Diversity and the maintenance of sex by parasites.

The Red Queen hypothesis (RQH) predicts that parasite-mediated selection will maintain sexual individuals in the face of competition from asexual lineages. The prediction is that sexual individuals will be difficult targets for coevolving parasites if they give rise to more genetically diverse offspring than asexual lineages. However, increasing host genetic diversity is known to suppress parasite spread, which could provide a short-term advantage to clonal lineages and lead to the extinction of sex. We test these ideas using a stochastic individual-based model. We find that if parasites are readily transmissible, then sex is most likely to be maintained when host diversity is high, in agreement with the RQH. If transmission rates are lower, however, we find that sexual populations are most likely to persist for intermediate levels of diversity. Our findings thus highlight the importance of genetic diversity and its impact on epidemiological dynamics for the maintenance of sex by parasites.

Exposure to parasites increases promiscuity in a freshwater snail.

Under the Red Queen hypothesis, outcrossing can produce genetically variable progeny, which may be more resistant, on average, to locally adapted parasites. Mating with multiple partners may enhance this resistance by further increasing the genetic variation among offspring. We exposed Potamopyrgus antipodarum to the eggs of a sterilizing, trematode parasite and tested whether this altered mating behaviour. We found that exposure to parasites increased the number of snail mating pairs and the total number of different mating partners for both males and females. Thus, our results suggest that, in host populations under parasite-mediated selection, exposure to infective propagules increases the rate of mating and the number of mates.

Dual stressors of infection and warming can destabilize host microbiomes.

Climate change is causing extreme heating events and intensifying infectious disease outbreaks. Animals harbour microbial communities, which are vital for their survival and fitness under stressful conditions. Understanding how microbiome structures change in response to infection and warming may be important for forecasting host performance under global change. Here, we evaluated alterations in the microbiomes of several wild Caenorhabditis elegans isolates spanning a range of latitudes, upon warming temperatures and infection by the parasite Leucobacter musarum. Using 16S rRNA sequencing, we found that microbiome diversity decreased, and dispersion increased over time, with the former being more prominent in uninfected adults and the latter aggravated by infection. Infection reduced dominance of specific microbial taxa, and increased microbiome dispersion, indicating destabilizing effects on host microbial communities. Exposing infected hosts to warming did not have an additive destabilizing effect on their microbiomes. Moreover, warming during pre-adult development alleviated the destabilizing effects of infection on host microbiomes. These results revealed an opposing interaction between biotic and abiotic factors on microbiome structure. Lastly, we showed that increased microbiome dispersion might be associated with decreased variability in microbial species interaction strength. Overall, these findings improve our understanding of animal microbiome dynamics amidst concurrent climate change and epidemics. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Infection burdens and virulence under heat stress: ecological and evolutionary considerations.

As a result of global change, hosts and parasites (including pathogens) are experiencing shifts in their thermal environment. Despite the importance of heat stress tolerance for host population persistence, infection by parasites can impair a host's ability to cope with heat. Host-parasite eco-evolutionary dynamics will be affected if infection reduces host performance during heating. Theory predicts that within-host parasite burden (replication rate or number of infecting parasites per host), a key component of parasite fitness, should correlate positively with virulence-the harm caused to hosts during infection. Surprisingly, however, the relationship between within-host parasite burden and virulence during heating is often weak. Here, we describe the current evidence for the link between within-host parasite burden and host heat stress tolerance. We consider the biology of host-parasite systems that may explain the weak or absent link between these two important host and parasite traits during hot conditions. The processes that mediate the relationship between parasite burden and host fitness will be fundamental in ecological and evolutionary responses of host and parasites in a warming world. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Does genetic diversity limit disease spread in natural host populations?

