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1.
Within-herd transmission of pathogens occurs either by direct or by indirect contact between susceptible and infected animals. In dairy herds that are structured into groups, the way in which animals encounter each other and share an environment can affect pathogen transmission. Dairy cattle are heterogeneous in terms of susceptibility and infectivity with respect to Mycobacterium avium subspecies paratuberculosis (Map) transmission. It is mainly young animals that are susceptible and adults that are infectious. Both vertical and horizontal transmission through the ingestion of Map shed into the environment by adults and transiently infected calves can occur. Our objective was to assess the effect of contact structure on Map transmission in persistently infected dairy herds and to examine the effect of isolating calves from other calves or from adults before weaning. We developed a stochastic compartmental model of Map transmission in a closed dairy herd. The model reflects the Map infection process and herd management characteristics. Indirect transmission via the environment was modelled explicitly. Six infection states (susceptible, resistant, transiently infectious, latently infected, subclinically infected, and clinically affected) and two contaminated farm area environments (whole farm and calf area) were modelled. Calves were housed in hutches, individual indoor pens, or group indoor pens. Two different levels of exposure of calves to a farm environment contaminated by adults were possible: no exposure and indirect exposure through fomites. Three herd sizes were studied. We found that contacts between calves before weaning did not influence Map transmission in a herd, whereas the level of exposure of calves to an environment contaminated by adults and the starting age of exposure of calves to adults were pivotal. Early culling of clinically affected adults led to a lower prevalence of infectious adults over time. The results were independent of herd size. Despite the many transmission routes that are known, the best control approach is to limit the exposure of calves to adult faeces through the systematic separation of adults and calves in combination with hygiene measures. Reducing contact between calves does not appear effective.  相似文献   

2.
In an outbreak of foot-and-mouth disease (FMD) it is important to identify animals at risk from airborne virus. Investigations have been carried out over the years to determine the dose required to infect cattle, sheep and pigs by the intranasal route. This paper reviews the results of investigations for animals which have been infected by instillation or spraying a virus suspension into the nostrils or by exposure to affected animals through a mask or by indirect contact. The lowest doses were found by use of a mask. With virus from affected pigs given through a mask, doses of 18 infectious units (IU) in cattle and 8 IU in sheep were found to cause infection and give rise to lesions. Overall, cattle required the least amount of virus followed by sheep. Pigs required a dose of 22 IU to cause infection and a dose of 125 IU to give rise to lesions. In many experiments pigs failed to become infected. With all three species the dose varied with the individual animal and the virus strain. For modelling previous outbreaks and in real time, a dose of 8 IU or 10 and 50% infectious doses (ID50) could be used where cattle and sheep were involved. Experience in the field, combined with the results from experiments involving natural infection, indicate that pigs are not readily infected by the intranasal route. However, for modelling purposes a dose of about 25 IU should be used with care. Investigations are needed to determine doses for virus strains currently in circulation around the world. In addition, the nature of the aerosol droplets needs to be analysed to determine how the respective amounts of infective and non-infective virus particles, host components and, in later emissions, the presence of antibody affect the survival in air and ability to infect the respiratory tract. Further work is also required to correlate laboratory and field findings through incorporation of the doses into modelling the virus concentration downwind in order that those responsible for controlling FMD are provided with the best available assessment of airborne spread. Finally, the doses found for infection by the intranasal route could be applied to other methods of spread where virus is inhaled to assess risk.  相似文献   

3.
The goal of this study was to establish a short list of zoonotic pathogens involving the domestic dog that can be prioritized for a companion animal surveillance program specific to the Prairie Provinces of Canada. A list of pathogens documented in dogs was created through a comprehensive review of infectious disease textbooks for the following taxonomical categories: bacteria, ectoparasites, fungi, helminths, protozoa, rickettsia, and viruses. This created an initial list of 594 pathogens that was then pared down through an extensive review of the literature using the following criteria: i) the pathogen is zoonotic/sapronotic/anthroponotic; ii) the dog is involved in transmission to humans, maintenance, or detection of the pathogen; and iii) there is a level of risk for occurrence of the pathogen in Canada. This process yielded a final list of 84 pathogens and 3 supplementary lists of canine zoonotic/sapronotic/anthroponotic pathogens that may become relevant to future surveillance programs.  相似文献   

