A model of the transmission and control of genital herpes.

BACKGROUND: Mathematical modeling of herpes simplex virus type 2 transmission can provide insight into the behavior of the epidemic and the effects of control measures. GOAL: To examine parameter sensitivity and assess control strategies. STUDY DESIGN: The model simulates transmission in a young, sexually active, nonmonogamous population. The population is divided into compartments representing disease status (susceptible, exposed, primary infectious, asymptomatic, recurrent, vaccinated), and flows between compartments are described by differential equations. RESULTS: With a base set of parameter values, the basic reproduction rate (R0) is 1.79, indicating that ultimate prevalence in this population will be 44%. The course of the epidemic is most sensitive to changes in behavioral parameters (time nonmonogamous and partner-change rate) and to the probability of transmission during the asymptomatic stage. CONCLUSION: In the absence of behavior change, efforts to control the epidemic must focus on vaccine development and prevention of transmission during both symptomatic and asymptomatic phases.

Unilateral ureteral obstruction impairs renal antioxidant enzyme activation during sodium depletion.

BACKGROUND: Obstructive nephropathy leads to progressive renal tubular atrophy and interstitial fibrosis and is associated with sodium wasting and sodium depletion. Renal damage resulting from unilateral ureteral obstruction (UUO) may be aggravated by reactive oxygen species (ROS), which are produced by a variety of processes. Ideally, deleterious effects of ROS are attenuated by antioxidant enzymes, including the superoxide dismutases, glutathione peroxidases, catalase, and glutathione-S-transferases. The general paradigm is that tissue damage occurs when ROS production is greater than the protective capacity of the antioxidant enzymes. METHODS: This study was designed to investigate the response of renal antioxidant enzymes to UUO and sodium depletion. Adult, male Sprague-Dawley rats received normal-sodium or sodium-depleted siets and were subjected to UUO or sham operation. Obstructed (UUO), intact opposite, or sham-operated kidneys were harvested after 14 days, and antioxidant enzyme activities were measured in kidney homogenates. Thiobarbituric acid reactive substances were measured in these homogenates at 3 and 14 days after UUO or sham operation as an index of ROS production. RESULTS: Renal interstitial area, a measure of fibrosis, was increased by UUO and was doubled in sodium-depleted animals. Sodium depletion increased manganese superoxide dismutase, glutathione peroxidases, and glutathione-S-transferase activities in sham-operated kidneys but not in UUO kidneys. Relative to intact opposite kidneys, UUO kidneys had reduced activities of catalase, manganese superoxide dismutase, and glutathione-S-transferase in normal-sodium animals and all antioxidant enzymes tested in sodium-depleted animals. Renal thiobarbituric acid reactive substances were increased by three days of UUO and were increased further by 14 days of sodium depletion. CONCLUSION: In summary, sodium depletion increased several renal antioxidant enzymes, consistent with a stress response to increased ROS production. Further, UUO not only reduced antioxidant enzyme activities but also inhibited increases seen with sodium depletion. We conclude that suppression of renal antioxidant enzyme activities by UUO contributes to the progression of renal injury in obstructive nephropathy, a process exacerbated by sodium depletion.

Effect of supplemental sodium chloride, sodium phosphate, or hydrochloric acid in starter pig diets containing dried whey.

Three experiments involving a total of 606 pigs weaned at 23 +/- 2 d of age were used to evaluate the effects of added dietary Na or Cl or both in combination (NaCl) on postweaning performance responses. A basal diet without added NaCl was formulated to 1.20% lysine using a corn-soybean protein mixture with 20% dried whey (C-SBP-DW) and was used in all experiments. The analyzed content of the basal diet for the three experiments averaged .19% Na, .37% Cl, and 1.37% K. In Exp. 1, NaCl was added to treatment diets at 0, .20, .40, and .60% at the expense of corn. The experiment was a randomized complete block (RCB) design conducted in 14 replicates using a total of 336 pigs (six pigs/ pen). The results demonstrated a linear (P < .01) growth response during the 0- to 7-d and a quadratic (P < .08) response during the 8- to 14-d period. Gain: feed ratio improved quadratically (P < .08) for the 0- to 14-d period. In Exp. 2, Na2HPO4 added to the C-SBP-DW basal diet provided supplemental Na levels of 0, .08, .16, and .24% Na to four treatment diets. The experiment was conducted in six replicates in a RCB design using a total of 144 pigs (six pigs/pen). The results demonstrated a linear (P < .05) growth response during the 0- to 7-d period as Na level increased, but not thereafter, and an improved gain: feed ratio (P < .05) for the 0- to 14-d period. In Exp. 3, Cl was added as HCl at 0, .05, or .10% Cl to the basal C-SBP-DW diet. The experiment was a RCB design conducted in six replicates using a total of 126 pigs (five or six pigs/pen between replicates). The results demonstrated a linear growth (P < .01) and feed intake (P < .08) response during the 0- to 7-d and the 0- to 14-d period to increasing levels of Cl. Feed intake also increased for the 0- to 7-d (P < .08), and 8- to 14-d (P < .05) periods. Stool looseness was unaffected by any of the dietary variables in the three experiments. These results suggest that the NRC (1988) recommendations for Na and Cl for young pigs (< or = 10 kg BW) may need to be increased.