It is a commonly held view that genetically homogenous host populations are more vulnerable to infection than genetically diverse populations. The underlying idea, known as the 'monoculture effect,' is well documented in agricultural studies. Low genetic diversity in the wild can result from bottlenecks (that is, founder effects), biparental inbreeding or self-fertilization, any of which might increase the risk of epidemics. Host genetic diversity could buffer populations against epidemics in nature, but it is not clear how much diversity is required to prevent disease spread. Recent theoretical and empirical studies, particularly in Daphnia populations, have helped to establish that genetic diversity can reduce parasite transmission. Here, we review the present theoretical work and empirical evidence, and we suggest a new focus on finding 'diversity thresholds.'

Is more better? Polyploidy and parasite resistance.

Ploidy-level variation is common and can drastically affect organismal fitness. We focus on the potential consequences of this variation for parasite resistance. First, we elucidate connections between ploidy variation and key factors determining resistance, including allelic diversity, gene expression and physiological condition. We then argue that systems featuring both natural and artificially manipulated ploidy variation should be used to evaluate whether ploidy level influences host-parasite interactions.

Virulence, cultivating conditions, and phylogenetic analyses of oomycete parasites in Daphnia.

We describe the infectivity, virulence, cultivating conditions, and phylogenetic positions of naturally occurring oomycete parasites of Daphnia, invertebrates which play a major role in aquatic food webs. Daphnia pulex individuals were found dead and covered by oomycete mycelia when exposed to pond sediments. We were able to extract 4 oomycete isolates from dead Daphnia and successfully cultivate them. Using the ITS and LSU rDNA sequences, we further showed these isolates to be distinct species. The isolates were experimentally demonstrated to be parasitic and not saprobic. After exposure to the parasites, Daphnia mortality was much higher than that reported for Daphnia infected with other known parasite species. Therefore, it is likely that oomycete parasites are important selective pressures in natural Daphnia populations. Moreover, their close phylogenetic relationship to parasites of fish and algae suggests that the stability of aquatic food webs (i.e. fish-Daphnia-algae) might be influenced by the shared parasite communities.

High parasite diversity accelerates host adaptation and diversification.

Host-parasite species pairs are known to coevolve, but how multiple parasites coevolve with their host is unclear. By using experimental coevolution of a host bacterium and its viral parasites, we revealed that diverse parasite communities accelerated host evolution and altered coevolutionary dynamics to enhance host resistance and decrease parasite infectivity. Increases in parasite diversity drove shifts in the mode of selection from fluctuating (Red Queen) dynamics to predominately directional (arms race) dynamics. Arms race dynamics were characterized by selective sweeps of generalist resistance mutations in the genes for the host bacterium's cell surface lipopolysaccharide (a bacteriophage receptor), which caused faster molecular evolution within host populations and greater genetic divergence among populations. These results indicate that exposure to multiple parasites influences the rate and type of host-parasite coevolution.

Effects of pregnancy on hemoglobin AIc in normal, gestational diabetic, and diabetic women.

Hemoglobin AIc, a normal minor hemoglobin, has glucose linked by a Schiff base to the N-terminal end of the beta chain. The glucose interferes with the binding of 2,3 diphosphoglycerate, probably resulting in an increased affinity of that hemoglobin for oxygen. Hb AIc is increased to twice normal levels in juvenile-onset (insulin-dependent) diabetes. In the present studies, the Hb AIc, when expressed as per cent of total hemoglobin, was found to be elevated slightly in pregnany normal (m = 6.97 per cent), pregnant nondiabetic obese (m = 6.89 per cent), and gestationally diabetic subjects (m = 8.77 per cent) above that of normal females (m = 5.68 per cent). A remarkable difference was observed between the nonpregnant diabetics (m = 12.77 per cent) and the pregnant diabetics (m = 8.46 per cent). This decrease in the level of Hb AIc in diabetics who are pregnant more than 30 weeks may reflect either a better state of diabetic control and/or a compensatory mechanism to protect the fetus by facilitating oxygen exchange from mother to fetus.

Maturational changes of theophylline pharmacokinetics in preterm infants.

