A Packed-Bed Filtration System for Collection of Myxobolus cerebralis Triactinomyxons

Abstract

Information on the distribution and abundance of Myxobolus cerebralis triactinomyxons in natural systems is limited because direct and accurate sampling methods for this life stage have not been developed. Existing methods are based on indirect measures of triactinomyxon densities and are therefore confounded. Direct estimation of triactinomyxon concentrations would more exactly pinpoint the ambient infection risk to wild fish and allow evaluation of management strategies designed to mitigate the effects of the disease. We developed a mobile packed-bed filtration system that quickly, accurately, and precisely collects, concentrates, and quantifies triactinomyxons. The system includes pumping, prefiltration, two rounds of packed-bed filtration, and centrifugation. Laboratory tests of the completed system using known quantities of triactinomyxons resulted in a mean recovery rate of 91% with a minimum detectable concentration of triactinomyxons of 0.04/L. We subsequently field-tested the system at a site known to be positive for the parasite and recovered triactinomyxons at densities of 0.7–1.4/L. The packed-bed filtration system has the potential to quickly determine the temporal and spatial variation in infection risk and to test the efficacy of various management strategies.     

Experimentally Induced Whirling Disease I. Dose Response of Fry and Adults of Rainbow Trout Exposed to the Triactinomyxon Stage of Myxobolus cerebralis

Abstract

The intensity and prevalence of whirling disease was tested by exposure of 2-monthold fry and 1-, 2-, and 3.5-year-old adults of rainbow trout Oncorhynchus mykiss to a known number of laboratory-produced Myxobolus cerebralis at the actinosporean triactinomyxon stage. Fry exposed to graded concentrations of infectivity (triactinomyxons) for 3 h were individually examined for spores of Myxobolus cerebralis 5 and 6 months later. Exposure of fish to the lowest doses, 1 and 10 triactinomyxons per fish, did not result in detectable myxosporean spores. Fish that became lightly infected by a dose of 100 triactinomyxons per fish experienced a decrease in the incidence of infection between 5 and 6 months after exposure. A linear relationship was found between the numbers of recovered myxosporean spores and doses of 100–10,000 triactinomyxons per fish, and the spore burden appeared to plateau at doses of 10,000–100,000 triactinomyxons per fish. Adult fish continuously exposed to the highest dose of triactinomyxons for 3.5 months were infected and asymptomatic, however, the severity of myxosporean infection decreased with increased age of fish. This information may help in controlling whirling disease in salmonids.     

Cattle herd vulnerability to rainfall variability: responses to two management scenarios in southern Ethiopia

We examine how the system of grazing management of cattle in savanna rangelands affects the herd response to drought. We have used long-term time series data to evaluate the effects of management on drought-induced cattle mortality using traditional livestock management practices. There was no control of stocking densities, as compared to a government ranch where stocking densities would be adjusted in accordance with available pasture. We tested the responses under two scenarios. Scenario 1: Response of cattle herds to inter-annual rainfall variability (IRV) under a regulated grazing management system; this provides more reliable predictions of cattle population and performance in terms of herd mortality and calving rates than does the communal land use system. Scenario 2: Regardless of the management system, similar trends in cattle populations will be observed in response to IRV. The results of the study showed that fluctuations in cattle numbers, herd mortality and calving rates were highly correlated with IRV, with stronger linear impacts in accordance with scenario 2. In both management systems, cattle herd sizes and calving rates declined during periods of drought, followed by slow recovery. Cattle populations in Borana rangelands in southern Ethiopia did not recover for a period of two decades. We conclude that a management system based on control of stocking densities did not improve herd survival, as compared with traditional drought management strategies. This contradicts common expectations. Increased drought frequencies aggravated cattle mortality and lowered calving rates. The implication of the findings is that regardless of adjusted stocking density, livestock populations in the arid savanna ecosystems of southern Ethiopia remain at risk from climate change.     

