Rapid diagnosis of ocular herpes simplex infections

Production of a polyclonal antibody against inosine-uridine preferring nucleoside hydrolase of Acanthamoeba castellanii and its access to diagnosis of Acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a rare disease but its prevalence throughout the globe continues to grow, primarily due to increased contact lens usage. Since early-stage symptoms associated with AK closely resemble those from other corneal infections, accurate diagnosis is difficult and this often results in delayed treatment and exacerbation of the disease, which can lead to permanent visual impairment. Accordingly, developing a rapid Acanthamoeba–specific diagnostic method is highly desired. In the present study, a rapid and differential method for AK diagnosis was developed using the secretory proteins derived from the pathogenic Acanthamoeba. Among the vast quantities of proteins secreted by the pathogenic Acanthamoeba, an open reading frame of the inosine-uridine preferring nucleoside hydrolase (IPNH) gene was obtained. After expressing and purifying the IPNH protein using the pGEX 4T-3 vector system, mice were immunized with the purified proteins for polyclonal antibody generation. Western blot was performed using protein lysates of the human corneal cell, non-pathogenic amoeba, pathogenic amoeba, and clinical amoeba isolate along with lysates from other causes of keratitis such as Staphylococcus aureus, Pseudomonas aeruginosa, and Fusarium solani to confirm Acanthamoeba-specificity. Western blot using the polyclonal IPNH antibody revealed that IPNH was Acanthamoeba-specific since these proteins were only observed in lysates of Acanthamoeba origin or its culture media. Our findings indicate that the IPNH antibody of Acanthamoeba may serve as a potential agent for rapid and differential AK diagnosis.

Difficulties imaging herpes simplex keratitis with fluorescein isothiocynate-labeled anti-HSV-1 antibodies in an ex vivo model

AIM

The aim of this study was to attempt to visualize herpes simplex keratitis in an ex vivo model using currently available ophthalmological equipment and anti-herpes simplex virus 1 (HSV-1) fluorescein isothiocynate-labeled antibody.

METHODS

Sixteen donor human corneas were included in this study. Eight corneas were infected with HSV-1, whereas 8 remained uninfected. Abrasions were made on 2 infected and 2 uninfected corneas to assess a possible nonspecific absorption of antibodies in the sites of corneal epithelial defects. Corneas were examined before and after antibody application using a slit lamp, the fluorescein enhancing filter settings of fundus camera, and Confoscan 3. All corneas were further imaged using multiphoton laser confocal microscopy.

RESULTS

Before anti-HSV-1 antibody application, no fluorescence was detected in donor corneas with the blue light of the slit lamp and fundus camera at fluorescein enhancing filter settings. Examination with the fundus camera after antibody application detected increased background fluorescence in all the corneas with more highlighted areas of epithelial defects in abraded infected and uninfected corneas. Confoscan 3 did not show a significant difference between the appearances of HSV-1-infected and control corneas with and without application of the antibody. However, specific staining was confirmed by multiphoton laser confocal microscopy in all infected corneas.

CONCLUSION

Further refinement of currently available ophthalmological tools is required to aid in vivo visualization of herpes simplex keratitis using fluorescein isothiocynate-labeled antibodies.

Diagnosis of herpes simplex virus-1 keratitis: Comparison of Giemsa stain, immunofluorescence assay and polymerase chain reaction

PURPOSE

To evaluate three different diagnostic tests against the gold standard of viral isolation, in the diagnosis of HSV-1 keratitis.

METHODS

Corneal scrapings from 170 patients with clinically suspected HSV keratitis were tested by; 1) Giemsa staining procedure for the presence of multinucleated giant cells and lymphocytes, 2) immunofluorescence assay for HSV-1 antigen, 3) polymerase chain reaction (PCR) for HSV-1 DNA and 4) virus isolation by shell vial culture in SIRC (Rabbit corneal epithelial cell line). The results of the former three tests were compared among 14 cases that were culture positive and 156 cases that were culture negative for HSV-1.

RESULTS

The sensitivity of PCR was 100%, while IFA and Giemsa had sensitivities of 85.7% and 57.1% respectively. The specificity of PCR, IFA and Giemsa were found to be 67.9%, 85.3% and 85.9% respectively.

CONCLUSIONS

In the present study, a combination of PCR and immunofluorescence assay appears to be the most suitable choice of tests for diagnosis of HSV-1 keratitis, while detection of MNGC by Giemsa staining procedure may give us a presumptive diagnosis of suspected viral infection.

