Transmission of Sarcocystis leporum from a cottontail rabbit to domestic cats.

Muscle tissue containing grossly visible cysts of Sarcocystis leporum from a cottontail rabbit (Sylvilagus floridanus) was fed to laboratory cats. Sporocysts averaging 13.2 x 9.7 micron were detected in the feces 14 days post-infection and were found until 69 days post-infection.     

Herpesvirus sylvilagus in cottontail rabbits: evidence of shedding but not transplacental transmission.

Herpesvirus sylvilagus was inoculated into five cottontail rabbits (Sylvilagus floridanus) at various stages of pregnancy; they subsequently had litters in the laboratory. Three other cottontails chronically infected with the virus were bred and bore young in large outdoor pens. Thirty-four living neonates and dead fetuses were weighed, measured and aseptically necropsied. A total of 31 liver, spleen and kidney samples, 16 lymph node, 28 heart and 10 brain samples were collected and processed for inoculation into rabbit kidney cell cultures to attempt virus isolation. Virus was not detected in the 147 tissue samples tested. Pre-conception viremias ranged from 10-21 plaque-forming units per 0.5 ml. Virus isolation was attempted from 26 oral and lacrymal, 23 genital, nine urine and fecal, and four milk and male ejaculate samples from eight infected rabbits. Virus was recovered from two salivary samples from the same rabbit. Triamcinolone acetonide administered daily for four days to five rabbits did not stimulate excretion of virus.     

Ectopic fetuses in two cottontail rabbits.

Mummified fetuses were discovered in the abdominal cavities of two cottontail rabbits (Sylvilagus floridanus) collected during separate years from the same geographical location in Virginia. One of these rabbits had a patent opening through the vaginal wall to the abdominal cavity. The uterus and vagina of the second rabbit appeared normal.     

Herpesvirus sylvilagus in cottontail rabbits: attempted laboratory transmission by two insect species.

The vector potential of the rabbit flea (Cediopsylla simplex) and a mosquito (Aedes triseriatus) was investigated for Herpesvirus sylvilagus transmission among cottontail rabbits (Sylvilagus floridanus). Twelve groups of 12-50 fleas were fed on three viremic cottontails for 2-21 days before transfer to 12 susceptible rabbits. Standard interrupted feeding trials employed five groups of 6-12 mosquitoes, two viremic donor cottontails anf five healthy recipients. No evidence of virus was detected from recipients' blood nor did they develop specific antibody. Virus acquisition and persistence in the insects was evaluated by attempting to recover the virus from 19 pools of mosquitoes engorged on viremic blood and 36 pools of engorged fleas or those living on viremic hosts for 1-21 days. Results were negative.     

Immune responses to Herpesvirus sylvilagus infection in cottontail rabbits

Immunologic changes produced by Herpesvirus sylvilagus infection of cottontail rabbits were investigated to evaluate this virus infection system as an animal model for EBV infection in humans. H. sylvilagus neutralizing antibodies appeared as early as 7 days after infection, peaked 2 to 4 wk postinfection and decreased to low levels by 8 to 10 wk postinfection. Complement-dependent antibodies mediating the protection of in vitro infection of monocytes and Con A-stimulated lymphoblasts with H. sylvilagus were observed as were complement-dependent cytotoxic antibodies against H. sylvilagus-infected cells. No cytolytic activity was present in sera taken either before or 3 days after infection; cytolysis was first observed 7 days after infection. The development of cytolytic antibodies appeared to be biphasic during an infection course of 12 to 16 wk. In vivo induction of a primary cytotoxic lymphocyte response to H. sylvilagus was also investigated. Splenic lymphocytes from infected animals lysed H. sylvilagus-infected skin fibroblasts; however, similar activity was not observed when PBMC or mesenteric lymph node lymphocytes were used as effector cells. H. sylvilagus-infected autologous skin fibroblasts were preferentially lysed as compared to heterologous skin fibroblasts. This virus-specific cytotoxic activity appeared 5 days postinfection and peaked 7 days postinfection. By 28 days postinfection, only low levels of cytotoxic activity were detected in spleen cells. Herpesvirus sylvilagus infection of cottontail rabbits provides an animal model for the study of lymphoproliferative disorders induced by herpesviruses.     

T-cell response to cottontail rabbit papillomavirus structural proteins in infected rabbits.

Cottontail rabbit papillomavirus (CRPV)-induced papillomas progress at a high frequency to carcinomas and thus can serve as a model for high-cancer-risk human papillomavirus infection. Previously, we have shown that antibodies to nonstructural and structural proteins are detected in only a fraction of papilloma-bearing animals. However, the antibody response to structural proteins drastically increases as papillomas progress to carcinoma (Y.-L. Lin, L. A. Borenstein, R. Selvakumar, R. Ahmed, and F. O. Wettstein, J. Virol. 67:382-389, 1993). Here we have monitored the cellular immune response to viral proteins during the course of infection and particularly during progression from papilloma to carcinoma. This was done by measuring the in vitro proliferation response of peripheral blood mononuclear cells (PBMCs) to CRPV structural proteins L1 and L2. The proliferating cells were identified as T cells by selective removal of B or T cells. In general, the T-cell response was low for rabbits at the papilloma stage and none responded to L2. Lymphocytes from animals with carcinomas more frequently and more strongly responded to L1, and more than half also responded to L2. In addition to stimulation of PBMCs, L1- and L2-specific proliferation could also be demonstrated with lymph node and spleen cells. Overall, our data show that progression of papilloma to carcinoma is associated with an increased T-cell response to CRPV structural proteins in addition to an increased humoral response. This greater immune reactivity, however, was not associated with a selectively increased expression of structural proteins, since RNA isolated from papillomas and carcinomas contained similar relative levels of late and early RNA as shown by dot blot analysis. Thus, the heightened immune reactivity seen in carcinoma-bearing rabbits most likely reflects greater stimulation of the immune system owing to dissemination of the tumor. These findings suggest that increased immune responses to papillomavirus proteins may be prognostic of progression to carcinoma and particularly of the development of metastases.     

