Effects of Chronic Viral Infection on Lymphocyte Populations in Middle-aged Baboons (Papio anubis).

Aging of the immune system is characterized by the loss of naïve T-cells, increased inflammation, and immune function impairment. Chronic infection with cytomegalovirus is thought to play a role in age-related changes in immunity. Therefore, to assess the effect of pathogens such as cytomegalovirus on the immune system, we determined lymphocyte populations and inflammatory markers over a 3-y period in captive, middle-age baboons, with various exposure to pathogens and shedding pressure. Groups included SPF (i.e., pathogen-negative; n = 14); large-group, conventionally housed (CONV LG; pathogen- positive; n = 14), and small-group, conventionally housed (CONV SM; pathogen-positive; n = 7). All baboon groups showed a decrease in CD45RA+ CD28+ (i.e., naive) cells over time during middle age, but the rate of decline appeared faster in CONV LG baboons than in the other groups. In addition, the reduction in CD45RA+ CD28+ cells in the CONV LG baboons coincided with higher IgG levels against baboon cytomegalovirus, increased serum cortisol concentration, and a greater inflammatory phenotype. The results of this project support a role for cytomegalovirus infection in immune system alterations in middle-aged baboons.

Effective Prophylactic Therapy for Exposure to Monkey B Virus (Macacine alphaherpesvirus 1).

Zoonotic monkey B virus (Macacine alphaherpesvirus 1; BV) infections are extremely serious and usually fatal. Drugs currently used for treatment were developed for the treatment of herpes simplex virus but are less effective against BV. Effective suppression of viral replication in the skin could prevent the virus from invading the nervous system. To test this hypothesis, the efficacy of topical administration of several drugs against lethal BV infection was evaluated in female BALB/c mice that were infected by scarification. Drugs were then applied to the site of inoculation. As 3% preparations, most drugs were only minimally effective or ineffective. In contrast, ganciclovir and cidofovir were very effective. The ED50 for cidofovir was 0.007%, compared with 1.1% for ganciclovir. At 0.5%, cidofovir protected against both death and neurologic signs, whereas 5% ganciclovir only protected against death but not neurologic involvement. All genotypes of BV were equally susceptible to cidofovir and ganciclovir. For maximal effectiveness, treatment with both cidofovir and ganciclovir had to be initiated within 8 h of infection. Cidofovir was completely protective when administered only on the day of infection, whereas a minimum of 5 d of treatment was required for maximal ganciclovir efficacy. These studies showed that topical cidofovir treatment started soon after BV exposure was very effective in preventing BV from invading the nervous system, whereas ganciclovir treatment was only partially effective. In addition, cidofovir was protective against a ganciclovir-resistant BV mutant, whereas ganciclovir was not. These studies showed that topical cidofovir treatment started soon after BV exposure is more effective than ganciclovir in preventing BV from invading the CNS.

The order Herpesvirales.

The taxonomy of herpesviruses has been updated by the International Committee on Taxonomy of Viruses (ICTV). The former family Herpesviridae has been split into three families, which have been incorporated into the new order Herpesvirales. The revised family Herpesviridae retains the mammal, bird and reptile viruses, the new family Alloherpesviridae incorporates the fish and frog viruses, and the new family Malacoherpesviridae contains a bivalve virus. Three new genera have been created in the family Herpesviridae, namely Proboscivirus in the subfamily Betaherpesvirinae and Macavirus and Percavirus in the subfamily Gammaherpesvirinae. These genera have been formed by the transfer of species from established genera and the erection of new species, and other new species have been added to some of the established genera. In addition, the names of some nonhuman primate virus species have been changed. The family Alloherpesviridae has been populated by transfer of the genus Ictalurivirus and addition of the new species Cyprinid herpesvirus 3. The family Malacoherpesviridae incorporates the new genus Ostreavirus containing the new species Ostreid herpesvirus 1.

Changes in the titer of anti-B virus antibody in captive macaques (Macaca fuscata, M. mulatta, M. fascicularis).

Changes in levels of antibody to B virus (Cercopithecine herpesvirus 1; BV) were examined in BV-positive macaques by ELISA. We observed increases in anti-BV IgG titers in a BV-infected cynomolgus monkey after overseas transportation by air and in a rhesus monkey after transfer from an outdoor group cage to an indoor individual cage. Although shedding of infectious virus was not examined, the increase in antibody titer suggested reactivation of BV. Interestingly, we also found an increase in anti-BV IgG levels during the breeding season in male but not female Japanese macaques kept in an enclosed outdoor colony. Further studies should be performed to investigate whether reactivation of BV led to the observed increase in the anti-BV antibody titer.

