Multidrug-resistant gram-negative organisms: a review of recently approved antibiotics and novel pipeline agents.

Background The discovery of antibiotics several decades ago was a defining moment in history. They were used to treat previously incurable diseases and save many lives. However, the use of antibiotics is not benign. Antibiotic resistance occurs due to the natural evolution of bacteria and gene transfer between bacteria via vertical and horizontal routes, resulting in protective mechanisms that render antibacterial agents ineffective. Aim of the review To list and describe current, novel pipeline antibiotics indicated for multidrug-resistant gram-negative bacteria. This review discusses the limited number of novel pipeline drugs available to combat the rapidly increasing number of multidrug-resistant bacteria and the need for initiatives to research and discover more novel antibiotics. Method A search of MEDLINE/PubMed using the search terms antibacterial pipeline OR antibiotic pipeline including publications between 1 January 2018 through 23 January 2020 resulted in 230 items. The results obtained were narrowed by adding the search term AND multi-drug resistant which resulted in 12 items. Then, ClinicalTrials.gov was searched for phase 2-3 "interventional" trials registered between 1 January 2018 and 23 January 2020 with the status "recruiting" or "completed" function and including World Health Organization-defined priority pathogens in the "condition or disease" field. The search process was then completed by introducing the term antibacterial agents in the "other terms" field. The trials search and selection resulted in 13 items. Relevant English-language studies and those conducted in humans were considered. Those drugs belonging to new antibiotic classes or to antibiotic classes already known but with new chemical structure were defined as "novel antibiotics". Results The studies selected and reviewed were those referring to a novel antibiotics. Thus, from MEDLINE/PubMed, we found only 1 item referred to a novel chemical class (Murepavadin n = 1). From ClinicalTrials.gov a total of 4 citations were identified (Ftortiazinon n = 1, Zoliflodacin n = 1, Gepotidacin n = 1, ETX2514 + sulbactam n = 1). Conclusion The antibiotics annually approved by the Food and Drug Administration (FDA) mostly belong to existing classes of antibiotics and have specific indications, limiting their use in many multidrug-resistant infections. There are limited novel drug classes targeting gram-negative infections in the pipeline. Providers must be vigilant with the use of current antibiotics, especially until research and development (R&D) advancements are made.

Haemostasis in oral surgical procedures involving patients with a ventricular assist device.

The purpose of this study was to determine whether tooth extraction for patients with ventricular assist devices (VADs) could be performed without interruption of anticoagulant and/or antiplatelet therapy and whether treatment with von Willebrand factor concentrates and desmopressin is required. The study consisted of three groups of patients undergoing oral surgery. The two experimental groups comprised patients with VADs, while the third group included cardiovascular patients without VADs who served as controls. All patients were treated intraoperatively with topical haemostatic agents (oxidized cellulose or collagen). The first group was additionally treated with fibrin glue. All 75 oral surgical procedures were performed under local anaesthesia without sedation. Three of 40 patients in the experimental groups and two of 20 patients in the control group suffered a haemorrhage, with no significant difference in the incidence of haemorrhage between the groups. The findings suggest that dental extraction can be performed without modification of oral anticoagulation or antiplatelet treatments, providing that INR is less than 3.5 on the day of the operation. It can further be hypothesized that an acquired coagulopathy in VAD patients does not influence the bleeding risk in dental extractions, and so the administration of desmopressin and/or von Willebrand factor concentrates is not required.

Is It Possible to Manipulate Scelionidae Wasps' Preference to a Target Host?

Parasitoid host selection is mainly mediated by chemical cues, which can be adjusted by experience, changing their innate behavior. Therefore, this study evaluated if immature experience (pre-imaginal conditioning) on eggs and volatiles from different host eggs has influence on parasitism and chemotaxic behavior of Telenomus podisi Ashmead and/or Trissolcus basalis Wollaston (Hymenoptera: Scelionidae). Both wasp species were submitted to a multiple-choice parasitism test among Euschistus heros (Fabricius), Piezodorus guildinii (Westwood), and Nezara viridula L. (Hemiptera: Pentatomidae) (Hemiptera: Pentatomidae) egg masses. Eggs from these three stink bugs were equally offered to female parasitoids. After that, adults which emerged from each host were also exposed to parasitism in a multiple-choice test for up to an additional generation. Moreover, in olfactometer "Y," the behavior of innate and experienced T. podisi females to volatiles from hosts' egg extracts was tested, to study their learning and memory ability. The original host had influence on T. podisi parasitism; however, T. basalis always parasitized more N. viridula eggs independently of its last rearing host. Innate T. podisi females responded positively to E. heros and P. guildinii egg volatiles, but this behavior was not observed in N. viridula. When T. podisi females were experienced on egg volatiles from a new host, they showed significant learning and memory ability for the specific host volatile for, at least, 24 h. Experienced wasps responded positively to N. viridula and through this result we have evidences about the possibility to manipulate wasp's preferences to a specific target host.

