|Year : 2014 | Volume
| Issue : 1 | Page : 26-30
A comparative study on microscopic agglutination test and counterimmunoelectrop- horesis for early detection of human leptospirosis
R Saravanan, P Saradhai, E Rani, V Rajasekar
Department of Biotechnology, Biomedical Engineering and Research Foundation, Periyar University, Salem, Tamil Nadu, India
|Date of Submission||25-Jan-2013|
|Date of Acceptance||22-Aug-2013|
|Date of Web Publication||4-Jan-2014|
Department of Biotechnology, Biomedical Engineering and Research Foundation, Periyar University, Salem, Tamil Nadu
Source of Support: Biomedical Engineering and Research Foundation
Salem,, Conflict of Interest: None
Background and Objectives: Leptospirosis is a potentially fatal bacterial disease that mimics many diseases; therefore, laboratory confirmation is pivotal. Though microscopic agglutination test (MAT) is accepted as World Health Organisation (WHO) reference test, it has got many pitfalls such as being hazardous, tedious, cumbersome and expensive. Counterimmunoelectrophoresis (CIE) is popularly used for diagnosing many infectious diseases but rarely for Leptospirosis. The aim of this study is to find suitability of CIE for the routine laboratory diagnostic purposes. Materials and Methods: Repeat sampling (paired sera) was possible from 401 subjects of which 181 were in-patients of Salem Government General and Private Hospitals and the remaining 220 MAT negative healthy College students gave their consent for the study. All the 802 sera samples were collected from January 2009 to November 2012 and subjected to the present study. After carrying out MAT and CIE on the suspected and control samples, a comparative evaluation was conducted. McNemars test method was used to find out the significant difference between the two tests in the early diagnosis. Result: The sensitivity, specificity, Positive Predictive value (PPV), Negative Predictive value (NPV) and Efficiency test for CIE were 96.80%, 89.28%, 95.23%, 92.59% and 94.47%, respectively. The corresponding values for MAT were 95.90%, 89.83%, 95.08%, 91.37% and 93.92%, respectively. There was no significant difference between MAT and CIE at 95% and 99% confidence intervals according to McNemars test. P value in the early stage of illness was greater for CIE than MAT when Polymerase Chain Reaction (PCR) was used as Gold Standard of diagnosis. Interpretation and conclusion: It was concluded that the CIE could be advantageous over MAT due to its safety, rapidity, simplicity, economic and easy for large number of samples. It can answer little earlier than MAT and found as reliable as that of MAT. Since both the tests had shown similar efficacies in the later stage of the illness, the importance could be given to CIE due to early diagnosis.
Keywords: Counterimmunoelectrophoresis, diagnosis, microscopic agglutination test, Salem, suspected leptospirosis, sensitivity, specificity
|How to cite this article:|
Saravanan R, Saradhai P, Rani E, Rajasekar V. A comparative study on microscopic agglutination test and counterimmunoelectrop- horesis for early detection of human leptospirosis. Indian J Med Microbiol 2014;32:26-30
|How to cite this URL:|
Saravanan R, Saradhai P, Rani E, Rajasekar V. A comparative study on microscopic agglutination test and counterimmunoelectrop- horesis for early detection of human leptospirosis. Indian J Med Microbiol [serial online] 2014 [cited 2020 Nov 24];32:26-30. Available from: https://www.ijmm.org/text.asp?2014/32/1/26/124291
| ~ Introduction|| |
Leptospirosis is a potentially fatal infectious disease, which is neglected and very widely prevalent in India causing a major public health problem. It can display a wide array of clinical symptoms mimicking better-known illnesses.  It may be confused with malaria, viral hepatitis, influenza, dengue fever, rickettsial infections, typhoid fever, melioidosis and others.  Leptospirosis is underreported due to lack of clinical suspicion and barriers to diagnostic capacity for confirmation. Early diagnosis and the ability to differentiate leptospirosis from other diseases are important to reduce the risk of more serious infection or mortality. 
Microscopic agglutination test (MAT) is accepted as World Health Organisation (WHO) reference test in spite of several pitfalls like being hazardous, tedious, cumbersome, requiring expensive medium for regular maintenance of culture, technically demanding etc.  MAT involves serial dilutions of patient sera mixed with live suspensions of Leptospira. If agglutinating antibodies against Leptospira are present, the spirochetes will clump. This can be observed only under dark field microscope.  MAT is available only in few research institutes.  It is not helpful for routine laboratory diagnosis of leptospirosis during acute illness.  For these reasons, MAT is not frequently employed for diagnosis other than research. Therefore, an alternate tool, which has got good sensitivity and specificity equivalent to MAT, is needed for rapid, economic and simple diagnosis of leptospirosis.
