Human herpesviruses in the cornea

Abstract

Aims: To determine the sensitivity and specificity of culture, immunohistochemistry (IHC), the polymerase chain reaction (PCR), and in situ hybridisation (ISH) for detecting herpes simplex virus (HSV-1) in the cornea of patients undergoing penetrating keratoplasty. To compare the incidence of HSV-1 in the cornea with that of varicella zoster virus (VZV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV).

Methods: The corneas of 110 patients, 52 with a documented history of herpes keratitis (HSK) and 58 with non-herpetic corneal disease, were investigated using IHC, PCR, ISH, and culture.

Results: HSV-1 DNA and antigen were detected in 82% and 74% respectively, of corneas of patients with HSK and in 22% and 15% of corneas of patients with no history of HSK. The sensitivity of PCR and IHC was 82% and 74% with a specificity of 78% and 85%, respectively. HSV-1 DNA and antigen were found more frequently and in increased amounts in corneas of patients with a short interval between their last attack of HSK and surgery. There was a good correlation between PCR and IHC in 71%. HSV-1 was isolated by culture in 2%. Latency associated transcripts were not detected using ISH. Evidence of VZV DNA or antigen was found significantly more frequently in the corneas of patients with a history of HSK (p<0.001). No evidence of EBV or CMV was found in any cornea.

Conclusions: PCR and IHC are both sensitive for the detection of HSV-1 in the cornea. A combination of PCR and IHC increases the specificity for the diagnosis of HSK to 97%. HSV-1 appears to be slowly removed from the cornea. VZV and HSV-1 may co-infect the cornea.

Figure 1

PCR with HSV-1 TK primers (287 bp amplicon: arrow) 3% agarose gel, ethidium bromide stain. DNA marker, Hae III pBR322 digest (lanes 1 and 14). HSV-1 positive controls (50 and 5 genome equivalents) (lanes 3 and 13) and negative control (lane 2). Corneal specimens from patients with a history of HSK and a relatively short history from last episode of HSK to surgery show a strong signal (lanes 5, 10, and 12), compared with a weaker signal in patients where the interval form HSK to surgery is much longer (lanes 8 and 9), or a patient with no history of HSK but with evidence of HSV-1 DNA, where the signal is also much less (lane 11). Corneas from patients with no history of HSK and no evidence of HSV-1 DNA (lanes 4, 6, 7).

Figure 2

Immunohistochemistry: HSV-1 antibody, DAB and haematoxylin counterstain. Posterior stromal keratocyte and endothelial cell positivity with HSV-1 antibody. No inflammation is present (original magnification ×320).

Figure 3

PCR with VZV gene 29 primers (333 bp amplicon: arrow). DNA marker, Hae III pBR322 digest (lanes 1 and 14). VZV positive control (lane 3), negative control (lane 2). Corneal samples from patients with a history of HSK and evidence of VZV (lanes 7, 8, 11-13). Patients with history HSK but no evidence VZV (lanes 4-6, and 9, 10).

Figure 4

Immunohistochemistry: VZV antibody, DAB and haematoxylin counterstain. The labelling is associated with keratocyte nuclei and nuclear membrane. No inflammation is present (original magnification ×800).