is the form that is transmitted from human host to the anopheles mosquito
4) Oocyst:
* releases thousands of sporozoites in the mosquito which then travel to salivary glands ready to infect a new host
Explain the lifecycle of malaria
Occurs in 2 stages (one in mosquito and one in human)
1) when a mosquito bites you, it sucks blood and at the same time spits anaesthetic contained within its saliva (prevents immediate detection of bite)
2) If mosquito is infected, sporozoites will also be injected
3) when sporozoites enter blood they immediately migrate to the liver cells where they remain for 9-14 days
4) In the liver cells they develop into their secondary stage, merozoites (1 sporozoites can develop into 10,000 merozoites)
4) these burst out of liver cells, and first detection of malaria by immune system occurs hence, symptoms begin developing
5) merozoites target RBCs and can develop into many more merozoites here. This takes around 1-3 days which is why we get the characteristic “cyclical fever”
6) merozoites can either go on to infect more RBCs OR they can differentiate into gametocyes (sexual stage)
7) when another mosquito bites, that isnt already infected, these gameotcytes can be taken up
8) within the mosquito they travel into the midgut and develop further by various sexual replication
9) gametocyes ➞ oocysts ➞ sporozoites
10) sporozoites enter salivary glands of mosquito
Process repeats
Mosquitoes can be anthropophilic or zoophilic, what does this mean?
What is the ideal temperature for these parasites?
Anthropophilic: prefer to bite humans
Zoophilic: prefer to bite animals
Prefer warmer temperatures because replication within mosquitoes occurs much faster
Why are only the older mosquitoes likley to transmit?
Lifespan in 2-3 weeks, it take around 9 days for plasmodium to replicate and develop within mosquitoes hence more likly to be transmitted through older mosquitoes
When do signs and symptoms develop following infection?
Typically start 8-25 days following infection
What are the sypmtoms of uncomplicated vs severe malaira?
Can individuals be asymptomatic?
Uncomplicated malaria:
- fever, headache, sweats, vomiting, enlarged spleen
Severe malaria
- Cerebral malaria: seizures, coma, death
- Severe anaemia, hypoglycaemia, acute kidney failure, acute respiratory distress syndrome
Individuals may be asymptomatic if they have aquired partial immunity or if they are in a low transmission area
List 3 things can malaria during pregancy can cause
- stillbirths
- low birth weight
- infant mortality
When may partial immunity be aquired and what does this mean for furthur infections/symptoms
Partial immunity may be aquired when you have been exposed to malaria mutiple times but it depends on age and transmission intensity
It does NOT stop you getting re-infected, but infections will be asymptomatic
Compare the burden of disease among differnt age groups in low vs high transmission areas?
In low transmission areas, burden is seen across all different areas (biggest burden is in children under 5)
In high transmission areas, biggest burden is more confined to children under 2, cases rapidly decrease by the time the age of 5 is reached and then number of cases is very low. This is because immunity has been developed due to more exposure
List 4 ways in which Malaria can be diagnosed
1) Clinical diagnosis
2) Microscopy
3) Rapid diagnostic test (RDT): finger prick
4) Molecular diagnostics
- Polymerase Chain Reaction (PCR)
- Loop-mediated isothermal amplification (LAMP)
If Malaria is curable why are their still so many deaths?
Often people don’t get treatment it in-time either because they go undiagnosed or because there isn’t any treatment available in the area they are living in
What is chemoprophylaxis?
Give an example of 2
the use of drugs to prevent disease, eg. if people are travelling to a high risk malaria area they are advised to take chemoprophylaxis
- Doxycyline or mefloquin
These can also be given to high risk populations who are living in endemic areas
What is IPT?
IPT: intermittent preventative treatment:
- It is a public health intervention aimed at treating and preventing malaria
- It is given to infants, children, schoolchildren and pregnant women
- they are automatically treated every 4 weeks
Describe the use of ACT for treatment of severe malaria
Quinine: was widley used, but less so now because of reisstance dangers
To combat this Artemisinin-based combination therapy (ACT) are used: this is a fast acting artemisinin-based drug that is combined with a drug from a different class
Artemisinin-based drug: Dihydroartemisinin, artesunate, artemether
Other class drugs: Lumefantrine, mefloquine, amodiaquine, sulfadoxine/pyrimethamine, piperaquine etc.