Transmission dynamics of simian T-lymphotropic virus type 1 (STLV1) in a baboon breeding colony: predominance of female-to-female transmission.

We investigated the prevalence, distribution, and transmission of simian T-lymphotropic virus type 1 (STLV1) in a baboon breeding colony over a 4-y period. We used polymerase chain reaction amplification of the proviral tax gene to assess the infection status of 272 animals housed in 4 separate corrals. Sequencing the proviral envelope gene from individual baboons detected several molecular subtypes (genotypes) of STLV1. At the start of the study, 31% (54 of 176) of all baboons were infected; the majority of infections (91%) were in mature females, with only 3 of 12 mature males and 2 of 48 infants and juveniles being infected. Over the next 4 years, 41 new infections were diagnosed. Of these, 83% occurred in sexually mature female baboons (at least 3 y of age), 17% in infants and juveniles (younger than 3 y), and 0% in mature males. The 7 infections in juveniles were probably derived from mother-to-infant transmission because mother-infant pairs consistently were infected with the same viral genotype. Of the 34 new infections in sexually mature female baboons, the genotyping data showed that 25 (73%) originated from other infected females as opposed to males. Male-to-female sexual transmission may have accounted for the remaining 9 new infections. There was no evidence of female-to-male sexual transmission. The high percentage of female-to-female transmission of STLV1 in our baboons was unexpected; we speculate that transmission may have occurred due to blood contamination from biting during aggressive behavior between females in establishing hierarchical dominance.

Experimental infection of baboons (Papio cynocephalus anubis) with apathogenic and neurovirulent subtypes of herpesvirus papio 2.

Cercopithecine herpesvirus 16 (Herpesvirus papio 2; HVP2) is an alpha-herpesvirus of baboons (Papio spp.) that generally causes minimal to inapparent disease in the natural host species. HVP2 is very closely related genetically and antigenically to Cercopithecine herpesvirus 1 (monkey B virus; BV) of macaques, which is well known for its extreme lethality in nonmacaque species including humans. Preliminary evidence suggests that a mouse model of HVP2 would be an excellent tool for studying zoonotic BV infections. Although the pathogenicity of different BV isolates in mice spans the full range of severity from apathogenic to extremely neurovirulent, testing of multiple HVP2 isolates revealed only two distinct phenotypes in mice regardless of route of inoculation: apathogenic (HVP2ap) and highly neurovirulent (HVP2nv). For the HVP2nv mouse model to truly reflect BV infection in both its natural host and the differential pathogenicity of BV in aberrant host species, HVP2nv should not produce severe disease in its natural host. To test this, juvenile baboons were inoculated with doses of 10(6) or 10(4) plaque-forming units of HVP2ap or HVP2nv by using an oral subdermal inoculation route. Parameters followed included the appearance of lesions, shedding of infectious virus, general health, and the immune response to the infection. Regardless of the inoculum dose used, no differences were noted between the two HVP2 subtypes in baboons in any of the parameters measured. These findings further support the use of the HVP2nv mouse system as a model to elucidate and study the viral determinants associated with cross-species BV neurovirulence.

Validation of an enzyme-linked immunosorbent assay kit using herpesvirus papio 2 (HVP2) antigen for detection of herpesvirus simiae (B virus) infection in rhesus monkeys.

Serologic testing for antibody to monkey B virus (BV) in macaque sera is problematic due to the biohazardous nature of BV antigens. Herpesvirus papio 2 (HVP2), a herpesvirus of baboons, is nonpathogenic to humans and is genetically and antigenically more closely related to BV than is human herpes simplex virus 1. This paper describes the results of our in-house laboratory that compared a BV antigen-based enzyme-linked immunosorbent assay (ELISA) by commercial testing laboratory and an HVP2-based ELISA in our laboratory by using 447 sera from 290 rhesus monkeys. The HVP2-based ELISA identified as positive 99.11% of the sera identified as BV-positive by the BV ELISA. The BV antigen-based ELISA identified as positive 98.21% of the sera identified as BV-positive by the HVP2-based ELISA. The HVP2 ELISA also identified two BV-negative and six BV-equivocal sera as positive. Both ELISAs identified the same 85 negative and three equivocal samples as negative and equivocal, respectively. The high degree of correlation (weighted kappa coefficient, 0.94) between the two tests indicates that the HVP2 ELISA is a sensitive and reliable assay for in-house testing of the BV status of rhesus monkeys.

