Reduced Attack Rates Research Articles

Antiviral Strategies for Emerging Influenza Viruses in Remote Communities

BackgroundDue to the lack of timely access to resources for critical care, strategic use of antiviral drugs is crucial for mitigating the impact of novel influenza viruses with pandemic potential in remote and isolated communities. We sought to evaluate the effect of antiviral treatment and prophylaxis of close contacts in a Canadian remote northern community.MethodsWe used an agent-based, discrete-time simulation model for disease spread in a remote community, which was developed as an in-silico population using population census data. Relative and cumulative age-specific attack rates, and the total number of infections in simulated model scenarios were obtained.ResultsWe found that early initiation of antiviral treatment is more critical for lowering attack rates in a remote setting with a low population-average age compared to an urban population. Our results show that a significant reduction in the relative, age-specific attack rates due to increasing treatment coverage does not necessarily translate to a significant reduction in the overall arrack rate. When treatment coverage varies from low to moderate, targeted prophylaxis has a very limited impact in reducing attack rates and should be offered at a low level (below 10%) to avoid excessive waste of drugs.ConclusionsIn contrast to previous work, for conservative treatment coverages, our results do not provide any convincing evidence for the implementation of targeted prophylaxis. The findings suggest that public health strategies in remote communities should focus on the wider availability (higher coverage) and timely distribution of antiviral drugs for treatment of clinically ill individuals.

IPv6 Packet Traceback: A Survey

Internet is expanding year by year and providing services of convenience and commercial value. It is also becoming prone for many attacks. Every day, new vulnerabilities are found, new threats are detected and attacks are launched. We need countermeasures for these attacks and IDS and firewalls are not able to defend all the attacks. In this situation we need to traceback the attacker and get to the source of the attacker so that there is deterrence to the cyber criminals, thereby reducing attack rate. In this paper we survey various traceback techniques for IPv6 after introducing the same for IPv4. We also analyze the differences between packet header fields of IPv4 and v6 and list the challenges for IPv6 traceback.

Increased transmissibility explains the third wave of infection by the 2009 H1N1 pandemic virus in England

In the 2009 H1N1 pandemic, the United Kingdom experienced two waves of infection, the first in the late spring and the second in the autumn. Given the low level of susceptibility to the pandemic virus expected to be remaining in the population after the second wave, it was a surprise that a substantial third epidemic occurred in the UK population between November 2010 and February 2011, despite no evidence for any significant antigenic evolution of the pandemic virus. Here, we use a mathematical model of influenza transmission embedded within a Bayesian synthesis inferential framework to jointly analyze syndromic, virological, and serological surveillance data collected in England in 2009-2011 and thereby assess epidemiological mechanisms which might have generated the third wave. We find that substantially increased transmissibility of the H1N1pdm09 virus is required to reproduce the third wave, suggesting that the virus evolved and increased fitness in the human host by the end of 2010, or that the very cold weather experienced in the United Kingdom at that time enhanced transmission rates. We also find some evidence that the preexisting heterologous immunity which reduced attack rates in adults during 2009 had substantially decayed by the winter of 2010, thus increasing the susceptibility of the adult population to infection. Finally, our analysis suggests that a pandemic vaccination campaign targeting adults and school-age children could have mitigated or prevented the third wave even at moderate levels of coverage.

Phenology, synchrony and host range of the Tasmanian population of Cotesia urabae introduced into New Zealand for the biocontrol of Uraba lugens

The population dynamics of Cotesia urabae (Austin and Allen) (Braconidae: Microgastrinae), a biological control agent from Tasmania, and its eucalypt feeding host, Uraba lugens (Walker) (Lepidoptera: Nolidae) was investigated prior to its introduction to New Zealand in 2011. Previous host range testing on potential New Zealand non-targets determined C. urabae had some potential to attack an endemic species, Nyctemera annulata (Boisduval) (Lepidoptera: Arctiidae). A closely related species in Tasmania, Nyctemera amica, was thus investigated as a potential host along with the native host U. lugens, to better understand the host range of C. urabae and the synchrony with its host in Tasmania. Adult C. urabae emerged from pupal cocoons in the field during January which confirmed a five month window in which its host, the larvae of U. lugens, was absent in the field. Experiments using sentinel N. amica and U. lugens larvae, field collections of N. amica and of larvae of other Lepidopteran species during this five month time window detected no parasitism by C. urabae. In the laboratory, host specificity testing showed reduced attack rates and no resultant C. urabae eggs or developing larvae or any successful pupation of C. urabae larvae from attacked N. amica larvae. It was concluded that N. amica is most unlikely to be a host for C. urabae in Tasmania and no evidence of any other alternative host was found.