Hematology and serum chemistry of cottontail rabbits of southern Illinois.

In 1983 and 1984 blood was collected from 79 cottontail rabbits (Sylvilagus floridanus) confined to an outdoor enclosure in southern Illinois to establish reference values for hematology and serum chemistry. Packed cell volume, sodium, potassium, chloride, glucose, calcium, carbon dioxide, blood urea nitrogen, creatinine, uric acid, cholesterol, albumin, bilirubin, alkaline phosphatase, aspartate transaminase, alanine aminotransaminase, total protein, albumin/globulin ratio, and osmolality were measured. Sex and age (adult versus juvenile) of rabbit as well as season (June to September versus October to May) and method of capture (trap versus shot) variously affected most hematology and serum chemistry variables.     

Expression of group b light chain allotypes in cottontail rabbits.

Group b allotypic determinants (b4, b5, b6, and b9) were detected on cottontail IgG by several assays including immunodiffusion, radioimmune binding, and inhibition of radiobinding. The results indicate that cottontail IgG possess some but not all of the subspecificities present on domestic rabbit IgG. Several cottontail rabbits exhibited three of the four possible allotypic markers. In these instances, however, only two populations of IgG molecules (i.e., phenogroups) could be detected, each bearing one, two, or three of the allotypes. Five separate and distinctive phenogroups were identified. The results suggest that the phenogroups represent products of multiple allelic genes for the constant region of cottontail rabbit kappa light chain.     

Epidemiology of Herpesvirus sylvilagus infection in cottontail rabbits

The epidemiology of Herpesvirus sylvilagus infection in wild cottontail rabbits was studied in a defined, natural cottontail population over a period of 13 months. Spread of this virus showed significant correlation with seasonal variation as well as with the sex and age of the host. The highest rate of infection occurred during the winter and spring seasons with males over the age of 4 months sustaining a significantly greater percentage of infections than younger males or females of all age groups.     

Serum antibodies to whole-cell and recombinant antigens of Borrelia burgdorferi in cottontail rabbits

Archived serum samples, from 95 eastern cottontail rabbits (Sylvilagus floridanus) captured in New York, New York, USA and Millbrook, New York, USA, during 1985-86, were analyzed in solid-phase enzyme-linked immunosorbent assays (ELISA) for total and class-specific immunoglobulin (Ig) M antibodies to whole-cell or recombinant antigens of Borrelia burgdorferi sensu stricto. Using a polyvalent conjugate, rabbit sera contained antibodies to whole-cell and recombinant antigens (protein [p]35, p37, or VlsE) during different seasons, but there was no reactivity to outer surface protein (Osp)A or OspB. Seventy-six of the 102 sera (75%) analyzed were reactive with one or more of the antigens; 61 of the positive samples (80%) reacted to whole-cell antigens, followed by results for the p35 (58%, 44/76), VlsE (43%, 33/76), and p37 (29%, 22/ 76) antigens. Fifty-eight sera (76%) contained antibodies to the VlsE or p35 antigens with or without reactivity to whole-cell antigens. High antibody titers (≥1:2,560) recorded for 52 sera indicate robust antibody production. In analyses for IgM antibodies in an ELISA containing whole-cell antigens, there were 30 positive sera; titers ranged from 1:160 to 1:640. There was minimal cross-reactivity when rabbit antisera to Treponema pallidum or four serovars of Leptospira interrogans were screened against B. burgdorferi antigens. Based on more-specific results, VlsE and p35 antigens appear to be useful markers for detecting possible B. burgdorferi infections.     

Hematologic comparisons of shot and live trapped cottontail rabbits

Comparisons were made between hematologic measurements of shot and box-trapped cottontail rabbits (Sylvilagus floridanus). Trapped rabbits had significantly (P less than 0.001) higher serum corticoid levels and segmented neutrophil percentages and significantly (P less than 0.001) lower lymphocyte percentages than did shot rabbits. Trapped rabbits also had significantly (P less than 0.05) higher packed cell volumes and blood urea nitrogen values than did shot rabbits.     

Circular Herpesvirus sylvilagus DNA in spleen cells of experimentally infected cottontail rabbits.

Cottontail rabbits (Sylvilagus floridanus) were infected with Herpesvirus sylvilagus, and spleen cells were analyzed for the presence of virus-specific, covalently closed circular, and linear DNA molecules by a simple electrophoretic technique, followed by transfer to nitrocellulose filters and hybridization with cloned viral DNA (Gardella et al., J. Virol. 50:248-254, 1984). Approximately 0.2 copies per cell of circular DNA and 0.2 copies per cell of linear DNA were detected by hybridization with a cloned viral DNA fragment. The size of the viral DNA was estimated at ca. 158 kilobase pairs. Restriction endonuclease patterns suggested structural similarities to cottontail herpesvirus DNA.