Influence of dose rate on the induction of simple and complex chromosome exchanges by gamma rays.

Single-color painting of whole chromosomes, or protocols in which only a few chromosomes are distinctively painted, will always fail to detect a proportion of complex exchanges because they frequently produce pseudosimple painting patterns that are indistinguishable from those produced by bona fide simple exchanges. When 24-color multi-fluor FISH (mFISH) was employed for the purpose of distinguishing (truly) simple from pseudosimple exchanges, it was confirmed that the acute low-LET radiation dose-response relationship for simple exchanges lacked significant upward curvature. This result has been interpreted to indicate that the formation of simple exchanges requires only one chromosome locus be damaged (e.g. broken) by radiation to initiate an exchange-not two, as classical cytogenetic theory maintains. Because a one-lesion mechanism implies single-track action, it follows that the production of simple exchanges should not be influenced by changes in dose rate. To examine this prediction, we irradiated noncycling primary human fibroblasts with graded doses of (137)Cs gamma rays at an acute dose rate of 1.10 Gy/min and compared, using mFISH, the yield of simple exchanges to that observed after exposure to the same radiation delivered at a chronic dose rate of 0.08 cGy/min. The shape of the dose response was found to be quasi-linear for both dose rates, but, counter to providing support for a one-lesion mechanism, the yield of simple aberrations was greatly reduced by protracted exposure. Although chronic doses were delivered at rates low enough to produce damage exclusively by single-track action, this did not altogether eliminate the formation of complex aberrations, an analysis of which leads to the conclusion that a single track of low-LET radiation is capable of inducing complex exchanges requiring up to four proximate breaks for their formation. For acute exposures, the ratio of simple reciprocal translocations to simple dicentrics was near unity.

Development of a green fluorescent protein reporter cell line to reduce biohazards associated with detection of infectious Cercopithecine herpesvirus 1 (monkey B virus) in clinical specimens.

Detection of infectious viruses in clinical samples typically relies on daily examination of inoculated cell cultures for appearance of virus-induced cytopathic effect (CPE), with subsequent immunologic or genetic analysis to identify the specific virus producing the CPE. Performing virus isolation on samples suspected of containing Cercopithecine herpesvirus 1 (monkey B virus [BV]) is dangerous due to the extreme neuropathogenicity of this virus in humans, and minimally requires biosafety level 3 (BSL-3) facilities. To provide a safer method of detecting infectious BV in clinical samples, the eucaryotic green fluorescent protein (GFP) coding sequence was flanked with BV sequences containing transcriptional control elements. This construct was placed into a stealth vector and transfected into Vero cells, then stable transformed cell lines were selected. These cells express GFP only when infected with BV or other related primate herpesviruses. Expression of GFP allows detection of infectious BV in cultures sooner and more reliably than does standard microscopic observation for CPE. The ability to detect BV by GFP expression eliminates the need for further testing to identify the virus as an alpha-herpesvirus following development of CPE, thus allowing cell cultures to be sealed at inoculation. Although not entirely specific for BV, this cell line will make detection of infectious BV in samples collected from macaques safer to perform.

Comparative transmission of multiple herpesviruses and simian virus 40 in a baboon breeding colony.

Little is known about the natural history of herpesviruses indigenous in baboons. Here, we describe the development of ELISAs for five herpesviruses. These assays were used to test more than 950 serum samples collected from approximately 210 infant/juvenile and 130 adult baboons in a captive breeding colony over a period of seven years. Results indicated that baboon cytomegalovirus, lymphocryptovirus, and rhadinovirus are transmitted efficiently within the colony and are acquired at an early age. Baboon alpha-herpesvirus HVP2 and polyomavirus simian virus 40 (SV40) were acquired later and by fewer juveniles than were the other three herpesviruses. More than 60% of baboons acquired HVP2 before reaching sexual maturity, indicating that oral infection of infants and juveniles, rather than sexual transmission between adults, is the predominant mode of transmission for this virus. Antibody to simian varicella virus (SVV) was found in about 40% of baboons. SVV was acquired principally by infants and juveniles; few adults seroconverted despite seronegative adults being in constant contact with infants and juveniles undergoing primary infection. Time of seroconversion was not statistically correlated to specific individual herpesviruses, suggesting that each virus is acquired as an independent infection event rather than multiple viruses being acquired at the same time. Several baboons that were delivered by cesarean section and were housed separate from, but in close proximity to, other baboons remained free of many or all viruses for several years, suggesting that, similar to human herpesviruses, baboon herpesviruses and SV40 are transmitted principally by direct contact.