Whirling disease dynamics: An analysis of intervention strategies

Whirling disease (WD), a severe and widespread disease of salmonids, is caused by the myxosporean parasite Myxobolus cerebralis. It is further characterized by a unique two-host life cycle, utilizing the oligochaete Tubifex tubifex as an intermediate host. M. cerebralis is an invasive species that has been affecting populations in the United States including epidemics that killed in excess of 90% of populations in Colorado and Montana streams within the past 20 years. Currently, there is no known cure for WD, and the accepted method of control is removal of infected fish from the population. We have created a compartmental model of the WD system in order to assess more efficient means of control and management of the disease. Using data gathered from the literature, we used Bayesian model fitting to estimate model parameters and estimated that R₀ ≈ 1.51 (95% CI: 1.39, 1.72), a value which implies that WD can be controlled using available strategies. To this end, we posit several parameters that we expect to be most influential to WD propagation, namely: release of triactinomyxons by T. tubifex, release of spores by salmonids, and infectious particle loads in each respective host. Based on currently available control strategies, approaches targeting the infectious particles and the oligochaete host appear the most effective alternative strategies for management and control of WD.     

Laboratory and Hatchery-Scale Evaluation of Sand Filters and Their Efficacy at Controlling Whirling Disease Infection

Abstract

In two separate tests rapid sand filtration was evaluated as a means of removing the waterborne triactinomyxon actinospores (TAMs) of Myxobolus cerebralis, the causative agent of salmonid whirling disease, from contaminated water. In the first test we independently evaluated two sizes of sandblast sands: #4010 (effective size, (ES) = 250 μm) and #4060 (ES = 300 μm). The product number relates to the sand's size composition, and each had a different effective size. Effective size is defined by that size fraction at which only 10% of smaller particles remain. Rainbow trout Oncorhynchus mykiss were stocked into two separate systems with filters containing either one or the other size of sand, and TAMs were added to each system three times per week for all but the final 2 weeks of the 16-week test. A positive control (in which fish were exposed to the same number of TAMs without filtration) and a negative control (in which fish were not exposed to TAMs) were also included. Infection quantified by the pepsin?trypsin digest method showed no infection in fish from the two filter treatments. The average myxospore load among the positive controls was over 90,000 spores per fish head. In a final test, a nonreplicated comparison of filtration systems was conducted. The three systems used were as follows: (1) a drum filter in line with a UV filter, (2) a media filter followed by an ultraviolet (UV) unit, and (3) a sand filter containing three layers of sand. Water contaminated with TAMS was run through each filtration system, as well as through a positive control system, to raceways containing rainbow trout. Both of the dual-component commercial systems were 100% effective at preventing infection; the sand filter was 92% effective.     

Experimentally Induced Whirling Disease II. Determination of Longevity of the Infective Triactinomyxon Stage of Myxobolus cerebralis by Vital Staining

Abstract

Effects of temperature and aging on viability and infectivity of laboratory-produced actinosporean triactinomyxon spores (infective stage of the organism causing whirling disease) were studied. In vitro staining of triactinomyxon spores with vital fluorescein diacetate correlated with the ability of the spores to infect fry of rainbow trout Oncorhynchus mykiss. The experimentally produced actinosporean stage of Myxobolus cerebralis was short-lived, persisting for only 3–4 d at 12.5°C and for less time at warmer temperatures. The vital staining method has potential for screening therapeutants intended to control myxosporean infection of fish.     

Control of Mycoplasma hyopneumoniae infections in pigs

Mycoplasma hyopneumoniae, the primary pathogen of enzootic pneumonia, occurs worldwide and causes major economic losses to the pig industry. The organism adheres to and damages the ciliated epithelium of the respiratory tract. Affected pigs show chronic coughing, are more susceptible to other respiratory infections and have a reduced performance. Control of the disease can be accomplished in a number of ways. First, management practices and housing conditions in the herd should be optimized. These include all-in/all-out production, limiting factors that may destabilize herd immunity, maintaining optimal stocking densities, prevention of other respiratory diseases, and optimal housing and climatic conditions. Strategic medication with antimicrobials active against M. hyopneumoniae and, preferably, also against major secondary bacteria may be useful during periods when the pigs are at risk for respiratory disease. Finally, commercial bacterins are widely used to control M. hyopneumoniae infections. The main effects of vaccination include less clinical symptoms, lung lesions and medication use, and improved performance. However, bacterins provide only partial protection and do not prevent colonization of the organism. Different vaccination strategies (timing of vaccination, vaccination of sows, vaccination combined with antimicrobial medication) can be used, depending on the type of herd, the production system and management practices, the infection pattern and the preferences of the pig producer. Research on new vaccines is actively occurring, including aerosol and feed-based vaccines as well as subunit and DNA vaccines. Eradication of the infection at herd level based on age-segregation and medication is possible, but there is a permanent risk for re-infections.     

