Epizootiological observations of natural and experimental infection with sialodacryoadenitis virus in rats

The epizootiology of sialodacryoadenitis (SDA) was studied in experimentally and naturally infected rats. The infectivity of SDA virus (SDAV) in intranasally infected rats was lost by seven days after infection as determined by contact transmission. After experimental infection, SN antibody appeared earlier and titers were detectable longer than CF antibody. The prevalence of SN antibody-positive rats in naturally infected colonies remained high, whereas an increase in the prevalence of CF antibody-positive rats appeared to coincide with the introduction or resurgence of SDAV. A SDAV-free colony was established by allowing recovered dams to litter in a separate room. A spontaneous cessation of SDAV infection also was observed in an enzootically-infected colony. Clinical observations indicated that SDA can occur as a mild or asymptomatic disease, and that its clinical expression may vary from one inbred strain to another.     

Chronic sialodacryoadenitis virus (SDAV) infection in athymic rats.

Sialodacryoadenitis virus (SDAV) was detected in athymic rats subcutaneously implanted with human tumor cell lines. Clinical signs included sneezing, dyspnea, weight loss and death. Necropsy revealed both upper and lower respiratory tract disease from which Staphylococcus aureus, Pasteurella pneumotropica and Pseudomonas aeruginosa were recovered. Histopathological changes consisted of suppurative rhinitis and bronchopneumonia. Lesions characteristic of SDAV infection were found in lacrimal and salivary glands, and viral antigens were detected in the salivary glands and respiratory tract by immunohistochemistry. Submaxillary salivary gland. Harderian gland and lung homogenates from affected athymic rats were inoculated intranasally into euthymic rats as a rat antibody production test. All euthymic rats seroconverted to SDAV. Seroconversion to SDAV was demonstrated in consecutive pairs of sentinel euthymic rats housed for 6 months with infected athymic rats. Inoculation of supernatants of the original tumor cell lines into euthymic rats did not result in seroconversion. The source of the virus was not determined. In this study, spontaneously acquired SDAV infection persisted for at least 6 months in athymic rats.     

Influence of viral infections on body weight, survival, and tumor prevalence in Fischer 344/NCr rats on two-year studies

Sendai virus (SV), pneumonia virus of mice (PVM), and rat coronavirus/sialodacryoadenitis virus (RCV/SDAV) were common viral infections of rats in the National Cancer Institute-National Toxicology Program (NCI-NTP) studies from 1977 to 1983. Influence of these viral infections on body weight, survival, and prevalences of spontaneous tumors in the F344/NCr rats of 28 diet control groups at five different laboratories were evaluated. Tumor prevalences evaluated in this investigation included the following: leukemia and tumors of the anterior pituitary, lungs, salivary glands and Harderian glands in both sexes; adrenal pheochromocytomas in male rats; and mammary tumors in female rats. SV and PVM but not RCV/SDAV infections were associated with significant (P less than 0.05) decreases in body weights of male and female rats. Male rat groups with PVM infection had a lower prevalence of leukemia and male rat groups with RCV/SDAV infection had a higher prevalence of anterior pituitary tumors than the corresponding uninfected groups. Female rat groups with SV infection had greater survival and a higher prevalence of lung tumors than groups without SV infection. However, none of the tumor prevalence and survival differences were statistically significant when interlaboratory variability and time-related effects were taken into account.     

Persistence of sialodacryoadenitis virus in athymic rats

To determine whether SDAV infection persists in athymic rats, weanling athymic rats and euthymic rats were inoculated intranasally with 10(4) TCID50 of SDAV and examined periodically for up to 90 days. Viral antigen and lesions characteristic of acute SDAV infection, including rhinotracheitis, bronchitis and sialodacryoadenitis, were detected in both groups of rats during the first week. In euthymic rats, tissues were under repair and viral antigen was undetectable by day 17, and tissues were histologically normal by day 31 except for mild focal dacryoadenitis. In athymic rats, viral antigen and chronic active inflammation of respiratory tract, salivary and lacrimal glands persisted through day 90. Inflammation and viral antigen also were observed in the transitional epithelium of the renal pelvis and urinary bladder as late as day 90. Virus was isolated from nasopharynx, lung, salivary gland and Harderian gland of athymic rats through day 90. All euthymic rats seroconverted to SDAV by day 6, whereas all athymic rats remained seronegative through day 31, and two of six were seropositive by day 90. As judged by seroconversion of contact sentinels, six of six athymic rats shed virus through 6 weeks, and five of six through 10 weeks. These results indicate that SDAV persists in athymic rats, and that normal T cell function is required for host defenses against SDAV.     