Use of a polymerase chain reaction assay to detect bovine herpesvirus type 2 DNA in skin lesions from cattle suspected to have pseudo-lumpy skin disease.

Beef cattle from a herd in north Alabama were examined because of an outbreak of nonfatal skin disease characterized by discrete circumscribed areas of inflammation that developed on the skin from the neck to the hips. Areas of inflammation, which tended to be superficial, underwent necrosis and scabbed over. The scabs eventually dropped off leaving discrete, round, whitish, hairless lesions that were 1.2 to 2.5 cm diameter. Because clinical signs were consistent with those expected with pseudo-lumpy skin disease (PLSD) caused by bovine herpesvirus type 2 (BHV-2), samples from 16 representative animals were submitted for BHV-2 testing. All 16 animals were seropositive for BHV-2, but the virus could not be isolated from skin biopsy specimens or buffy coat samples. Results of a polymerase chain reaction assay incorporating primers designed to amplify 2 DNA sequences from BHV-2 were positive for 3 of the 10 cattle, suggesting that skin lesions in these cattle were a result of PLSD. Our findings suggest that PLSD may be more common and widespread in the United States than suggested by the frequency with which BHV-2 has been isolated from cattle with PLSD-like skin lesions.

Role of the virion host shutoff protein in neurovirulence of monkey B virus (Macacine herpesvirus 1).

Monkey B virus (Macacine herpesvirus 1; BV) is noted for its extreme neurovirulence in humans. Since the vhs protein encoded by the UL41 gene has been shown to be a neurovirulence factor in the related human herpes simplex viruses, the role of the UL41 gene in BV neurovirulence was investigated. BV mutants were constructed that lacked the entire UL41 ORF (Δ41) or had the RNase active site mutated (Δ41A). Neither mutant shut off host protein synthesis, degraded ß-actin mRNA, or prevented an IFN-ß response, indicating that the vhs protein and its RNase activity are both necessary for these activities. Replication of both mutants in primary mouse cells was impaired and they exhibited a prolonged disease course in mice. Whereas Δ41 infected mice were euthanized for symptoms related to central nervous system (CNS) infection, Δ41A infected mice were euthanized primarily for symptoms of autonomic nervous system dysfunction. While neuroinvasiveness was not affected, lesions in the CNS were more limited in size, anatomical distribution, and severity than for wild-type virus. These results indicate that the vhs protein affects the general replicative efficiency of BV in vivo rather than being a specific neurovirulence factor critical for invasion of or preferential replication in the CNS.

The effects of age and cytomegalovirus on markers of inflammation and lymphocyte populations in captive baboons.

The human immune system undergoes age-related changes that can lead to increased disease susceptibility. Using the baboon as a model for human immune system aging, we examined age-related changes in relative and absolute numbers of T cell subpopulations, cytomegalovirus (CMV) titer and markers of inflammation. In addition, the effect of gender, social status and peer group on lymphocyte subpopulations was determined. Relative and absolute numbers of total lymphocytes (CD3+), T helper cells (CD4+), and cytotoxic T cells (CD8+) increased with age. The proportion of naïve T cells (CD45RA+) decreased, while the total number of cells negative for the co-stimulatory receptor, CD28 (CD28-) increased in an age-dependent manner. Furthermore, CMV titers were negatively correlated with the number of naive CD4+ cells. IL-6 and cortisol concentration were also negatively associated with T cell subpopulations. Additionally, socially dominant baboons exhibited decreases in naïve CD4+ and CD8+ cells (by 65% and 52%, respectively) compared to subordinate animals. These results suggest that factors such as CMV exposure and inflammation may contribute to the age-related decline in immune health and indicate that factors like social status should be considered when studying immunosenescence in animal models.

Papiine herpesvirus 2 as a predictive model for drug sensitivity of Macacine herpesvirus 1 (monkey B virus).