Back-projection and sensitivity analysis of the HIV-AIDS epidemic in the Caribbean.

In this study we estimated past human immunodeficiency virus (HIV) incidence in 19 nations in the primarily English-speaking Caribbean and projected the course of the epidemic to the year 1999. We compared the results obtained from several different models of HIV incidence and different assumed incubation distributions. Linear and nonlinear optimization methods were used to fit several models (power, logistic, spline, and step) to adult (age 15 years or older) AIDS incidence data derived from our existing surveillance system. All four models tested gave good fits to the data, with estimates of cumulative HIV incidence in 1993 ranging from 16,504 to 21,732. An increase in the assumed median of the AIDS incubation distribution by one year increased the estimates of current cumulative adult HIV incidence by approximately 12%; these estimates varied by as much as 6% between models. An adjustment of the data for possible reporting delay increased the estimates by approximately 7% and for underreporting by 25%. Despite their sensitivity to underlying assumptions, back-projection estimates provide useful insights into the patterns of HIV and AIDS incidence. The models indicate that HIV and AIDS incidences in the English-speaking Caribbean have been rising steadily, with adult HIV prevalence in the general population still less than 1%.

Effect of initial breeding weight on macro- and micromineral composition over a three-parity period using a high-producing sow genotype.

A total of 36 high-producing F1 (Landrace x Yorkshire) gilts and sows were used to determine total body minerals as influenced by initial breeding weight, age, and reproductive state. Four gilts at 9 mo of age were killed at 120, 135, or 150 kg BW for the determination of total body ash and minerals. An additional two gilts from each weight group were maintained in a nonpregnant state until 24 mo of age and then killed, and six sows from each breeding weight group were killed after completing three reproductive cycles (i.e., 24 mo of age). Total body minerals were quantified from the mineral analysis of all body components, including blood. The mineral spectrum of 25 elements was determined by the Inductively Coupled Plasma spectroscopic method. The results suggested that as BW increased at 9 mo of age, P, K, Na, and Cu contents seemed to reach a plateau at 135 kg BW, whereas Ca increased. Non-pregnant gilts at 24 mo of age had higher (P < .01) body mineral contents than at 9 mo and Ca, P, Mg, K, and Na linearly increased (P < .01) as body weight increased in the older gilts. When sows had completed three reproductive cycles, Ca, P, Mg, K, Na, Al, Zn, and Cu contents were lower (P < .01) than those in similarly aged, nongravid gilts.(ABSTRACT TRUNCATED AT 250 WORDS)

Modeling the HIV/AIDS epidemic in the English-speaking Caribbean.

The study reported here examines the past and potential future impact of HIV/AIDS in 19 nations of the primarily English-speaking Caribbean. The authors use DemProj, a demographic projection model, to explore two different HIV scenarios. In the low scenario adult HIV prevalence stabilizes at 2% in the year 2000, and in the high scenario adult HIV prevalence stabilizes at 5%. By the year 2010, annual AIDS incidence exceeds 11,000 cases in the low scenario and 28,000 in the high scenario. In both scenarios, 70% of the cases are in young adults 20-45 years old and 12% are in children 0-15. Age-specific mortality is more than doubled in the 20-40 age range in the low scenario, and more than quadrupled in the high scenario. The impact on death rates is also severe among children 0-10. In assessing the economic impact, the authors estimate that the total annual costs of the epidemic will approach US$ 500 million (in constant 1989 US$) or 2% of GDP in the low scenario, and will exceed US$ 1,200 million or 5% of GDP in the high scenario.

Evaluation of feed grains with dried skim milk and added carbohydrate sources on weanling pig performance.