Duration of mouse hepatitis virus infection: studies in immunocompetent and chemically immunosuppressed mice

The duration of mouse hepatitis virus (MHV) infection was examined in mice inoculated intranasally with selected strains of MHV. Following inoculation with virulent MHV-JHM, genetically susceptible BALB/c mice and resistant CD1 mice had detectable virus in the brain at 1 month, but not later intervals up to 12 months. BALB/c mice infected with avirulent MHV-S or MHV-1 had no detectable virus in brains at 1 month or thereafter. Immunosuppression of BALB/c mice with treatment regimens of hydrocortisone acetate or cyclophosphamide at 1 and 2 months after infection with MHV-JHM did not activate detectable virus in liver or increase the prevalence or degree of brain infection. Immunosuppression with these drugs during the acute phase of MHV-JHM infection influenced MHV infection, based on virus quantification in livers, but timing of drug treatment relative to MHV infection was critical. Mice infected with MHV developed IgG serum antibody titers that persisted without decline for up to 1 year after infection. Antibody titers varied with mouse genotype and infecting virus. These studies, using intranasal inoculation, support the conclusions of others, using other routes of inoculation, that MHV infection is not persistent in adult, immunocompetent mice.     

Diagnosis of bovine respiratory syncytial virus infection by complement fixation test.

The complement fixation test by the microtiter method was applied to the serological diagnosis of bovine respiratory syncytial (RS) virus infection. When used as complement fixing antigens, untreated infected cell culture fluid, fluorocarbon-treated, and ether-treated materials showed no differences in antigenicity among them. The complement fixing antigenicity of bovine RS virus appeared in bovine kidney and Vero cell cultures for the first time 4 days after inoculation. Both the infectivity and complement fixing antigenicity reached a maximum 6 days after inoculation. In detecting complement fixing antibody from infected cattle, the most outstanding specific reaction was obtained when 5% fresh normal calf serum had been added to the diluent of complement. Neutralizing and complement fixing antibodies were examined in serum samples from two cattle in the course of experimental infection. It was found that both antibodies turned to be positive 2 weeks after inoculation. There was a linear correlation between neutralizing and complement fixing antibody titers, when serum samples from 40 natural cases were tested in the acute and convalescent stages. In addition, common antigenicity was demonstrated between the virus of bovine origin and the Long strain of human RS virus by complement fixation test.     

Susceptibility of laboratory mice to intranasal and contact infection with coronaviruses of other species

The susceptibility of laboratory mice to intranasal and contact infection with mouse hepatitis virus (MHV)-related coronaviruses was tested in infant CD1 mice. One day old mouse pups were inoculated intranasally with respiratory MHV-S, enteric MHV-Y, rat sialodacryoadenitis virus (SDAV), human coronavirus OC43 (HCV-OC43) or bovine coronavirus (BCV). Twenty-four hours later, they were placed in direct contact with age matched sham inoculated pups. Indices of infection in virus inoculated mice included lesions by histopathology and viral antigen by immunoperoxidase histochemistry in brain, lung, liver and intestine at 3 days after inoculation. Indices of infection in contact mice included mortality or seroconversion by 21 days after exposure. Infant mice were susceptible to infection with all five viruses. Transmission by direct contact exposure occurred with MHV and SDAV, but not HCV or BCV. Furthermore, adult mice were not susceptible to infection with HCV. Tissue distribution of lesions and antigen varied markedly among viruses, indicating that they do not induce the same disease as MHV. This study demonstrates that although these coronaviruses are antigenically closely related, they are biologically different viruses and disease patterns in susceptible infant mice can be used to differentiate viruses.     