Infection of Lymnaea truncatula and Lymnaea glabra by Fasciola hepatica and Paramphistomum daubneyi in farms of central France

Natural infection of Lymnaea glabra and Lymnaea truncatula by Fasciola hepatica and/or Paramphistomum daubneyi was studied at two periods of risk (June-July and September-October) in 11 French farms known for their high prevalences of F. hepatica infection in ruminants. A total of 1,778 L. truncatula and 2,396 L. glabra measuring 6 mm or more in height were collected to determine the prevalence of natural infection with F. hepatica and P. daubneyi. The role of four factors, i.e. season, snail co-infection (F. hepatica-P. daubneyi), ruminant host and the existence of single or mixed intermediate host communities, was investigated. There were no differences in prevalences between the two risk periods. Co-infections in L. glabra were more frequent than expected. The prevalences of infection with F. hepatica or P. daubneyi in L. glabra were higher in farms rearing sheep than in farms rearing cattle. A similar finding was also noted for L. truncatula infected with P. daubneyi only. L. glabra was a much better intermediate host for F. hepatica and P. daubneyi when it was the only available snail, possibly indicating an adaptation of parasites to their less usual host in local conditions. The two trematodes preferably developed in L. truncatula rather than in L. glabra when both host species lived in the same places.     

甘肃、宁夏地区奶牛衣原体血清流行病学调查及风险因素分析

本研究旨在查明甘肃与宁夏地区奶牛衣原体的感染情况并分析影响其感染的风险因素。本试验采用间接血凝试验(IHA)方法检测了甘肃榆中(751份)、宁夏青铜峡(450份)和宁夏吴忠(456份)3个地方总计1 657份奶牛血清样品,并应用流行病学调查及统计学方法对影响奶牛衣原体感染的因素进行了分析。流行病学调查结果显示,奶牛衣原体抗体总阳性率为29.33%;应用logistic回归分析评估奶牛衣原体感染的风险因素,结果显示年龄和胎次不是显著风险因素(P>0.05),而地区因素是影响奶牛衣原体感染的风险因素(P<0.05)。奶牛衣原体抗体滴度最高达1:1 024。结果表明,甘肃和宁夏地区奶牛衣原体普遍流行。因此,应当提高对调查地区奶牛衣原体感染的重视,采取适当的综合控制方法和有效的管理措施以防控奶牛衣原体病,以保证奶牛养殖业的经济效益。     

Seroprevalence Investigation and Risk Factors Analysis of Chlamydia Infection in Dairy Cattle in Gansu and Ningxia Areas

The objective of the present investigation was to examine seroprevalence of Chlamydia in dairy cattle in Gansu and Ningxia areas, Northwest China, and to analyze the factors affecting Chlamydia infection in dairy cattle.Indirect hemagglutination assay (IHA) was used to detect antibodies against Chlamydia in 1 657 dairy cattle serum samples from Gansu and Ningxia areas.Epidemiological investigation and statistical methods were used to analyze the data.The results showed that the overall seroprevalence was 29.33%, logistic regression analysis was applied to evaluate the risk factors of Chlamydia infection in dairy cattle, and the results indicated that age and numbers of pregnancy of dairy cattle were not the significant risk factors (P>0.05), and were left out of the final model, however, region was considered as the main risk factor associated with Chlamydia infection (P<0.05).The highest titer was 1:1 024.In conclusion, the results of the present survey indicated the widespread of Chlamydia infection in Gansu and Ningxia areas.In order to ensure the economic benefit of dairy farming, we should pay more attention to Chlamydia infection in dairy cattle, and integrated control strategies and efficient management measures should be implemented to prevent and control Chlamydia infection in dairy cattle.     

