Malaria Flashcards
How is Malaria transmitted and why is it so specific?
Hint; specific for four major reasons
Through blood transfusions which can include vertical transmission, but it’s so specific as it requires a vector from a
- FEMALE anopheline mosquito as they require blood to make eggs (male mosquitos just eat nectar)
- only 30-40 species of all female anopheles mosquitos can transmit malaria
- Mostly biting at night (many sleep under mosquito nets)
- They have different behaviours
- Anthropophilic/zoophilic; can prefer to bite humans or animals (or both)
- Endophagy/esophagy: prefer indoors/outdoors
- diverse breeding sites
What organisms/hosts can malaria exist inside of, how many species of it can exist inside humans? Name them
Mammals, reptiles, birds but only 5 species affect humans
- P. Falciparum
- P. Vivax
- P malariae; long lived infections
- P. Ovale
- P knowlesi (monkey malaria but can be fatal to humans)
How transmissible are vector-borne diseases?
Highly transmissible, as there are many carriers that can bite someone and spread the infection
What vector borne disease has the highest morbidity and mortality? Which continent has it not infected?
Malaria! Hasn’t infected Antarctica
What was malariotherapy?
People discovered that when they had neurosyphilis they could be cured by experiencing fevers so scientists intentionally infected people with malaria to cause fevers and kill the temperature sensitive syphilis bacteria (Many died, but since neurosyphilis was terminal this was considered better)
What’s DDT and who originally started to use it? What happened because of it?
The Rockefeller foundation started to use DDT is an insecticide to spray households, had a long residual effect to prevent malaria. However, it also soon after caused a resistant strain of mosquitos - this pushed the WHO to initiate a global malaria education campaign to eliminate the disease
Name four reasons that the WHO’s initiative to eliminate malaria initially work?
- only provided funding to countries saying elimination was their main goal (excluding high prevalence areas like sub Saharan Africa)
- difficult to spray all households with DDT, and resistance and vector behaviour changed
- main drug used for treatment was chloroquine and a resistant strain emerged soon after
- governmental funding was not maintained
What is the commonest strain of malaria and where geographically is it greatest?
P falciparum, Sub Saharan Africa
What is the second commonest strain of malaria and where geographically is it greatest? Why does it not most prevalent in the same geographical area as the most common strain and where is generally found?
P. Vivax, not fatal but quite dehabilitating. Generally found in temperate zones but it isn’t as common in sub Saharan Africa as many have the ‘Duffy negativity phenotype’ providing resistance to this strain
Why is P falciparum the most fatal malaria and what is different about the pathology between P. Falciparum and P. Vivax species of malaria?
Can develop into cerebral malaria (parasites sequester in the brain causing coma and death). P. Vivax can incubate in the liver and reactivate even after treatment
Who is resistant to malaria?
Those that carry the sickle cell gene are resistant to malaria
Which species of malaria is similar to P. Vivax?
P. Ovale
Describe the life cycle of malaria (including the two stages)
Primary stage:
1. Infected mosquito bites, sucks blood and injects some anaesthetic (so you don’t feel it) and the sporozoite (developmental stage of plasmodium parasite)
- Sporozoite heads to the liver and stays there for 9-14 days
Secondary stage: merozoite, 1 sporozoite = ~10,000 merozoites
3. Burst out of liver cells and induce an immune reaction, symptoms begin
- Cyclical symptoms begin: Merozoites invade blood cells and continually replicate inside, bursting out every 1-3 days and infecting more RBCs
At this point, merozoites can continue infecting blood cels or differentiate into their sexual stage = gametocytes and the next mosquito that bites you may take up the gametocytes
- Once inside the mosquito the parasite takes 9-12 days to develop: Gametocytes become oocytes and go into the mosquito midgut and develop further into sporozoites which stay in the salivary glands = mosquito becomes a malaria carrier
How long after exposure to symptoms tend to occur? What does the presence of symptoms depend on?
8-25 days following infection (when merozoites burst out of blood cells).
Symptoms depend on the age and an area’s intensity of transmissibility: after repeated exposure an individual may develop immunity to symptoms (but not immunity to the disease) - therefore, children tend to present with clinical symptoms in areas where malaria is prevalent. Some individuals are also naturally asymptomatic
What influences the speed of the parasite’s development inside a mosquito
The temperature (faster when warm) and efficiency/behaviour of the mosquito (does it prefer humans>animals, indoors or outdoors, etc)
Name two other characteristics female anopheline mosquitos should require (other than being female) to effectively transmit malaria
- Need to be older; as many mosquitos are thought to have a half life of >1 week in the wild, but the parasite requires 9-12 days to develop
- Longer flight range to spread the disease further
Other than sub-Saharan Africa where else is there an abundance of anophaline species?
Southeast Asia (due to all the islands, many have developed separately which make them harder to target)