Importance of food composition data to nutrition and public health.

INTRODUCTION: Adequate nutrition is one of the pillars of public health. Before developing and implementing effective intervention programmes to improve nutrition at the population level, it is important to know the nutritional situation of the target group. ASSESSMENT OF ENERGY AND NUTRIENT INTAKE: The estimation of nutrient intake from food consumption requires reliable data on food composition. These data are also the fundamentals of food-based dietary guidelines for healthy nutrition, containing the necessary information on food sources for different nutrients. Furthermore, food composition tables can provide information on chemical forms of nutrients and the presence and amounts of interacting components, and thus provide information on their bioavailability. For some nutrients such as vitamin A, vitamin E and niacin, the concept of equivalence has been introduced to account for differences in the availability and biological activity of different chemical forms. NON-NUTRITIVE FOOD COMPONENTS: Although most food composition tables focus on energy, macro- and micronutrients, interest in non-nutritive components is increasing. Considering the beneficial effects of biologically active secondary plant cell compounds such as polyphenols and carotenoids, more data on these are needed. On the other hand, there are a number of naturally occurring or 'man-made' non-nutritive substances with negative effects, and to control exposure, the main dietary sources must be known. Another aspect is contaminants, which could have detrimental effects on consumers' health. Among these are agrochemicals, industrial pollutants reaching the food chain and substances formed during food preparation. A valid risk assessment requires data on exposure, and thus on the contents of contaminants in foods. However, these data are highly variable and may significantly differ even within narrowly confined regions. CURRENT FOOD COMPOSITION DATABASES ARE FAR FROM COMPLETE: The fact that composition tables generally do not provide information about the origin of substances found in food can also influence their usability. For example, the German Nutrient Data base does not discriminate between naturally occurring and added sucrose impeding the estimation of added sucrose intake that should be limited. Points of focus: Considering the increasing number of persons relying on community nutrition and catering, healthy menu lines can improve the consumers' diets and contribute to nutrient supply. The development and implementation of appropriate guidelines also need food composition databases (FCBs) to compose meals. The ever-increasing number of new food preparations and manufactured products has resulted in a need for procedures for regularly updated data. Moreover, there is a lack of data particularly for essential trace elements such as copper, chromium or molybdenum and also vitamin K, as well as the already mentioned non-nutritive components. Limited comparability between countries is another issue. Regional differences arise especially from the use of local varieties, different soil quality or meteorological aspects. This variability is further increased with composite meals because of variation in recipes. CONCLUSION: Information about food composition is necessary for the assessment of diet quality and the development and application of food-based dietary guidelines, providing a useful tool for the field of public health nutrition. In this regard, more attention should be paid to the preparation, extension and maintenance of FCBs.

Comparative immunogenicity of recombinant influenza hemagglutinin (rHA) and trivalent inactivated vaccine (TIV) among persons > or =65 years old.

Alternative substrates for influenza vaccine production are needed to ensure adequate supplies. We evaluated the relative safety and immunogenicity of recombinant hemagglutinin (rHA) or trivalent inactivated vaccine (TIV) among 869 > or =65-year-old subjects in a randomized clinical trial. Virologic surveillance for influenza-like illness (ILI) was conducted during the 2006-2007 epidemic. Vaccines were well tolerated. Seroconversion rates vs. influenza A/H1N1 and H3N2 antigens were superior in the rHA group, but were inferior vs. influenza B; however, results for influenza B are confounded since the vaccine antigens were different. ILI frequencies were low and similar in both groups. Studies assessing relative immunogenicity of vaccines using identical B Ags are warranted.

Probiotic, as well as conventional yogurt, can enhance the stimulated production of proinflammatory cytokines.

