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On
This Page:
Overview | Clinical Diagnosis | Presumptive
Treatment | Microscopic Diagnosis | Antigen
Detection | Molecular Diagnosis | Serology | Drug Resistance Tests
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Little girl with suspected malaria seen at the Moronacocha Health Center, in the outskirts of Iquitos, on the Peruvian Amazon. The clinical suspicion was confirmed when the blood smear (being taken here by a health worker) confirmed the presence of malaria parasites. (Image contributed by Dr. Jaime Chang, USAID/Peru.)
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Overview
Malaria must
be recognized promptly in order to treat the patient in time and to prevent
further spread of infection in the community.
Malaria
should be considered a potential medical emergency and should be treated
accordingly. Delay in diagnosis and treatment is a leading cause of
death in malaria patients in the United States. |
Malaria can
be suspected based on the patient's symptoms and the physical findings
at examination. However, for a definitive diagnosis to be made, laboratory
tests must demonstrate the malaria parasites or their components.
Diagnosis
of malaria can be difficult:
- Where
malaria is not endemic any more (such as the United States), health
care providers are not familiar with the disease. Clinicians seeing
a malaria patient may forget to consider malaria among the potential
diagnoses and not order the needed diagnostic tests. Laboratorians
may lack experience with malaria and fail to detect parasites when
examining blood smears under the microscope.
- In some
areas, malaria transmission is so intense that a large proportion of
the population is infected but not made ill by the parasites. Such
carriers have developed just enough immunity to protect them from
malarial illness but not from malarial infection. In that situation,
finding malaria parasites in an ill person does not necessarily mean
that the illness is caused by the parasites.
- In many
malaria-endemic countries, lack of resources is a major barrier to reliable
and timely diagnosis. Health personnel are undertrained, underequipped
and underpaid. They often face excessive patient loads, and must divide
their attention between malaria and other equally severe infectious
diseases such as pneumonia, diarrhea, tuberculosis and HIV/AIDS.
Clinical
Diagnosis
Clinical
diagnosis is based on the patient's symptoms and on physical
findings at examination.
The first
symptoms of malaria (most often fever, chills, sweats, headaches, muscle
pains, nausea and vomiting) are often not specific and are also found
in other diseases (such as the "flu" and common viral infections).
Likewise, the physical findings are often not specific (elevated temperature,
perspiration, tiredness).
In severe
malaria (caused by Plasmodium falciparum), clinical findings
(confusion, coma, neurologic focal signs, severe anemia, respiratory
difficulties) are more striking and may increase the suspicion index
for malaria.
Thus, in
most cases the early clinical findings in malaria are not typical and
need to be confirmed by a laboratory test.
"Presumptive
Treatment"
In
highly endemic areas (particularly in Africa), the great prevalence
of asymptomatic infections and lack of resources (such as microscopes
and trained microscopists) have led peripheral health facilities
to use "presumptive treatment". Patients who suffer
from a fever that does not have any obvious cause are presumed
to have malaria and are treated for that disease, based only
on clinical suspicion, and without the benefit of laboratory
confirmation.
This
practice is dictated by practical considerations and allows the
treatment of a potentially fatal disease.
But
it also leads frequently to incorrect diagnoses and unnecessary
use of antimalarial drugs. This results in additional expenses and
increases the risk of selecting for drug-resistant parasites. |
Microscopic
Diagnosis
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Blood
smear stained with Giemsa, showing a white blood cell (on left
side) and several red blood cells, two of which are infected with Plasmodium
falciparum (on right side). |
Malaria
parasites can be identified by examining under the microscope
a drop of the patient's blood, spread out as a "blood smear" on
a microscope slide. Prior to examination, the specimen is stained
(most often with the Giemsa stain) to give to the parasites a distinctive
appearance. This technique remains the gold standard for laboratory
confirmation of malaria. However, it depends on the quality of
the reagents, of the microscope, and on the experience of the laboratorian.
more:
Diagnosis (Microscopy)
Alternate methods for laboratory diagnosis include:
Antigen Detection
Various test kits are available to detect antigens derived from malaria parasites. Such
immunologic ("immunochromatographic") tests most often use a dipstick or cassette format, and
provide results in 2-15 minutes. These "Rapid Diagnostic Tests" (RDTs) offer
a useful alternative to microscopy in situations where reliable microscopic
diagnosis is not available. Malaria RDTs are currently used in some clinical
settings and programs. However, before malaria RDTs can be widely adopted,
several issues remain to be addressed, including improving their accuracy;
lowering their cost; and ensuring their adequate performance under adverse
field conditions. The World
Health Organization's Regional Office for the Western Pacific (WHO/WPRO) provides
technical information, including a list of commercially available malaria
RDTs, at http://www.wpro.who.int/rdt/.
On June 13, 2007, the U.S. Food and Drug Administration (FDA) approved the first RDT for use in the United States. This RDT is approved for use by hospital and commercial laboratories, not by individual clinicians or by patients themselves. It is recommended that all RDTs are followed-up with microscopy to confirm the results and if positive, to quantify the proportion of red blood cells that are infected. The use of this RDT may decrease the amount of time that it takes to determine that a patient is infected with malaria.
more:
Diagnosis (Rapid Diagnostic Test)
Molecular Diagnosis
Parasite nucleic acids are detected using polymerase chain reaction (PCR). This technique is
more accurate than microscopy. However, it is expensive, and requires a specialized laboratory
(even though technical advances will likely result in field-operated PCR machines).
Related Source:
Molecular Diagnosis of
Malaria and Babesiosis
Other techniques related to malaria diagnosis are:
Serology
Serology
detects antibodies against malaria parasites, using either indirect immunofluorescence
(IFA) or enzyme-linked immunosorbent assay (ELISA). Serology does not
detect current infection but rather measures past experience.
more:
Serology
Drug
Resistance Tests
Drug resistance
tests are performed in specialized laboratories to assess the susceptibility
to antimalarial compounds of parasites collected from a specific patient.
Two main laboratory methods are available:
- In vitro
tests: The parasites are grown in culture in the presence of increasing
concentrations of drugs; the drug concentration that inhibits parasite
growth is used as endpoint;
- Molecular
characterization: molecular markers assessed by PCR or gene sequencing
allow also the prediction, to some degree, of resistance to some drugs;
however, the predictive values of these molecular tests are still being
evaluated.
more:
Drug Resistance
Page last modified : June 27, 2007
Content source: Division of Parasitic Diseases
National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED)
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