Mouse hepatitis virus S in weanling Swiss mice following intranasal inoculation

Three-week-old outbred mice were inoculated intranasally with a mildly pathogenic strain of mouse hepatitis virus (MHV-S). Tissues were analyzed for distribution of infectious virus, lesions, and viral antigen at intervals up to 49 days after inoculation. Sera were tested for neutralizing antibody to MHV-S. Within the first week of infection, virus was isolated from lung and brain of most mice and liver of one mouse, but not from blood, spleen, or intestine. Microscopic lesions consisted of mild olfactory mucosal necrosis, neuronal necrosis of olfactory bulbs and tracts, lymphoplasmacytic infiltrates and vacuolation in the brain, mild nonsuppurative pulmonary perivascular lymphocyte infiltration, focal interstitial pneumonia, and focal necrotizing hepatitis. The presence and distribution of MHV antigen, as determined by indirect immunofluorescence, correlated with virus recovery and acute lesions. No virus or antigen was demonstrable beyond day 7. Serum antibody was first detected on day 10, and titers peaked on day 28 after infection.     

Immunoglobulin G is the main protective antibody in mouse vaginal secretions after vaginal immunization with attenuated herpes simplex virus type 2.

We investigated the protective role of antibodies in vaginal secretions of mice that were immune to vaginal challenge with herpes simplex virus type 2 (HSV-2). Unfractionated vaginal immunoglobulins from immune and nonimmune mice and affinity-purified immunoglobulin G (IgG) and secretory IgA (S-IgA) from immune secretions were adjusted to their concentrations in vivo. Wild-type HSV-2 was incubated in the immunoglobulin preparations for 15 min in vitro, followed by inoculation into vaginae of nonimmune mice. HSV-2 was neutralized by unfractionated antibody and purified IgG from immune secretions but not by unfractionated nonimmune antibody or by purified immune S-IgA. The protective effect of IgG in vivo was investigated by passively transferring purified serum IgG from immune and nonimmune donors to nonimmune recipients before vaginal challenge infection. Immune IgG significantly reduced the percentage of vaginal epithelium infected, concentrations of shed virus protein in the vaginal lumen, and illness scores, even though the viral antibody titers in serum and vaginal secretions of recipient mice at the time of challenge were only 29 and 8%, respectively, of those in actively immunized mice. Additionally, removal of vaginal secretions from immune mice 10 min before vaginal challenge with HSV-2 significantly increased the concentration of shed virus protein in the vaginal lumen after challenge. Collectively, the data indicate that IgG antibody in vaginal secretions of immune mice provides early protection against vaginal challenge infection, probably by neutralizing virus in the vaginal lumen. In contrast, S-IgA antibody contributed relatively little to immune protection of the vagina.     

Humoral immunity and protection of mice challenged with homotypic or heterotypic parvovirus.

BACKGROUND AND OBJECTIVES: Two serotypes of autonomously replicating parvoviruses infect laboratory mice. Genome regions coding for the nonstructural proteins of minute virus of mice [MVM] and mouse parvovirus [MPV] are almost identical, whereas capsid-coding sequences are divergent. We addressed these questions: Does humoral immunity confer protection from acute infection after challenge with homotypic or heterotypic parvovirus, and if it confers protection against acute MPV infection, does it also protect against persistent MPV infection? METHODS: Infant mice without maternal antibody or antibody to MVM or MPV and young adult mice given normal mouse serum or antibody to MVM or MPV were challenged with homotypic or heterotypic virus. In situ hybridization with target tissues was the indicator of infection. RESULTS: Humoral immunity failed to confer protection against acute heterotypic parvovirus infection. In passive transfer studies, MPV DNA was observed occasionally in lymph nodes, intestine, or the spleen of MPV-challenged mice given homotypic antibody and kept for 6 or 28 days. Variable proportions of mice given MPV antibody and homotypic challenge had viral DNA in lymphoid tissues 56 days after virus inoculation. CONCLUSION: A mouse or colony that has sustained infection with MVM or MPV is probably fully susceptible to infection with the heterotypic virus.     

