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Indian Journal of Community Medicine

Test for Rapid Diagnosis of Plasmodium Falciparum Infection

Author(s): A. Chitkara, F.U. Ahmed

Vol. 29, No. 4 (2004-10 - 2004-12)

Abstract

Research question: 1. How effective is the new strip test as compared to the microscopic examination of the Giemsa stained blood film under field conditions for rapid diagnosis of falciparum malaria?

Objective: To compare the results obtained by the new strip test and those obtained by Giemsa stained blood film under field conditions.

Design: Cross-sectional study.

Setting: Malaria endemic area of Assam and Arunachal Pradesh.

Participants: Persons reporting with fever at the fever treatment camp.

Interventions: Presumptive treatment was given to all fever cases and treatment for Plasmodium falciparum malaria to those testing positive for falciparum malaria.

Results: The sensitivity, specificity, positive predictive value and negative predictive value of P. falciparum malaria were 98.5%, 99.1%, 96.4% and 99.6% respectively.

Conclusions: The strip test was easy to handle and the results were rapid. It is an effective diagnostic tool for diagnosis of plasmodium falciparum malaria in endemic areas with adverse field conditons.

Key Words: Plasmodium falciparum malaria, Rapid diagnosis, Strip test.

Introduction

Malaria is evolving as a disease, which now threatens more than 40% of the world's population. The WHO sponsored ministerial conference on malaria in Amsterdam in 1992 stressed the need for its control1. The most effective strategy of malaria control is "Early Diagnosis and Prompt Treatment." Early diagnosis involves microscopy and prompt treatment involves assessment of general condition and prescribing specific chemotherapy in adequate doses at the earliest and its compliance by the patient.

Microscopy of peripheral blood is universally used as the field diagnostic tool for malaria, but this requires a good microscope & trained personnel and the treatment of malaria at the field level is often made presumptively based only on clinical findings. This is frequently inaccurate and ultimately contributes to the development and spread of drug-resistance2. The lag period between the clinical manifestation and treatment in cases of Pf infection is an important determinant of mortality. Therefore, the urgent need is for a reliable field test for diagnosis of malaria, especially in areas with predominant Pf infection. The falciparum Immunochromatographic strip test is one such test. It provides a practical, simple, rapid, qualitative and cost-effective invitro method for detection of Plasmodium falciparum in blood. The effectiveness of such tests has been globally assessed in endemic and non-endemic areas. It was also suggested that further evaluation should be focussed on the role of this dipstick antigen-capture assay in managing malarial patients in different situations of P.falciparum transmission3.

North Eastern India is malaria endemic. In most of the area, Pf malaria is the predominant species. The Pf infested area are mostly located in forest fringes and remote riverine areas where the health infrastructure is poor. If at all the manpower is available, because of lack of facilities, early diagnosis cannot be done and treatment is mostly presumptive. In order to find out the efficacy of a rapid test, the ParaHIT f test (developed indigenously by Span Diagnostics) was chosen.

Materials and Methods

The study was undertaken by the Department of Community Medicine, Assam Medical College, Dibrugarh from June 2000 to June 2001.

Study Population

The study was conducted in malaria endemic areas of Assam and Arunachal Pradesh. In Assam, the study was conducted in Nonoi T.E. in Nagaon district; the forest fringed villages of Jorajan, Lakhipathar, Nagajan and Saraipung in Tinsukia district; Titabor P.H.C. in Jorhat district; Hathigarh T.E. and its surrounding villages in Sonitpur district. In Arunachal Pradesh, the test was carried out in the Oil India Limited drilling site field camps of Manabhum and Kharsang and the surrounding villages.

The field team consisted of one doctor and two laboratory technicians. They visited all the areas along with the local health staff and organized fever treatment camps. The team first apprised the population of the area about the test and requested them to attend the fever treatment camp. On the day of the camp, all reporting fever cases were registered and their clinical history was recorded in a pre-tested proforma, which included the patient's demographic and clinical profile and drug history. Blood was tested for the ParaHIT f test and two sets of blood slides were taken. ParaHITf test was done on the spot. All those testing positive with the ParaHITf test were treated for Pf malaria and the others were given presumptive treatment. Blood slides were brought back to the department and examined. The results of the slide examination were intimated to the local health authorities within three days.

ParaHITf test

It is a strip test which uses monoclonal antibodies against PfHRP-II protein. A capture monoclonal antibody is immobilized on the nitrocelulose membrane.

Procedure

The strips were given unique identification numbers and the same numbers were used on the slides. 5 ml of capillary blood was added to the test strip just below the arrows on the absorbent pad. The test result was interpreted after 15 minutes. If two lines develop on the test strip, it indicate positive test.

