Re-emphasizing mechanism in the community ecology of disease.

1. Hosts and their parasites exist within complex ecological communities. However, the role that non-focal community members, species which cannot be infected by a focal pathogen, may play in altering parasite transmission is often only studied in the lens of the "diversity-disease" relationship by focusing on species richness. This approach largely ignores mechanistic species interactions and risks collapsing our understanding of the community ecology of disease down to defining the prominence of "amplification" vs. "dilution" effects. 2. However, non-focal species vary in their traits, densities, and types of interactions with focal hosts and parasites. Therefore, a community ecology approach based on the mechanisms underlying parasite transmission, host harm, and dynamic species interactions may better advance our understanding of parasite transmission in complex communities. 3. Using the concept of the parasite's basic reproductive ratio, R0, as a generalizable framework, we examine several critical mechanisms by which interactions among hosts, parasites, and non-focal species modulate transmission and provide examples from relevant literature. 4. By focusing on the mechanism by which non-focal species impact transmission, we can emphasize the similarities among classic paradigms in the community ecology of disease, gain new insights into parasite invasion and persistence, community traits correlated with disease dilution or amplification, and the feasibility of biocontrol for parasites of conservation, agricultural, or human health concern.

Effect of acute anemia on the healing of intestinal anastomoses in the rabbit.

BACKGROUND: Considering the potential deleterious effects of transfusion, the effect of severe, acute anemia on small intestine (SI) and large intestine (LI) anastomoses was evaluated. METHODS: Thirty-six rabbits underwent segmental resection of the midileum and distal colon. Half underwent preanastomotic removal of 30% of their blood volume with crystalloid resuscitation. At 1 or 2 weeks, the anastomotic bursting pressure (ABP) and histologic grade of white blood cell influx, blood vessel ingrowth, fibroblast proliferation, and collagen deposition were assessed. RESULTS: SI ABP was decreased in anemic rabbits at 2 weeks (190 +/- 6 mm Hg vs. 257 +/- 17 mm Hg). LI ABP was decreased at 1 week in anemic rabbits. In the test rabbits, histologic parameters were altered in both the SI and LI with decreased white blood cell infiltration, attenuated blood vessel ingrowth, and decreased collagen content at both 1 and 2 weeks. Decreased SI fibroblast proliferation was present at 1 week. CONCLUSION: Acute anemia in the rabbit undergoing intestinal resection decreases the SI ABP at 2 weeks and alters histologic parameters of wound healing in both the SI and LI.

Clinical versus sonographic evaluation of acute appendicitis in children: a comparison of patient characteristics and outcomes.

PURPOSE: Abdominal sonography has gained popularity in establishing the diagnosis of appendicitis in children with equivocal clinical presentations. However, no clear outcome benefits have been demonstrated to date. The authors conducted a retrospective study to compare the characteristics and outcomes of patients undergoing appendectomy after clinical evaluation only with those undergoing the procedure after sonography. METHODS: The charts of 454 consecutive patients undergoing appendectomy for acute appendicitis between January 1, 1998 and December 4, 1999 were reviewed. Patients operated on after clinical evaluation only were compared with patients operated on after abdominal sonography. RESULTS: Forty-two percent of patients (n = 191) constituted the sonography group. When compared with the clinical group, these patients had higher prevalence of female gender (52% v 38%; P =.004), longer symptom duration (2.2 +/- 2.5 v 1.6 +/- 1.6 days; P =.003), higher incidence of preoperative in-patient observation (19% v 4%; P <.001), longer duration between evaluation and operation (8.0 +/- 3.9 v 4.9 +/- 2.9 hours; P <.001), higher incidence of normal appendices on pathologic examination (13% v 6%; P =.006), and higher incidence of postoperative abscesses or phlegmons (4.4% v 1.2%; P =.04). The groups did not differ significantly in age, hospital stay, incidence of complicated appendicitis, or incidence of wound infection. CONCLUSIONS: Patients undergoing sonography before appendectomy have a longer delay before operation, a higher rate of misdiagnosis, and more postoperative complications. Limiting sonography to truly equivocal cases and using it early in the diagnostic workup may improve outcomes in this group of patients.