Pathogenesis of human parainfluenza virus 3 infection in two species of cotton rats: Sigmodon hispidus develops bronchiolitis, while Sigmodon fulviventer develops interstitial pneumonia.

Human parainfluenza virus 3 replicates well in the noses and lungs of two species of cotton rats, Sigmodon hispidus and Sigmodon fulviventer. Peak viral titers of nearly 10(6) PFU/g are reached 2 days after infection in both tissues, are maintained through day 5, and are equivalent in the two species. Infectious virus is eliminated by day 8 after infection. Both species produce a strong neutralizing antibody response with titers of 1:10,000 4 weeks after infection. Viral replication in the nasal epithelium results in only minor histological changes, and viral antigen is found only in the apical portion of epithelial cells. Infection of S. hispidus causes a bronchiolitis with a peribronchiolar lymphoid cell infiltration that reaches a peak 6 days after infection, and there is only a minor component of interstitial pneumonia. In contrast, infection of S. fulviventer causes an interstitial pneumonia, and this lesion reaches its maximal extent by 6 days after infection. There is minimal peribronchiolar lymphoid cell infiltration in infected S. fulviventer. Lung lesions in both species of cotton rats are largely healed 9 days after infection, and the lungs are indistinguishable from those of uninfected controls 16 days after infection. These species of cotton rats offer separate models for the two major pulmonary manifestations of human parainfluenza virus 3 infection. The models may be useful for basic studies of the pathogenesis of this infection and for initial evaluation of candidate vaccines.     

禽呼肠孤病毒感染对鸡法氏囊及免疫应答的影响

研究LY株禽呼肠孤病毒(ARV)感染1日龄SPF鸡后对法氏囊发育影响,对传染性法氏囊病毒(IBDV)、禽流感病毒(AIV)、新城疫病毒(NDV)疫苗免疫诱发的抗体的影响,及对强毒株IBDV致病作用的影响。结果表明,LY株ARV感染1日龄SPF鸡可引起法氏囊萎缩和部分淋巴细胞减少,但对增重及AIV和NDV疫苗免疫后抗体滴度却没有显著影响。ARV感染可降低弱毒IBDV疫苗免疫后的抗体反应,但对随后IBDV强毒株攻毒的抵抗力却与对照鸡无显著差异。经IBDV弱毒疫苗免疫后,再接种强毒株IBDV,不会引起死亡,但却仍能显著抑制对AIV、NDV疫苗免疫后的抗体滴度。然而,对于1~7日龄经ARV感染的鸡,IBDV强毒的这种免疫抑制作用又显著低于未经ARV感染的对照鸡。     

Prevalence of rat virus infection in progeny of acutely or persistently infected pregnant rats

Infant rats are susceptible to persistent rat virus (RV) infection, but risk of persistent infection after prenatal exposure to virus is unclear. We examined this aspect of RV infection in the progeny of dams inoculated with virus during or prior to pregnancy. Sprague-Dawley (SD) dams were infected during pregnancy (gestation day 9) by oronasal inoculation with 10(5) TCID50 of the UMass strain of RV. SD rats were infected prior to pregnancy by oronasal inoculation of two-day-old females with 10(2) TCID50 of RV-UMass, which induced persistent infection. They were mated to non-immune males after reaching sexual maturity. Rats were assessed for RV infection by virus isolation, in situ hybridization, contact transmission, or serologic testing. The progeny of dams inoculated with virus during gestation had high prevalence of infection through postpartum week 9 (9 of 12 rats were virus positive at week 3, and 7 of 10 were virus positive at week 9). Additionally, 2 of 10 rats were virus positive at least through postpartum week 15. The progeny from persistently infected, seropositive dams had no evidence of infection and did not transmit infection to contact sentinels. However, 12 dams were virus positive at necropsy and 9 had transmitted infection to their breeding partners. These results indicate that prenatal infection in non-immune dams can lead to RV persistence in their progeny. By contrast, the progeny of persistently infected dams are protected from infection, presumably by maternal antibody, although their dams can transmit infection to their breeding partners.     

