Lecture 28: Malaria Flashcards
(30 cards)
What are the common modes of transmitting disease?
- direct transmission
- indirect transmission
what is direct transmission?
Direct contact
- e.g. skin to skin contact, kissing, sexual intercourse, contact with contamination soil
Droplet spread
- coughing, sneezing, e.g. influenza, measles, covid-19
what is indirect transmission?
Airborne
- droplet nuclei suspended in the air e.g. measures
Vehicles
- food, water, blood, fomites (e.g. bedding, tissues)
Vectors
- mosquitoes, fleas ticks
what are the transmission by vector methods?
- mechanical transmission
- biological transmission
what is mechanical transmission?
a mechanical vector (an animal) picks up the pathogen, carries it and transmits it to the host through some sort of physical contact
e. g. a fly walking through feces/disease contaminated materials and leaving on food
e. g. a rat ingesting disease organism and passing it through waste with no change and leaving on food
what is biological transmission?
the pathogen reproduces within the biological vector (e.g. a mosquito) and that transmits the pathogen from one hose to another
- diseased organism may undergo essential change/development within vector before transmitting to victim
- vector is usually essential to transmission of that disease
what are vector borne diseases?
vectors are living organisms that can transmit infectious pathogens between humans, or from animals to humans
e.g. mosquitos, ticks and blackflies
what diseases do mosquitos transmit?
viruses: chikungunya, dengue, rift valley fever, yellow fever, zika, japanese encephalitis, west nile fever
parasites: malaria (protozoa), lymphatic filariasis (worm)
what diseases do ticks transmit?
viruses: tick-borne encephalities, crimean-congo haemorrhagic fever
bacteria: lyme disease, rickettsial diseases
what diseases do blackflies transmit?
parasites: onchocerciasis (worm)
what is the distribution of vector borne diseases globally?
These are the 7 major vector borne diseases
- malaria, lymphatic filariasis, leishmaniasis, dengue, japanese encephalitis, yellow fever and chagas disease
Grey = affected by 0
Blue = affected by 6
Green = affected by 1
major burden in africa, south america and southern europe
affects poorer countries the most
Climate makes a huge difference to the survival of the vectors
All of these countries are equatorial, its hot
Less well of places have less things to protect them. E.g. repellent
how many people are affected by malaria?
212 million get malaria and 40,000 die every year
what does this figure show?
Climate change tranmission scenarios for 2 types of mosquito: aedes aegypti and albopictus
Colours = number of months suitable for for vectors
Can see the equatorial countries are suitable all year round. Northern Africa, south america, southern europe.
Climate change results in the red shifting southwards, away from equator
what are the problems/solutions of malaria?
risk of introduction and establishment of vector species in a growing problem.
- climate change, globalisation, travel and urbanisation
Prevention focuses on preventing the introduction/establishment or futher spread of vectors. e.g. mosquitos
where vectors are established the emphasis is on inegrated disease a vector surveillance
what happens to R0 in vector borne diseases?
R0 becomes more complicated with vector borne diseases. There are more things to consider, but this also means that there are more places you can act/prevent
what are ways of controling vectors?
- Malaria breed in still water so removing/draining water in an environmental control
- Chemical control - insecticides, spraying, nets
- Physical control - clothing, nets
- Improved living conditions
what is the global distribution of malaria?
Dark = had malaria in 2002
Pink = had malaria in 1900
Scandinavia had it in 1900
Not just temperature, also to do with sanitation of water and living conditions
In 2002, malaria in the same places as most other vector diseases.
Equatorial areas.
explain malaria data from 2018?
in 2018:
- nearly half of the world’s population at risk of malaria
- 228 million cases of malaria
- 405,000 deaths
- 68% of deaths occur in children under than age of 5
what causes malaria?
Malaria is caused by the Malaria parasite: Plasmodium species
There are 5 species of Plasmodium known to infect humans:
- P. falciparum: most common, found world-wide but mostly in Africa. can cause severe disease, responsible for majority of malaria deaths.
- P. vivax: mainly gounf in asia and south america, causes milder symptoms than P. falciparym
- P. ovale: common, West Africa
- P. malarie: quite rare, Africa
- P. knowlesi: very rare, SE Asia
what is the vector for malaria?
the vector = anopheles mosquito
- malaria is spread via the bite of the female anopheles mosquito
- often bite between dawn and dusk
- they breed in water
- transmission intensity is influenced by the lifespan of the mosquito, biting habits and density as well a climatic conditions (rainfall, humidity, temperature)
what is the malaria transmission lifecycle?
It involves 2 hosts: The human and the Mosquito
1st mosquito picks up plasmodium from a human or animal
Initial human host - plasmodium gets into bloodstream from mosquito
Then travels into liver and gets into rest of blood supply and invades red blood cells- some RBCs explode.
When blood cells burst it causes fever and chills in the person. Happens in a cycle. This cycle happens every few days
Then second vector bites and it gets spread onto another person
A developing baby can get malaria transmitted if a pregnant woman gets bitten.
what are the symptoms of malaria?
- uncomplicated malaria usually presents with fever and non-specific symptoms
- headache
- fever
- muscle fatigue and pain
- back pain
- chills
- sweating
- dry cough
- spleen enlargement
- nausea
- vomitting
what are the complications of malaria?
babies, young children, pregnant women and the elderly at particular risk of malaria complications
- severe malaria, caused by P. falciparum characterised by multi organ failure
- in children, complicated malaria can lead to severe anaemia and cerebral malaria
- malaria in pregnancy can lead to premature birth, low birth weight, stillbirth, miscarriage and maternal death
- Not easy to distinguish malaria from other diseases
- In countries with high malaria rates, people who display symptoms are thought to have malaria (but they don’t always)
what is the global distribution of risk?
Half of the world’s population is at risk
- 93% of cases and 94% of deaths occur in the African Region
