The Yankton Model Program.

Changes in medical education towards a student-centered, problem-based learning, with continuity care experience in ambulatory settings have been recommended. The University of South Dakota School of Medicine has developed such an educational model for third year medical students named the Yankton Model Program and is herein described.

Restriction to human cytomegalovirus replication in vitro removed by physiological levels of cortisol.

Since viral infection is in most cases contrary to the survival of the host cell, it is reasonable to assume that cells possess innate viral replication inhibitory mechanisms. Even between strains of permissive cells, degrees of permissiveness are observed. Restriction to human cytomegalovirus (CMV) replication in vitro is well known, especially in epithelioid cells or cells derived from certain organs. We have studied restriction in a fibroblastic strain of human embryonic kidney cells. By treatment of cell cultures with maximum physiologic concentration of the hormone cortisol (25 micrograms%) both pre and post virus inoculation, susceptibility to laboratory strain Ad169 CMV and low-passaged clinical isolate JSS CMV was enhanced by factors of 6.4 +/- 0.7 and 11.1 +/- 0.4, respectively; effectively converting these cells to a totally permissive state. A linear dose response, which peaks at 25 micrograms% and declines thereafter up to 300 micrograms%, is evident for both virus strains in this enhancement system. Breakdown of restriction increases in linear fashion with increasing time of cortisol pretreatment of cells. The characterization of cortisol effects converting restrictive human fetal cells in vitro to the permissive state further indicates that human hormones may play a significant role in CMV susceptibility in vivo.

Lytic cytomegalovirus replication and the hormones of human pregnancy.

The frequency of human cytomegalovirus (CMV) excretion during pregnancy denoting active infection has been demonstrated to increase as gestation advances and at term involves a significant percentage of women. This increase enhances the risk of congenital infection of the fetus. Thus it appears that some factor(s) unique to the condition of pregnancy favors susceptibility to maternal CMV infection. We designed our studies to investigate the possible association of the continuously rising levels of selected hormones and this increased susceptibility. Progesterone, 17 beta-estradiol, and cortisol were added to tissue culture media in final concentrations to match those occurring in term pregnancy serum. Two strains of human foreskin cells, one neonatal and the other fetal, were treated with either single or paired combinations of hormone-containing media. Lytic CMV replication in neonatal foreskin cells was enhanced by a maximum of 5.7-fold when these cells were treated with cortisol. Such enhancement did not occur in the fetal cells. No synergistic effects were seen when cortisol was used in combination with other hormones nor when neonatal foreskin cells were replicated for at least three generations in either single or paired combinations of hormones prior to use. Differential hormonal enhancement of CMV replication in vitro suggests a possible mechanism for the increased incidence of CMV infection observed during human pregnancy.

Infection by human cytomegalovirus associated with chronic hematospermia.

Hematospermia, or blood in the ejaculate, is not an infrequent urologic condition most often occurring without recognizable physical dysfunction. It is regarded as benign and self-resolving. In its chronic form, however, it may manifest periodic recurrences or persistence for months to years. We had opportunity to follow the course of cytomegalovirus (CMV) infection in a patient experiencing both chronic hematospermia and CMV mononucleosis. The level of virus output in urine (representing systemic CMV infection) remained constant over a period of forty-four weeks during and after convalescence from the mononucleosis syndrome. However, virus isolation from semen (representing localized CMV infection) appeared to parallel the course of and concomitantly terminate with the resolution of the urologic condition. The concentration and temporal association of CMV with the course of chronic hematospermia is suggestive of a causative role in this genital pathology.

Characterization of a reptilian epithelioid skin cell line derived from the green sea turtle, Chelonia mydas.

A continuous line of epithelioid cells was established from explant skin tissues of the green sea turtle, Chelonia mydas. These cells, designated GTS, have been subcultured more than 60 times in commercially available mammalian cell culture medium supplemented with 5% bovine calf serum. Of those temperatures tested, optimal growth was achieved at 30 degrees C although replication occurred between 16 and 37 degrees C. These cells may be held as monolayers at 8 degrees C or stored frozen in growth medium containing 10% dimethyl-sulfoxide at -70 or -196 degrees C. The modal number of 55 chromosomes per cell is in agreement with the heterogametic female diploid number of this species. The GTS line represents the first established culture of normal epithelioid skin cells to be reported for a poikilothermic species.

Temperature-sensitive host range mutants of herpes simplex virus type 2.

Herpesviruses are capable of several types of infection of a host cell. To investigate the early events which ultimately determine the nature of the virus-host cell interaction, a system was established utilizing temperature-sensitive mutants of herpes simplex virus type 2. Four mutants have been isolated which fail to induce cytopathic effects and do not replicate at 39 C in hamster embryo fibroblast cells. At least one mutant is virus DNA negative. Since intracellular complementation is detectable between pairs of mutants, a virus function is known to be temperature sensitive. However, all four mutants induce cytopathic effects and replicate to parental virus levels in rabbit kidney cells at 39 C. This suggests that a host cell function, lacking or nonfunctional in HEF cells but present in rabbit kidney cells at 39 C, is required for the replication of these mutants in hamster embryo fibroblasts cells at 39 C. Therefore, we conclude that these mutants are both temperature sensitive and exhibit host range properties.

In vivo characteristics of temperature-sensitive host range mutants of herpes simplex virus type 2.

The in vivo properties of four host range temperature-sensitive (ts) mutants of herpes simplex virus type 2 (HSV-2) were correlated with known in vitro characteristics. Mutants and parental virus were inoculated into newborn and weanling mice and weanling hamsters by intracranial and subcutaneous routes, and into weanling rabbits by corneal scarification. In all cases the pattern of attenuation of mutants in vivo correlated with their stability in vitro at 39 degrees. The most attenuated mutant (mutant 69) was also the most consistent in its inability to induce cytopathic effects (CPE) in vitro or to replicate under nonpermissive conditions. Conversely, the most virulent mutant (mutant 41) was the least stable under nonpermissive conditions.