Monkey B virus (Macacine herpesvirus 1; BV) is endemic in macaques. BV (a BSL4 agent) is the primary zoonotic concern for persons working with macaques in research, and human BV infections frequently are fatal. We assessed the use of a BSL2 baboon herpesvirus (Papiine herpesvirus 1; HVP2) for predicting the drug sensitivity of BV by comparing the sensitivity of the 2 viruses to 12 antiherpetic drugs. Plaque reduction assays showed that 4 drugs (HBPG, BVdU, PFA, and BrdU) were ineffective against both viruses. Of the 8 effective drugs, both viruses were most sensitive to TFT, whereas sensitivity to the remaining 7 drugs varied between BV and HVP2 as well as between strains of HVP2. In addition, the efficacy of 5 drugs (ACV, PCV, GCV, CDV, and EDU) was tested by using a murine model. ACV and EDU were completely ineffective against both HVP2 and BV, and high doses of PCV only delayed death by a few days. GCV and CDV both protected mice against death, and CDV also prevented the development of neurologic symptoms. When the initiation of drug therapy was delayed until after virus gained access to the CNS, both GCV and CDV were ineffective. The similarity of the drug sensitivities of HVP2 and BV in both models validates the use of HVP2 as a BSL2 level model that can be used to predict drug sensitivity of BV. The greater efficacy of CDV relative to GCV suggests the potential for use of CDV in the treatment of zoonotic BV infections.

Simian T-lymphotropic Virus-associated lymphoma in 2 naturally infected baboons: T-cell clonal expansion and immune response during tumor development.

Two young female baboons naturally infected with simian T-lymphotropic virus type 1 (STLV1) were euthanized due to chronic respiratory disease that was unresponsive to treatment. Massive lymphocytic infiltration of the lung interstitium suggested a diagnosis of STLV-associated lymphoma. In each case, the diagnosis was confirmed through inverse PCR (IPCR) that detected monoclonally integrated STLV1 provirus in cellular DNA extracted from lymphoma tissue and peripheral blood cells (PBC). One dominant STLV1-infected T-cell clone and 3 minor clones were detected in PBC from each baboon. Using archived PBC DNA and primers within the proviral genome and chromosomal DNA flanking the STLV1 integration sites in PCR analyses, we determined that the dominant clone in one baboon had first appeared approximately 8 mo after infection and had circulated for 4 y before clinical disease developed. ELISA testing of archived serum revealed that both baboons seroconverted to the p19 and p24 gag proteins and the envelope gp46 protein but not to the viral tax protein. Titers to p24 and gp46 rose significantly after infection and remained relatively constant until death, whereas titers to p19 increased with time. Although spontaneous STLV1-associated lymphomas have been described in baboons, the STLV1-associated lymphomas described here occurred in 2 relatively young baboons, both of whom had become infected with STLV at 3 to 4 y of age and developed lymphoma within 5 y of infection.

Generation of a specific-pathogen-free baboon colony.

We undertook establishing an SPF baboon colony in response to requests from researchers. To enable the widest possible future use of SPF baboons, our aim was to develop an SPF colony of baboons (Papio hamadryas anubis) free of 12 target viruses: 5 herpesviruses, 4 retroviruses, simian virus 40, measles, and monkeypox. Infant baboons were removed from their mothers within 24 h of birth and nursery-reared. Groups of 3 to 8 age-matched conspecifics were isolated in separate rooms for 1 y while undergoing repeated testing for target viruses. During the initial 7 y of the SPF program, 171 infants were enrolled, of which 76 (44.4%) subsequently were removed from the program. Of those removed, 54 (71.0%) were culled due to breaks in virus-free status, 12 (15.8%) died of various causes, 4 (5.3%) developed seizures, and 6 (7.9%) were removed for other reasons. The most problematic viruses were baboon cytomegalovirus (25.9% of culls), Herpesvirus papio 1 (51.9%), and simian foamy virus (7.4%). Using conspecific groups of 3 to 4 infants reduced first-year program losses as compared with groups of 6 to 8. There have been 17 births in the SPF colony, and all these infants have been free of all target viruses since birth. On the basis of these results, early removal of infants from their dams, housing in small peer groups, frequent virus testing, and aggressive culling of virus-positive animals is an effective approach for development of a baboon colony free of multiple viruses.

Effect of combinations of antiviral drugs on herpes simplex encephalitis.