Diagnosis of herpes simplex virus-1 keratitis using Giemsa stain, immunofluorescence assay, and polymerase chain reaction assay on corneal scrapings

AIMS

To evaluate three tests used routinely for the diagnosis of herpes simplex virus (HSV) keratitis.

METHODS

Corneal scrapings from 28 patients with clinically typical dendritic corneal ulcer suggestive of HSV keratitis, and 30 patients with clinically non-viral corneal ulcers, were tested by (i) Giemsa stain for multinucleated giant cells, (ii) immunofluorescence assay (IFA) for HSV-1 antigen, and (iii) polymerase chain reaction (PCR) for HSV-1 DNA, by investigators masked to clinical diagnosis. The control subjects were also investigated by smears and cultures for bacteria, fungus, and Acanthamoeba.

RESULTS

The specificity and positive predictive values of all three tests for the diagnosis of HSV keratitis were between 95-100%. The sensitivity of IFA and PCR was 78.6% and 81.2%, respectively, and the difference was not significant; however, their sensitivity and negative predictive value were significantly higher than Giemsa stain.

CONCLUSIONS

While a combination of IFA and PCR constitute the choice of tests in clinically suspected cases of HSV keratitis, multinucleated giant cells in Giemsa stain can pre-empt testing by IFA and PCR in otherwise atypical cases of HSV keratitis.

Comparison of an immortalized human corneal epithelial cell line with Vero cells in the isolation of Herpes simplex virus-1 for the laboratory diagnosis of Herpes simplex keratitis

BACKGROUND

Herpes simplex keratitis (HSK) is a sight threatening ocular infection often requiring a specific and prompt laboratory diagnosis. Isolation of Herpes simplex virus (HSV-1) in culture provides the most reliable and specific method and is considered as the "Gold Standard" in the laboratory diagnosis of HSK in spite of its low sensitivity. Using "cell lines of corneal origin" for virus isolation may be beneficial under such circumstances, since these cells have been shown to be excellent substrates for the growth of HSV-1 isolated from the cornea. We report a comparative study of a novel human corneal epithelial cell line (HCE) and the Vero cell line in the isolation of HSV-1 from corneal scrapings employing a shell vial assay.

METHODS

Corneal scrapings were obtained from 17 patients with a clinical diagnosis of HSK. All the cases were confirmed by virological investigations (PCR and viral antigen detection positive, n = 15, PCR positive, n = 1, Viral antigen positive, n = 1). Scrapings obtained from 10 patients with infectious keratitis of non-viral origin were included as controls. All the scrapings were simultaneously inoculated into shell vials of HCE and Vero cells. Cultures were terminated at 24 h post-infection. Isolation of HSV-1 was confirmed using an indirect immunofluorescence/ immunoperoxidase assay.

RESULTS

Virus could be isolated using both or either of the cell lines in 10/17 (58.82%) patients with HSK. HSV-1 was isolated from 10/17 (58.82%) and 4/17(23.52%) specimens in HCE and Vero cells, respectively (P = 0.036). None of the controls yielded HSV-1. While all the 10 (100%) strains were isolated in HCE, Vero yielded only 4/10 (40%) strains in the shell vial culture (P = 0.014).

CONCLUSIONS

HCE showed a statistically significant difference in the virus isolation rate with respect to Vero cells. HCE may be an excellent alternative cell line for the isolation of HSV-1, especially from corneal scrapings, for the laboratory diagnosis of HSK.

Collection of corneal impression cytology directly on a sterile glass slide for the detection of viral antigen: an inexpensive and simple technique for the diagnosis of HSV epithelial keratitis - a pilot study

BACKGROUND

Herpes simplex keratitis (HSK) is a sight threatening ocular infection and occurs worldwide. A prompt laboratory diagnosis is often very useful. Conventional virology techniques are often expensive and time consuming. We describe here a highly economical, simple, rapid and sensitive technique for the collection of impression cytology, for the laboratory diagnosis of HSK.

METHODS

Fifteen patients with a clinical diagnosis of HSK (either dendritic or geographic ulcers) and five patients with other corneal infections (Mycotic keratitis, n = 3, Bacterial keratitis, n = 2) were included in the study. Corneal impression cytology specimens were collected using a sterile glass slide with polished edges instead of a membrane, by pressing the surface of one end of the slide firmly, but gently on the corneal lesion. Additionally, corneal scrapings were collected following the impression cytology procedure. Impression cytology and corneal scrapings were stained by an immunoperoxidase or immunofluorescence assay for the detection of HSV-1 antigen using a polyclonal antibody to HSV-1. Corneal scrapings were processed for viral cultures by employing a shell vial assay.

