Serologic analyses of cottontail rabbits for antibodies to Borrelia burgdorferi.

An enzyme-linked immunosorbent assay was developed to detect antibodies to Borrelia burgdorferi in cottontail rabbits captured in Millbrook, N.Y., and New York, N.Y. Five antigenically variable strains of B. burgdorferi were analyzed to determine the variability of serologic test results. In analyses of 79 serum samples, seropositivity ranged from 56% for a strain cultured from kidney tissues of a cottontail rabbit to 68% for a strain isolated from a larva of Ixodes dentatus, a tick that parasitized a cottontail rabbit. There were false-positive results when reference rabbit antisera to B. hermsii and Treponema pallidum were screened against B. burgdorferi. Cross-reactivity with antisera to Leptospira interrogans serovars was less pronounced. Western blot (immunoblot) analyses revealed reactivities of test sera to two or more surface or subsurface proteins of B. burgdorferi with approximate molecular masses of 18, 25 to 27, 34, 36, 41, and 59 kilodaltons. Cottontail rabbits respond immunologically to B. burgdorferi, but the observed variations in serologic test results should not be a limitation in field and laboratory investigations of Lyme borreliosis.     

Enzootic transmission of Anaplasma bovis in Nantucket cottontail rabbits

Serological studies of cottontail rabbits sampled from Nantucket Island, Mass., have suggested exposure to at least two ehrlichiae. The agent of human granulocytic ehrlichiosis (Anaplasma phagocytophilum) is intensely enzootic in rabbits there, but the identity of the other ehrlichial infection remains undescribed. We sampled rabbits over five transmission seasons and tested their blood and tissues for evidence of infection using PCR targeting an Ehrlichia genus-wide 16S rDNA target. Sequence analysis of positive amplicons revealed the presence of Anaplasma bovis, an agent not known to be present in North America. The average annual prevalence of A. bovis within rabbits, as determined by PCR of blood samples, was 18%. Haemaphysalis leporispalustris appears to serve as vector. The public health (human or veterinary) significance of this finding remains speculative.     

Pathogenesis of rotavirus infection in mice.

Three parameters of rotavirus infection, i.e., clinical disease, viral antigen in infected intestines, and infectious virus in feces, were assessed in infant mice nursed by mothers with or without preexisting rotavirus antibody. Diarrhea was the only consistent sign of clinical disease, and its course followed that of infection by about 1 day. Infected intestinal epithelial cells, except crypt cells, were observed by immunofluorescence microscopy in the duodenum, jejunum, ileum, and colon. Infection progressed in a proximal-to-distal direction with time. Viral antigen appeared in intestinal tissue later, was present in lower amounts, and disappeared sooner from infants nursed by mothers with preexisting rotavirus antibody, indicating that protection was passively transferred to these infants although the course of clinical disease was not changed.     

New member of the herpesvirus group isolated from wild cottontail rabbits

A viral agent has been isolated from naturally infected wild cottontail rabbits (Sylvilagus floridanus). The virus appears to have the general physical, chemical, and biological properties of the herpesvirus group. It differs significantly in host range and antigenic structure from the previously recognized herpesviruses and is proposed as a new member of this group of viruses. The name of Herpesvirus sylvilagus is suggested for the agent.     

Constant region IgG allotypes in cottontail rabbits: Group E allelic polymorphism

Alloantisera prepared against domestic rabbit IgG allotypes were used in hemagglutination-inhibition and direct radioimmune binding tests to detect the C_γ region allotypes in cottontail rabbits. The absence of the group d allotypes (d11 and d12) in cottontail rabbits was confirmed. However, allelic variants of the group e markers (e14 and e15) were found in some of the cottontail rabbits examined. For example, all cottontails exhibited the e15 marker and 6 out of 10 animals exhibited the e14 marker as well. Several experiments were conducted to show that the e14 and e15 antigens of domestic rabbit and cottontail IgG are identical. Other results are consistent with the hypothesis that the e14 and e15 antigens in cottontail rabbits are products of allelic genes.     

Passive immunization in experimental Herpesvirus hominis infection of newborn mice.

Infection of newborn mice with Herpesvirus hominis type 2(HVH-2) was used as an experimental model of disseminated HVH infection in newborn humans. Mice were challenged with 103 plaque-forming units of HVH-2 intranasally and were given 0.2 ml of rabbit serum intraperitoneally. Passive immunizations with rabbit anti-HVH-2 serum resulted in a significant decrease in mortality and prolongation of survival time. This effect correlated with the neutralizing antibody titer of the serum against HVH-2 and was more pronounced when immune serum was administered 1 h after infection as compared with 24 h. These results suggest that administration of high-titer anti-HVH-2 immunoglobulins shortly after delivery could afford significant protection to the newborn of a mother with genital HVH-2 infection.     

