Pathogenesis of Herpes simplex virus infections in guinea pigs.

The pathogenesis of herpes simplex virus types 1 and 2 has been studied in guinea pigs after inoculation by various routes (subcutaneous and intradermal infection in footpads and vaginal infection). Clinical observations as well as virus isolation studies are reported. Herpes simplex virus type 2 infection by all three routes of inoculation led to acute primary and recurrent lesions. Virus persisted in the nervous system, particularly in sensory ganglia, and locally at the site of inoculation. Herpes simplex virus type 1 infection induced no or very mild primary symptoms. Recurrent lesions were only observed after intradermal inoculation. Invasion of the nervous system and consequent establishment of latent ganglionic infection was less efficient than after herpes simplex virus type 2 infection. Peripheral persistence was, however, equally common.     

Respiratory Marburg virus infection in guinea pigs

Summary Marburg virus (MV) reproduction in organs, hematological and pathological changes were studied by virological and clinical methods, light and electron microscopy in guinea pigs respiratory challenged by the virus. Liver and spleen were most affected by MV, as in parenteral infection. The sequential involvement of cells in virus replication was also the same as in parenteral infection, with monocytoid-macrophagal cells infected first, followed by hepatocytes, spongiocytes, endotheliocytes and fibroblasts. Hemopoietic cells showed evidence of severe damage in respiratory infected guinea pigs. A distinguishing feature of the respiratory infection was close contact of leucocytes with MV infected cells. It is suggested that the entrapment and accumulation of MV in the lungs of respiratory infected guinea pigs makes possible the enfoldment leucocyte attack which does not, however, result in destruction of the infected cells.     

Protection of guinea pigs from Lassa fever by vaccinia virus recombinants expressing the nucleoprotein or the envelope glycoproteins of Lassa virus

A recombinant vaccinia virus that expresses the nucleoprotein gene of Lassa virus (Josiah strain) under the control of the P7.5 promoter was constructed using the lacZ coexpression transfer vector pSC11. Southern blot analysis demonstrated that recombination of the sequences inserted within the thymidine kinase gene of the transfer vector into the HindIII J fragment of vaccina virus genomic DNA occurred properly. A 63-kDa protein identical in electrophoretic mobility to authentic Lassa nucleoprotein was observed in recombinant virus-infected cell lysates. The reactivity of vaccinia-expressed Lassa proteins to a panel of monoclonal antibodies representing multiple epitopes on each of the N, G1, and G2 proteins was determined by indirect immunofluorescence. Lassa proteins expressed in recombinant vaccinia virus-infected cells reacted in a manner indistinguishable from that of the proteins expressed in Lassa virus-infected cells, indicating that there are no significant differences between authentic and recombinant virus-expressed proteins. Vaccine efficacy trials in guinea pigs indicated that both the nucleoprotein and the envelope glycoproteins are capable of eliciting a protective immune response against a lethal dose of Lassa virus. Ninety-four percent of the animals vaccinated with V-LSN, 79% vaccinated with V-LSGPC, and 58% vaccinated with both recombinant viruses survived a Lassa virus challenge in which only 14% of unvaccinated animals and 39% of animals vaccinated with the New York Board of Health (NYBH) strain of vaccinia virus survived. The protection resulting from vaccination with the recombinant virus vaccines did not correlate with the levels of prechallenge serum antibodies, suggesting that a cell-mediated immune response is a critical component of protective immunity to Lassa fever.     

Experimental hepatitis A virus infection in guinea pigs

Although many of the properties of hepatitis A virus (HAV) are known, several aspects of HAV pathogenesis are still not understood, such as the mechanism underlying the hepatotropism or HAV replication in extrahepatic sites. Detailed studies of these aspects were hampered mostly by the lack of accessible animal models, since only nonhuman primates are susceptible to experimental infections. An alternative animal model would also be of interest to assess the primary replication site and for the evaluation of the safety and efficacy of vaccines. A study was undertaken to determine whether HAV can infect guinea pigs and whether they are useful as a model for studying aspects of HAV pathogenesis and for the evaluation of vaccines. HAV variants adapted to primate or guinea pig tissue culture were used to inoculate guinea pigs intraperitoneally and by the oral route. The animals were observed for clinical disease, shedding of HAV in stools, viremia, seroconversion, evidence for liver damage by biochemical liver function tests, virus presence in the liver, development of hepatic histopathological changes, and occurrence of HAV in extrahepatic organs. The animals developed an active, clinically inapparent infection with specific histopathological changes in the liver. Although virus replication occurred, as shown by RT-PCR and isolation of infectious virus from feces and serum, it seems unlikely that guinea pigs are suitable for studying the clinical features of hepatitis A, because the clinical and laboratory parameters remained normal. However, guinea pigs appear useful for studying some aspects of HAV pathogenesis and for testing the safety of vaccines.     

