Transcript The Diagnosis of Malaria

The Diagnosis of Malaria
Norman Moore, PhD
Director of Medical Affairs
The majority of the statistics and facts used
in this presentation are available on the
Centers for Disease Control Website.
Historical Perspective
• Malaria has been around for a minimum of 4,000 years
– China described the symptoms in 2700 BC
– Thought responsible for the decline of many Greek
city-states in 400 BC
• The name comes from Italian for “bad air”
• Quinine – Comes from the bark of the Cichona tree in
South America
Malaria Parasite
• Parasite first discovered in 1880 by a French army
surgeon by seeing the parasites in blood.
• A British officer in the Indian Medical Reserve in 1897
showed that the parasite could be passed to mosquito
from person.
– He later showed it could go bird-to-bird through
mosquito vector.
• Life cycle shown in 1898-1899 when mosquitoes that
had bitten a malaria patient in Rome were sent to
London and able to infect volunteers there.
Anopheles Mosquito
US Malaria Issues
• Panama Canal – Out of the 26,000 people working on the canal,
21,000 were hospitalized with malaria at some point.
– Construction only possible after the control of malaria and
yellow fever put in.
• US Public Health Service started controlling malaria in US around
1914.
• Tennessee Valley Authority had authority to control malaria.
When it started in 1933, 30% of the population was affected and
by 1947, it was eradicated.
• CDC and states started eradication program in 1947 and it was
considered eliminated in 1951.
Malaria in the US
• Approximately 1,500 cases of malaria are reported each year in
the US.
– Cases are due to travel to endemic regions and immigration.
• Since 1957, there have been 63 reported outbreaks of malaria in
the US.
– Occurred by local mosquitoes biting an infected person.
• The mosquito species previously responsible for disease in the
US are still here.
• Since 1963, there have been 96 cases of transfusion-transmitted
malaria.
– Donors SHOULD defer depending on where/when they have
been in malaria-infected regions.
Malaria in the World
• 3.3 billion people live in malaria regions
– Half of the world’s population
• In 2008, estimated that there were 190-311 million
cases with 708,000- 1,003,000 deaths.
– 89% of the deaths occurred in Africa.
• Malaria is the 5th most common death due to infectious
disease worldwide.
Life Cycle
• Two types of hosts – humans and female Anopheles
mosquitoes.
• In humans, the parasite first grows in liver cells and
then in red blood cells.
– In the blood cells, parasites grow, lyse the cell, and
then other red blood cells infected.
• In mosquitoes, if gametocyte ingested, a new cycle is
initiated.
– 10-18 days later, sporozoite is found in mosquito’s
salivary glands.
– Can be injected in person and go to liver cells.
Life Cycle
Note: P. vivax and P. ovale can lie dormant in
liver for weeks or even years.
Types of Malaria Affecting Humans
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Plasmodium falciparum – most virulent
P. vivax
P. ovale
P. malariae
Rare cases of P. knowlesi
Disease
• Symptoms vary dramatically
– None to very mild to severe/death
• Toxins are dumped into the bloodstream when the
infected red blood cells lyse.
• Some toxic factors stimulate the macrophages to
produce cytokines that in turn produce fever and
shaking.
• Red blood cells infected with P. falciparum don’t freely
circulate. When they sequester in the brain, can
cause cerebral malaria, which has high mortality.
Incubation Period
• After acquiring Plasmodium, the incubation period
ranges from 7 to 30 days.
– Shorter incubation periods usually associated with
P. falciparum, while longer ones can be
P. malariae.
• Prophylactic anti-malarial drugs may delay symptoms
for weeks to months.
– May result in missed or delayed diagnosis.
– Patients should let health care professionals know
if they have traveled to malaria endemic regions
during the last 12 months.
Uncomplicated Malaria Symptoms
• “Classic” attack (rarely observed – lasts 6-10 hours)
– Cold stage (patient feels cold, shivering)
– Hot stage (fever, headache, vomiting, seizures in
young children)
– Sweating stage (sweat, then return to normal temp)
• Common symptoms
– Fever, chills, sweats, headache, nausea &
vomiting, body aches, and general malaise
• If in non endemic region, these symptoms could be
confused for other sicknesses
• If in endemic region, may believe it is malaria without
checking other causes
Severe Malaria Symptoms
• Cerebral malaria – unconscious, seizure, coma,
other neurological difficulties
• Severe anemia
• Blood in the urine
• Acute respiratory distress syndrome (ARDS)
• Problems with blood coagulation
• Kidney failure
• Hypoglycemia
Diagnosis of Malaria
Specimen Collection
• Ideally, blood can be collected by finger
prick
– If other tests being performed, can use
venipuncture
– EDTA is preferred as the anticoagulant as
heparin may lead to morphological distortion
• Smears should be prepared and stained
within an hour of drawing the specimen.