2-Phenylamino-6-oxo-9-(4-hydroxybutyl)purine (HBPG) is a thymidine kinase inhibitor that prevents encephalitic death in mice caused by herpes simplex virus (HSV) types 1 and 2, although its potency is somewhat less than that of acyclovir (ACV). The present study was undertaken to determine the effect of combinations of HBPG and either ACV, phosphonoformate (PFA), or cidofovir (CDF) against HSV encephalitis. BALB/c mice were given ocular infections with HSV-1 or HSV-2, and treated twice daily intraperitoneally for five days with HBPG, alone or in combination with ACV, PFA, or CDF. Animals were observed daily for up to 30 days, and the day of death of each was recorded. All of the combinations showed additivity, and the combination of HBPG + ACV appeared to be synergistic, ie, protected more mice against HSV-1 encephalitis compared with each drug given alone. Delay of treatment with HBPG for up to two days was still effective in preventing HSV-2 encephalitis. The combination of the thymidine kinase inhibitor HBPG and the antiherpes drug ACV may have synergistic activity against HSV encephalitis. The development of a potent and safe combination therapy for the prevention and/or treatment of HSV infection of the central nervous system can improve the outcome of this infection in humans.

Monkey B virus (Cercopithecine herpesvirus 1).

Macaques are a particularly valuable nonhuman primate model for a wide variety of biomedical research endeavors. B virus (Cercopithecine herpesvirus 1; BV) is an alpha-herpesvirus that naturally infects conventional populations of macaques. Serious disease due to BV is rare in macaques, but when transmitted to humans, BV has a propensity to invade the central nervous system and has a fatality rate greater than 70% if not treated promptly. The severe consequences of human BV infections led to the inclusion of BV in the original NIH list of target viruses for elimination by development of specific pathogen-free rhesus colonies. In macaques and especially in humans, diagnosis of BV infection is not straightforward. Furthermore, development and maintenance of true BV specific pathogen-free macaque colonies has proven dif cult. In this overview we review the natural history of BV in macaques, summarize what is known about the virus at the molecular level, and relate this information to problems associated with diagnosis of BV infections and development of BV-free macaque colonies.

Lethargy, ulcers, bronchopneumonia and death in two aged female bonnet macaques presumed to be caused by Cercopithicine herpes virus I.

Over the course of 4 weeks, two female aged bonnet macaque (Macaca radiata) group-housed females died after the dominant male was removed from the group and the newly dominant male persistently chased, caught and bred all females in the pen. The two aged affected females were observed exhibiting lethargy, dyspnea, with widespread necroulcerative lesions in and around the mouth, muzzle and bridge of their noses. Extensive ulcerative glossitis, necrotic bronchopneumonia with intra-nuclear inclusions and the absence of other evidence is highly suggestive that death was caused by an alphaherpes virus commonly known as herpes B virus. Herpes B virus is a potentially zoonotic disease periodically shed by macaques, which is structurally related to herpes simplex viruses I and II of humans. The emergence of fatal B virus to primates in this pen may have been associated with the combination of age and stress in the affected individuals.

Evidence of simian virus 40 exposure in a colony of captive baboons.

Simian virus 40 (SV40) is a polyomavirus for which non-human primates are the permissive host. The baboon (Papio spp.) is an old world monkey that is used in a variety of research investigations; however, natural infection of SV40 among baboons has not been thoroughly examined or reported. Initially, we were interested in determining the prevalence of SV40 infection among a captive colony of baboons based on the presence of antibodies to SV40 large T-antigen (Tag). An overall seroprevalence rate of >50% was found after screening sera from 142 baboons in the colony based on ELISA. Endpoint titer values for serum antibody binding to SV40 Tag reached as high as 1280 for 5 out of 142 baboons. Peptide binding assays revealed that a range of SV40 Tag epitopes are immunogenic in the baboon, and that individual animals differ in their humoral immune responses to SV40 Tag based on epitope recognition. Specificity to SV40 Tag and not some other primate polyomavirus encoded large Tag was further examined by serologic reactivity to peptide epitopes unique to SV40 Tag. Additional serology was performed to assess SV40 Tag reactivity by Western blot and whether antibodies were capable of neutralizing SV40 infectivity in vitro. Although antibodies with high levels of SV40 neutralization were observed in a number of the baboons, there was a lack of correlation between viral neutralization and antibodies to SV40 Tag. Further examination using molecular-based diagnosis and SV40 Tag specific real-time quantitative PCR determined that some of the baboons appeared to be exposed to SV40. DNA sequence analysis of the PCR products confirmed that SV40 Tag specific sequences were detected in baboons.