Performance of an immunochromatography test for vivax malaria in the Amazon region , Brazil

Descritores Malária vivax, diagnóstico. Plasmodium vivax. Cromatografia. Abstract The study was carried out to evaluate the diagnostic performance of the ICT malaria Pf/PvTM test for vivax malaria diagnosis in Belém, Amazon region, Brazil. The results of blood malaria parasites examination using an immunochromatography test were compared with thick blood film (TBF) examination. It was also evaluated the performance of this test storaged at three different temperatures (25°C, 30°C, and 37°C) for 24 hours before use. Overall sensitivity of ICT Pf/PvTM was 61.8% with a specificity of 100%, positive and negative predictive value of 100% and 71.8%, respectively and accuracy of 80.6%. The test sensitivity was independent of the parasite density. This test needs to be further reviewed in order to have better performance for P. vivax malaria diagnosis.

Malaria is one of the most prevalent infectious diseases in tropical areas world-wide and is one of the main causes of human morbidity in the Amazon region, north of Brazil.In this area, Plasmodium vivax is the most common human malaria parasite, causing more than 80.2% of all cases reported in 2000.
The rapid and accurate diagnosis of malaria is essential for reducing its morbidity and mortality as well as for its control.The diagnosis of malaria has been tradi-tionally based on microscopic examination of thick and thin blood films.Although simple and cheap, this procedure is however labor-intensive, time consuming and dependent upon training and expert knowledge of morphologic differentiation of plasmodial species. 3Alternative immunochromatography tests have been developed, particularly for Plasmodium falciparum that showed to be effective, quick and easy to use. 1 P. vivax malaria blood samples from Turkey were analyzed by ICT-Malaria Pv TM test (it detects P. Subjects seen at the Evandro Chagas Institute, Belém, from January to March 2000 with symptoms and signs suggestive of malaria and later had a positive slide test for P. vivax malaria were randomly tested using ICT Pf/Pv TM .Informed consent was obtained and symptoms details were registered.There were 20 asymptomatic individuals in the negative control groups, and the same number of P. falciparum infected individuals with positive thick blood film (TBF) was selected.P. vivax malaria patients had been treated with chloroquine 25 mg/kg of body weight divided in three days (10 mg/kg in day 1 and 7.5 mg/kg in days 2 and 3) plus primaquine 0.25 mg/kg of body weight for 14 days starting five days after the vivax malaria diagnosis.
The results of blood obtained through finger-prick and immediate evaluation using ICT Malaria Pf/Pv TM test (as by the manufacturer's instructions) on day 0 and days 1, 2, 3 and 4 after treatment start were compared with standard microscopy examination of malaria parasites in TBF.Fifteen samples were also evaluated using ICT Malaria Pf/Pv TM test storaged at three different temperatures (25°C, 30°C and 37°C) for 24 hours before use.TBF were examined by independent experienced microscopists who were unaware of the results, following the World Health Organization 5 recommended procedures.
In order to compare the performance of ICT Pf/Pv TM test, 30 vivax malaria patients before (day 0) and after chloroquine treatment (day 1 to 4) were included in the study.On day 0, 30 samples of P. vivax patients showed parasite density between 200 and 7,750 infected red blood cells/mm 3 , while on day 1 the parasitemia had ranged from 10 to 1,020 infected red blood cells/mm 3 .Three samples were negative.On day 2 15 samples had parasite density between 10 and 300 infected red blood cells/mm 3 , and 15 samples were negative.The parasitemia in day 3 was detected only in four samples and ranged from 10 to 40 infected red blood cells/mm 3 .In day 4 all 30 samples were negative.The ICT Pf/Pv TM test detected P. vivax in 28 samples in day 0, while in day 1 it was detected in sixteen and in day 2 only in four samples.None P. vivax sample was detected using ICT Pf/Pv TM test in day 3.Both TBF and ICT Pf/Pv TM test were negative in day 4.The ICT Pf/Pv TM was negative in all 20 samples (control group) with no parasites in the microscopy examination.The ICT Pf/Pv TM test detected all 20 P. falciparum samples that were seen in the microscopy examination.
A total of 150 paired samples were analyzed.The test performance was assessed in terms of its sensitivity and specificity.Overall sensitivity of ICT Pf/Pv TM for vivax malaria diagnosis was 61.8%, specificity of 100%, positive and negative predictive values of 100% and 71.8%, respectively and accuracy of 80.7% (Table ).The results of ICT Pf/Pv TM were variable for the three different temperatures tested.It was observed that the color of positive results (pink line) losses its intensity with increasing temperatures.
The great area of land and water, and the uncontrolled occupation of the Brazilian Amazon region, associated with the lack of personnel to carry out rapid diagnosis, all contribute to the elevated number of malaria cases in this region.
The Quantitative Buffy Coat and serological tests are useful but have limitations for the diagnosis of malaria infections and alternative methods are needed to overcome these problems.Molecular techniques are sensitive, accurate and specific 4 but expensive and require expert knowledge.Complementary and alternative diagnosis methods not dependent on microscopy are commercially available.
Although the ICT Pf/Pv TM test is known for its ease of use even for personnel not familiar with the test format, it has showed variable results in P. vivax detection and low sensitivity in the present study.The study results suggest that differences in the sensitivity of ICT Pf/Pv TM test for vivax malaria infections were independent of P. vivax density in blood sam- -vitro immunochromatography test for the detection and speciation of both P. falciparum and P. vivax malaria parasites.The aim of this study is to evaluate the diagnostic performance of the ICT Pf/ Pv TM test for diagnosis of vivax malaria in Belém, Amazon region, Brazil.

Table -
Performance of the ICT Malaria Pf/Pv TM test in diagnosing Plasmodium vivax in Belém, Brazil, compared to thick blood film (TBF).