Counterimmunoelectrophoresis (CIE) is a popular method used for the diagnosis of numerous infectious diseases but less utilised for leptospirosis diagnosis.  CIE is safe, fast, easy to perform, inexpensive and ideal for analysis of large number of samples.  CIE is able to detect acute infection earlier than MAT, employing only one genus specific antigen, which can be conveniently adapted for leptospirosis cases.  The test gives result within 10-15 minutes. Antigen stability for CIE technique remains 6 months without loss of titre,  whereas for MAT live antigens needed to be sub-cultured every week in the costly Ellinghausen-McCullough-Johnson-Harris (EMJH) liquid medium. The suitability of CIE compared with MAT in leptospirosis diagnosis has not been well researched on. The aim of this study is to compare the relative sensitivity, specificity and efficiency of CIE with MAT for early detection of leptospirosis to find the suitability of CIE for laboratory diagnosis where MAT is not possible. The present study is essential for a developing country like India which has leptospirosis outbreaks during rainy season and the preponderance of simple diagnostic laboratories throughout our country.
| ~ Materials and Methods|| |
Repeat sampling (paired sera) was possible from 401 subjects of which 181 were in-patients of Salem Government General and Private Hospitals and the remaining 220 were MAT negative healthy College students who came as volunteers for the study. All the 802 sera samples were collected from January 2009 to November 2012 after taking their written consent from them or their legal guardian (if they were minor). Suspected cases were selected based on Faine's criteria. The clinical signs and symptoms were pyrexia, meningitis, myalgia, conjunctival suffusion, nausea, vomiting, petechial haemorrhages, rashes, hepatitis and acute renal failure. About 5 ml of the whole blood sample were collected in sterile 5 ml serum vials (TARSON), repeat sampling was done in the same patient with a gap of 7 days from the day of first sampling. Blood samples were transported within 1 h by any one of the researchers and the sera were separated and preserved at −20°C until further use. Of the 181 patient samples in the age group 1-15, 57% were from males and 43% from females. Among the 104 male samples, 25% were in the age group 1-5, 44% in the age group 6-10 and 31% in the age group 11-15. Similarly, for 77 female samples, 16% were in the age group 0-5, 52% in the age group 6-10 and 32% in the age group 11-15 [Table 1].
The antigens used for the study namely Leptospira interrogans serovars autumnalis, australis, canicola, javanica and patoc 1 were taken for the study and cultured in EMJH containing 1% Bovine Serum Albumin (BSA) and incubated at 30°C for 10 days. The antigen extract from these strains were obtained as described by Myers (1987)  with some modifications. Each strain was grown in 250 ml of medium and harvested by centrifugation at 11,000 × g for 15 min. The pellet was treated with 10 ml Triton X-100 (4%) in 0.01 M phosphate buffered saline (PBS), pH 7.2 and heated in a water bath for 4 h at 50°C, with periodic shaking. This suspension was centrifuged at 11,000 × g for 20 min. The supernatant was preserved with sodium azide (1%). For the purpose of standardisation, antigens were titrated by doubling dilutions in PBS against 10 MAT and Polymerase Chain Reaction (PCR) positive serums and 10 MAT and PCR negative serum samples, for finding the concordant results to pass the quality control. The working concentration for standardisation of antigen for CIE was found to be 1:4 dilutions to get a clear positivity by precipitin arc for the positive samples.
Glass slides (75 by 50 mm) were covered with a thin layer of 0.9% molten agarose (Sigma Chemical Co., St. Louis, USA.) in 0.05 M Veronal buffer (pH 7.5) containing 0.01% sodium azide and allowed to dry. 8 ml volume of the same agar solution was layered onto each slide with a clean pipette. It was allowed to gel at room temperature. Slides were placed in petri dishes and refrigerated at 4°C for at least 10 min. A template was then placed under each glass slide, and wells of diameter 2 mm were made in the gel with a punch. The design consisted of two parallel rows of six wells each separated by a distance of 5 mm. Within each row, the distance between wells was 5 mm.