Maintenance of a captive flock of house finches free of infection by Mycoplasma gallisepticum

Since the beginning of an epidemic of conjunctivitis in wild house finches caused by Mycoplasma gallisepticum (MG), all captive colonies established by capturing free-ranging house finches from the eastern population have also either been infected at the time of capture or developed infection shortly after capture. In an attempt to avoid this infection in captive flocks being maintained for studies of the finches' behavior and ecology, we compared two different flock management strategies and were able to prevent the development of mycoplasmal conjunctivitis with one of the strategies. Single-sex flocks were built by introducing only seronegative wild-caught birds showing no clinical signs of conjunctivitis and covering their outdoor flight cages with netting to prevent interaction with other wild birds although only the female flocks were initially treated with a 6-wk course of tylosin tartrate (0.3 mg/ml). The female flocks never developed conjunctivitis although the disease did develop in the male flocks. Furthermore, serologic assessments of the healthy flock by serum plate agglutination assays for MG indicated that the females remained free of MG infection in the final 7 wk of the study, during which they were unmedicated. We conclude that any low-level MG infection not diagnosed by the initial test for seroconversion was cleared by the prolonged drug treatment.     

Management Strategies for Reducing the Risk of Equines Contracting Vesicular Stomatitis Virus (VSV) in the Western United States

Vesicular stomatitis viruses (VSVs) cause a condition known as vesicular stomatitis (VS), which results in painful lesions in equines, cattle, swine, and camelids, and when transmitted to humans, can cause flu-like symptoms. When animal premises are affected by VS, they are subject to a quarantine. The equine industry more broadly may incur economic losses due to interruptions of animal trade and transportation to shows, competitions, and other events. Equine owners, barn managers, and veterinarians can take proactive measures to reduce the risk of equines contracting VS. To identify appropriate risk management strategies, it helps to understand which biting insects are capable of transmitting the virus to animals, and to identify these insect vectors’ preferred habitats and behaviors. We make this area of science more accessible to equine owners, barn managers, and veterinarians, by (1) translating the most relevant scientific information about biting insect vectors of VSV and (2) identifying practical management strategies that might reduce the risk of equines contracting VSV from infectious biting insects or from other equines already infected with VSV. We address transmission risk at four different spatial scales—the animal, the barn/shelter, the barnyard/premises, and the surrounding environment/neighborhood—noting that a multiscale and spatially collaborative strategy may be needed to reduce the risk of VS.     

苜蓿褐斑病接种方法研究

以苜蓿假盘菌为接种菌源,对3个不同抗性的苜蓿品种(即伊鲁瑰斯、沙湾和泾阳)采用3种活体整株接种方法,即接种盘倒扣接种法、活体病株覆盖接种法和孢子悬浮液喷雾接种法,进行比较,以筛选出稳定、可靠、操作简便、发病速度较快的接种方法.结果表明,病株覆盖接种和孢子悬浮液喷雾接种为较理想的接种方法,可以比较准确、快速的鉴定出品种及单株的抗病性,其中孢子悬浮液最佳缓冲液组成为:0.5%吐温-20 4.5%葡萄糖 9mg/L萘乙酸 1g/L菌落.     

Hendra virus in Queensland,Australia, during the winter of 2011: Veterinarians on the path to better management strategies

Following the emergence of Hendra virus (HeV), private veterinarians have had to adopt additional infection control strategies to manage this zoonosis. Between 1994 and 2010, seven people became infected with HeV, four fatally. All infected people were at a higher risk of exposure from contact with horses as they were either veterinary personnel, assisting veterinarians, or working in the horse industry. The management of emerging zoonoses is best approached from a One Health perspective as it benefits biosecurity as well as a public health, including the health of those most at risk, in this case private veterinarians. In 2011 we conducted a cross-sectional study of private veterinarians registered in Queensland and providing veterinary services to horses. The aim of this study was to gauge if participants had adopted recommendations for improved infection control, including the use of personal protective equipment (PPE), and the development of HeV specific management strategies during the winter of 2011. A majority of participants worked in practices that had a formal HeV management plan, mostly based on the perusal of official guidelines and an HeV field kit. The use of PPE increased as the health status of an equine patient decreased, demonstrating that many participants evaluated the risk of exposure to HeV appropriately; while others remained at risk of HeV infection by not using the appropriate PPE even when attending a sick horse. This study took place after Biosecurity Queensland had sent a comprehensive package about HeV management to all private veterinarians working in Queensland. However, those who had previous HeV experience through the management of suspected cases or had attended a HeV specific professional education programme in the previous 12 months were more likely to use PPE than those who had not. This may indicate that for private veterinarians in Queensland personal experience and face-to-face professional education sessions may be more effective in the improvement of HeV management than passive education via information packages. The role of different education pathways in the sustainable adoption of veterinary infection control measures should be further investigated.     