4.
Veterinary practices are unique environments that bring humans into close contact with many different species of animals; therefore, the risk of exposure to infectious pathogens is inherently different in veterinary medicine than in human medicine. In contrast to the risk of exposure to blood in human medicine, infections from zoonotic diseases in veterinary personnel are primarily related to exposure to animal faeces, infected skin, wounds, droplets and puncture wounds. Infection-control measures in veterinary practices are often insufficient to prevent zoonotic disease transmission. The Veterinary Standard Precautions (VSP) Compendium is designed to help prevent transmission of zoonotic pathogens from animal patients to veterinary personnel in private practice.  相似文献   

5.
Ticks transmit pathogens that cause diseases which greatly impact both human and animal health. Vaccines developed against Boophilus spp. using Bm86 and Bm95 tick gut antigens demonstrated the feasibility of using vaccines for control of tick infestations. These vaccines also reduced transmission of tick-borne pathogens by decreasing exposure of susceptible hosts to ticks. The recently discovered tick antigens, 64P putative cement protein and subolesin involved in the regulation of tick feeding and reproduction, were also shown to reduce tick infestations. These antigens, together with the TROSPA receptor for Burrelia burgdorferi OspA were effective against tick-borne pathogens by reducing the infection levels in ticks and/or the transmission of the pathogen. Development of a vaccine targeted at both the tick vector and pathogen would contribute greatly to the control of tick infestations and the transmission of tick-borne diseases. These results have demonstrated that tick vaccines can be developed for control tick infestations and show promise for the prevention of the transmission of tick-borne pathogens.  相似文献   

6.
持续感染是指病原体在宿主体内持续存在而不被清除的状态,其潜伏期长达数月至数年甚至终生,但不引起症状,病原体不一定持续增殖。不同病原体所致持续感染的定义不同,如口蹄疫病毒(FMDV)引起的持续感染被定义为动物感染28d后仍然携带活的病毒。持续感染是造成免疫失败、肿瘤形成或药物敏感性下降的重要原因。存在持续感染的宿主是重要的传染源,还是病原体发生变异的来源,但因无症状常被忽视。充分了解持续感染的形成机理及持续感染状态中宿主与病原体之间的相互作用,有助于寻找诊断、治疗和预防感染性疾病的最佳方法。论文从病原体和宿主因素两个方面阐述了持续感染的形成机理。  相似文献   

7.
Ticks transmit pathogens that cause diseases which greatly impact both human and animal health. Vaccines developed against Boophilus spp. using Bm86 and Bm95 tick gut antigens demonstrated the feasibility of using vaccines for control of tick infestations. These vaccines also reduced transmission of tick-borne pathogens by decreasing exposure of susceptible hosts to ticks. The recently discovered tick antigens, 64P putative cement protein and subolesin involved in the regulation of tick feeding and reproduction, were also shown to reduce tick infestations. These antigens, together with the TROSPA receptor for Burrelia burgdorferi OspA were effective against tick-borne pathogens by reducing the infection levels in ticks and/or the transmission of the pathogen. Development of a vaccine targeted at both the tick vector and pathogen would contribute greatly to the control of tick infestations and the transmission of tick-borne diseases. These results have demonstrated that tick vaccines can be developed for control tick infestations and show promise for the prevention of the transmission of tick-borne pathogens.  相似文献   