Defence Cheats Can Degrade Protection of Chemically Defended Prey

AbstractMany species defend themselves against enemies using repellent chemicals. An important but unanswered question is why investment in chemical defence is often variable within prey populations. One explanation is that some prey benefit by cheating, paying no costs of defence, but gaining a reduced attack rate because of the presence of defended conspecifics. Two important assumptions about predator behaviour must be met to explain cheating as a stable strategy: first, predators increase attack rates as cheats increase in frequency; second, defended prey survive attacks better than non‐defended conspecifics. We lack data from wild predators that evaluate these hypotheses. Here, we examine how changes in the frequency of non‐defended ‘cheats’ affect predation by wild birds on a group of otherwise defended prey. We presented mealworm larvae that were either edible (‘cheats’) or unpalatable (bitter tasting), and varied the proportion of cheats from 0 to 1 by increments of 0.25. We found strong frequency‐dependent effects on the birds' foraging behaviour, with the proportion of prey attacked increasing nonlinearly with the frequency of cheats. We did not, however, observe that birds taste‐rejected defended prey at the site of capture. One explanation is that wild birds may not assess prey palatability at the site of capture, but do this elsewhere. If so, defended and undefended prey may pay high costs of initial attack and relocation away from ecologically favourable locations. Alternatively, defended prey may not be taste‐rejected because with acute time constraints, wild birds do not have time to make fine‐grained decisions during feeding. We discuss the data in relation to the evolutionary ecology of prey defences.

The Push-Pull Tactic for Mitigation of Mountain Pine Beetle (Coleoptera: Curculionidae) Damage in Lodgepole and Whitebark Pines

In an attempt to improve semiochemical-based treatments for protecting forest stands from bark beetle attack, we compared push-pull versus push-only tactics for protecting lodgepole pine (Pinus contorta Douglas ex Loudon) and whitebark pine (Pinus albicaulis Engelm.) stands from attack by mountain pine beetle (Dendroctonus ponderosae Hopkins) in two studies. The first was conducted on replicated 4.04-ha plots in lodgepole pine stands (California, 2008) and the second on 0.81-ha plots in whitebark pine stands (Washington, 2010). In both studies, D. ponderosae population levels were moderate to severe. The treatments were 1) push-only (D. ponderosae antiaggregant semiochemicals alone); 2) push-pull (D. ponderosae antiaggregants plus perimeter traps placed at regular intervals, baited with four-component D. ponderosae aggregation pheromone); and 3) untreated controls. We installed monitoring traps baited with two-component D. ponderosae lures inside each plot to assess effect of treatments on beetle flight. In California, fewer beetles were collected in push-pull treated plots than in control plots, but push-only did not have a significant effect on trap catch. Both treatments significantly reduced the rate of mass and strip attacks by D. ponderosae, but the difference in attack rates between push-pull and push-only was not significant. In Washington, both push-pull and push-only treatments significantly reduced numbers of beetles caught in traps. Differences between attack rates in treated and control plots in Washington were not significant, but the push-only treatment reduced attack rates by 30% compared with both the control and push-pull treatment. We conclude that, at these spatial scales and beetle densities, push-only may be preferable for mitigating D. ponderosae attack because it is much less expensive, simpler, and adding trap-out does not appear to improve efficacy.

