Malaria is a mosquito-borne
disease caused by a parasite; intraerythrocytic protozoa of the genus Plasmodium
(e.g., P. falciparum, P. vivax, P. ovale, and P. malariae among
other species). The first two species cause the most infections worldwide. P.
falciparum is the agent that most commonly causes severe and potentially
fatal malaria. P. vivax and P. ovale may have dormant liver stage
parasites, which can reactivate and cause malaria several months or years after
the infecting mosquito bite. P. malariae can result in long-lasting
infections and if untreated can persist asymptomatically in the human host for
years, even a lifetime. About 1600 cases of malaria are reported each year in
the United States, most of which are imported, i.e., acquired in malaria-endemic
countries.
Clinical Description
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 influenza
and other common viral infections). Likewise, the physical findings are often
not specific (elevated temperature, perspiration, tiredness). In severe malaria
(caused by P. falciparum), clinical findings (confusion, coma, neurologic
focal signs, severe anemia, respiratory difficulties) are more striking and may
increase the suspicion index for malaria.
Laboratory Criteria for Diagnosis:
Detection of circulating malaria-specific antigens using
rapid diagnostic test (RDT), OR
Detection of species specific parasite DNA in a sample of peripheral blood using
a Polymerase Chain Reaction test.
(Note: Laboratory-developed malaria PCR tests must fulfill Clinical Laboratory
Improvement Amendments [CLIA] requirements, including validation studies), OR
Detection of malaria parasites in thick or thin peripheral blood films, determining the species by
morphologic criteria, and calculating the percentage of red blood cells infected
by asexual malaria parasites (parasitemia).
Criteria to Distinguish a New Case from an Existing Case
A subsequent attack experienced by the same person but caused by a different
Plasmodium species is counted as an additional case.
A subsequent attack experienced by the same person and caused by the same
species in the United States may indicate a relapsing infection or treatment
failure caused by drug resistance or a separate attack.
Case classification
Suspected
Detection of Plasmodium species by rapid diagnostic antigen testing
without confirmation by microscopy or nucleic acid testing in any person
(symptomatic or asymptomatic) diagnosed in the United States, regardless of
whether the person experienced previous episodes of malaria while outside the
country.
Confirmed
Detection and specific identification of malaria parasite species by microscopy
on blood films in a laboratory with appropriate expertise in any person
(symptomatic or asymptomatic) diagnosed in the United States, regardless of
whether the person experienced previous episodes of malaria while outside the
country. OR
Detection of Plasmodium species by nucleic acid test* in any person
(symptomatic or asymptomatic) diagnosed in the United States, regardless of
whether the person experienced previous episodes of malaria while outside the
country. OR
Detection of unspeciated malaria parasite by microscopy on blood films in a
laboratory with appropriate expertise in any person (symptomatic or
asymptomatic) diagnosed in the United States, regardless of whether the person
experienced previous episodes of malaria while outside the country.
* Laboratory-developed malaria PCR tests must fulfill CLIA requirements,
including validation studies.
Case Classification Comment
Clinical samples including Blood
smears or EDTA whole blood from all cases can be referred to the CDC Division of
Parasitic Diseases and Malaria Diagnostic Laboratory for confirmation of the
diagnosis and antimalarial drug resistance testing. Any questionable cases
should be referred to the CDC Division of Parasitic Diseases and Malaria
Diagnostic Laboratory for confirmation of the diagnosis.
Comments
Blood smears from questionable cases should be referred to the CDC Division of
Parasitic Diseases Diagnostic Laboratory for confirmation of the diagnosis.
Cases also are classified according to the following World Health Organization
categories:
Autochthonous:
Indigenous: malaria acquired by mosquito transmission in an area where
malaria is a regular occurrence
Introduced: malaria acquired by mosquito transmission from an imported
case in an area where malaria is not a regular occurrence
Imported: malaria acquired outside a specific area (e.g., the United
States and its territories)
Induced: malaria acquired through artificial means (e.g., blood
transfusion, common syringes, or malariotherapy)
Relapsing: Recurrence of disease after it has been apparently cured. In
malaria, true relapses are caused by reactivation of dormant liver-stage
parasites (hypnozoites) of P. vivax and P. ovale.
Cryptic: an isolated case of malaria that cannot be epidemiologically
linked to additional cases.