8.
Trade patterns of animal movements in a specific industry are complex and difficult to study because there are many stakeholders, premises that are heterogeneously spread over the country, and a highly dynamic flow of animals exists among them. The Danish cattle industry was defined as a network of animal movements and graph theory was used to analyse the movements of cattle within this network. A premise was defined as a farm, an abattoir or a market. These premises constituted the network nodes in the graph and the animal movements between them were the links. In this framework, each premise had a sub-network of other premises to which it was linked by these animal movements. If no movement of animals were registered for a specific farm, then the sub-network for that premise consisted of only that premise. Otherwise, the sub-network linked the premise of interest to all premises from which and to which animals were moved, as long as there was a path linking animal movements to that specific premise. This approach allowed visualization and analyses of four levels of organization that existed in Denmark animal registers: (1) the animal that was moved, (2) the movements of all animals between two premises, (3) the specific premise network, and (4) the overall industry network. When contagious animals are moved from one premise to another, then to a third and so forth, these movements create a path for potential transfer of pathogens. The paths within which pathogens are present identify the transmission risks. A network of animal movements should provide information about pathogen transmission and disease spread. The network of the Danish cattle industry network was a directed scale-free graph (the direction of a movement was known), with an in-degree power of 2 an out-degree power of 1.46, consisted of 29,999 nodes, and 130,265 movements during a 6-month period. The in clustering coefficient was calculated to be 0.52 for the inward direction (movement to), while it was 0.02 for the outward direction (movement from). In Denmark, the cattle movements between premises demonstrated a large degree of heterogeneity. This heterogeneity in movements between farms should be used to evaluate the risk potential of disease transmission for each premise and must be considered when modelling disease spread between premises. The objective of this research was to describe the network of animal movements and not just the animal movements per se.  相似文献   

9.
There is increasing evidence that activation of innate immunity, in animals and man, by live vaccines, sub-unit vaccines or synthetic or non-synthetic stimulants can induce a profound and rapidly induced resistance to pathogens, including infectious agents that are unrelated to the stimulating antigen or agent. We review the evidence for this phenomenon and present the proposition that this approach might be used to stimulate immunity during the life of the animal when susceptibility to infection is high and when normal vaccination procedures may be inappropriate.  相似文献   

10.
A general model is proposed for predicting the effects of subclinical pathogen challenges of different doses and virulence on the relative feed intake (RFI) of animals. The RFI is defined as the feed intake (FI, kg/d) of the animal challenged by a pathogen divided by its FI in the same state had it not been challenged. Actual FI can be predicted from the RFI and the animal's state. The RFI was assumed to be affected only when animals were na?ve to a particular pathogen (i.e., had not previously experienced it) and when the challenge dose was above a predetermined threshold. The model is for the period from recognition of a pathogen through acquisition and subsequent expression of immunity. The way in which RFI changes with time is described by 5 main parameters and is based on data for RFI during different pathogen challenges of a range of hosts. Lag time (L, d) is the delay from a pathogen challenge until any effects on RFI are seen. Reduction time (R, d) describes the time it takes for the lowest value of RFI (lambda) to be achieved. The duration time (D, d) describes the time that lambda is maintained for, and rho (RFI/d) describes the rate of recovery of RFI until RFI = 1. There is no compensatory intake, and RFI is always < or = 1. The effects of host resistance on the values of the model parameters are proposed. Attempts were made to parameterize the model; when data were scarce, initial parameter values were derived on conceptual grounds. Predictions of the effects of pathogen dose, virulence, and host resistance are described and discussed. When comparing the responses in RFI for different genotypes, it is crucial to define the pathogen challenge (in terms of dose and virulence) and the degree of resistance of different hosts. Possible interactions between dose, virulence, and resistance were explored. Feed intake of healthy and challenged animals, at a time, may be different once the challenged animal has recovered (RFI = 1). The issue of reductions in FI during pathogen challenges is important for nutritionist and animal breeders. The large variation that has been observed for reductions in FI during pathogen challenges may be a viable point of selection. The points highlighted will aid selection strategies by quantifying the effects of pathogen dose and virulence, and time, on the FI of challenged animals. The proposed model may be integrated with other models of growth to predict animal performance during exposure to pathogens.  相似文献   

11.
Bovine viral diarrhoea virus (BVDV) is an endemic pathogen worldwide and eradication strategies focus on the identification and removal of persistently infected (PI) animals arising after in utero infection. Despite this, acute infections with BVDV can persist for months or years after the removal of the PI source despite repeated screening for PIs and tight biosecurity measures. Recent evidence for a prolonged duration of viraemia in the testicles of bulls following acute BVDV infection suggests the possibility of a form of chronic persistence that may more closely resemble the persistence strategies of hepatitis C virus (HCV). To investigate the potential for virus transmission from infected and recovered cattle to virus naïve hosts we established an acute infection of 5 BVDV-naïve calves and monitored animals over 129 days. Infectious BVDV was detected in white blood cells between days 3 and 7 post-challenge. The animals seroconverted by day 21 post-infection and subsequently were apparently immune and free from infectious virus and viral antigen.Animals were further monitored and purified white blood cells were stimulated in vitro with phytohaemagglutinin A (PHA) during which time BVDV RNA was detected intermittently.Ninety-eight days following challenge, blood was transferred from these apparently virus-free and actively immune animals to a further group of 5 BVDV-naïve calves and transmission of infection was achieved. This indicates that BVDV-infected, recovered and immune animals have the potential to remain infectious for BVDV-naïve cohorts for longer than previously demonstrated.  相似文献   

