Malaria rapid diagnostic tests (RDTs)

MALARIA:Rapid diagnostic tests

Dr Jerin Kuruvilla

What is Malaria RDT???

•A malaria RDT or “dipstick RDT detects specific antigens or protiens developed by malaria parasites•Principle-lateral flow or immunochromatographic stick method•Signifies presence of an antigen by colour change on adsorbing nitrocellulose strip.•RDTs sensitive to malarial antibodies-used for screening of donated blood

Types Of Malaria RDTs

•Three main group of antigens detected by commercially available RDTs are:Histidine rich protien(HRP2)-specific to plasmodiumSoluble,heat stable antigen present abundantly in cytoplasm and membrane of affected erythocytes.

Parasite specific Lactate dehydrogenase(pLDH)-falciparum specific,pan specific or vivax specific

Aldolase(pan specific)-conserved major enzymes in malarial glycolytic pathway

Appropriate use of RDTS

•Diagnosis-to identify ,confirm or rule out malaria in symptomatic patients

•Case Management-accurate prescription of therapeutic interventions and to monitor treatment

•Epidemiology-to detect and monitor incidence and prevalence of malaria for targetting prevention and evaluating health programmes

•Available formats: Plastic cassette, card, dip stick, hybrid cassette dipsticks

Strengths of Malaria RDTs Challenges of Malaria RDTs

Relatively easy to use with minimal training required

Costs per test may exceed those of microscopy

Relatively rapid, giving timely results

Short shelf-life, requiring efficient procurement, transportation, storage and distribution systems

Little or no manipulation of sample required, can be performed in places without laboratories

Most tests are qualitative (i.e. gives a yes or no answer). Any quantification of parasitemia will require further laboratory-based tests

Most of the RDTs do not require refrigeration, hence tests can be performed where there is no power supply

Intensity of test band varies with amount of antigen present at low parasite densities-this may lead to reader variation in test results

Uses whole blood (prick or venous blood-prick preferred)

less sensitive than lab tests

Choosing a Malaria RDT

•The plasmodium species to be detected

•Accuracy(sensitivity and specificity)

•Shelf life and temperature stability during storage,transport and use ( -minimum of 18 months)

•Ease of use (including format of tests)

•Cost

Plasmodium species to be detected

•Zone 1 -Plasmodium falciparum only(Sub Saharan Africa & Papua New Guinea) – HRP2 kits preferred

•Zone 2 –Falciparum and non falciparum infections occur as single species infection(endemic areas of Asia and Americas)

•Zone 3 –non falciparum malaria only(mainly vivax only)(areas of east asia and central asia)

Despite all these advances, malaria will likely be with us as long as there are humans on this earth.

Guidelines for use of Malaria RDTs in health programmes

•Batches of RDTs should be tested and monitored throughout shelf life

•Evidence of good manufacturing practice(GMP) and good field experience of manufacturer

•Cold chain for transport and storage

•Health worker training and monitoring

•Clear guidelines & diagnostic as well as treatment guidelines

26/04/07

ChloroquineFansidar

(Sulfadoxine/pyrimethamine)Quinine

ArtesunateHalofantrinDoxycycline

Malarone (Atovaquone/proguanil)

Primaquine

Treatment Prophylaxis

ChloroquineDaraprimproguanil

Chloroquine/proguanilSulfadoxine/

pyrimethamineSulfa/dapsone

MefloquineAtovaquone/proguanil

DoxycyclinePrimaquine

Antimalarial drugs

Treatment of Chloroquine resistant malaria

Quinine + tetracyclineor clindamycin

or Fansidar (sulfadoxine and pyrimethamine)Malarone (paludrine/atovaquone)Mefloquine (a quinoline methanol)

Qinghaosu (artemesinin)

Malaria Prevention

Mosquito avoidance - evening and night behavior

- mosquito nets- air conditioning

- screens- mosquito repellants

- pyrethrin coilsMosquito killing - destroying breeding sites

- fog spraying- residual spraying

Plasmodium killing - chemoprophylaxis