Predicting the optimal prey group size from predator hunting behaviour

1. How group size affects predator attack and success rate, and so prey vulnerability, is important in determining the nonlethal consequences of predation risk on animal populations and communities. Theory predicts that both predator attack success rate and the dilution effect decline exponentially with group size and that selection generates optimal group sizes at a 'risk threshold' above which antipredation benefits are outweighed by costs, such as those owing to higher attack rates. 2. We examined whether flock size risk thresholds for attack rate, success rate or dilution differed, and therefore whether the strength of selection for group size differed for these three factors, using a system of redshank Tringa totanus flocks being hunted by Eurasian sparrowhawks Accipiter nisus. We also asked which of the three thresholds, on their own or in combination, predicted the most commonly observed group size. 3. Mean redshank flock size increased with a very gradual quadratic function (i.e. approximately linearly) with population size, although at a rate half that possible; when population size was not limiting, individuals almost always avoided flocks of less than 30 and birds were frequently in flocks up to at least 80. Sparrowhawk attack rate showed a quadratic relationship with flock size and peaked at 55 redshanks. Sparrowhawk attack success rate, however, declined exponentially, becoming less steep at flock sizes of about 40 and remaining uniformly low (a 95% decrease) by 70. Combined with dilution, individual risk of death per attack decreased by 95% when group size reached 30 (20 for the dilution effect alone). 4. Redshanks most commonly formed group sizes that gained the maximum individual predation risk reduction. They also commonly formed group sizes far above any further substantial advantages from the dilution effect or from reducing attack rate, but that continued to reduce predation risk by lowering attack success rate. Individuals did not always form the largest groups possible which we suggest is because individual variation in risk-taking subdivides the population. This places a constraint on the ability of individuals to compensate for predation risk and will have a variety of important effects on animal populations.

Botulinum Toxin as Preventive Treatment for Migraine: A Randomized Double-Blind Study

Aim: To determine if botulinum toxin type A (BoNT-A) injections can reduce the frequency and severity of migraines. Methods: Patients (n = 127) were randomized to receive placebo or two doses of BoNT-A (Dysport®). The primary endpoint was reduction in number of migraine attacks up to week 8 and between weeks 8 and 12 after injection. Patient diaries were used to record secondary endpoints, including frequency, severity and duration of migraine attacks. Results: There was a mean reduction of 0.54 and 0.94 attacks/month with placebo and BoNT-A, respectively, and absolute attack count was less in the verum group (3.6 vs. 4.2 attacks/month), but this was not statistically significant. The patients’ global assessment of efficacy was significantly better than placebo in the high-dose group (p = 0.02) but no effects were seen for the other secondary efficacy parameters. Conclusion: Our study showed a trend towards a reduced attack rate with verum but did not show any statistically significant efficacy of BoNT-A in the prophylactic treatment of migraine.

Description of the Food Safety System in Hotels and How It Compares With HACCP Standards

Tourism is an important earner of foreign exchange in Jamaica; hence, the protection of the visitors' health is very important. A study of travelers to Jamaica in 1996 to 1997 found that travelers' diarrhea (TD) affected almost 25% of visitors. The Ministry of Health (Jamaica) initiated a program for the prevention and control of TD aimed at reducing attack rates from 25.0% to 12.0% over a 5-year period through environmental health and food safety standards of hotels. This article examines the food safety systems in Jamaican hotels located in a popular resort area to find out how comparable they are with the Hazard Analysis Critical Control Point (HACCP) strategy. A cross-sectional study was done of hotels in St. Mary and St. Ann. Quantitative data were obtained from food and beverage/sanitation staff and qualitative data through in-depth interviews with hotel managers. Observation of the food safety operations was also done. The majority (75%) of larger hotels used a combination of HACCP and Ministry of Health food safety strategies (p = 0.02) and offered all-inclusive services (r =-0.705, p = 0.001). Larger hotels were more likely to have a better quality team approach, HACCP plan, and monitoring of critical control points (CCPs) and more likely to receive higher scores (p < 0.05). More than two thirds of hotel staff were knowledgeable of HACCP. Significantly smaller hotels (87.5%) received less than 70% in overall score (r = 0.75, p = 0.01). Identification of CCPs and monitoring of CCPs explained 96.6% of the change in the overall HACCP scores (p = 0.001). Hotel managers felt that some hotels' systems were comparable with HACCP and that larger properties were ready for mandatory implementation. Conclusions. While some components of the HACCP system were observed in larger hotels, there were serious shortcomings in its comparison. Mandatory implementation of HACCP would require that sector-specific policies be developed for smaller hotels and implemented on a phased basis.