BACKGROUND: Lactic acid bacteria have been shown to stimulate the secretion of cytokines by lymphocytes and monocytes in a strain-dependent manner. Therefore, in this study, the effect of a daily intake of probiotic yogurt on cytokine production in young healthy women was compared with that of a conventional product. METHODS: For 2 weeks each, subjects consumed 100 g, then 200 g of either a probiotic or a conventional, commercially available yogurt, both containing Lactobacillus bulgaricus and Streptococcus thermophilus with additional Lactobacillus casei DN 114 001 in the probiotic product. Cytokine production in blood culture following stimulation with phytohaemmaglutinin and lipopolysaccharide was measured using Cytometric Bead Array and enzyme-linked immunosorbent assay. RESULTS: Stimulated production of tumour necrosis factor-alpha increased significantly following consumption of conventional or probiotic yogurt (+63% and +24% compared with baseline, respectively, P < 0.001). There was also a significantly higher production of interleukin (IL)-1beta in the conventional (+40%, P = 0.006) and of interferon gamma in the probiotic group (+108%, P < 0.05). IL-10 decreased following consumption of the probiotic product, but increased significantly after intake cessation (+129%, P < 0.001). No significant differences in cytokine responses between the conventional and the probiotic yogurt were observed. CONCLUSION: Both conventional and probiotic yogurt enhanced the stimulated production of pro-inflammatory cytokines.

Evaluation of Responding in Peaceful and Positive Ways (RIPP): a school-based prevention program for reducing violence among urban adolescents.

Evaluated Responding in Peaceful and Positive Ways (RIPP)--a 6th-grade universal violence prevention program. Classes of 6th graders at 3 urban middle schools serving predominantly African American youth were randomized to intervention (N = 321) and control groups (N = 305). Intervention effects were found on a knowledge test but not on other mediating variables. RIPP participants had fewer disciplinary violations for violent offenses and in-school suspensions at posttest compared with the control group. The reduction in suspensions was maintained at 12-month follow-up for boys but not for girls. RIPP participants also reported more frequent use of peer mediation and reductions in fight-related injuries at posttest. Intervention effects on several measures approached significance at 6-month and 12-month follow-up. The program's impact on violent behavior was more evident among those with high pretest levels of problem behavior.

PD0084430: a non-nucleoside inhibitor of human cytomegalovirus replication in vitro.

Human cytomegalovirus (HCMV) is a major opportunistic pathogen in immunocompromised individuals. Current therapies target viral DNA replication and accumulate mutations that yield cross-resistance among the approved drugs. A novel, non-nucleoside inhibitor of HCMV replication, PD0084430, was identified in a screening assay using the HCMV beta-galactosidase recombinant RC256. The EC(50) for PD0084430 by inhibition of beta-galactosidase production is 1+/-0.7 microM. This antiviral activity was confirmed by yield reduction and plaque reduction assays using HCMV strain AD169. The TC(50) of PD0084430 as measured by (4C)thymidine incorporation is approximately 30 microM and by XTT is approximately 90 microM. The TC(50) for inhibition of cellular proliferation is approximately 20 microM. Time of addition experiments displayed a similar drop in efficacy for both PD0084430 and GCV when added after the onset of viral DNA replication. The transcomplementation assay for viral DNA replication, using a transfected ori(Lyt) containing plasmid, confirmed that viral DNA synthesis was inhibited at the same concentrations that showed antiviral activity. Western blots showed no apparent block of immediate early or early gene expression. Two ganciclovir (GCV) resistant isolates of HCMV tested showed no cross-resistance to PD0084430. These data suggested a potentially promising novel compound that inhibited HCMV at or before viral DNA replication. However, in vivo testing in mice dosed either orally or intraperitoneally showed rapid glucuronidation on the -OH group. SAR studies on this backbone showed that the -OH group was essential for the antiviral activity in vitro.

Development and evaluation of school-based violence prevention programs.

Discusses key issues in developing and evaluating school-based violence prevention interventions. Schools provide a natural setting for implementing programs directed at teaching youth attitudes, knowledge, and skills to reduce their involvement in violence. Although multitudes of these programs exist, few have been rigorously evaluated. Developers of violence prevention programs need to pay particular attention to the type of violence being addressed, the target population, relevant risk and protective factors, and the target of the intervention. Conducting sound evaluations of such programs requires careful attention to the unit of randomization, treatment conditions, outcome measures, timing of data collection, and potential moderator variables. Efforts to develop effective prevention programs can be greatly facilitated by adopting an action-research strategy in which evaluation findings provide a basis for continual program refinement.