Two experiments were conducted to evaluate the effects of 1) two grain mixtures and 2) various carbohydrate sources and levels fed to weanling pigs during the initial 2 wk postweaning. A total of 720 crossbred pigs were weaned at 23 +/- 2 d of age at an average BW of 5.8 kg. In Exp. 1, a 2 x 3 factorial experiment in a randomized complete block design was conducted in 12 replicates. Treatment diets formulated to 1.40% lysine were fed for a 14-d period. These diets contained dried skim milk (DSM) at a 45% level and an oat groat-soybean meal (OG-SBM-DSM) or a corn-soybean meal (C-SBM-DSM) mixture. In addition, the diets contained one of three carbohydrate sources (cornstarch, dextrose, lactose) at a 12% level. From 15 to 35 d postweaning, all groups were fed a 1.15% lysine corn-soybean meal (C-SBM) diet. The results demonstrated that during the period from 0 to 14 d weight gains were similar when either grain source was provided, but gain:feed ratio was superior and serum urea N was lower when the OG-SBM-DSM diet was fed. The addition of lactose or dextrose to either grain mixture resulted in greater weight gains (P <.05) than when cornstarch was the carbohydrate source. The second experiment was a randomized complete block design conducted in six replicates. The C-SBM-DSM diet of Exp. 1 served as the positive control diet. The other diets used corn gluten meal (CGM), SBM, and DSM with the three carbohydrate sources added at 22.5 or 35.5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of initial breeding weight and management system using a high-producing sow genotype on resulting reproductive performance over three parities.

A study was conducted with sows of a high-producing genotype to evaluate their reproductive performance using three breeding weights over a three-parity period in two management systems. A total of 114 F1 gilts (Landrace x Yorkshire) were used in a split-plot, randomized, complete block experiment conducted as a 3 x 2 factorial arrangement of treatments in two replicates. Three gilt breeding weights of 120, 135, and 150 kg were achieved by feeding 1.8, 2.3, or 3.2 kg/d of a .73% lysine corn-soybean meal (C-SBM) diet, respectively, from 5 to 8 mo of age. Two locations, each with different management systems, were considered the main plot and consisted of 1) outside, concrete-floored gestation lots and indoor farrowing pens or 2) indoor gestation pens and farrowing crates. All sows were fed 1.8 (Parity 1) or 2.1 (Parity 2 and 3) kg/d of a .73% lysine C-SBM diet during the breeding and gestation periods, whereas a .82% lysine C-SBM diet with 5% added fat was available ad libitum during lactation. All sows lost weight during the first lactation; larger weight losses occurred as breeding weight increased (P < .01). During the second and third lactations the 135- and 150-kg sow breeding groups had less lactation weight change, whereas the 120-kg group lost more weight, resulting in a breeding weight x parity interaction (P < .01). The 120-kg breeding weight group consumed less feed (P < .05) for the three lactation periods than did the heavier weight groups. Initial breeding weight had no effect on number of pigs born (total, live) or pig and litter weights at birth. Pig mortality increased with increasing breeding weight (P < .01) and parity (P < .05), a response that was exacerbated when sows farrowed in pens vs crates. Postweaning breeding intervals and sow removal from the experiment were not significantly affected by initial breeding weight, but a numerically higher percentage of sows in the 120-kg group were anestrous or failed to conceive than the percentage of such sows in the heavier weight groups. These data suggest that an initial breeding weight of approximately 135 kg at 8 mo of age may be best when sows farrow in crates, whereas when sows farrow in pens a lower breeding weight may be more desirable.

Effect of feed intake during late development on pubertal onset and resulting body composition in crossbred gilts.

A total of 105 nonboar-exposed, F2 ([Landrace x Yorkshire] x Duroc) gilts were used in two replicates of a randomized complete block experiment to evaluate the effect of dietary feed intake on pubertal onset and subsequent body composition. Feed intakes were established at 50% of ad libitum (AL-50), 75% of ad libitum (AL-75), or at ad libitum (AL-100) levels from 4.5 to 9 mo of age. A corn-soybean meal diet fed to all gilts was formulated to meet or exceed nutrient requirements except for energy. Puberty was measured by two methods: 1) monitored once daily by back pressure applied by the herdsman or 2) from elevated plasma progesterone concentrations. Body composition was evaluated by the deuterium oxide method after plasma progesterone concentrations were elevated. Daily feed intake for the experimental period averaged 1.6, 2.3, and 3.2 kg, and the BW of gilts at 8 mo of age were 111, 131, and 154 kg for the AL-50, AL-75, and AL-100 groups, respectively. Body weight, backfat thickness, and body fat content increased linearly (P < .01) as feed intake increased, but age at puberty was not severely influenced. A minimum body fat content or percentage did not seem to initiate pubertal onset. There was a trend for a lower percentage of the AL-50 gilts to ovulate (P = .08) than those fed the AL-75 and AL-100 intakes. An inverse relationship resulted between the percentage of gilts that ovulated to the percentage that showed behavioral estrus.(ABSTRACT TRUNCATED AT 250 WORDS)

A model of the transmission of dengue fever with an evaluation of the impact of ultra-low volume (ULV) insecticide applications on dengue epidemics.