Habitat modification alters the structure of tropical host–parasitoid food webs

Global conversion of natural habitats to agriculture has led to marked changes in species diversity and composition. However, it is less clear how habitat modification affects interactions among species. Networks of feeding interactions (food webs) describe the underlying structure of ecological communities, and might be crucially linked to their stability and function. Here, we analyse 48 quantitative food webs for cavity-nesting bees, wasps and their parasitoids across five tropical habitat types. We found marked changes in food-web structure across the modification gradient, despite little variation in species richness. The evenness of interaction frequencies declined with habitat modification, with most energy flowing along one or a few pathways in intensively managed agricultural habitats. In modified habitats there was a higher ratio of parasitoid to host species and increased parasitism rates, with implications for the important ecosystem services, such as pollination and biological control, that are performed by host bees and wasps. The most abundant parasitoid species was more specialized in modified habitats, with reduced attack rates on alternative hosts. Conventional community descriptors failed to discriminate adequately among habitats, indicating that perturbation of the structure and function of ecological communities might be overlooked in studies that do not document and quantify species interactions. Altered interaction structure therefore represents an insidious and functionally important hidden effect of habitat modification by humans.

Strategies for mitigating an influenza pandemic

Development of strategies for mitigating the severity of a new influenza pandemic is now a top global public health priority. Influenza prevention and containment strategies can be considered under the broad categories of antiviral, vaccine and non-pharmaceutical (case isolation, household quarantine, school or workplace closure, restrictions on travel) measures. Mathematical models are powerful tools for exploring this complex landscape of intervention strategies and quantifying the potential costs and benefits of different options. Here we use a large-scale epidemic simulation to examine intervention options should initial containment of a novel influenza outbreak fail, using Great Britain and the United States as examples. We find that border restrictions and/or internal travel restrictions are unlikely to delay spread by more than 2-3 weeks unless more than 99% effective. School closure during the peak of a pandemic can reduce peak attack rates by up to 40%, but has little impact on overall attack rates, whereas case isolation or household quarantine could have a significant impact, if feasible. Treatment of clinical cases can reduce transmission, but only if antivirals are given within a day of symptoms starting. Given enough drugs for 50% of the population, household-based prophylaxis coupled with reactive school closure could reduce clinical attack rates by 40-50%. More widespread prophylaxis would be even more logistically challenging but might reduce attack rates by over 75%. Vaccine stockpiled in advance of a pandemic could significantly reduce attack rates even if of low efficacy. Estimates of policy effectiveness will change if the characteristics of a future pandemic strain differ substantially from those seen in past pandemics.

Interventions to Prevent and Control Food-Borne Diseases Associated with a Reduction in Traveler-s Diarrhea in Tourists to Jamaica

In 1996 a study found that approximately one in four tourists to Jamaica were affected with traveler's diarrhea (TD) during their stay. That year the Ministry of Health initiated a program for the prevention and control of TD. The aim of this ongoing program was to reduce attack rates of TD from 25% to 12% over a 5-year period by improving the environmental health and food safety standards of hotels. Hotel-based surveillance procedures for TD were implemented in sentinel hotels in Negril and Montego Bay in 1996, Ocho Rios in 1997, and Kingston in 1999. A structured program provided training and technical assistance to nurses, food and beverage staff, and environmental sanitation personnel in the implementation of Hazard Analysis Critical Control Point principles for monitoring food safety standards. The impact of interventions on TD was assessed in a survey of tourists departing from the international airport in Montego Bay in 1997-1998 and from the international airport in Kingston in 1999-2000. The impact of the training and technical assistance program on food safety standards and practices was assessed in hotels in Ocho Rios as of 1998 and in Kingston from 1999. At the end of May 2002, TD incidence rates were 72% lower than in 1996, when the Ministry of Health initiated its program for the prevention and control of TD. Both hotel surveillance data and airport surveillance data suggest that the vast majority of travelers to Kingston and southern regions are not afflicted with TD during their stay. The training and technical assistance program improved compliance to food safety standards over time. Interventions to prevent and control TD in visitors to Jamaica are positively associated with a reduction in TD in the visitor population and improvements in food safety standards and practices in hotels.