Autoimmune mechanisms in antibiotic treatment-resistant lyme arthritis.

In about 10% of patients with Lyme arthritis in the United States, joint inflammation persists for months or even several years after the apparent eradication of the spirochete, Borrelia burgdorferi, from the joint with antibiotic treatment. We propose a model of molecular mimicry affecting genetically susceptible individuals to explain this treatment-resistant course. The majority of patients with treatment-resistant Lyme arthritis have HLA-DRB1*0401 or related alleles, and the severity and duration of their arthritis correlate with cellular and humoral immune responses to outer-surface protein A OspA) of the spirochete. Using an algorithm, the immunodominant epitope of OspA presented by the DRB1*0401 molecule was predicted to be located at aa 165-173. In a search of the Genetics Computer Group gene bank, only one human protein was identified, lymphocyte function associated antigen-1 (hLFA-1), that had sequence homology with OspA(165-173)and predicted binding in the DRB1*0401 molecule. Synovial fluid T cells from most patients with treatment-resistant arthritis responded to both OspA and hLFA-1, whereas those from patients with other forms of chronic inflammatory arthritis did not. Molecular mimicry between a dominant T cell epitope of OspA and hLFA-1 may be an important factor in the persistence of joint inflammation in genetically susceptible patients with treatment-resistant Lyme arthritis.

Molecular mimicry in Lyme arthritis demonstrated at the single cell level: LFA-1 alpha L is a partial agonist for outer surface protein A-reactive T cells.

Antibiotic treatment-resistant Lyme arthritis is a chronic inflammatory joint disease that follows infection with Borrelia burgdorferi (BB:). A marked Ab and T cell response to BB: outer surface protein A (OspA) often develops during prolonged episodes of arthritis. Furthermore, cross-reaction between the bacterial OspA and human LFA-1alpha(L) at the T cell level and the inability to detect BB: in the joint implicate an autoimmune mechanism. To analyze the nature of response to OspA and LFA-1alpha(L), we used OspA-specific T cell hybrids from DR4 transgenic mice, as well as cloned human cells specific for OspA(165-184), the immunodominant epitope, from five DRB1*0401(+) patients, using OspA-MHC class II tetramers. Although OspA(165-184) stimulated nearly all OspA-specific human T cell clones tested to proliferate and secrete IFN-gamma and IL-13, LFA-1alpha(L326-345) stimulated approximately 10% of these clones to proliferate and a greater percentage to secrete IL-13. Assays with LFA- or OspA-DR4 monomers revealed that higher concentrations of LFA-DR4 were needed to stimulate dual-reactive T cell hybrids. Our analysis at the clonal level demonstrates that human LFA-1alpha(L326-345) behaves as a partial agonist, perhaps playing a role in perpetuating symptoms of arthritis.

Rapid depletion of peripheral antigen-specific T cells in TCR-transgenic mice after oral administration of myelin basic protein.

In myelin basic protein (MBP)-specific TCR-transgenic (Tg) mice, peripheral T cells express the Valpha2.3/Vbeta8.2-Tg TCR, demonstrate vigorous proliferative responses to MBP in vitro, and can exhibit experimental autoimmune encephalomyelitis (EAE) within 5 days of pertussis toxin injection. We explored the effects of oral administration of MBP on the cellular trafficking of the MBP-specific TCR-Tg cells and the ability of oral MBP to protect Tg mice from EAE. Tg mice were fed MBP, OVA or vehicle and sacrificed at various times after feeding. An immediate and dramatic decrease in Valpha2.3/Vbeta8.2(+)-Tg cells was observed in the periphery within 1 h after feeding. By 3 days after feeding, the percentage of Tg cells increased to near control levels, but decreased again by 10 days. When MBP or vehicle-fed Tg mice were challenged for EAE at this point, disease was severe in the vehicle-fed mice and reduced in the MBP-fed mice over the 40-day observation period. In vitro studies revealed a biphasic pattern of MBP proliferative unresponsiveness and an induction of Th1 cytokines. Immunohistochemical staining showed that the number of Tg cells found in the intestinal lamina propria increased dramatically as the number of Tg cells in the periphery decreased. There was no apparent proliferation of Tg cells in the lamina propria, indicating that Tg cells trafficked there from the periphery. Taken together, these results suggest that T cell trafficking into the site of Ag deposition acts to protect the TCR-Tg mouse from EAE.

