Typing and Acyclovir susceptibility of Herpes Simplex Viruses

Abstract

HSV infection can occur at various parts of human body site such as mouth, skin, genital, eyes, and brain. Both types, HSV-1 and HSV-2, can cause many diseases such as herpes labialis, genital herpes, herpes keratoconjunctivitis, and herpes encephalitis, etc. Normally, in immunocompetent patients, HSV infection is less severe and extensive but HSV causes a variety of infections with significant morbidity and mortality among immunocompromised persons. Nowadays, many medications are available for treatment of HSV. However, acyclovir (ACV) is the drug of choice for the treatment of HSV infections. It has been proven to have a high efficacy in suppressing HSV replication and an excellent safety profile to host. Virus-specified thymidine kinase (TK) phosphorylates ACV to its monophosphate derivation. ACV is further phosphorylated by cellular enzymes to its triphosphate derivative. ACV triphosphate binds viral DNA polymerase, active as a DNA chain terminator. ACV is only effective against actively replicating viruses and does not affect vimses in persistent or latent state. Since HSV is specifically characterized by its ability to establish and maintain latent infection in sensory nerve ganglion that can be reactivated to become reinfection. Repeated therapy of ACV is common and long term treatment in some cases is recommended. These are the possible factors to induce the ACV resistant HSV strain (ACV HSV). Recently, detection of ACV1 HSV has been reported. Occasionally, ACV resistance can be due to an alteration of the TK protein as a result of mutation in genes that codes for TK (TK gene) or more rarely, a mutation may occur in the viral DNA polymerase (pot) gene. In this study, all HSV isolates collected from January 1998 to June 2002 were typed by using indirect immunofluorescent (IFA) method with a fluorescence isothiocyanate-conjugated (FITC) monoclonal (MAb) HSV-type specific antibodies and determined the susceptibility to ACV by PRA in order to estimate the prevalence of AC\/ HSV in Thai patients. And characterization of TK-mutation in ACV HSV by DNA sequencing method will be performed, if ACV HSV was detected. Only 86 isolates (71.07%) from 121 specimens were successfully propagated. They were from male 18.60% and female 81.40%. They were typed by indirect IFA using MAb HSV-type specific. Among these clinical samples, HSV-1 was found predominately 62.79%, followed by HSV-2 34.88% and only 2.32% were mixed infection. When the samples were divided according to the site of infection, specimens from the non-genital lesion (25.58%) were 90.91% of HSV-1, and 9.09% of HSV-2. No mixed infection was found. In genital specimens (74.42%), HSV-1 was detected 53.12%, 43.75 % of HSV-2, and 3.12% of mixed infection. Only 80 HSV isolates were assayed for ACV susceptibilities. The range of IC50 of 52 HSV-1 isolates was 0.07-0.97 µg/ml and 28 HSV-2 isolates were 0.17-1.66 µg/ml. The mean IC50 of ACV for HSV-1 and HSV-2 isolates were 0.36 µg/ml (SD: 0.23) and 0.54 (SD: 0.36). No ACV HSV was detected in this study. The study showed that genital specimens were from female more than those from male (81.40%). Moreover, they were mostly collected from suspected genital herpetic lesion. Interestingly, a prevalence of HSV-1 infection in genital lesion was 53.12%. That indicated a trend of genital HSV-1 infection was increasing in Thailand. The ACV susceptibility of HSV isolates exhibited a wide spectrum from the range of IC50 both types, were 0.07-1.66 µg/ml. HSV-1 isolates were more susceptible to ACV than HSV-2 isolates and the mean IC50 of HSV-1 isolates, 0.36 (SD=0.23), and that of HSV-2 isolates, 0.54 (SD=0.36), were statistically significant difference (p= 0.02).