Malaria Case Study Flashcards
In endemic areas, which two groups of people are at greatest risk of death from malaria?
Pregnant women and infants are at greatest risk of death from malaria in endemic areas.
What is the usual reservoir of infection for malaria parasites and how is this different for Plasmodium knowlesi?
Humans are the normal reservoir and the intermediate host of Plasmodium (thus the disease is an anthroponosis). The exception is P. knowlesi, for which monkeys are the reservoir of infection for human transmission (i.e. a zoonosis)
What climatic conditions favour malaria transmission?
Factors include a required relative humidity above 45% (mosquitoes do not feed below this limit) and sufciently warm temperatures. The time required
for the parasite to mature in the mosquito is temperature dependent. Below a threshold temperature, the maturation time of the parasite exceeds the lifespan of the mosquito, so transmission becomes impossible.
What human behaviours can help limit or prevent malaria transmission?
Public health education programmes and knowledge of the malaria cycle.
Also, the use of insecticides, insecticide-impregnated bed nets, and the draining or covering of pools where the mosquitos could otherwise lay eggs and hatch.
Describe the two diagnostic techniques for malaria?
Microscopy and antibody techniques which are field techniques and are rapid
There are also molecular techniques which are slower and require specific equipment etc
Describe the two microscopy techniques when diagnosing malaria?
Thick blood film and thin blood film
Thick blood film
Several drops of blood are dropped onto a microscopy slide and stained with Giesma which lyses the blood cells allowing the parasites to be identified in the sample.
Thin blood film
One blood droplet is placed onto a slide and smeared down the slide. It is fixed by heat and then stained using Giesma.
The cells are not lysed, instead the white blood cells are stained, their nuclei blue and their cytosol pink.
Slower technique compared to thick blood film
Allows the species of the parasite to be identified
Describe the antibody technique used when diagnosing malaria?
A blood droplet it place onto a dipstick or plastic cassette which had been impregnated with antibodies specific to malaria
If a series of specific bands appear in 15-30 mins then the patient has malaria
These tests are rapid and cheap and can diagnose each causative agent of he malarial strain
What are the low cost and simplest forms for preventing malaria?
Programmes of education about malaria and the malaria cycle teach people how to reduce their risk of getting the disease, and how to care for those that are affected.
Drainage or removal of the wet, stagnant breeding places of mosquito larvae is very important.
Spraying with insecticides for the control of mosquitoes can be effective, and often involves pyrethroids or DDT.
Indoor residual spray (IRS) and insecticide-treated bed nets (ITN) are also effective techniques for
prevention and control.
Name the three anti malarial drugs used to treat malaria and their method of treatment?
Quinolines
Inside the erythrocyte, Plasmodium gains its nutrition from digesting haemoglobin within its food
vacuole. Toxic heme is produced as a by-product
of this proteolysis, which the parasite converts to
non-toxic hemozoin. Quinoline drugs are
transported to the food vacuole and inhibit this
conversion, thereby poisoning the parasite with
it’s own waste products
Antifolates
Products of the folate metabolic pathway are
essential for producing the purines and pyrimidines
needed for DNA synthesis, and for the metabolism of certain amino acids
Plasmodium synthesises folates from simple
precursors
parasite relies heavily on its own enzymes for folate
biosynthesis.
Antifolate drugs inhibit the enzymes dihydrofolate
reductase (DHFR) and dihydropteroate synthase
(DHPS); thereby starving the parasite of this
essential nutrient.
Artemisinin-based combination therapies (ACTs)
act in a similar way to quinolines by blocking the
conversion of heme to hemozoin. Although highly
effective, artemisinins are rapidly broken down in the body. Thus, they are often used in combination with longer-lasting quinoline drugs or antifolates.
Some strains of Plasmodium have developed resistance to quinoline drugs. What biological mechanism might lead to such resistance?
Many resistant strains have acquired mutations in genes encoding membrane transporters that are required to transport the quinoline drug into the food vacuole. Thus, the drug never reaches its target in sufcient quantities to kill the parasite.
Other strains of Plasmodium have developed resistance to antifolate drugs. What biological mechanism might lead to such resistance?
These strains of Plasmodium have mutations in the genes encoding the DHFR and DHPS enzymes that hinder the binding of antifolate drugs,
thus minimising their impact on the parasites ability to make folate.
What are the three main life cycle stages that vaccines target and why?
Pre-erythrocytic stage: covering the stages from when the mosquito injects sporozoites into the blood and they infect hepatocytes, to when
the merozoites burst out of the hepatocytes into the bloodstream.
Asexual erythrocytic stage: occurring within red blood cells in a cycle of invasion, replication, rupture and release of further infective merozoites.
Gametocyte stage: covering the stages when a small number of asexual merozoites convert to sexual gametocytes in the host, and the entire
developmental stages within the mosquito vector.
What are the three lifecycle stages of the plasmodium species which are responsible for malaria?
(i) the exo-erythrocytic cycle within the human liver
(ii) the erythrocytic cycle within human blood
(iii) the sporogenic cycle within the mosquito vector.
What is the causative protist of malaria?
mosquito-borne disease, caused by apicomplexan protists of the genus Plasmodium.