Technologies to support the creation of complex systems models—using StarLogo software with students

Research on complex, adaptive systems has made significant advances in recent years in the study of natural and social phenomena that exhibit random variation and selection, resulting in learning or evolution. Unfortunately, students (including K-12, undergraduate and graduate) in most biology programs have little opportunity to explore complex systems during the course of their studies. StarLogo and the Adventures in Modeling Curriculum [Adventures in Modeling: Exploring Complex, Dynamic Systems with StarLogo. Teachers College Press, New York] provide an easily accessible entry point into complex systems modeling for students and other novice modelers. These specialized tools can provide powerful insights into the dynamics of systems and create opportunities to explore challenging and meaningful domains in the biological sciences. Specific applications to epidemiological and ecological systems are explored, including the often debated topic of the evolution of reduced attack rates in predator–prey systems.

Approaches to improved influenza vaccination

Inactivated influenza vaccine (Ivac) has had an important impact on reducing attack rates of influenza and reducing the severity of illness amongst the vaccinees who still acquire infection. Ivac is most efficacious amongst young, otherwise healthy subjects and least effective against elderly at high risk. This is in part because Ivac does not appear to significantly reduce infection rates and in part because response rate and final antibody titer are lower in the elderly. Therefore Ivac does not eliminate disease in the elderly who are prone to complications when any virus replication occurs. Simultaneous administration of intra-nasal live attenuated influenza vaccine (Livac) and Ivac reduces the infection rate and thus illness rate amongst high-risk elderly. Presumably this is because of the ability of Livac to stimulate secretory antibody which neutralizes virus at the mucosal surface. Other approaches are examining the benefit of baculovirus recombinant vaccine or adjuvanted Ivac to determine if the higher serum antibody these vaccines produce compared to Ivac, will diffuse onto the mucosal surfaces and in a similar fashion, neutralize virus at that site.

Randomized trials of dichlorphenamide in the periodic paralyses

Although the carbonic anhydrase inhibitors have been used in the treatment of the primary periodic paralyses (PPs), their efficacy has not been demonstrated in double-blind, placebo-controlled trials. Therefore, we tested the efficacy of dichlorphenamide (DCP; Daranide), a potent carbonic anhydrase inhibitor, in the treatment of episodic weakness in the primary PPs. We performed two multicenter, randomized, double-blind, placebo-controlled crossover trials, one involving 42 subjects with hypokalemic periodic paralysis (HypoPP) and the other involving 31 subjects with potassium-sensitive periodic paralysis (PSPP). In each trial, two 8-week treatment periods were separated by an active washout period of at least 9 weeks. The primary outcome variable in the HypoPP trial was the occurrence of an intolerable increase in attack severity or frequency (end point). The primary outcome variable in the PSPP trial was the number of attacks per week. In the HypoPP trial, there were 13 subjects who exhibited a preference (in terms of the end point) for either DCP or placebo, and 11 of these preferred DCP. In the PSPP trial, DCP significantly reduced attack rates relative to placebo. DCP also significantly reduced attack rates relative to placebo in the HypoPP subjects. We conclude that DCP is effective in the prevention of episodic weakness in both HypoPP and PSPP.

Side effect profile of interferon beta-1b in MS: results of an open label trial.

To determine which patients are prone to side effects from interferon beta-1b and which side effects are most troublesome, we studied 72 patients with clinically definite MS who were started on interferon beta-1b after its release and found that the side effects significantly associated with treatment included skin reactions, flu-like symptoms, fatigue, leukopenia, new or worsened depression, and new or worsened headache. Of these, only fatigue and depression were significantly associated with discontinuance of therapy. Moreover, the course of disease before initiation of treatment also had a significant impact on the likelihood of discontinuing medication. Thus, despite an apparently similar therapeutic benefit (as judged by the similarly reduced attack rate in each group), patients with a secondary chronic progressive course were more likely to discontinue treatment (63%) than patients with either a relapsing/progressive course (18%) or a remitting/relapsing course (7%). Indeed, in the final regression equation, the only factors significantly related (r = 0.875) to the discontinuance of therapy were fatigue (p < 0.0001), a fatigue-depression interaction (p < 0.0001), and a chronic progressive course of disease (p<0.0001). Thus, if future clinical trials are to provide useful information on the value of interferon beta-1b in progressive MS, the side effects of fatigue and depression will need to be ameliorated to limit the drop-out rate from such trials.