Electrophoresis was carried out with 0.05 M Veronal buffer (pH 7.5) in the buffer reservoirs. The wells corresponding to the anode were filled with the serum samples diluted in PBS buffer. The pH of the buffer was 7.2 in serial two fold up to 1:32. A constant electric current (6 mA/slide) was applied to each side of the slide for 30 min, at a potential difference of 10 V, with the same buffer. Connecting filter-paper saturated in buffer was placed on both ends of the slide. Subsequently, the cathode side of slide was filled with the antigen, and the run was continued for additional 90 minutes. Positivity of the CIE test consisted of visual detection of one or more precipitin arc between the wells. Results were read immediately after electrophoresis and again after setting overnight. Positive and negative controls were used in each run. 
Microscopic agglutination test
MAT was performed on the paired samples using a battery of five live leptospiral strains as antigens. The pathogenic strains were: L. australis, L. autumnalis, L. Icterohaemorrhagiae and L. javanica. The non pathogenic (genus specific) strain used was L. semaranga (Patoc I). The antigens used were 5-7 days old auto agglutination free cultures grown in EMJH liquid medium (Difco, Sparks, UK) with approximately 1 × 10 8 −2× 10 8 organisms/mL. The test was performed by a modified Galton (1965) technique.  Twenty-five micro litres of sera were diluted with Phosphate Buffer Saline (PBS) pH 7.2 and loaded into six wells of micro titre plate from 1:20 to 1:640, respectively. Twenty-five micro litres of each serogroup antigen was added into each well. The specimens were mixed gently. After leaving for 2-3 h at room temperature, 3 μl of the suspension was dropped on a slide. The agglutination was observed under dark field microscope at a final magnification of 200×. Sera showing positive reaction were then retested against the respective serogroup using doubling dilutions starting from 1:20 up to end titres. A titre of 1:80 or above was considered as positive.
Polymerase chain reaction
PCR (Eppendorf Master Cycler, Germany) was attempted as Gold Standard of diagnosis for the comparative study. CIE positive and MAT negative cases (acute samples of GH 21, 84, 151 and 168) were confirmed using the forward primer 5'-CTG AATCGCTAGTATAAAGT -3' and reverse primer 5'- GG AAAACAAATGGTGGGAAG-3' (Ab gene, UK) for the amplification of Leptospira deoxyribonucleic acid (DNA). In a sterile 0.5 ml microfuge tube, the following contents were added 4 μl of 10 × PCR buffer, 7 μl of Template DNA, 1 μl of forward and reverse primer, 2 μl of 25 mm magnesium chloride, 4 μl of deoxynucleotide triphosphates (dNTPs), 2 μl of Taq DNA polymerase and 29 μl of triple distilled deionised water. Vortex the tubes gently and the tubes were spun for 10 seconds to settle the contents and the tubes were placed in a controlled temperature heat block of the thermocycler. The thermal profiler involved 30 cycles of each as described by the following steps. Denaturation at 94°C for 1 minute 30 seconds, Primer annealing at 56°C for 1 minute and Polymerisation at 72°C for 1 minute. The final steps were allowed at 72°C for 3 minutes extension to ensure the complete polymerisation.  Amplified PCR products were separated by electrophoresis on 1.5% agarose gel stained with ethidium bromide and visualised under ultraviolet (UV) transilluminator and documented.  L. semeranga (Patoc I) was used as positive control and distilled water was used as negative control.
The indices of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) and efficiency test for CIE and MAT were calculated as follows. 
- % Sensitivity = true positive/(true positive + false negative) × 100
- % Specificity = true negative/(false positive + true negative) × 100
- PPV = true positive/all positive test
- NPV = true negative/all negative test
- Efficiency of test = (true positive + true negative)/total samples.
The McNemar test was used to compare the confidence interval and P values of CIE and MAT. 
| ~ Results|| |
When CIE and MAT tests were conducted separately for the sera samples with reference to PCR as the Gold Standard, the following results were obtained. The sensitivity, specificity, PPV, NPV and Efficiency test for CIE were 96.80%, 89.28%, 95.23%, 92.59% and 94.47% the corresponding values for MAT were 95.90%, 89.83%, 95.08%, 91.37% and 93.92% [Table 2]. Four cases from the Government General Hospital (GH 21, 84, 151 and 168) were clearly positive in the first set of samples collected during the acute phase (7-11 days) of the illness when tested by CIE [Table 3]. The four samples were found to be clearly positive only in the repeat samples taken after 7 days when tested by MAT. Interestingly, for the above four cases, the PCR revealed positivity in both the acute and convalescent samples as that of CIE. However, no CIE negative samples were found to be MAT positive in the present study [Table 3].