Herpesvirus infection in patients with chronic glomerulonephritis

Virological examinations of blood, urine and saliva in 75 patients with chronic glomerulonephritis (CG) revealed, in 95% of them, herpes-virus infections caused by herpes simplex virus, type 1 (34.4%), herpes simplex virus, type 2 (2.6%) and cytomegalovirus (12%) or mixed infections (46%). The infection rate in the control group of children without renal pathology was reliably lower. A majority of CG patients (94%) had a diagnostically significant level of antiherpetic antibodies, class IgG, which also evidence to chronic herpes-virus infection.     

Antigenically variable Borrelia burgdorferi isolated from cottontail rabbits and Ixodes dentatus in rural and urban areas.

Spirochetes were isolated from 71 subadult Ixodes dentatus removed from cottontail rabbits captured in Millbrook, N.Y., and in New York, N.Y. Spirochetes were also cultured from kidney tissues of six rabbits. While all isolates reacted with monoclonal antibody H9724, which identifies the spirochetes as borreliae, more than half did not bind with antibody H5332 and even fewer reacted with H3TS, both of which were produced to outer surface protein A of Borrelia burgdorferi. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles of three isolates differed from one another and from all previously characterized B. burgdorferi strains from humans, ticks, and wildlife in North America. The 12 periplasmic flagella that originated subterminally from each pointed end of a rabbit Borellia isolate contrasted with the 11 or fewer flagella for B. burgdorferi reported previously from North America. Although DNA homology and restriction endonuclease analysis also revealed differences among a rabbit kidney isolate, an I. dentatus isolate, and B. burgdorferi B31, similarities were sufficient to lead us to conclude that the borreliae in rabbits and I. dentatus are B. burgdorferi. Enzyme-linked immunosorbent assay titers of sera from humans with diagnosed Lyme disease to rabbit tick B. burgdorferi were often similar to one another and to those recorded for a reference B. burgdorferi strain.     

Latent infection induced with cottontail rabbit papillomavirus. A model for human papillomavirus latency.

Latent human papillomavirus infection, a very common event, is most likely the source of primary and recurrent papillomas of the respiratory and genital tracts and might also be the source of neoplastic lesions of the female genital tract and the penis. We have developed a simple model for papillomavirus latency using cottontail rabbit papillomavirus. Skin of domestic rabbits was minimally scarified and inoculated with dilutions of a crude virus suspension ranging from 200 ng to 20 pg viral DNA per inoculated site. Dilution of virus to less than 10 ng/site resulted in delayed and reduced efficiency of inducing warts. After follow-up of 1 to 6 months, sites immediately adjacent to papillomas and inoculated sites where papillomas did not form were biopsied and analyzed by Southern blot and polymerase chain reaction. Inoculated tissues that were clinically and histologically normal contained viral DNA at low levels, detectable by polymerase chain reaction. Ability of the latent virus to induce warts was confirmed by activation with mild skin irritation causing wart formation. This simple model system for latent papillomavirus can be used to study mechanisms of viral activation, therapies to prevent activation, and therapies to eliminate latent virus and thus cure the infection.     

Pathogenesis of K virus infection in newborn mice.

Newborn mice were inoculated with a murine papovavirus, K virus, by intracranial, intraperitoneal, oral, and intranasal routes, and the pathogenesis of infection was studied with immunofluorescence, virus assay, and histopathology. Inoculation by each route produced a fatal interstitial pneumonia. Pulmonary vascular endothelium and, to a lesser extent, cells lining hepatic sinusoids were the major sites of viral replication, but intranuclear antigen or inclusions or both were also found in extrapulmonary vascular endothelia, spleens, lymph nodes, and brains. Although K virus produced a predominantly respiratory illness, the virus was less infectious by intranasal than by oral inoculation and did not replicate in respiratory epithelial tissues. The earliest site of K virus replication was the jejunal submucosa, suggesting that in nature K virus may be transmitted by the oral route. Viral antigen was present in brains of animals inoculated by each route and correlated with the duration of viremia. Despite the presence of abundant viral antigen, however, the nervous system remained morphologically normal. The present study indicates that a member of the papovavirus group may produce clinically silent, noninflammatory involvement of the central nervous system during the initial infection of its natural host.     

Pathogenesis of Lassa virus infection in guinea pigs.