Frugivory and Coexistence in a Resident and a Migratory Vireo on the Yucatan Peninsula

The White-eyed Vireo (Vireo griseus) and the Mangrove Vireo (V. pallens) are two of the most common species of insectivorous bird on the Yucatan Peninsula. Mangrove Vireo pairs maintain year-long territories primarily in scrub, whereas individual White-eyed Vireos defend territories in a broad range of terrestrial habitats. The two species show a strong reciprocal distribution along a successional gradient from regenerating pasture and old field to mature dry forest. Within second growth scrub, White-eyed Vireos are primarily associated with patches of trees. Despite minor morphological differences typical of migrant- resident comparisons, we found no significant differences in the rates of different locomotory movement, in the relative proportion of attack type used, nor in foraging substrate. The major foraging differences were a lower reduced attack rate and greater use of fruit (primarily Bursera simaruba) in the White-eyed Vireo. Playback experiments failed to draw significant interspecific responses to song playback and elicited weak responses to conspecific and heterospecific chatter calls. Simultaneous call-in experiments and opportunistic observations failed to provide evidence of interspecific aggression. White-eyed Vireos, however, consis- tently chased Mangrove Vireos out of fruiting Bursera. We hypothesize that the extensive use of Bursera fruit allows White-eyed Vireos to over-winter in mature forest on the Yucatan Peninsula, a habitat that apparently cannot support breeding by vireos in the White-eyed Vireo complex.

Field measurement of population recruitment of Apanteles glomeratus (L.) (Hymenoptera: Braconidae), a parasitoid of Pieris rapae (L.) (Lepidoptera: Pieridae), and factors influencing adult parasitoid foraging success in kale

AbstractThe attack rate by the parasitoid Apanteles glomeratus (L.) on laboratory-reared larvae of Pieris rapae (L.) exposed for 3–4 day periods in a kale field in Massachusetts was greater when five larvae rather than two were placed on plants. The attack rate was greatest if host larvae were in the first instar when placed in the field, and little or no attack occurred when second- or third-instar larvae were exposed. The co-occurrence of unoccupied P. rapae larval feeding sites on plants where larvae were exposed reduced attack rates. Parasitism rates in trap-host larvae and in field-collected larvae (counting only cases in which the parasitoid was still in the egg stage) did not differ as estimators of recruitment to the population of parasitized hosts either in terms of total recruitment achieved per host generation or in the temporal pattern of the recruitment. In both simple and multiple linear regressions, the density of young P. rapae larvae (either parasitized or not) was the strongest correlate of parasitoid recruitment for the whole season, whereas average air temperature was the strongest correlate in the last month of observations (September).

Attachment sites of parasitic lampreys: comparisons among species

Distribution of attachment sites varies with the species of lamprey being considered. Large anadromous species (Petromyzon marinus and Lampetra tridentata) tend to attach ventrally, especially near the pectoral fins, while smaller freshwater species in shallow habitats (Ichthyomyzon castaneus and I. unicuspis) and species that feed on muscle tissue (Lampetra ayresi) tend to attach dorsally. Catostomids tend to be attacked on the head and, by the Ichthyomyzon species, on the paired fins. Distribution of attachments by P. marinus in laboratory studies may be affected by tank size. Attachments to the head and pectoral regions are probably associated with greater host mortality rates and may be underrepresented in field samples. Attachments to the pectoral region appear to combine low costs, in terms of handling time prior to feeding, with greater rates of energy intake once feeding has been initiated. Dorsal attachments by species that inhabit relatively shallow rivers and streams may be a compromise to avoid abrasion against the bottom. A consequence of dorsal attachments may be a reduced impact on host populations through prolonged attachments to individual hosts and reduced attack rates.

Catheter-associated bacteriuria: Failure to reduce attack rates using periodic instillations of disinfectant into urinary drainage system: Thompson RL, Haley CE, Searcy MA, et al: JAMA 251:747–751, 1984. Reprint requests: Dr. R. P. Wenzel, Division of Virology and Epidemiology, P.O. Box 473, University of Virginia Medical Center, Charlottesville, VA 22908

Catheter-associated bacteriuria: Failure to reduce attack rates using periodic instillations of disinfectant into urinary drainage system: Thompson RL, Haley CE, Searcy MA, et al: JAMA 251:747–751, 1984. Reprint requests: Dr. R. P. Wenzel, Division of Virology and Epidemiology, P.O. Box 473, University of Virginia Medical Center, Charlottesville, VA 22908