Give 3 difficulties with ACT
1) requires a minimum of 6 doses for around 3 days, which can be difficult for people
2) some people may have bad reactions
3) resistance in some countries have began developing during the last 2-3 years (mainly due to counterfeit drugs)
Guve 3 ways we can measure malaria transmission intensity?
1) Vector monitoring:
* Entomological Inoculation rate (EIR)
2) Community monitoring:
* Parasite prevalence (parasite rate)
3) Clinical monitoring: Incidence
What is Entomological Inoculation Rate (EIR)
How do you measure the EIR and why is this difficult?
Defined as the mean number of infectious bites a person receives over a specified time
eg. an EIR of 100 means on average you are receiving 100 infectious bites per person per year
How to measure:
1) collect Anopheline mosquitoes (chemical/light traps)
2) take to lab and determine the “human biting rate” (how many are actually biting humans- anthropophilic)
3) determine the ‘sporozoite rate’ (how many of these that have bitten humans are infected)
Difficult because it is labour intensive and difficult to standardise (methods across and within countries vary). Infected mosquitoes can also be hard to find especially at low transmission intensity
What is Parasite prevalence (parasite rate)?
Give a difficulty of this
What proportion of the population is currently infected i.e have parasites in their blood
Determined by microscopy, rapid diagnostic tests (RDTs) or molecular tests, such as Polymerase Chain Reaction (PCR)
Difficulties include skill a of microscopist and can be subjective. RDT/micro have a detection limit of ~100p/ul and PCR is expensive and not field friendly
What are the 2 ways in which we can monitor Incidence and how would each be done?
Give some challenges of the most commonly used one
1) Passive case detection: Important for long term monitoring and elimination (most common method)
- waiting for people to show clinical symptoms at health care facilities
- can use hospital/health facility records
Challenges:
- Not all cases are symptomatic
- Some communities do not use public health facilities
- Quality of data Confounders
2) Active case detection: going out into the community and activly screening people
What are the 2 main targets for control of Malaria?
1) Targeting the vectors
- Insecticide treated nets (ITN)
- Indoor residual spraying (IRS)
2) Targeting the parasite in humans
- Mass Screen and Treat (MSAT)
- Intermittent Preventative Treatment (IPT)
- Seasonal Malaria Chemoprevention (SMC)
- Mass Drug Administration (MDA)
Give 4 positives and 2 negatives of Insecticide treated nets (ITNs)
Positives
- a physical barrier
- repellent effect (for treated nets)
- community effect
- cost effective
Negatives:
- not all vectors bite inside
- alternative uses for nets
Give 3 positives and 3 negatives of Indoor residual spraying (IRS)
Positives:
- Spraying households with an effective insecticide
- Credited for huge reductions in malaria during the Malaria
- Eradication Campaign in the 1960s (using DDT)
Negatives:
- vectors need to be endophilic
- coverage of community
- recommended need >80% of houses to be sprayed
- community resistance
- logistics
What are the 4 classes of Insecticides?
Note: resistance is showing to all of these
1) Organochlorides (i.e DDT)
2) Organophosphates (highly toxic to mammals, short residual life)
3) Carbamates (more expensive than DDT, regular respray)
4) Pyrethroids (only insecticide currently used to impregnate nets)
Give 2 reasons why resistance develops
Give 3 management strategies
Resistance develops when:
- there is widespread use
- vectors are exposed to ineffectual doses
Resistance management strategies
- Insecticide combinations
- rotational spraying
- monitoring
What is the first malaria vaccine? (it is currently in phase 3 trials)
Give 3 problems with the vaccine
RTS,S vaccine, requires 4 doses
Problems:
- unfortunatly it is more effective in older children than infants
- if 4th dose is not taken, there is no effect at all
- it is thought this vaccine is only protective for a short amount of time
WHO reccomends this vaccine should be used in combination with other protective methods