Pathogenesis of amyotrophic leukospongiosis reproduced in guinea pigs by retrobulbar infection

Pathogenesis of amyotrophic leukospongiosis (ALSP) with a short incubation period induced in guinea pigs was studied. After retrobulbar inoculation, the unconventional ALSP virus disseminated both neurogenically (along the optic nerve) and hematogenically. At early stages of the disease the spleen appeared to play the leading role in multiplication and/or accumulation of the agent. The earliest morphological sign of the CNS involvement was vacuolation of motoneuron cytoplasm. The ALSP agent first affected the spinal motoneurons, then an ascending pathological process developed. In the terminal stage of the disease, the unconventional ALSP virus was also detected in visceral tissue, besides the CNS, spleen, and peripheral blood lymphocytes.     

Outcome of herpes simplex virus type 2 infection in guinea pigs.

Factors that influence the outcome of genital herpes simplex virus (HSV) infection were explored in a guinea pig model. The viral inoculum required to establish infection in 50% of animals (ID50) was similar for inbred (strain 2) and outbred (Hartley) guinea pigs. However, the viral inoculum required to produce clinical disease in 50% of the animals (CD50) was 10 times greater for strain 2 compared to Hartley animals. HSV infection of both inbred and outbred animals was more likely to result in death of weanling than adult animals. The duration and severity of genital disease and the magnitude of vaginal viral replication were similar for strain 2 and Hartley animals in both young and adult animals. The lethal dose for 50% of animals (LD50) was 100-fold greater than the CD50 for Hartley animals, but the LD50 and the CD50 were equal in strain 2 guinea pigs. Viral cultures of homogenized neural tissues from infected animals revealed that HSV ascended to the level of the temporal cortex in strain 2 guinea pigs while virus was never recovered above the lumbar spinal cord in Hartley animals. Endogenous peripheral blood mononuclear cell-mediated cytolytic activity against HSV-infected targets was greater prior to HSV inoculation in survivors compared to animals that died. A fatal outcome of genital HSV-2 may relate to the failure to limit CNS viral replication. Death is more common among guinea pigs that have low endogenous HSV-directed natural killer activity, such as occurs among strain 2 and young animals whether inbred or outbred.     

Experimental Lassa virus infection in the squirrel monkey.

Experimental Lassa virus infection was investigated in a nonhuman primate in order to elucidate the target organs of the viral infection and the course of pathologic events. Four squirrel monkeys (Saimiri scirreus) were inoculated intramuscularly with Lassa virus and sacrificed for organ titrations and histopathology, one each day, on Days 7, 12, 14, and 28 after inoculation. The animals showed a variable clinical course, with an incubation period of 8 to 18 days. The virus was demonstrated to be virtually pantropic; however, lymph node, liver, and kidney were key early targets. After the onset of overt disease, patterns of lymphoreticulotropism, hepatotropism, nephrotropism, adrenotropism, and persistent viremia were evident. Complement-fixing antibody failed to develop after 28 days of infection. Histopathologic findings included germinal center necrosis in spleen and lymph node; myocarditis; acute arteritis; renal tubular necrosis and regeneration; hepatocytic regeneration; chronic inflammation of choroid plexus, ependyma, and meninges; and cerebral perivascular cuffing. There is a relationship between many of these lesions and certain features of other arenavirus infections. The model offers the opportunity to pursue investigations of experimental pathogenesis, transmissibility, and efficacy of immunotherapy.     

Experimental infection and immune response of guinea pigs with varicella-zoster virus.

An immune response (fluorescent antibody to membrane antigen) was detected in guinea pigs inoculated with varicella-zoster virus (VZV) adapted to guinea pig embryonic cells, including the Oka vaccine strain, even when inoculation was by an external route, i.e., nasal or corneal. Live or UV-inactivated virus having the same virus titer before irradiation was administered to guinea pigs by the corneal route, and antibody induction was detected only with live virus. The transmission of VZV from infected guinea pigs to noninfected ones was suggested by the appearance of antibody in the serum of the latter, who were kept in the same cage. The time course of the appearance of humoral and cellular immune responses in guinea pigs was examined by the fluorescent antibody to membrane antigen test and the skin reaction, with varicella antigen representing delayed-type hypersensitivity. When VZV was injected subcutaneously, skin reaction appeared as early as 4 days after inoculation, which preceded the appearance of detectable antibody by 2 to 6 days. In in vitro studies, the Oka vaccine showed a higher adsorption rate and better growth in guinea pig embryonic cells than did other wild-type strains when assayed by the infectious center assay. These results suggest that a system of VZV adapted to guinea pig cells and guinea pigs provides a good animal experimental model for immunological study of VZV infection.     