We have developed a deterministic susceptible, exposed, infectious, resistant or removed (SEIR) model of dengue fever transmission that enables us to explore the behavior of an epidemic, and to experiment with vector control practices. Populations of both host and vector are divided into compartments representing disease status (susceptible, exposed, infectious, and, for humans, resistant), and the flow between compartments is described by differential equations. Examination of the equilibrium points leads to a formulation of the basic reproduction rate (Z0) of the disease. With a base set of parameters, Z0 = 1.9 and the model realistically reproduces epidemic transmission in an immunologically naive population. Control of adult mosquitoes by ultra-low volume (ULV) aerosols is simulated by an abrupt decrease in vector densities, followed by gradual recovery of the vector population. The model indicates that ULV has little impact on disease incidence, even when multiple applications are made, although the peak of the epidemic may be delayed. Decreasing the carrying capacity of the environment for mosquitoes, and thus the basic reproduction rate of the disease, by source reduction or other means, is more effective in reducing transmission.

Influence of duration of litter separation and boar exposure on estrous expression of sows during and after lactation.

The influence of litter separation (LS) that included a change in housing environment and social status of sows, boar exposure (BE), and parity on estrous expression by sows during and after lactation was examined in two experiments utilizing 140 crossbred sows. In Exp. 1 (Yorkshire X Duroc sows), limiting duration of LS to 6 or 3 h/d during the last 8 d of lactation in two trials, while maintaining 1 h BE, resulted in similar proportions of sows in estrus during lactation (65 vs 79% for 3- and 6-h sows). However, 6-h LS tended to reduce (P = .08) the interval to estrus by .6 d for those sows that expressed a preweaning estrus. Postweaning intervals to estrus were unaffected by duration of LS in the remaining sows. In Exp. 2, sows (Yorkshire X Duroc X Chester White) were assigned to four treatment groups during the last 8 d of lactation: 1) BE (1 h/d), 2) LS (6 h/d), 3) LS + BE and 4) no LS + no BE (control). Only nine sows expressed estrus during lactation; four of 28 LS sows and five of 28 LS + BE sows. No sows were in estrus before weaning during August 1985 and only one sow (LS group) was in estrus before weaning during October 1986. Postweaning intervals to estrus were reduced (P less than .05) by .9 d after preweaning BE compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine changes before and after weaning in response to boar exposure and altered suckling in sows.

Eighteen sows (6 primiparous and 12 multiparous) were allotted randomly within parity to two lactational treatments: litter separation (LS; 6 h/day) plus boar exposure (BE; 1 h/day; N = 14) beginning 8 days before weaning (4 weeks) and no LS + no BE (controls; N = 4). Blood was collected from all sows via indwelling venous catheters at 20-min intervals for 5 h on Days -1, 0, 1, 2 and 3 from start of treatment. Control sows and those exposed to LS + BE not exhibiting oestrus during lactation were resampled on Days -1, 0, 1 and 2 from weaning. All 10 multiparous sows receiving LS + BE exhibited oestrus during lactation, whereas none of the 4 primiparous sows exposed to LS + BE or the 2 control multiparous and 2 control primiparous sows exhibited lactational oestrus. Overall concentrations of LH in serum were higher (P less than 0.05) in sows receiving LS + BE than in control sows during lactation, whereas overall FSH was higher (P less than 0.05) in primiparous than multiparous sows. Number and amplitude of pulses of LH were greater (P less than 0.05) for treated primiparous than multiparous sows during lactation. Oestradiol-17 beta increased (P less than 0.05) in sows during LS + BE and was higher (P less than 0.01) in multiparous sows of this group than control multiparous or treated primiparous sows. Preweaning concentrations of cortisol and progesterone in serum were higher (P less than 0.05) in treated than control sows for multiparous and primiparous animals. In sows resampled at weaning, the number of pulses of LH was greater (P less than 0.05) in treated primiparous than in control sows. Postweaning concentrations of FSH in serum were unaffected by preweaning treatments. It was concluded that (1) litter separation and boar exposure increased basal and pulsatile secretion of LH in multiparous and primiparous sows; (2) lack of ovarian follicular development and oestradiol secretion may preclude expression of oestrus in primiparous sows during lactation, despite elevated concentrations of FSH and LH in serum; and (3) if elevated concentrations of cortisol and progesterone inhibit the onset of oestrous cycles, in response to litter separation and boar exposure during lactation, the effect is limited to primiparous sows.