Comparison of Blood Smear, Antigen Detection, and Nested-PCR Methods for Screening Refugees from Regions Where Malaria Is Endemic after a Malaria Outbreak in Quebec, Canada

Abstract

The importation of malaria into a region where it is not endemic raises many concerns, including the timely delivery of appropriate care, safety of the blood supply, and the risk of autochthonous transmission. There is presently no consensus on the best way to screen mobile populations for malaria. Between August 2000 and March 2001, 535 refugees arrived in Quebec, Canada, from Tanzanian camps. Within 4 weeks of resettlement of the first group of 224, the McGill University Centre for Tropical Diseases noted an outbreak of malaria across the province (15 cases over a 3-week period). This group (group 1) was traced and screened for malaria between 3 and 4 months after arrival in Canada. Subsequent groups of 106 and 205 refugees were screened immediately upon arrival in Canada (group 2) and immediately prior to their departure from refugee camps (group 3), respectively. A single EDTA-blood sample was obtained from 521 refugees for testing by thick and thin blood smears (groups 1 and 2), antigen detection (ICT Malaria Pf and OptiMAL; group 1 only), and nested PCR (all groups). Overall, 98 of 521 refugees were found to be infected (18.8%). The vast majority of infections (81 of 98) were caused by Plasmodium falciparum alone. Using PCR as the "gold standard," both microscopy (sensitivity, 50%; specificity, 100%) and antigen detection (ICT sensitivity, 37.5%; ICT specificity, 100%; OptiMAL sensitivity, 29.1%; OptiMAL specificity, 95.6%) performed poorly. None of the PCR-positive subjects were symptomatic at the time of testing, and only two had recently had symptoms compatible with malaria (with or without diagnosis and treatment). Active surveillance of migrants from regions of intense malaria transmission can reduce the risk of morbidity in the migrant population and mitigate against transmission to the host population. Our data demonstrate that PCR is, by far, the most powerful tool for such surveillance.

Evaluation of Two Nested PCR-Based Diagnostic Assays for Plasmodium Falciparum Infection

“…The result of this study indicated that the nested PCR protocol A was more efficacy and superior for detection of P. falciparum over protocol B. The detection limit of this protocol was good and similar as found in previous nested PCR studies [5,[23][24][25].…”

“…However, the limitations of microscopy are the requirement of skill and experience of the investigators. In addition, low sensitivity (100-200 parasites/μl of blood), time-consuming, and irregularity in species identification have been reported [5]. Hence, mixed infections have been found to misdiagnose.…”

Comparison of the diagnosis of malaria by microscopy, immunochromatography and PCR in endemic areas of Venezuela

“…Other studies from Thailand, USA, Honduras and Colombia (22)(23)(24)(25) have shown sensitivities and specificities close to 100%, while one study from Canada (26) showed a sensitivity of 29.1 but a specificity of 95.6%.…”

Immunochromatographic Methods in Malaria Diagnosis

“…ICT may also be used as an initial investigation in critically ill patients who are suspected to have malaria where the parasites may be sequestrated. Polymerase chain reaction based diagnosis of malaria although gives far better results is confined to few centres in India [17] . Cooke et al [11] 91.3 9 2 Gupta et al [9] 87.5 100 Palmer et al [12] 94 (P vivax) 100 88 (P falciparum) 99.9 This study 100 (P vivax) 100 96 (P falciparum) 100…”