Risk assessment strategies for Europe: integrated safety strategy or final product control: Example of Listeria monocytogenes in processed products from pork meat industry

The European regulation 2160/2003 of November 17th, 2003 clearly shows the European strategy of zoonosis monitoring and control as an integrated approach, including the entire food production chain with a first application to Salmonella control in different animal species. This regulation is the consequence of a risk assessment performed with a "farm to fork" philosophy. European strategy is scarcely different from the American strategy, despite the fact that both were achieved by a quantitative risk assessment, as for instance, in the USA the control of Salmonella in eggs is supposed to be completed by refrigeration. Nevertheless, the EU will still have a final product control approach towards future regulations on microbiological criteria for foodstuffs. The final production monitoring and control with HACCP (93/43/EC) and microbiological criteria is the only one available for L. monocytogenes in foodstuffs. The purpose of this paper is to discuss alternative control strategies for L. monocytogenes in pig production including integrated risk assessment. In France, most of the food-borne outbreaks associated with L. monocytogenes in delicatessen were due to one particular group of strains belonging to serovar 4b and presenting a particular RFLP/PFGE (Restriction Fragment Length Polymorphism/Pulsed Field Gel Electrophoresis) profile. The outbreak itself is always associated with the initial contamination of a RTE ("ready to eat") product and re-contamination by inappropriate handling after cooking. Consequently, in most cases the RTE product is subject to inadequate refrigeration during an excessive shelf-life. The responsibility of the food industry and the consumer is clearly engaged during this scenario of foodborne diseases. The question is how to avoid the introduction of this particular strain of L. monocytogenes in the food chain. In a study we tried to evaluate the risk of pig carcass contamination at slaughterhouse level and to identify the main risk factors associated with the infection of live pigs. In most cases inappropriate cleaning and disinfection of surfaces were associated with the contamination of raw meat, but in some cases the introduction of epidemic strains in the food chain was also associated with primary production. Feeding with soup in piggeries seemed to select a particular microbial ecology associated to L. monocytogenes contamination of live pigs. The possible strategies that may be used to control L. monocytogenes in live pig production are not yet developed sufficiently to be included in the EC regulation but should be discussed in more detail.     

Estimation of the age-dependent risk of infection to BSE of dairy cattle in Great Britain

An important aspect of the bovine spongiform encephalopathy (BSE) epidemic has been an apparent age-dependent risk of infection, with younger cattle being more likely to become infected than older cattle. Our objective was to determine the age-dependent risk of infection of dairy cattle. We first reviewed unpublished data on the feeding patterns of proprietary concentrates for dairy-replacement cattle. These data showed that autumn- and spring-born cattle would receive different feeding patterns of proprietary concentrates, and so age-dependent risk of infection profiles were obtained separately for autumn- and spring-born cattle. We used back-calculation methods to analyse BSE-epidemic data collected in Great Britain between 1984 and 1996.

Dairy cattle were most at risk in the first 6 months of life; adult cattle were at relatively low risk of infection. Between 6 and 24 months of age, risk profiles reflected feeding patterns of proprietary concentrates in each of the autumn- and spring-born cohorts.     

Coprological methods for the diagnosis of Anoplocephala perfoliata infection of the horse

Objective To compare the sensitivities of three coprological techniques for the diagnosis of Anoplocephala perfoliata infection in horses and to assess the value of the methods for diagnosis of horses at risk of clinical cestodiasis.
Design Faecal samples were collected from necropsied horses with or without A perfoliata infection and examined using one sedimentation and two different flotation methods. The coprological results were compared with worm counts performed at necropsy of the horses and the degree of mucosal damage. In addition, the efficiency of recovery of A perfoliata eggs from faeces was tested.
Results The overall sensitivities of the methods ranged from 22.5 to 37.5%, and the capacity of the methods to diagnose infection increased with the intensity of infection. A simple flotation method achieved a better sensitivity (37.5%) at all intensities of infection compared with the other two methods (22.5 to 25%). That method was also more sensitive in detecting eggs in 'negative' faecal samples spiked with known numbers of A perfoliata eggs.
Conclusion The results indicated that, despite the low sensitivities of present methods, faecal flotation is likely to be of value in detecting horses at risk of clinical disease.     