To eliminate observer bias, two different technicians did the microscopic examination of the Giemsa stained blood films and the ParaHITf test independently and the results of their observations were compared later. The quality assurance of microscopy was ensured by two stage checks. In the first stage, the chief microscopist of the District Malaria Office examined all the slides independently. The second stage consisted of independent examination of all the positive slides and 20% of all negative slides randomly by two pathologists of Assam Medical College.

Data Analysis

Results of the Giemsa stained thick blood films were used as the gold standard. Sensitivity and specificity of the ParaHITf test were calculated for microscopically positive malaria cases, Pf positives and Pv positives, separately. Positive and negative predictive values of the test were also calculated.

Results and Discussion

The present study was conducted in different endemic areas of Assam and Arunachal Pradesh from June 2000 to June 2001. On microscopic examination, out of 673 smears, 143 were found to be positive for malaria (137 P.falciparum and 6 P.vivax). The ParaHITf test was test was found positive for 140 samples. None of the P.vivax showed ParaHITf test positive. Five P. falciparum negative slides tested positive and two P. falciparum positive slides negative by the ParaHITf test [Table II & III].

Table I : Slide Examination on Microscopy

S1. No. Location Total No. of Slides Examined Slide Positivity Rate (%) Slide Falciparum Rate (%)
1. Forest Fringe Areas: Jorajan, Lakhipathar, Nagajan, Saraipung 400 18.5 17.5
2. PHC: Tengakhat: Titabor 120 7.5 7.5
3. Tea Estates: Nonoi; Hatigarh 153 39.22 37.91
  Total 673 21.25 20.36

* 2 P.falciparum and 6 P.vivax

Table II: Malaria (Pf/Pv) Postitive Cases on Microscopy

ParaHITf Test Microscopic Examination of Giemsa Stained Blood Films. Total
  Pf/Pv Positive Pf/Pv Negative  
Positive 135 5 140
Negative 8* 525 533
Total 143 530 673

For all malaria positive cases, Sensitivity, Specificity, Positive Predictive value and negative predictive value are 94.4%, 99.1%, 96.4 and 98.5% respectively.

Table III : Pf Positive Cases on Microscopy

ParaHITf Test Microscopic Examination of Giemsa Stained Blood Films. Total
  Pf Positive Pf Negative  
Positive 135 5 140
Negative 2 531** 533
Total 137 536 673

** 6 P. vivax and 525 true negatives

The sensitivity of the ParaHITf test for P.falciparum was found to be 98.54% with a specificity of 99.07%. The positive and negative predictive values of the test were 96.43% and 99.63% respectively.

The 98.54% sensitivity of th ParaHITf test was due to two false-negatives observed in patients with a proven P.falciparum parasitaemia (on thin blood smears). This was assumed to be due to insufficient concentration of HRP-II, although positive results were obtained with patients having low parasitaemias.

The specificity and negative predictive values of 99% were noted. Five confirmed false-positives were observed. All these false-positive patients had taken anti-malarial treatment (chloroquine tablets or quinine drip) prior to the test.

No problems were encountered in the performance and interpretation of the Para HITf test. The ease of handling the test and the rapid results will help the clinicians to institute prompt treatment of complicated, especially cerebral malaria cases, thereby reducing the morbidity and mortality.

In Northeast India, cases of Japanese encephlitis are also prevalent during the malaria transmission period. Both Japanese encephalitis and cerebral malaria present with similar features making prompt diagnosis and institution of specific treatment difficult in field situation. So, the test will help in early diagnosis of Pf malaria, thus enabling the treating physician to institute specific treatment of those suffering from Pf malaria and reduce the case fatality rate.

The only limitation of the test is that the PfHRP-II antigen may persist in the blood for upto 2 weeks after parasite clearance. This enhances the chance of getting more false-positive results by the test. But, this should not affect the course of treatment in a suspected case of malarial fever in an endemic area.

Acknowledgement

The authors wish to thank the Principal-cum-Chief Superintendent, Assam Medical College and Hospital, Dibrugarh for giving permission to carry out this study in the institution. We are obliged to Tata Tea Ltd.; Oil India Ltd., Joint Director of Health Services (Jorhat); Department of Pathology, Assam Medical College and District Malaria Office (Dibrugarh) for their help. We thank Span Diagnostics Ltd. for providing us with the kits and accessories.

References

  1. Uguen C, Rabodonirina M, DePina JJ, Vigier JP, Martet G, Maret M, Peyron F. ParaSingh-F rapid manual diagnostic test of Plasmodium falciparum infection., Bulletin of the World Health organisation 1995, 73 (5): 643-649.
  2. Mills CD, Burgess DCH, Taylor HJ, Kain KC. Evaluation of a rapid and inexpensive dipstick assay for the diagnosis of Plasmodium falciparum malaria. Bulletin of the World Health Organisation 1999, 77 (7): 537-559.
  3. Beadle C et al. Diagnosis of malaria by detection of Plasmodium falciparum HRP-2 antigen with a rapid dipstick antigen-capture assay. Lancet 1994, 343: 564-568.
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