Should malrotation in children be treated differently according to age?

PURPOSE: The aim of this study was to better define the mode of presentation, rate of volvulus, and surgical findings in children younger than 2 versus older than 2 years of age with malrotation. METHODS: The authors reviewed the charts of all patients with malrotation admitted to their hospital between January 1980 and December 1998, excluding patients having malrotation as a secondary finding. RESULTS: An upper gastrointestinal series was done in 90 patients (6% falsely negative) and a barium enema in 20 patients (40% read as normal). Fifty-eight patients had 114 associated congenital anomalies. Volvulus was found at the time of surgery in 28 patients, 5 of whom were older than 2 years. Three presented with acute symptoms and 2 with chronic symptoms. Surgery was performed by laparotomy in 103 patients and by laparoscopy in 3. Mean length of stay was 13.6 days. Mean follow-up was 19 months. Death occurred in 4 patients; postoperative bowel obstruction was seen in 3 patients (only 1 required surgery). CONCLUSIONS: Children with malrotation who are older than 2 years old have a significant risk of volvulus that is difficult to predict radiologically. They require surgical attention even if asymptomatic. Laparoscopy allows evaluation of the base of the mesentery and completion of the Ladd's procedure.

Chromosomal anomalies in newborns with omphalocele.

Omphalocele is the most common congenital abdominal wall defect; its reported incidence is 1 in 4,000 to 5,000 live births. With large defects, the liver is a median organ and lies within the sac (extracorporeal liver [ECL]). With small defects, only bowel or stomach is found outside the abdominal cavity (intracorporeal liver [ICL]). The goal of this study was to determine whether a relationship exists between the sac contents or the timing of diagnosis and the incidence of chromosomal abnormalities or survival among fetuses and newborns with omphalocele. From 1985 to 1995, 83 cases of omphalocele were managed at the authors' institution. In 50 cases the diagnosis was made using prenatal ultrasonography. All patients underwent fetal cardiac echography and amniocentesis. Twenty-four pregnancies were terminated electively because of severe associated anomalies. Of the 59 live births, 41 patients (69%) survived. The incidences of cardiac, chromosomal, and other anomalies were 24% (14), 10% (6), and 21% (16), respectively. Omphalocele with ICL is associated with a better survival rate than omphalocele with ECL (82% v 48%; P < .01) despite the significantly higher rate of karyotype abnormalities (16% v 0%; P < .05). The prognosis was poorer for patients with prenatally diagnosed omphalocele than for those with a postnatal diagnosis (mortality rate, 42% v 21%) because the former group had a higher percentage (70% v 9%) of ECL. Although the incidence of cardiac anomalies was similar for the ECL and ICL groups (33% v 18%), the former had more complex malformations. Death usually occurred in newborns who had neonatal respiratory distress owing to prematurity, or in those with chromosomal or cardiac anomalies. Chromosomal anomalies occurred mainly in cases of small omphaloceles that contained gut only, and it was the major cause of death among this group. In ECL cases, survival was primarily affected by the associated complex cardiac anomalies.

Recurrent intussusception: safe use of hydrostatic enema.

Recurrent intussusception (RI) occurs in 5% to 8% of patients with intussusception. The authors reviewed their 15-year experience to better define the management of RI. Among 258 patients, 28 (10.8%) had episodes of RI (37 episodes altogether). Twenty-two patients had a single recurrence, four had double recurrence, one had triple recurrence, and one had quadruple recurrence. RI and non-RI patients were compared with respect to symptoms. The incidence of vomiting and bloody stools was significantly lower in the RI group. Ten percent of RI patients had lead points. Thirty percent of RI episodes occurred within 24 hours, and 74% occurred within 6 months. The success rate of hydrostatic enema reduction for recurrent episodes was 62.8%, which is comparable to that for the initial episode (68.9%). Among patients with previous surgery, 36.3% of enemas were successful; after previous enema reduction, 75% were successful. There was no complication related to the enema. Enema reduction is safe and has a good success rate in cases of RI, even after previous surgical reduction.