The pharmacokinetics of theophylline were studied at steady state by stable isotope methodology in nine individual preterm infants. Maturational variables such as postnatal age, postconceptional age, gestational age, duration of treatment, and body weight at the time of the study were analyzed for their influence on theophylline kinetics during the first 6 months of life. The strongest statistical correlations were found between the logarithm of theophylline half-life (t1/2) and the postnatal age (r = 0.98; p less than 0.001) and the postconceptional age (r = 0.96; p less than 0.001). Step-wise multiple regression analysis revealed postnatal age as the most powerful predictor for theophylline t1/2 in the neonatal period (partial correlation coefficients were 0.78 for postnatal age, 0.19 for postconceptional age, and 0.10 for gestational age). Gestational age, duration of treatment, and weight did not correlate significantly with any pharmacokinetic parameters. We propose that theophylline metabolizing function of the liver increases in a logarithmic fashion during the first 6 months of life.

Developmental aspects of theophylline metabolism in premature infants.

The metabolic degradation of theophylline was studied in nine premature infants with postconception ages of 28 to 42 wk. Urinary and plasma metabolites (caffeine; theobromine; 3-methylxanthine; 1,3-dimethyluric acid; and 1-methyluric acid) and unchanged theophylline were analyzed with selected ion monitoring gas chromatography-mass spectrometry. The anticipated decrease in plasma caffeine (which is absent in adult human and children) did not occur in the postconception age range studied, but the urinary percentages of unchanged theophylline decreased from 61% at a postconception age of 28 to 32 wk to 43% at 38 to 42 wk. This suggests increasing theophylline metabolism with age due to developing hepatic cytochrome P-450 enzyme systems. The increased degradation of theophylline is largely explained by the production of 1,3-dimethyluric acid (from 20% to 34%). In infants of an older postconception age, theobromine, a caffeine metabolite, was also detected. To explain the difference of caffeine pathway between adults and premature infants, it is hypothesized that the caffeine pathway of theophylline is equally active in both age groups. The absence of caffeine metabolite in adults is due to the maturing caffeine-metabolizing enzymes, which degrade caffeine immediately to its metabolites.

Theophylline metabolism in premature infants.

The theophylline metabolite pattern in premature infants was studied with gas chromatography-mass spectrometry. The identities of metabolites were established by retention time indices and mass chromatograms. In the steady state of a multiple-dose regimen, the urinary metabolites of theophylline identified and quantified were caffeine (9.6 plus or minus 4.8%), theophylline (50.4 plus or minus 6.7%), 3-methylxanthine (1.3 plus or minus 0.7%), 1,3-dimethyluric acid (27.7% plus or minus 8.8%), and 1-methyluric acid (9.3 plus or minus 5.4%). Those in plasma were caffeine (21.4 plus or minus 6.1%), theophylline (73.6 plus or minus 6.5%), 3-methylxanthine (0.7 plus or minus 0.4%), 1,3-dimethyluric acid (2.6 plus or minus 1.2%), and 1-methyluric acid (0.6 plus or minus 0.3%). Occasionally, theobromine, the metabolic breakdown product of caffeine, was found in urine and plasma in small quantities. The demethylation pathway occurring predominantly in adults was substituted by N-methylation to caffeine in premature infants; the other major metabolic pathway of theophylline in adults, C-8 oxidation to 1,3-dimethyluric acid, was slightly diminished. We concluded that the enzyme systems responsible for the C-8 oxidation of theophylline are relatively active in premature infants and that the development of the enzyme systems responsible for oxidative demethylation of theophylline lags behind. The oxidation and demethylation pathways of theophylline in premature infants are significant.

Obesity in pregnancy: risks and outcome.