RESULTS

This simple technique allowed the collection of adequate corneal epithelial cells for the detection of HSV-1 antigen in a majority of the patients. HSV-1 antigen was detected in 12/15 (80%) cases while virus was isolated from 5/15 (33.3%) patients with HSK. All the patients with a clinical diagnosis of HSK (n = 15) were confirmed by virological investigations (viral antigen detection and/or viral cultures). HSV-1 antigen was detected in the impression cytology smears and corneal scrapings in 11/15 (73.3%) and 12/15 (80%) of the patients, respectively (P = 1.00). None of the patients in the control group were positive for viral antigen or virus isolation. Minimal background staining was seen in impression cytology smears, while there was some background staining in corneal scrapings stained by the immunoassays.

CONCLUSIONS

Collection of impression cytology on a sterile glass slide is a simple, rapid and inexpensive technique for the diagnosis of HSK. Immunological techniques applied on such smears provide virological results within 2-5 hours. This technique could be modified for use in the diagnosis of other external eye diseases, which needs further evaluation.

Polymerase chain reaction in the diagnosis of herpetic keratitis: experience in a developing country

BACKGROUND

Herpetic ocular disease is a major cause of blindness. Rapid and accurate diagnosis is essential for prompt, proper treatment. We evaluated the usefulness of detection of herpes simplex virus (HSV) DNA by polymerase chain reaction (PCR) in the laboratory diagnosis of herpetic keratitis.

METHODS

A retrospective study was conducted involving 234 patients who attended the cornea clinic at the Regional Ophthalmic Institute, Chennai, India, between March 1995 and September 1997. Inclusion in the study was based on clinical diagnosis of herpetic keratitis. Oligonucleotide primers directed against the HSV-I thymidine kinase gene were used, yielding a 110 base pair amplicon. The utility of PCR analysis was assessed against other diagnostic markers: HSV isolation on cell culture, HSV antigen detection by indirect immunofluorescence, detection of anti-HSV IgG by enzyme-linked immunosorbent assay (ELISA) and detection of HSV-specific tear secretory IgA (sIgA) by ELISA. These tests showed overall sensitivity values of 22.4%, 39.8%, 30.4% and 20.3% respectively.

RESULTS

In epithelial keratitis all 35 specimens from which virus was cultured were positive by PCR. PCR gave a positive result in 23 (82.1%) of the 28 specimens in which HSV antigen was detected and in 4 (57.1%) of the 7 specimens that showed HSV-specific IgG. In addition, PCR detected HSV DNA in 5 of the 30 cases in which these three tests gave a negative result. PCR of two pooled tear samples (collected 1 week apart from the same patient) from 40 patients with stromal keratitis gave a positive result in 12 cases (30%). In stromal keratitis the sensitivity of PCR in detecting HSV DNA in tear samples was 85.7% with culture, indirect immunofluorescence and detection of anti-HSV IgG as the gold standard, and 80% with detection of sIgA as the gold standard.

INTERPRETATION

The results confirm the good correlation with the clinical picture that can be obtained with PCR analysis. They also highlight the diagnostic utility of PCR in detecting HSV DNA in tear samples. This is particularly important in herpetic stromal keratitis, in which collection of corneal scrapings is not advised and, hence, conventional techniques such as virus isolation and antigen detection become difficult.

Tear secretory IgA: evaluation of usefulness as a diagnostic marker in herpetic keratitis

In a South Indian study, an 'in-house' enzyme-linked immunosorbent assay (ELISA) was developed to evaluate the potential of herpes simplex virus (HSV)-specific tear secretory IgA (sIgA) in the diagnosis of herpes simplex keratitis (HSK). The presence of HSV-specific tear sIgA was found to be diagnostic in 20.28% of cases. The usefulness of the sIgA ELISA system was evaluated against HSV isolation, which is the 'gold standard' and HSV antigen detection, a more sensitive, commonly employed method. Analysis of HSV-specific IgG and IgM results showed their failure as reliable indicators of active or ongoing infection. Comparison of sIgA ELISA with culture as 'gold standard' showed its sensitivity, specificity, and positive and negative predictive values to be 60% (95% CI 36.4-80), 93.2% (95% CI 86.7-96.8), 60% (95% CI 36.4-80), and 93.2% (95% CI 86.7-96. 8), respectively. This study is the first report on the complete evaluation of the usefulness of tear anti-HSV sIgA in the laboratory diagnosis of HSK, taking into account both epithelial and stromal keratitis cases.