Acyclovir-resistant Virus Research Articles

Prolonged Cutaneous Herpes Zoster in Acquired Immunodeficiency Syndrome

We described the development of prolonged disseminated cutaneous herpes zoster in two patients with acquired immunodeficiency syndrome. Both patients developed hyperkeratotic, verrucous lesions that progressed despite acyclovir therapy. The biopsy specimens were typical of herpes infection. The development of acyclovir-resistant varicella-zoster virus during therapy was suspected clinically in the first patient and documented in vitro in the second patient. The inability to mount an effective cell-mediated immune response contributed to the prolonged course of cutaneous zoster in our patients. The hyperkeratotic nature of the skin lesions may reflect their chronic nature. Treatment with inadequate doses of acyclovir, allowing viral persistence and the selection of resistant strains of virus, may also be implicated. We recommend prolonged high-dose intravenous acyclovir therapy in the initial management of herpes zoster in patients with acquired immunodeficiency syndrome.

Acyclovir-Resistant Herpes Simplex Virus Causing Pneumonia after Marrow Transplantation

Three marrow transplant patients developed pneumonia due to acyclovir-resistant thymidine-kinase-deficient herpes simplex virus (HSV) type 1. In all three, pneumonia was evident at autopsy by both standard and immunohistology, and virus was recovered from culture of lung tissue. Two patients also had other pulmonary infections at death; one had only HSV pneumonia. All had received prophylaxis and repeated treatment courses with acyclovir, and all initially had acyclovir-sensitive virus. The acyclovir-resistant HSV strains were sensitive to foscarnet, and in at least one case to vidarabine, but as expected were resistant to ganciclovir. These cases represent potentially severe visceral infection in which acyclovir-resistant virus strains were primary or important copathogens. Although acyclovir-resistant HSV is generally considered less virulent, these cases illustrate the potential importance of infection due to acyclovir-resistant HSV in severely immunocompromised patients. They also highlight the need to test HSV strains for antiviral sensitivity and to consider alternative therapies to acyclovir in appropriate clinical situations.

Thymidine kinase-negative herpes simplex virus mutants establish latency in mouse trigeminal ganglia but do not reactivate.

Herpes simplex virus infection of mammalian hosts involves lytic replication at a primary site, such as the cornea, translocation by axonal transport to sensory ganglia and replication, and latent infection at a secondary site, ganglionic neurons. The virus-encoded thymidine kinase, which is a target for antiviral drugs such as acyclovir, is not essential for lytic replication yet evidently is required at the secondary site for replication and some phase of latent infection. To determine the specific stage in viral pathogenesis at which this enzyme is required, we constructed virus deletion mutants that were acyclovir resistant and exhibited no detectable thymidine kinase activity. After corneal inoculation of mice, the mutants replicated to high titers in the eye but were severely impaired for acute replication in trigeminal ganglia and failed to reactivate from ganglia upon cocultivation with permissive cells. Nevertheless, latency-associated transcripts were expressed in neuronal nuclei of ganglia from mutant-infected mice and superinfection of the ganglia with a second virus rescued the latent mutant virus. Thus, contrary to a widely accepted hypothesis, the thymidine kinase-negative mutants established latent infections, implying that neither thymidine kinase activity nor ganglionic replication is necessary for establishment of latency. Rather, thymidine kinase appears to be necessary for reactivation from latency. These results suggest that acyclovir-resistant viruses could establish latent infections in clinical settings and have implications for the use of genetically engineered herpesviruses to deliver foreign genes to neurons.

Severe, Progressive Herpetic Whitlow Caused by an Acyclovir-Resistant Virus in a Patient with AIDS

Severe, Progressive Herpetic Whitlow Caused by an Acyclovir-Resistant Virus in a Patient with AIDS

Oral acyclovir therapy of genital herpes simplex virus type 2 infections in guinea pigs.

Oral acyclovir was evaluated for its effectiveness in treating guinea pigs with primary herpes simplex virus type 2 infections. Guinea pigs inoculated intravaginally with acyclovir-susceptible strains (for which 50% inhibitory concentrations of acyclovir in cell culture were found to be in the range of 0.15 to 1.2 micrograms/ml) and treated with 5.0 mg of acyclovir per ml in the drinking water beginning 48 h postinfection showed significant reductions in lesion severity. This dosage produced serum acyclovir levels of 1.3 micrograms/ml. Lower concentrations of oral acyclovir (less than or equal to 2.5 mg/ml in the drinking water), which produced serum acyclovir levels of less than 1.0 microgram/ml, were less consistently effective against these same virus strains. When an acyclovir-resistant isolate (for which the 50% inhibitory concentration of acyclovir in cell culture was found to be 8.5 micrograms/ml) was used to initiate infection, treatment with 5 or 10 mg/ml (yielding serum levels of 1.3 and 3.5 micrograms/ml) in the drinking water had only minimal clinical benefit. However, the degree of response was difficult to determine because of the attenuated disease produced by the acyclovir-resistant virus. In vitro virus sensitivity may be predictive of the serum drug levels that need to be obtained to produce a successful response to therapy.

Identification of small DNA fragments synthesized in herpes simplex virus-infected cells in the presence of acyclovir.

The effect of acyclovir on DNA synthesized in cells infected with herpes simplex virus type 1 was examined. DNA that was synthesized in infected cells in the presence of acyclovir during a short pulse with [3H]thymidine remained near the top of an alkaline sucrose gradient after centrifugation. The sedimentation characteristics of labeled DNA were not changed after chasing in isotope-free medium. The slowly sedimenting DNA was identified as viral in origin by hybridization to purified herpes simplex virus nucleocapsid DNA. When cells were infected with acyclovir-resistant virus containing mutations in the polymerase gene, the viral DNA synthesized in the presence of acyclovir was chased into high-molecular-weight DNA. These findings are consistent with chain termination of herpes simplex virus DNA in virus-infected cells.

Drug-resistant herpes simplex virus in vitro and after acyclovir treatment in an immunocompromised patient

An acyclovir-resistant herpes simplex vims (HSV) has been isolated from an immunocompromised patient during treatment for severe orofacial HSV infections with acyclovir. The resistant virus is deficient in expression of the HSV thymidine kinase (TK). Emergence of acyclovir resistance during clinical use appears to parallel the in vitro observations of selection for TK-deflcient, acyclovir-resistant viruses following serial passage in the presence of the drug. The clinical importance of drug-resistant HSV is unclear, and further investigations are required to determine whether it will be an impediment to successful therapy of HSV infections.