The confidence intervals at 95% and 99% and proportion of positive cases according to McNemars test is presented in [Table 4]. The four CIE positive and MAT negative cases (GH 21, 84, 151 and 168) acute phase samples were confirmed as positive by PCR test which was taken as gold standard of diagnosis. Among the control group of sera, 213 of the 220 were negative by both tests. The agreement between both the tests was 96.8%.
| ~ Discussion|| |
Leptospirosis has been either un-diagnosed or under-diagnosed and under-reported in India. This is due to lack of awareness of the disease, inadequate epidemiological data, and most importantly, non-availability of appropriate standardised laboratory diagnostic facilities in most parts of our country. Although, both MAT and CIE serve the same purpose, MAT is generally considered as WHO reference test and gold standard test worldwide. It is also a traditional technique for diagnosing leptospirosis. The general opinion among researchers is that MAT is the only useful technique for epidemiological studies. But recent studies reveal that even in epidemiological studies, the statistics shown on MAT is not reliable.  Human error is possible in MAT because it depends on microscopic visual examination which differs from person to person and from one laboratory to the other laboratory. This problem is absent in CIE. CIE does not require the costly dark field microscope, live hazardous Leptospira and sub culturing on costly medium is not required, standardisation is simple in comparison with MAT and the test system is not only non-cumbersome but also rapid.
McNemars test was also used to find out the significant difference between CIE and MAT in the diagnosis of leptospirosis. At both 95% and 99% confidence intervals, CIE and MAT does not differ significantly. Both the tests are reliable since they express similar confidence levels. The P values calculated had shown 2% increase in CIE than MAT keeping PCR as the reference test. Though, this might not be a significant statistical difference, it cannot be ignored [Table 4]. Four suspected cases were declared positive by CIE and not by MAT at their acute phase of illness. When these sera samples were tested by PCR, they were clearly positive which was considered as the gold standard of diagnosis in the present study. It was interesting to note that the above mentioned four suspected acute and convalescent samples were clearly positive by PCR as that of the standardised CIE of the current study.
PCR was found useful for early and rapid diagnosis of leptospirosis. PCR detects L. interrogans DNA in body fluids [(Serum and cerebrospinal fluid (CSF)] early in the course of illness with appropriate clinical suspicion. The use of PCR to diagnose leptospirosis may eliminate the need for MAT and culture which are cumbersome and delayed diagnosis. 
The performance of a diagnostic test is judged by its sensitivity and specificity. The sensitivity of the MAT (95.90%) for the diagnosis of leptospiral antibodies was lower than that of the sensitivity of the CIE (96.80%). The paired samples collected after 7 days the sensitivity of both the test systems was found to be equal (96.80%) at the later stage of illness. The probability that CIE will be positive given a patient with the leptospiral antibody is higher than that of MAT. But specificity and PPV for both the tests appear to be more or less the same. Importantly, for NPV and - Efficiency Test (ET), the CIE test was found to be not inferior in comparison with MAT. This clearly indicates that the CIE standardised in this study was reliable. Thus, when laboratory diagnostic facilities are too limited for examining sera by the MAT, the CIE could offer a useful method for screening human sera for leptospirosis irrespective of the infecting serogroups.
Earlier studies have identified agreements between the results from both the tests. CIE technique employed a soluble antigen, which was found very useful in screening the human sera for anti-leptospiral antibodies to multiple leptospiral serogroups. In the present study, the soluble extract prepared from the serovars L. interrogans serovars autumnalis, australis, canicola, javanica and patoc I. These serovars were used mainly because of the broad cross reactivity against other serovars in the MAT that are frequently associated with human infections. The present study corroborates an earlier such study by Meyer (1987) in comparison of CIE with MAT for suspected leptospirosis in giving 97.9% efficiency.
Our findings are in agreement with an earlier study on swine Leptospirosis which reported that the precipitating antibodies were detected in 5.1 days. Around 7 th day, 90% of the sample were positive while by MAT they were still negative. On the 9 th day, positivity of CIE reached 100% and only 50% by MAT. Interestingly, from the day 11 th to 13 th , the CIE and MAT results were equivalent. 
| ~ Conclusion|| |
The authors concluded that the CIE could be advantageous over MAT due to many reasons. It is safe, rapid, simple, economical and ideal for large number of samples. It can detect antibodies earlier than MAT and is as reliable as MAT. Since both the tests had shown similar efficacies, only in the later stage of the illness the importance could be given to CIE which was found to be more reliable than MAT in diagnosing positive cases of leptospirosis at an earlier phase of illness. CIE definitely has an additional advantage of carrying out such studies in the field set up also.
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[Table 1], [Table 2], [Table 3], [Table 4]