Transmission of experimentally-induced rat virus infection

The duration of transmission of rat virus (RV) infection was determined using Sprague-Dawley rats inoculated oronasally as juveniles (4 weeks old) or as infants (2 days old). Contact transmission from rats inoculated as juveniles was detected for 3 weeks, whereas transmission from rats inoculated as infants occurred for 10 weeks. Transmission continued for at least 7 weeks after seroconversion occurred in rats inoculated as infants. Two of three rats that had ceased to transmit infection harbored infectious virus as detected by explantation of kidney. Intrauterine transmission occurred only after pregnant dams were inoculated with large doses of virus and was more efficient when virus was inoculated intravenously than by the oronasal route. Enzyme immunoassay antibody titers to RV in offspring of previously infected dams decreased steadily during the first 13 weeks of life and 27 of 29 offspring tested by immunofluorescence assay at 12 or 13 weeks of age were seronegative. These results indicate that RV was transmitted by rats inoculated as infants for long periods after seroconversion occurred. They also suggest that the offspring of previously-infected dams were not infected. In utero transmission of RV-Y is unlikely to occur after oronasal inoculation unless rats are exposed to large doses of virus.     

Antibody estimation by indirect complement fixation test for foot-and-mouth disease in cattle.

Antibody against foot-and-mouth disease (FMD) virus was measured by the indirect complement fixation (ICF) test. For this test serum samples were collected from cattle experimentally infected with FMD virus of O, A and Asia 1 types, as well as cattle infected in the field. Two types of antigen were used. One was antigen derived from infected lingual epithelial culture prepared by Frenkel's method with each type of the virus. The other was antigen derived from the lingual epithelium of cattle infected by virus inoculation. ICF antibody began to be dectected about 4 5 days after inoculation. It reached a maximum titer 10 14 days after inoculation, remaining at this titer for about a week or two, and then decreased gradually. It was, however, detectable even 63 days after inoculation. The rise and fall of ICF antibody was parallel with that of neutralizing antibody, although that antibody was always lower in titer than this. ICF antibody was detected type-specifically from cattle infected experimentally and naturally. These results indicated that the ICF test was available for the routine serological diagnosis and epizootiological investigation and research.     

Transmission of sialodacryoadenitis virus (SDAV) from infected rats to rats and mice through handling, close contact, and soiled bedding.

Thirty mice and six rats were exposed through handling, soiled bedding, or close contact to rats previously inoculated with sialodacryoadenitis virus (SDAV). All exposed rats developed coronaviral antibody without clinical signs or lesions of SDAV infection. Exposed mice had no lesions or clinical signs of coronavirus infection. Mice exposed by handling or by soiled bedding did not develop coronavirus antibody. Two of 10 mice exposed to SDAV-inoculated rats by close contact were coronavirus seropositive when tested 3 weeks postexposure. SDAV-inoculated rats and mice developed coronavirus lesions and antibody. These results suggest that rat-to-rat transmission of SDAV is likely via fomites or handling; however, rat-to-mouse transmission is unlikely when animals are housed and husbanded using modern techniques. Results also suggest that coronavirus antibody in mice is due to exposure to mouse coronavirus and not to rat coronaviruses.     

Reactivation of persistent papovavirus K infection in immunosuppressed mice.

Papovavirus K (K virus) is a murine papovavirus that produces a fatal interstitial pneumonia in newborn mice and a clinically inapparent infection in older animals. The present study was conducted to determine whether the virus produces latent infection in animals surviving acute infection and whether the infection can be reactivated by immunosuppression. Mice were inoculated by the oral route with 100 newborn mouse 50% lethal doses at 12 days of age and followed for 8 months by using immunofluorescence staining. Cells positive for K virus capsid antigen were found in lungs, livers, kidneys, intestines, and brains for 6 months, but not thereafter. Organ examined at 8 months were negative for virus by tissue culture assay, mouse inoculation, explantation, and cocultivation. Immunosuppression of the remaining animals with 8 weekly injections of cyclophosphamide (150 mg/kg) resulted in the reappearance of viral antigen and infectious virus in multiple organs including brains. The highest titers of virus were present in kidneys. One animal sacrificed after 42 days of immunosuppression was found to have a small pulmonary adenoma or alveologenic carcinoma, but efforts to explant this tumor into tissue culture were unsuccessful. The present study demonstrates that K virus produces a latent infection that is reactivated by immunosuppression, and our results raise questions as to whether reactivated infection may occasionally be associated with the development of neoplasia.     

