Viruses of guinea pigs: considerations for biomedical research

Molecular and biological characterization of a new isolate of guinea pig cytomegalovirus

Development of a vaccine against congenital infection with human cytomegalovirus is complicated by the issue of re-infection, with subsequent vertical transmission, in women with pre-conception immunity to the virus. The study of experimental therapeutic prevention of re-infection would ideally be undertaken in a small animal model, such as the guinea pig cytomegalovirus (GPCMV) model, prior to human clinical trials. However, the ability to model re-infection in the GPCMV model has been limited by availability of only one strain of virus, the 22122 strain, isolated in 1957. In this report, we describe the isolation of a new GPCMV strain, the CIDMTR strain. This strain demonstrated morphological characteristics of a typical Herpesvirinae by electron microscopy. Illumina and PacBio sequencing demonstrated a genome of 232,778 nt. Novel open reading frames ORFs not found in reference strain 22122 included an additional MHC Class I homolog near the right genome terminus. The CIDMTR strain was capable of dissemination in immune compromised guinea pigs, and was found to be capable of congenital transmission in GPCMV-immune dams previously infected with salivary gland‑adapted strain 22122 virus. The availability of a new GPCMV strain should facilitate study of re-infection in this small animal model.

Animal cytomegaloviruses

Cytomegaloviruses are agents that infect a variety of animals. Human cytomegalovirus is associated with infections that may be inapparent or may result in severe body malformation. More recently, human cytomegalovirus infections have been recognized as causing severe complications in immunosuppressed individuals. In other animals, cytomegaloviruses are often associated with infections having relatively mild sequelae. Many of these sequelae parallel symptoms associated with human cytomegalovirus infections. Recent advances in biotechnology have permitted the study of many of the animal cytomegaloviruses in vitro. Consequently, animal cytomegaloviruses can be used as model systems for studying the pathogenesis, immunobiology, and molecular biology of cytomegalovirus-host and cytomegalovirus-cell interactions.

Guinea pig cytomegalovirus immediate-early transcription

Guinea pig cytomegalovirus (GPCMV) immediate-early (IE) gene expression was analyzed. GPCMV IE RNA was defined as RNA obtained from GPCMV-infected guinea pig cells treated with cycloheximide for 1 h before infection and for 4 h postinfection. Mapping studies showed that GPCMV IE genes are located at several distinct sites on the GPCMV genome. A total of 17 GPCMV IE transcripts were identified, and 9 IE transcripts coded for by three specific regions of the genome (regions I, II, and III) were characterized in detail. A series of recombinant DNA clones were generated to identify the nine IE transcripts. Three of the IE transcripts from region I and three from region III were transcribed in the same direction from overlapping sequences. The 2.0-kilobase (kb) transcript encoded by the EcoRI E DNA fragment (region II) was the most abundant IE GPCMV transcript. The cloned GPCMV DNA subfragment that was used to identify the region II EcoRI E 2.0-kb transcript did not hybridize to GPCMV early or late RNA, indicating that this transcript is expressed only under IE conditions. Expression of RNAs from the IE genes was also measured during a natural GPCMV infection in the absence of cycloheximide. During the natural infection, the transcripts previously identified under IE cycloheximide block conditions were expressed, and the region II EcoRI E 2.0-kb transcript was the most abundant transcript at 1 h postinfection. In addition, a rise and fall in RNA levels was observed during the natural infection, demonstrating the transient nature of expression of these transcripts. We conclude that GPCMV IE gene expression is complex, involving a reasonably large number of genes, and demonstrates some similarities with IE transcription by other CMVs.

Activities of two new antiviral agents against guinea pig lymphotropic herpesvirus infection in vitro

Two new antiviral agents, compound 164, also known as 2'-nor-cGMP (9-[(2-hydroxy-1,3,2-dioxaphosphorinan-5-yl)oxymethyl]-guani ne P-oxide), and compound 102 [4-amino-5-bromo-7-(2-hydroxyethoxymethyl)-pyrrolo(2,3-d)pyrimidine], together with acyclovir for comparison, were evaluated for activities against the guinea pig lymphotropic herpesvirus infection in vitro by plaque reduction and virus yield reduction assays in guinea pig embryo cells. The two new compounds were demonstrated to be more potent against guinea pig lymphotropic herpesvirus infections than acyclovir. Compound 164 was the most potent of the three; drug concentrations required to reduce the number of plaques by 50% were 2, 35.5, and 144.5 microM for compounds 164, 102, and acyclovir, respectively. The two new compounds were cytostatic but not cytotoxic to guinea pig embryo cells in cultures. Attempts were made to investigate the inhibition of viral replication by these compounds, and the influence of test conditions on antiviral evaluations is discussed.

Experimental viral pneumonia in guinea pigs: an ultrastructural study

Homogenized lung tissue was used to experimentally reproduce lethal viral pneumonia in guinea pigs. The resultant lesions corresponded with those of the spontaneous disease. Pneumonia with necrotic bronchiolar epithelium accompanied by basophilic intranuclear inclusion bodies was the primary finding. With transmission electron microscopy, numerous viral particles were found--mainly within the nucleus of pulmonary epithelial cells but also within the cytoplasm and in extracellular space. The appearance of viral particles, in particular their paracrystalline and crystalline deposition within the nucleus, indicates that our experimentally induced pneumonia was caused by an adenovirus.