A rodent model for human Lassa fever was developed which uses inbred (strain 13) and outbred (Hartley) guinea pigs. Strain 13 guinea pigs were uniformly susceptible to lethal infection by 2 or more PFU of Lassa virus strain Josiah. In contrast, no more than 30% of the Hartley guinea pigs died regardless of the virus dose. In lethally infected strain 13 guinea pigs, peak titers of virus (10(7) to 10(8) PFU) occurred in the spleen and lymph nodes at 8 to 9 days, in the salivary glands at 11 days, and in the lung at 14 to 16 days. Virus reached low titers (10(4) PFU) in the plasma and brain and intermediate titers in the liver, adrenal glands, kidney, pancreas, and heart. In moribund animals, the most consistent and severe histological lesion as an interstitial pneumonia. In contrast, the brain was only minimally involved. The immune response of lethally infected strain 13 guinea pigs, as measured by the indirect fluorescent antibody test, was detectable within 10 days of infection and was similar in timing and intensity to the fluorescent antibody test response of both lethally infected and surviving outbred animals. In contrast to the fluorescent antibody response, neutralizing antibody developed late in convalescence and was thus detected only in surviving outbred guinea pigs. The availability of a rodent model for human Lassa fever in uniformly susceptible strain 13 guinea pigs should facilitate detailed pathophysiological studies and efficacy testing of antiviral drugs, candidate vaccines, and immunotherapy regimens to develop control methods for this life-threatening disease in humans.     

Virus-induced atherosclerosis. Herpesvirus infection alters aortic cholesterol metabolism and accumulation.

Infection of normocholesterolemic, specific-pathogen-free chickens with Marek's disease herpesvirus (MDV) has been shown histologically to lead to chronic atherosclerosis like that in humans. The development of herpesvirus-induced atherosclerosis in vivo and the presence of specific Marek's antigen within aortic cells suggested that MDV infection may modify lipid metabolism and lead to significant lipid accumulation. Experiments reported herein were designed to determine the types and quantity of lipid present in aortas from MDV-infected and uninfected chickens between 2 and 8 months of age following infection and assess one possible mechanism of lipid accumulation by evaluating the effect of MDV infection on aortic cholesterol and cholesteryl ester (CE) metabolism. Chromatographic-fluorometric analyses indicated that at 4 and 8 months of age after MDV inoculation, MDV-infected animals had a significant (P less than 0.05) two-fold to threefold increase in total aortic lipid accumulation characterized by significant increases in cholesterol, CE, triacylglycerol, and phospholipid as compared with aortas from uninfected animals. At 8 months of age, similar increases in aortic lipid accumulation were observed in MDV-infected animals as compared with those animals vaccinated with turkey herpesvirus and later challenged with MDV. CE synthetic activity was increased significantly by 50% at 4 months of age in the MDV-infected group as compared with the uninfected group, which could explain the initial increase in CE accumulation. By 8 months of age, the authors also observed a twofold increase in CE synthetic activity and a 30% and 80% reduction in lysosomal and cytoplasmic CE hydrolytic activities, respectively, in aortas of MDV-infected chickens as compared to controls. Moreover, infection with MDV blocked the activation of cytoplasmic CE hydrolytic activity by dibutyryl cyclic AMP or exogenous cyclic AMP-dependent protein kinase. Taken together, these results suggest that lipid accretion in aortas of MDV-infected chickens results, in part, from alterations in cholesterol/CE metabolism during early stages of the disease. These findings support the hypothesis that human atherosclerosis may result from specific herpesvirus infection which can alter lipid metabolism and lead to lipid accretion.     

Pathogenesis of reactivated latent murine cytomegalovirus infection.

Sixteen weeks after inoculation, murine cytomegalovirus (MCMV) can no longer be detected in the tissues of mice. However, a 2-week course of immunosuppression with antilymphocyte serum and cortisone acetate results in reactivation and dissemination of the latent virus in all animals. In this study of reactivation, MCMV was first detected in the liver, usually during the first week of immunosuppression, and virus replication was shown to be restricted to hepatocytes. Subsequently, a viremia occurred, with spread of infection to other organs. The highest titers of virus were reached in salivary glands in which replication occurred in serous acinar cells. In the lung, virus-specific abnormalities were difficult to detect because of superimposed bacterial and fungal infections. However, interstitial pneumonitis could be produced when cortisone acetate was deleted from the immunosuppressive regimen. Although the site of virus latency has not been defined, this model system will be useful for study of reactivation of latent cytomegalovirus infection.