Direct enumeration of Borrelia-reactive CD4 T cells ex vivo by using MHC class II tetramers.

We characterized antigen-specific CD4(+) T cells in six patients with treatment-resistant Lyme arthritis, using an HLA-DRB1*0401 major histocompatibility complex (MHC) class II tetramer covalently loaded with OspA(164-175), an immunodominant epitope of Borrelia burgdorferi. Direct analysis of OspA-tetramer binding CD4(+) cells in patients expressing the HLA-DRB1*0401 allele revealed frequencies of between <0.005 and 0.1% in peripheral blood (n = 6), and between <0.005 and 3.1% in synovial fluid (n = 3). OspA-tetramer(+)CD4(+) cells were directly cloned at 1 cell per well and expanded by mitogen and IL-2 on allogeneic feeder cells. As measured by [(3)H]thymidine incorporation, 95% of 168 T cell clones from synovial fluid binding the OspA-tetramer were antigen-reactive. Clones generated from peripheral blood revealed a different pattern of responsiveness when compared with clones generated from synovial fluid, as measured by proliferation, IFN-gamma, and IL-13 secretion. These clones, selected on the basis of their peptide binding, also responded to whole protein, but with a different cytokine profile. Our studies demonstrate that MHC class II tetramers can be used in humans to directly identify, isolate, and characterize antigen-reactive T cells from an inflammatory compartment.

Identification and assessment of problematic interpersonal situations for urban adolescents.

Identified and developed a scale to assess problematic interpersonal situations among urban adolescents. In Study 1, problematic situations were identified by focus groups of 6th graders (N = 43). Their relevance was verified in Study 2 by assessing their reported frequency and difficulty in a sample of 6th graders (N = 457) that included mostly African American youth from low-income families. Scales representing 3 dimensions, peer provocation, perceived injustice, and environmental stressors were verified by confirmatory factor analyses. In Study 3, the internal consistency and structure of these scales were cross-validated in a sample of 7th graders (N = 459). All 3 scales were correlated with self-reported violent behavior, drug use, and anxiety and uniquely accounted for 11% to 19% of the variance. These findings have implications for identifying youth at risk for emotional and behavioral problems and for designing more relevant interventions.

The effectiveness of a school-based curriculum for reducing violence among urban sixth-grade students.

OBJECTIVES: In this study, we examine the impact of a school-based curriculum designed to reduce violence among urban sixth-grade students. METHODS: This study used a staggered implementation design in which sixth-graders in six middle schools were taught an 18-session violence-prevention curriculum during either the fall or spring semester. Outcome measures were completed at the beginning, middle, and end of the school year. RESULTS: For boys, participation in the program during the fall resulted in significant posintervention differences in the self-reported frequency of violence and several other problem behaviors. Most of these differences were maintained at the end of the school year. Girls, in contrast, did not appear to benefit from the program. CONCLUSION: These results support the use of a school-based curriculum for reducing violence among sixth-grade boys. They also underscore the importance of early intervention and the necessity of examining gender effects in evaluating such programs.

Pathogenesis of ovine lentiviral encephalitis: derivation of a neurovirulent strain by in vivo passage.

The lentiviruses of sheep replicate almost exclusively in macrophages and cause chronic interstitial pneumonia, arthritis, and mastitis, but only rarely encephalitis. This study was undertaken to determine whether a non-neurovirulent field strain of ovine lentivirus isolated from joint fluid that replicated productively in lung and joint macrophages could be adapted to enter and replicate in the brain and cause encephalitis. The field isolate was passed seven times sequentially by intracerebral inoculation of sheep. The neuroadapted strain of virus caused severe encephalitis typical of visna in four of four sheep inoculated intracerebrally. The virus replicated to high titers in the brains of these animals and in cultured microglia. The inflammatory response in the brain was characterized by intense infiltrates of macrophages and CD8+ and CD4+ T cells. Many of the perivascular macrophages demonstrated TNF-alpha expression and there was upregulation of MHC Class II antigen expression on both inflammatory cells and endothelium. Inoculation of this neuroadapted virus into the bone marrow of three animals resulted in persistent infection and cell-associated viremia, but not encephalitis. Virus was not detected in brains from these animals, indicating that the virus was not neuroinvasive. These data suggest that neuroinvasiveness and neurovirulence are separate pathogenic determinants, both of which are required for the development of encephalitis during natural infection.

