Detection of varicella-zoster virus DNA in disciform keratitis using polymerase chain reaction

Longitudinal analysis of varicella-zoster virus DNA on the ocular surface associated with herpes zoster ophthalmicus

PURPOSE

Longitudinal analysis of varicella-zoster virus DNA on the ocular surface of patients with herpes zoster ophthalmicus.

METHODS

Clinical specimens were obtained from the bulbar conjunctival surface with a cotton-tipped swab at weekly intervals for 6 consecutive weeks from 21 patients with acute ophthalmic zoster with a skin rash duration of less than 7 days. All patients received oral valacyclovir 1000 mg three times daily for 10 days without additional corticosteroids. The swabs were analyzed by means of polymerase chain reaction for the presence of varicella-zoster virus and herpes simplex virus type 1 DNA. Conjunctival swabs were also obtained from a control group of 20 patients with cataract.

RESULTS

On inclusion, varicella-zoster virus DNA was present on the ocular surface of 19 of the 21 patients. Six varicella-zoster virus DNA-positive patients had no signs of ocular inflammation. All control swabs were negative for both varicella-zoster virus and herpes simplex virus DNA. The duration of varicella-zoster virus DNA detection from rash onset varied from 2 to 34 days. The number of days between the onset of herpes zoster skin rash and the latest positive varicella-zoster virus DNA test was significantly longer in patients whose age was equal to or above the median age of 66 years than in the younger patients (Mann-Whitney test: P =.0004). At 6-week follow-up, all conjunctival swabs were negative for varicella-zoster virus DNA. However, at that time, the eyes of seven patients were still inflamed.

CONCLUSION

The duration of varicella-zoster virus DNA shedding in herpes zoster ophthalmicus is highly variable and age dependent, and is probably related to the host immune response.

Detection of herpes simplex virus DNA in atypical epithelial keratitis using polymerase chain reaction

AIM

To study herpes simplex virus (HSV) DNA in tears from patients with atypical epithelial keratitis of unknown aetiology.

METHODS

Tear samples were collected from 17 affected eyes of 17 consecutive patients suffering from epithelial keratitis in whom HSV keratitis was suspected but whose diagnosis was difficult on the basis of clinical manifestations alone. Using reduced sensitivity polymerase chain reaction (PCR), tear samples were tested for HSV DNA. Tears from the unaffected eyes of the 17 patients were also examined, along with 38 tear samples from 19 normal volunteers. Southern blot analysis was performed to confirm that amplified DNA bands were specific for HSV. Clinical correlation with photographs of corneal lesions was also investigated.

RESULTS

HSV DNA was detected in tears from the affected eyes of eight of the 17 patients with suspected HSV keratitis. Tears from the affected eyes of the other patients were PCR negative, as were tears from the unaffected eyes of all 17 patients, and from the 38 normal eyes. There was no correlation between PCR results and clinical manifestation of keratitis.

CONCLUSIONS

Based on the sensitivity of the PCR system, eight of 17 suspected HSV keratitis patients were confirmed as suffering from HSV keratitis. HSV keratitis should therefore be considered as a possible diagnosis in atypical epithelial keratitis.

Diagnosis of Fusarium keratitis in an animal model using the polymerase chain reaction

AIMS/BACKGROUND

The purpose of this study was apply the polymerase chain reaction (PCR) to develop a sensitive, specific, and rapid test to diagnose Fusarium keratitis. Fusarium is the most common cause of fungal corneal infection in some parts of the world. It is often difficult to establish that a keratitis is due to fungal infection.

METHODS

Fusarium solani keratitis was induced in three eyes of three rabbits by injection of a suspension of the fungus into the anterior corneal stroma. In one rabbit the contralateral eye served as a control. From four to 28 days after inoculation, the corneas were scraped for culture, then scraped and swabbed for PCR analysis. The PCR was performed with primers directed against a portion of the Fusarium cutinase gene, and the presence or absence of this amplified target sequence was determined by agarose gel.

RESULTS

The amplified DNA sequence was detected in 25 of 28 samples from the corneas infected with Fusarium, for a sensitivity of 89%. Only three of the 14 samples from these eyes with Fusarium keratitis were positive by culture, for a sensitivity of 21%. Seven of eight control samples were negative by the PCR based test, for a specificity of 88%.

CONCLUSION

This PCR based test holds promise of being an effective method of diagnosing Fusarium keratitis as well as Fusarium infections at other sites.

Advances in rapid laboratory diagnosis of infectious endophthalmitis

Infectious endophthalmitis is a serious ocular condition which always requires rapid medical or surgical intervention. At present this, in a number of situations, remains empirical as a consequence of problems inherent in unequivocal identification of the causative organism, should one be present. Aqueous humor smears and culture have limited value in diagnosis. Vitreous samples can often reveal the presence of microbes, but these may not necessarily be detected in all cases, principally due to suboptimal sampling or pretreatment with antimicrobials which render microbes non-culturable on routine media. Use of electron microscopy and/or immunocytochemistry offers an alternative means of identification, but these approaches have drawbacks principally associated with interpretation. Molecular methods which identify conserved sequences from common causative microbes of endophthalmitis, or which can specify whether the organism is a bacterium or a fungus may become especially important as diagnostic tools in this clinical scenario.