Improved survival for congenital diaphragmatic hernia, based on prenatal ultrasound diagnosis and referral to a combined obstetric-pediatric surgical center.

Between January 1990 and January 1993, 36 patients with antenatal ultrasound (US) diagnosis and/or postnatal diagnosis of congenital diaphragmatic hernia (CDH) were referred to the authors' high-risk obstetric and pediatric hospital. Among the 36, there were four spontaneous abortions (11%), five deaths after live births (14%), one false-positive US examination, and 26 patients who underwent surgery, 23 of whom survived (66% overall, 74% of live births, and 89% postoperatively). Only one survivor had extracorporeal membrane oxygenation (ECMO). Thirty-five ultrasound examinations were performed in 24 patients; there were 18 true-positives results (51%), one false-positive (3%), and 16 false-negatives (46%). In this series, there were 25 left-sided CDHs, eight right-sided, one bilateral, and one central. Of the four right-sided hernias having antenatal US, only one was diagnosed prenatally; 15 of the 17 left-sided CDHs were diagnosed correctly (88%). All 19 babies with the prenatal diagnosis were born at the authors' institution. US diagnosis before 25 weeks' gestation and polyhydramnios separately resulted in a mortality rate of only 50%. Patients born at this institution tend to be sicker than those transferred from elsewhere, as reflected by the lower 1- and 5-minute Apgar scores (3.7 v 6.9, P < .001, and 5.4 v 6.9, P < .16, respectively), lower gestational ages (37.0 v 39.2 weeks, P < .007), and lower birth weights (2,525 v 3,049 g, P < .02). Nevertheless, transferred patients had a mortality rate (3 of 15 patients, 20%) similar to that of nontransferred patients (5 of 20 patients, 25%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prenatal dexamethasone administration: fetal rabbit intestinal nutrient uptake and disaccharidase development.

To examine the effect of prenatal steroids on fetal intestinal maturation, eight pregnant rabbits received either dexamethasone (Dex) or saline (Cont) on Days 25-27 of a 31-day gestation. As the rabbit provides a model of growth retardation based on uterine position, fetuses were identified as favored (Fav) or runt (Runt), generating four study groups: ContFav, ContRunt, DexFav, and DexRunt. On Day 31 the small intestinal uptake of glucose and proline was measured by an everted sleeve technique. Additionally, lactase and maltase activity was determined. Small intestinal length and nutrient uptake was significantly increased in the Dex fetuses. Control runts had a trend to decreased levels of nutrient uptake when compared to their favored counterparts. This trend reversed in the Dex fetuses with runt nutrient uptake surpassing that of the favored fetus. A trend to increased enzyme activity of both lactase and maltase was demonstrated. This report provides the first description of maternal steroid administration causing a marked increase in fetal small intestinal length and glucose and proline absorption in an in vivo model of intrauterine growth retardation.

Selective management of gastroschisis according to the degree of visceroabdominal disproportion.

OBJECTIVE: This study analyzed the factors influencing the postoperative results after the repair of gastroschisis defects during the past 27 years. SUMMARY BACKGROUND DATA: The clinical results after the repair of gastroschisis abdominal defects have improved appreciably during the past 25 years, with the long-term survival rate in most large children's centers currently being approximately 90%. The improvement in survival has been largely attributed to advances in perioperative care, frequent use of parenteral nutrition, and better techniques of surgical repair. METHODS: Between 1965 and 1992, 84 infants with gastroschisis underwent surgical repair. The management of 52 infants after 1979 was compared with that of 32 during the previous 14 years. Associated anomalies were present in 29%. The average birth weight was 2412 g. In 31%, primary fascial closure was performed. In another 31% with moderate visceroabdominal disproportion (VAD), a silastic chimney was used initially, and complete repair was performed at a second operation. For 25% who had severe VAD, more than two operative reconstructions were necessary. Seven of 52 infants with moderate VAD underwent initial skin-flap closure and secondary repair within 12 days. RESULTS: Almost all complications (27%) and deaths (4%) occurred in infants with severe VAD and were largely unrelated to associated malformations or birth weight. The length of postoperative mechanical ventilation, need for parenteral nutrition, need for multiple operations, and length of hospitalization were all directly related to the severity of the VAD. CONCLUSIONS: Complete repair of gastroschisis at the initial operation is the optimal goal; however, the severity of VAD has permitted this approach in only one third of patients in this study. Delayed repair with a silastic chimney and one or more reconstructive procedures has provided excellent long-term survival with low morbidity and mortality rates. Although skin-flap closure is no longer used initially, this technique has been helpful for the residual defect in infants with severe VAD who have had multiple silon chimney repairs (Applied Biomaterial, Silverdale, WA).