Suppression of murine chronic relapsing experimental autoimmune encephalomyelitis by the oral administration of myelin basic protein.

Chronic relapsing experimental autoimmune encephalomyelitis (EAE), induced in mice by the injection of myelin basic protein (MBP), is a T cell-mediated autoimmune disease characterized by periods of paralysis and remission. We have shown previously that the oral administration of MBP or MBP peptides renders Lewis rats refractory to EAE. This study was undertaken to examine the conditions necessary to produce oral tolerance in a chronic relapsing model of EAE in B10.PL mice. The optimal tolerizing regimen for the mouse was found to be a single feeding of 20 mg of MBP suspended in PBS. To determine the ability to suppress chronic disease, a range of doses (0.4-100 mg) was administered orally in a single dose before challenge. Larger oral doses (20 or 100 mg) of MBP provided the best protection from EAE, while 0.4 mg exacerbated the clinical course of disease. Secretion of the proinflammatory cytokines, IL-2 and IFN-gamma, were lowest in the group fed 20 mg. A single feeding of MBP before challenge or as late as the first day of clinical signs showed significant protection over the relapsing disease course. Once relapsing EAE was established, multiple oral doses of MBP were required to achieve suppression of clinical signs of disease. These findings suggest that vehicle, dosage, and timing are important considerations in the successful application of oral tolerance strategies for suppression of chronic disease processes.

Richmond youth against violence: a school-based program for urban adolescents.

The Richmond Youth Against Violence Project teaches middle school students in the Richmond Public Schools knowledge, attitudes, and skills for reducing their involvement in violence. These students are primarily African Americans, many of whom come from low-income, single-parent households in neighborhoods with high rates of crime and drug use. The program, "Responding in Peaceful and Positive Ways," employs a developmentally anchored health promotion model. Its goal is to promote peaceful and positive alternatives to interpersonal and situational violence, by creating environments that teach and encourage health-enhancing behaviors and intrapersonal attributes and weakening supports for health-compromising behaviors and intrapersonal attributes. The 16-session school-based program was implemented by prevention specialists with sixth graders during the 1994-1995 school year. Students are taught a seven-step problem-solving model. Program implementation was staggered to allow an intervention group to participate during the fall semester and a control group to participate during the spring semester. Outcome measures include school data and measures completed by students. There were few significant baseline differences between the intervention and control groups. A high percentage of students, particularly boys, reported exposure to community violence; more than 92% had heard gunshots. Many have also engaged in risk behaviors; 70% of the boys and 44% of the girls reported being in a fight in the preceding 30 days. The impact of the curriculum is being examined. The program has provided valuable lessons about conducting community-based research, particularly designing, implementing, and evaluating prevention programs.

Detection of ovine lentivirus in seronegative sheep by in situ hybridization, PCR, and cocultivation with susceptible cells.

Serological surveys for ovine lentivirus (OvLV), a worldwide cause of pneumonia and chronic debilitation in sheep, have demonstrated a wide range of seroprevalence rates. This study analyzed OvLV infection in a purebred sheep flock with a history of OvLV disease (flock 1), and compared the prevalence with that of a flock lacking previous OvLV-associated disease (flock 2). Serological tests (ELISA and Western blot assay) indicated that 25% of sheep of all ages in flock 1 (Group A) and 33% of animals of all ages in flock 2 (Group B) had antibodies to OvLV. In situ hybridization, however, detected viral RNA in a much larger proportion of sheep (72 and 67%, respectively). Animals less than 1 year of age rarely had antibodies to OvLV, although most harbored viral RNA. Twenty animals in this age group from flock 1 (Group C) were therefore studied more closely for infection. These yearling animals were tested serologically by ELISA and their peripheral blood-derived macrophages were cultured for 14 days to amplify any infection in these target cells. The macrophages were then tested by in situ hybridization, PCR, and cocultivation with susceptible target cells. The results of these tests showed that while only 10% of animals in Group C were seropositive, 70% were positive by in situ hybridization, PCR, and cocultivation. These data suggest that latent OvLV infection is common in sheep and that infection is frequently undetected by serological tests.