Congenital and perinatal infection with Junin virus in guinea pigs

Junin virus infection in guinea pigs is known to be similar to human Argentine hemorrhagic fever (AHF). The guinea pig was chosen as a model for transplacental transmission of Junin virus, as both guinea pig and man have a similar placental structure. Pregnant guinea pigs were infected with the pathogenic XJ strain of Junin virus intramuscularly route at different stages of pregnancy. The group infected during the last third of pregnancy produced 16 newborn, but mortality reached 100%: 18% were born with typical AHF hemorrhagic signs, 54% without signs, and the remainder were stillborn. Virus was recovered from organs of newborns, as well as placental tissues. A second group, infected in the second third of pregnancy, died with intrauterine fetuses, all of which showed hemorrhagic signs and virus present. In a last group, infected in the first third of pregnancy, fetuses were free from macroscopic lesions. In order to determine whether lactation may be an alternative infection route in guinea pigs, mother guinea pigs were infected with Junin virus at different times postparturition. The 84% noninfected newborn housed together with their infected mothers died during the suckling period, half with typical AHF signs. Junin virus transmission from mother to fetus was thus proved, and lactation may be considered as an alternative perinatal infection route.     

Changes in bronchial response after Sendai virus infection in guinea pigs

Enhanced bronchial reactivity to inhaled histamine was observed in guinea pigs infected with Sendai virus with concomitant decrease of beta-adrenergic receptor density in the pulmonary parenchyma 2 to 3 weeks after the inoculation. Histologic examination of the bronchi showed shedding of epithelial cells with a marked infiltration of mononuclear cells. These observations suggest that damage of the bronchial epithelium and decreased density of beta-adrenergic receptor may be the causes of observed bronchial reactivity.     

Cell-mediated immunity to varicella-zoster virus infection in strain 2 guinea pigs

Young adult male strain 2 guinea pigs were inoculated intramuscularly with varicella-zoster virus (VZV) cultured in fetal guinea pig tissue cultures. Lymphocyte proliferation and interleukin 2 secretion in response to viral antigen challenge in vitro were measured at weekly intervals for 2 months and periodically thereafter. VZV-specific immunity was apparent 2 weeks after infection, peaking after 2 weeks (lymphoproliferation) or 1-2 months (interleukin 2 secretion). Diminished but significant anamnestic responses were detected as late as 30 months after infection.     

Pathogenesis of a Chinese strain of bovine adenovirus type 3 infection in albino guinea pigs

Bovine adenovirus type 3 (BAV-3) is considered one of the most important respiratory tract agents of cattle and is widespread among cattle around the world. A BAV-3 strain was isolated from a bovine nasal swab for the first time in China in 2009 and named HLJ0955. Subsequently, BAV-3 has frequently been isolated from calves with respiratory diseases in China. To date, only limited study on the pathogenesis of BAV-3 infection in cotton rats has been conducted, and the pathogenesis of BAV-3 infection in guinea pigs has not been reported. Therefore, sixteen albino guinea pigs were inoculated intranasally with HLJ0955. All of the infected guinea pigs had apparently elevated rectal temperatures (39.2 °C–39.9 °C) at 2–7 days post-inoculation (PI). Consolidation and petechial hemorrhage were also observed in guinea pigs experimentally infected with HLJ0955. Viral replication was detectable by virus isolation and titration and by immunohistochemistry in the lungs of guinea pigs as early as 24 h PI. Viral DNA was detectable in the lungs of infected guinea pigs during 11 days of observation by real-time PCR. Virus-neutralizing antibodies against BAV-3 were detectable from 11 days PI and reached a peak titer at 15 days PI. Histopathological changes mainly occurred in the lungs of infected guinea pigs and were characterized by thickening of alveolar septa, mononuclear cell infiltration, hemorrhage and alveolar epithelial necrosis. These results indicate that HLJ0955 can replicate in the lungs of guinea pigs and cause fever and gross and histological lesions. The guinea pig infection model of BAV-3 would serve as a useful system for monitoring the infection process and pathogenesis of the Chinese BAV-3 strain HLJ0955, as well as immune responses to BAV-3 vaccines.     