– Alterations in morphology may occur if
delayed.
Information to Collect
• Travel history (Time between bite & symptoms)
– Help suggest likelihood of infection
• 9 to 14 days for P. falciparum, P. vivax, and P. ovale (or
months for vivax and ovale)
• Up to 40 days for P. malariae
• After one month, probably not P. falciparum
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History of prophylaxis or treatment of malaria
History of transfusion or shared needles
History of malaria in person (relapse?)
Knowledge of fever pattern
Microscopy – The Gold Standard
• Benchmark diagnostic standard for over
100 years.
• In expert hands: highly sensitive, specific.
• Results provide a wealth of clinically
important data.
• Stained slide serves as permanent record.
Microscopy
• Thick film considered “gold standard” for
detection of parasites due to being able to use
larger volume (10µl of blood)
• Thin film considered “gold standard” in species
identification
• Smear examinations should be under oil
immersion
– Negatives should not be reported until 200 oil
immersion fields have been examined
– Additional specimens should be examined at 12-hour
intervals for a subsequent 36 hours.
Microscopy Limitations
• Microscopy skills may be lacking in areas
not routinely doing malaria evaluations
– Smear preparation, staining
– Interpretation
• Mixed infections - can be difficult to
diagnose.
• Low parasitemia - can be difficult to
diagnose.
• Hands on time is very high.
BinaxNOW® Malaria Test
BinaxNOW® Malaria Test
Clinical Trial by US Army
BinaxNOW® Malaria Test
• Detects circulating malaria antigens in
whole blood.
• 15 minute test
• The only FDA cleared rapid malaria test.
* For parasitemia levels >5,000 (parasites/µl).
Refer to product insert for additional information.
Performance
• Plasmodium falciparum:
– Sensitivity 95.3%
– Specificity 94.2%
• Plasmodium vivax:
– Sensitivity 68.9%
– Specificity 99.8%
• Note: Publications report P. ovale as being
harder to detect as it only attacks young
erythrocytes
How the Test Works
• Histidine-rich protein II (HRP II) is specific
to P. falciparum while aldolase is a panmalarial agent.
• Test has monoclonal antibodies directed
against these proteins, which detects them
in a modified lateral flow format.
BinaxNOW® Malaria Test
• Procedure
– Apply 15 µl of whole blood to the purple pad.
• Venous or capillary whole blood.
• EDTA collection tubes.
• Mylar-coated capillary tubes included in kit.
– Apply 2 drops of Reagent to the white pad
below where the blood is applied.
– Apply 4 drops of Reagent to the pad located
at the top of the left side of the test device.
– Close the device and read in 15 minutes.
BinaxNOW® Malaria Test
TEST RESULTS
T1 Positive
T2 Positive
DESCRIPTION / INTERPRETATION
Positive result for P. falciparum (P.f.)
Positive result for P. vivax (P.v.) or P. malariae (P.m.) or P.
ovale (P.o.) In some cases the appearance of only the T2 Line
may indicate a mixed infection with two or more of P.v., P.m.,
and P.o.
T1 + T2 Positive
Positive result for P. falciparum (P.f.) In some cases the
appearance of both the T1 and T2 Lines may indicate a mixed
infection of P.f. with another species.
No T1 or T2 Lines
Negative result
(no malaria antigens were detected)
Microscopy vs. BinaxNOW®
Microscopy
TOTAL TIME: 3-6 HOURS
–
–
–
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Obtain blood
Prepare thick smears
Prepare thin smears
Stain blood smears
Microscopic examination
of thick smears
– Microscopic examination
of thin smears
vs.
BinaxNOW Malaria
TOTAL TIME: 20 MINUTES
– Obtain blood
– Add blood and reagent to
test device
– Close test device and read
results in 15 minutes
Conclusions
• Malaria continues to be a major worldwide
disease.
• Although it has been eradicated in the US,
it is important to be able to diagnose the
disease to treat as fast as possible.
• Microscopy remains the diagnostic gold
standard, but a rapid test is FDA-cleared
to help with suspected malaria cases.