Effect of transamniotic administration of epidermal growth factor on fetal rabbit small intestinal nutrient transport and disaccharidase development.

As fetal swallowing is documented in utero, supplementation of the ingested amniotic fluid with nutrients or hormones has been postulated as a potential prenatal treatment for intrauterine growth retardation (IUGR). To study the effect of epidermal growth factor (EGF) on the developing fetal small intestine, 12 pregnant rabbits underwent operation on day 24 of a normal 31-day gestation. Bilateral ovarian end fetuses underwent catheterization of their respective amniotic cavities with attachment to a miniosmotic pump. Study fetuses received recombinant human EGF at approximately 300 micrograms/kg/d for 1 week; controls received carrier solution only at an equivalent rate. On gestational day 31, fetuses were delivered by cesarean section and somatic measurements were recorded. The small intestine was harvested and proximal, middle, and distal regions were analyzed for lactase and maltase enzyme activity. Additionally, the uptake of radiolabeled glucose and proline was measured by a standard everted mucosal sleeve technique for each segment. Results were analyzed by Student's paired t test and reported as mean +/- SEM. Nine fetal pairs survived (75%). Small intestinal (SI) length was increased in EGF fetuses (54.8 +/- 1.9 cm) versus control (50.4 +/- 2.7 cm) (P = .02). Lactase activity, reported as UE/g protein, was significantly increased in the proximal segments in the EGF-infused fetuses; maltase was significantly increased in both the proximal and middle segments (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Upregulation of nutrient transport in fetal rabbit intestine by transamniotic substrate administration.

Delivery of nutrients to the developing fetal gastrointestinal tract has been advocated as a potential prenatal treatment for intrauterine growth retardation. To examine the effect of intrauterine nutrient administration on the uptake capacity of the intestine, 16 maternal rabbits underwent bilateral ovarian-end transamniotic catheter placement on gestational Day 24. Study fetuses received a galactose solution; the contralateral controls received mannitol, a physiologically inert carbohydrate. Infusions were continued until Day 30 when an everted sleeve technique was used to measure radiolabeled uptake of both galactose and glucose in the proximal, middle, and distal small intestine. Mucosal scrapes were obtained, weighed, and the percentage of weight was calculated. Results were analyzed by ANOVA and Student's t test with P less than 0.05 being considered significant. There were 2 maternal deaths with 11 fetal pairs surviving (79%). There was increased uptake of galactose in the study fetuses compared to controls reaching significance in the middle and distal segments. Similarly, glucose uptake was significantly increased in the proximal and distal segments. Mucosal weight was increased in all regions, reaching significance in the proximal segment. Total intestinal uptake of galactose and glucose was significantly increased in the study fetuses compared to controls. Intraamniotic galactose infusion caused not only upregulation of its own mucosal transport but also that of glucose, along the entire fetal small intestine, achieving statistical significance particularly in distal segments. Fetal implications for transamniotic feeding are under investigation.

Identification of some volatile compounds in the odor of fecal pellets of the rabbit,Oryctolagus cuniculus.

A study has been made of the volatile constituents in the vapors collected from fecal pellets of wild rabbits,Oryctolagus cuniculus. Measurements of changes in the heart rates of adult male rabbits exposed to the effluent of a gas chromatographic capillary column were used to indicate the presence of compounds which may be of behavioral significance. Combined with the use of high-resolution columns in gas chromatography and gas chromatography-mass spectrometry, this approach has implicated several classes of compounds, including volatile fatty acids and phenols, which in certain absolute or relative concentrations may be involved in the formation of signals of territorial importance.