Differences and similarities among experts' opinions on Salmonella enterica dynamics in swine pre-harvest

A workshop was conducted to elicit expert opinion on infection status and transmission of salmonella in pigs at the farm of origin, during transport and during lairage. A second objective was to compare opinions regarding risk factors for salmonella introduction and control at the farm level between experts from different countries. Thirty-six experts from 11 countries filled in a paper-and-pencil questionnaire during an international conference. Experts from all countries agreed on the risk of salmonella introduction related to live animals and the importance of general hygiene and all-in/all-out management for salmonella control. However, workshop participants from Denmark put more weight on factors related to feed while experts from USA rated factors related to rodents and people contact higher. The experts believed that 21-33% of pigs coming from a chronically infected farm would be infected with salmonella, but only one-third of the infected pigs would be shedders. Regarding transport and lairage, the US participants believed that contamination was occurring in the majority of pigs regardless of initial infection status and particularly during lairage; in contrast, the Danish experts were more optimistic with respect to the contamination and infection risk. US experts believed that the incidence of salmonella shedding would be high among pigs infected during transport and lairage and that an important proportion of 'carrier' pigs would start shedding.Our results reflect the differences in the level of salmonella infection and implemented control strategies between countries as well as the different philosophies that professionals have. The differences in opinion regarding salmonella dynamics could be due either to true differences in risk as a consequence of distinct management and transport practices in Denmark and USA or to a difference in perception.     

Spatio-temporal factors influencing the occurrence of Syngamus trachea within release pens in the South West of England

Syngamus trachea is a pathogenic tracheal nematode that causes syngamiasis in wild and game birds, especially when birds are managed at high densities. Despite its pathogenic nature, very little is known about its epidemiology and relationship with ambient temperature and humidity. The spatial and temporal modelling of disease was undertaken on two pheasant estates within the South West of England from April 2014 to August 2014. Significant differences between the mean numbers of eggs per gram of soil were identified between pens at both site 1 and site 2 but did not differ significantly between sites. Egg abundance was significantly associated with soil moisture content, with greater egg survival between years in pens with higher average volumetric soil moisture content. Previous years stocking density and pen age were also associated with greater egg survival between years with more eggs being recovered in pens with greater stocking densities, and pens that had been sited longer. The greatest model to explain the variation in the numbers of eggs per gram of soil per pen was a combination of soil moisture content, stocking density and pen age.Larval recovery differed significantly between sites. Larval abundance was significantly and positively associated with temperature and relative humidity at site 1. Similarly, temperature and humidity were also positively and significantly associated with larval abundance at site 2. Rainfall did not influence larval recovery at either site 1 or site 2. The model with the greatest ability to explain larval abundance at both sites, was a combination of temperature, humidity and rainfall. Infection status (positive faecal egg counts) was significantly and positively associated with larval abundance at both sites, but rainfall was only positively associated at site 1. Temperature and humidity were positively associated with infection status at site 2, but not at site 1. The present study highlights the influence of climatic variables on both egg survival and larval abundance, and could therefore be used to develop more targeted treatment strategies around periods of higher disease risk. The frequent use of release pens is a clear factor in the epidemiology of syngamiasis, and it is recommended that pens be rested and/or rotated in order to reduce infection pressure in subsequent flocks.     

猪链球菌感染风险因子分析及控制要点

为控制猪场链球菌感染的风险,降低猪链球菌发病率。我们对猪链球菌感染的可能风险因素进行了分析,引入HACCP理念,绘制了猪场猪链球菌感染的流程图,识别出猪场猪链球菌感染的风险因子及关键控制点(CCP-like),即隐性带菌猪、混群饲养、精液、蓝耳病、伪狂犬及PCV-2型感染等病毒性免疫抑制病、疫苗免疫、药物预防。针对各关键控制点制定出相应的防控措施,为猪链球菌的防控提供了技术思路。