Acyclovir resistance in herpes simplex virus isolates from keratitis cases: an analysis from a developing country

Area of Science:

• Ophthalmology
• Virology
• Molecular Biology

Background:

• Herpes simplex keratitis (HSK) is a significant cause of corneal blindness.
• Acyclovir (ACV) is a primary antiviral medication used to treat HSK.
• Clinical resistance to ACV in HSK cases necessitates understanding underlying resistance mechanisms.

Purpose of the Study:

• To investigate the frequency and mechanisms of ACV resistance in clinical HSV-1 isolates from HSK.
• To characterize genetic mutations associated with ACV resistance in these isolates.
• To raise awareness among ophthalmologists regarding ACV resistance in HSK.

Main Methods:

• Analysis of seven ACV-resistant HSV-1 isolates from HSK patients.
• In vitro plaque reduction assays to determine ACV susceptibility.
• Thymidine kinase (TK) activity assays.
• Polymerase chain reaction (PCR), single-strand conformation polymorphism (SSCP) analysis, and DNA sequencing of the TK gene.

Main Results:

• Four out of seven HSV-1 isolates exhibited ACV resistance via plaque reduction assay.
• Three resistant isolates showed reduced thymidine kinase activity.
• DNA sequencing revealed a deletion at nucleotide position 336 in the TK gene of two isolates, leading to a premature stop codon and impaired TK function.

Conclusions:

• Mutations in the thymidine kinase gene are a significant mechanism of acyclovir resistance in HSV-1 causing HSK.
• The identified deletion in the TK gene disrupts viral enzyme function, conferring resistance.
• Clinical and molecular surveillance of ACV resistance in HSV is crucial for effective HSK management.