Biology Reference
In-Depth Information
Clinical diagnostic algorithms are generally limited to falciparum malaria
and are site-specific (
Chandramohan et al., 2002
;
Hozhabri et al., 2002
;
Perisse and Strickland, 2008
). However, clinical diagnostic algorithms do
not reduce drug wastage, and in higher prevalence areas, risks patients
with symptomatic malaria being left untreated (
Chandramohan et al.,
2002
). In a low malaria prevalence region of Pakistan, for example, pres-
ence of fever for >3 days in the absence of cough was highly sensitive
(100%), but poorly specific (63%) (
Hozhabri et al., 2002
). The problem
with such an algorithm with respect to timely treatment of malaria is
inherent. Sensitivity also declines with increasing age in moderate malaria
transmission areas (
Mwangi et al., 2005
). Because a reliable, universally
applicable clinical diagnostic algorithm has not, and will most likely not
be established, timely laboratory diagnosis remains a critical component
of management of malaria illness.
5.2. Microscopic Diagnosis
Diagnosis of vivax malaria should be established by microscopic examina-
tion of Giemsa-stained thick and thin smear blood samples obtained every
8-12 h over a 24-48 h period. Unfortunately, the quality of microscopic
diagnosis of malaria is highly variable because of lack of standards or means
of validating proficiency among microscopists. Slide preparation and staining
methodology, microscopist skill and quality of microscope all contribute to
the risk of diagnostic error. Even in the hands of presumed expert micros-
copists, results can vary significantly depending on the species, parasite den-
sity and method of enumeration (
Milne et al., 1994
;
Maguire et al., 2006b
;
O'Meara et al., 2006
). In a study of United Kingdom clinical laboratories,
microscopists correctly identified only 63% of confirmed
P. vivax
-positive
blood films (
Milne et al., 1994
). Twenty-eight expert microscopists from
13 countries who reviewed polymerase chain reaction (PCR)-confirmed
Giemsa smears from
P. vivax
-infected individuals correctly diagnosed only
86% of vivax malaria, and agreed on only 47% of mixed infection species
(
Maguire et al., 2006b
). Even in the best hands, diagnosis to species of early
ring stage parasites is extremely difficult and hence in the context of a
busy service laboratory, the first sighting of parasites is often assumed to
be
P. falciparum
, classically regarded as the most threatening and clinically
important species, i.e. the safest diagnosis for the patient. This also results in
underestimates of mixed infections.
In recent years, the World Health Organization has made significant
progress in establishing standards for microscopic diagnosis of malaria as