Obesity has been associated in the literature with other pregnancy risks such as hypertension and diabetes mellitus, but disagreement persists about the expected course and complications of labor. Also, the effects of obesity on intrauterine growth and gestational duration have not been well defined. This study of 2746 consecutive deliveries used a computer-based uniform perinatal record to compare 300 pregnancy risk and outcome factors for obese and nonobese patients. The 279 obese women (more than 90 kg at some time during the pregnancy) were found to be older and of higher parity than the 2467 who were not obese. Those in the obese group were at increased antepartum risk and had increased frequencies of chronic hypertension, inadequate pregnancy weight gain, twin gestation, and diabetes mellitus. Oxytocin induction and repeat cesarean sections were performed more frequently for the obese patients, with no increase in complications during the current labor. The frequency of labor abnormalities, oxytocin augmentation, and primary cesarean section was similar to that of the comparison group. Examination of infant outcome revealed similar Apgar scores and perinatal mortality in the 2 groups, but fewer low-birth-weight infants (under 2500 g) and more macrosomic babies (over 4000 g) occurred in the obese population. This increase in birth weight was accounted for not only by an increase in the birth weight percentile, but also by a significant lengthening of the period of gestation.

Lorazepam in the treatment of refractory neonatal seizures.

We report the results of treatment of intractable seizures with lorazepam in seven neonates. All of the patients were part of a prospective study, who failed to respond to 40 mg/k of phenobarbital. Lorazepam was given intravenously at 0.05 mg/k and repeated up to a total dose of 0.15 mg/k if necessary. The diagnosis of seizures and the efficacy of treatment was assessed clinically and by EEG during the administration of lorazepam in three patients and on clinical grounds in four patients. Six patients were full term and one was premature; there were five males and two females. Four patients had hypoxic-ischemic encephalopathy, two had intracranial hemorrhage, and one had bacterial meningitis. Two patients received one dose of lorazepam, three received two doses, and two received three doses. Six patients responded with a complete cessation of seizures within three minutes of their last dose; the remaining patient (who received two doses) had a reduction in seizures. No patients developed apnea or hypotension during or immediately after the infusion of lorazepam and no other adverse effects were observed. Four patients remained seizure-free for the rest of the neonatal period and no other anticonvulsant medications were added. Seizures recurred in one patient at 16 hours; subsequent intermittent seizures were managed with additional phenobarbital. In another patient, seizures recurred at 12 hours and subsequent intermittent seizures were managed with phenytoin. In one patient, seizures continued with reduction of frequency and duration. We conclude that lorazepam may be effective in the treatment of neonatal seizures refractory to phenobarbital and that further treatment with intravenous phenytoin may be unnecessary under these circumstances.

Propoxyphene and acetaminophen. Possible effects on the fetus.

Propoxyphene (Darvon) and acetaminophen (Tylenol) are widely prescribed analgesic agents. Both can cross the placenta, and propoxyphene can produce serious withdrawal symptoms in newborns. Neither propoxyphene nor acetaminophen is considered a teratogen, yet, three malformed infants who were antenatally exposed to propoxyphene have previously been reported. We report a fourth case of an infant, with withdrawal symptoms and cranial-facial and digital malformations, born to a women who used propoxyphene and acetaminophen throughout her pregnancy. We suggest that possibility that the antepartum use of propoxyphene and acetaminophen, in combination, may be teratogenic.

The dental care of the psychiatric patient.

The dental care of the psychiatric patient requies careful observatio and history taking. Medications used in the treatment of psychiatric illnesses demand care in treatment planning and prescibing. The nature and sequellae of many psychiatric conditions have a direct bearing on the clinical picture presented by the patient and the success of dental care. Implementation of care must have a significant component of flexibility in terms of treatment outcomes and the time and method of providing treatment. Particular emphasis must be placed uppon the establishment of effective oral hygiene programmes. The psychiatric patient suffers not only from a socially debilitating disease but also from society's opprobrium. With a modicum of effort, the dental profession can rise above that.

Using therapeutic silence in home healthcare nursing.

This article examines the role of silence in the practice of home healthcare nursing. The literature is limited regarding the use of silence in therapeutic relationships in home healthcare nursing. Silence is often uncomfortable for the home healthcare nurse and the client, but when silence is used purposefully by the nurse, effective communication can be a successful intervention.