Ascaris suum: Immunosuppression in mice during acute infection

Mice inoculated by stomach intubation with 10,000 embryonated Ascaris suum eggs, 4, 11, or 21 days before an intraperitoneal (ip) immunization with 2 × 10⁸ sheep erythrocytes (SRBC) had reduced numbers of direct (IgM) splenic hemolytic plaques measured at 4 days after immunization and only a marginal reduction in indirect plaques (IgG) measured at 9 days after immunization. Lower dosages of Ascaris eggs or simultaneous inoculation of Ascaris eggs and SRBC did not suppress antibody responses to SRBC. No reduction in a secondary antibody response to SRBC injected 4 days after Ascaris inoculation was observed. IgM and IgG hemagglutinin titers, as distinguished by 2-mercaptoethanol sensitivity, were suppressed in mice injected ip with 10⁸ SRBC 10 days following inoculation of 10,000 Ascaris eggs, but titers in both Ig classes were similar in infected and control mice injected with 2 × 10⁹ SRBC. At Day 20, antibody titers following ip injection of 1.0 or 100 μg of ovalbumin in alum were reduced in mice infected with 10,000 Ascaris eggs 4 days before antigen injection.Contact hypersensitivity to oxazalone was not altered in mice sensitized at 5 or 14 days after inoculation of 10,000 Ascaris eggs. The delayed hypersensitivity response, measured by footpad swelling, to an optimum intravenous sensitizing dosage of SRBC was inhibited in mice sensitized 10 days after Ascaris infection, but not inhibited in mice sensitized at 21 or 32 days after infection. In contrast, the delayed hypersensitivity response to subcutaneous sensitization with SRBC 10 days after Ascaris infection was not altered.     

Experimental Parker's coronavirus infection in Wistar rats

Specific Pathogen Free (SPF) male Wistar rats were inoculated intranasally with Parker's rat coronavirus (PRC), then killed at various intervals post-inoculation (pi). PRC inoculated rats had transient respiratory signs. Intermandibular swelling was evident in some rats at 6-8 days pi. During the acute stages of the disease, inflammatory lesions were present in the respiratory tract and in the salivary and lacrimal glands. Regenerative lesions were observed in the salivary and lacrimal glands at 2 weeks pi. Inoculated rats seroconverted at 8-14 days pi, and significant coronaviral antibody titers were present in inoculated rats examined at 21 days pi with PRC. Changes in the respiratory tract and salivary and lacrimal glands were identical in incidence, distribution and nature to those observed in sialodacryoadenitis (SDA) virus inoculated Wistar rats. Thus, in the absence of viral isolation and characterization, "rat coronavirus infection" is a more appropriate term than either PRC infection or sialodacryoadenitis (SDA).     

Persistent infection with mouse hepatitis virus of low virulence in nude mice.

A persisting type of infection with wasting syndrome was established in congenitally athymic nude mice after intraperitoneal inoculation with a mouse hepatitis virus which was not fully pathogenic for heterozygous haired littermates. From the liver, spleen, lymph nodes, and brain of most infected nude mice, the virus was detected at high titers during aperiod from 6 to 35 days postinfection, occurrence of degenerative and necrotic lesions being correlated with virus titers in these organs. The titer of serum neutralizing antibody remained undetectable or very low in most diseases nude mice, whereas some animals resisting the infection could produce antibody at a later stage. In heterozygous haired mice, some lesions were detectable at a very early stage of infection in the spleen and liver, but they seemed to disappear with a marked elevation of the neutralizing antibody titer. Nude mice were able to resist the virus infection when they had previously received transfer of thymocytes from weanling heterozygous littermates.