Recurrent genitalHerpes simplex virus (HSV) infection of guinea pigs

Intravaginal infection of guinea pigs with HSV type 2 induced lesions resembling genital herpes in humans. Chronic latent infection with spontaneously recurring genital lesions developed in animals surviving the primary disease. Clinical observations and viro-logical studies during the acute and chronic infection are reported.     

Pathogenesis of swine influenza virus subtype H1N2 infection in pigs

The purpose of this study was to elucidate pathogenesis and viral distribution in pigs infected with swine influenza virus subtype H1N2, over a period of 10 days, by morphometric analysis and in-situ hybridization. Fifteen colostrum-deprived pigs aged 3 weeks were inoculated intranasally with virus. Pneumonia was severe at 1 day post-inoculation (dpi), moderate at 3 and 5 dpi, and mild at 7 and 10 dpi. The pulmonary lesion score was correlated with the score of cells positive by in-situ hybridization for swine influenza virus (r(s)= 0.9114, P< 0.05). The distribution of swine influenza virus varied according to the duration of infection. At 1 and 3 dpi, hybridization signals were detected mainly in the bronchial and bronchiolar epithelial cells, but they were detected mainly in the pneumocytes and macrophages (alveolar and interstitial) at 7 and 10 dpi. The results confirmed that swine influenza virus subtype H1N2, isolated in Korea, is a virulent pathogen causing severe pneumonia.     

Pathogenesis of latent herpes simplex virus infection of the trigeminal ganglion in guinea pigs: effects of age, passive immunization, and hydrocortisone.

Latent herpes simplex virus (HSV) infection of the trigeminal ganglion, after corneal inoculation of virus, was investigated in guinea pigs. The effects of several factors on the establishment of ganglionic latency were investigated. Latently infected guinea pigs were clinically normal, and virus was isolated from the trigeminal ganglia by co-cultivation. It was found that newborn guinea pigs were significantly more susceptible than adult animals to the development of latent HSV infection of the trigeminal ganglion. The susceptibility of newborn guinea pigs was very much decreased, however, if they received passive immunization with immune serum or if they were born of actively immunized mothers. On the other hand, the susceptibility of adult animals, usually somewhat resistant to the development of latent HSV ganglionic infection, was markedly increased by the parenteral administration of hydrocortisone.     

Herpes simplex virus infection in guinea pigs: an animal model for studying latent and recurrent herpes simplex virus infection.

Footpad infection of guinea pigs with herpes simplex virus led to an acute local inflammatory reaction, followed by a persistent latent infection of lumbosacral dorsal root ganglia. Spontaneous reactivation of the latent virus occurred, leading to recurrent lesions at the site of the initial infection. Clinical observations and virological studies during the acute latent and recurrent infection are reported.     

Experimental infection with Treponema hyodysenteriae in guinea pigs.

Outbred and inbred (Hartley strain) guinea pigs (GP) were inoculated intragastrically with pathogenic and nonpathogenic Treponema hyodysenteriae. GP 3 to 16 weeks old received T. hyodysenteriae after a fasting period of 36 to 72 h. Infected GP with pathogenic T. hyodysenteriae developed a diarrheal and/or depressive condition, with mucus but not blood in the feces. Of 88 GP, 40 had gross lesions resembling those of swine dysentery. Lesions were limited mainly to the large intestine. TP used as controls or inoculated with nonpathogenic T. hyodysenteriae did not develop these lesions in the large intestine. These studies suggest that the GP may be used as an animal model for swine dysentery.     

Latent pseudorabies virus infection in pigs.

Latent infection with the TOP strain of pseudorabies virus (PRV) was established in 6 weeks old piglets. Infectious virus was found in oropharyngeal swabs till day 10 post infection (p.i.); later on, attempts to detect the virus remained unsuccessful. However, PRV could be isolated by explantation of tonsils, cervical lymph nodes, nasal mucosa and gasserian ganglia. These tissues were removed between 160 and 181 days p.i., during cultivation, infectious PRV was released into the culture fluid from the 3rd to the 11th day of the explantation. PRV antigen was seen by immunofluorescence only in explants coming from gasserian ganglia. It was localized in both neurons and satellite cells. In piglets given hydrocortisone before explantation, the number of virus-producing explants was not enhanced as compared to that of virus-producing explants from untreated animals.     

Use of guinea pigs for assessing the efficacy of vaccines against Lassa fever

The use of guinea pigs as a laboratory model was proven to be appropriate in investigating the vaccines developed against Lassa fever at the preclinical study stage. An adapted variant of Lassa virus was cultivated, which caused death of guinea pigs with respect for an agent's dose. Finally, it was shown to be possible to investigate the immunogenic and protective properties of the inactivated antigen of Lassa virus in experiments with guinea pigs.