12.
In urban environments, raccoons (Procyon lotor) may act as reservoirs for an array of pathogenic organisms, presenting spillover risks for human, domestic animal, and captive (zoo) animal populations. Over 5 yr, 159 raccoons from a high-density raccoon population in St. Louis, Missouri (USA), were surveyed for exposure to canine distemper virus (CDV), canine adenovirus 1 (CAV-1); feline parvovirus (FPV; =feline panleukopenia), and several serovars of Leptospira interrogans. Exposure to each of the viruses and two Leptospira serovars (grippotyphosa and icterohemorrhagiae) was detected (prevalence of CDV = 54.1%; FPV = 49.7%; CAV-1 = 6.9%; L. interrogans icterohemorrhagiae = 8.9%; L. interrogans grippotyphosa = 6.3%). Eighty percent of raccoons showed evidence of exposure to at least one of the five primary pathogens, and 39% were positive for multiple species. Among the viruses, there was a significant co-occurrence of CDV and CAV-1. Longitudinal data on a subset of animals revealed that among individuals who were diagnosed as seropositive on first capture, 33-100% became seronegative for the pathogen of interest when reexamined at a later date. Thus, free-ranging urban raccoons have been exposed to multiple infectious agents, some of which may pose risks to humans and to nonvaccinated domestic and captive animal populations.  相似文献   

13.
A young cat with signs of chronic rhinitis was evaluated for underlying anatomical, inflammatory, or infectious disease. Initial diagnostics were significant for the isolation of an unusual pathogen, Haemophilus species. Isolation using a human RapID NH system erroneously identified the isolate as H. segnis, a human pathogen. No database of veterinary pathogens (Haemophilus) are included in the system and animal pathogens will either be erroneously identified or yield a unique biocode not listed. Because of the unique nature of the pathogen we explored the possibility of immunosuppression as a contributory factor to infection. A variety of laboratory tests were employed to evaluate immune function. The clinical indications and utility of immune function testing are discussed. No immune dysfunction was identified.  相似文献   

14.
Captive coyotes (Canis latrans) were inoculated intragastrically (1 coyote), and intratracheally (6 coyotes) with Histoplasma capsulatum to simulate natural routes of exposure. In addition, the infectious organism was inoculated IV into another coyote and into a dog (C familiaris) to simulate hematogenous dissemination of H capsulatum. Isolation of the pathogen from various tissue specimens, using direct plating and mouse inoculation methods, provided mycologic evidence of infection. The presence of anti-Histoplasma serum antibodies also was monitored. Of the 6 coyotes challenged intratracheally, one developed a benign pulmonary form of histoplasmosis. This coyote developed a transient cough, and intracellular yeasts typical of H capsulatum were observed microscopically in pulmonary tissue specimens. The pathogen was isolated from specimens of pulmonary tissue and associated lymph nodes. The coyote that was fed Histoplasma-infected mice (intragastric challenge) did not develop clinical disease. The coyote and the dog inoculated IV developed a multifocal, nonsuppurative infection, without clinical evidence of histoplasmosis. Pathologic findings in the coyote and dog were similar; both animals had splenitis, lymphadenitis, and petechiation of the lungs. The liver and spleen were considered the primary extrapulmonary target organs on the basis of mycologic and histologic findings.  相似文献   

15.
A longitudinal study of sero-conversion of youngstock to the tick-borne pathogens Theileria parva, T. mutans, Anaplasma marginale, Babesia bigemina and B. bovis was conducted over two years on smallholder dairy farms in Tanga region, Tanzania. There was evidence of maternal antibodies to all tick-borne pathogens in animals less than 18 weeks of age. Seroprevalence increased as expected with age in animals older than this but seroprevalence profiles underestimated the force of infection due to waning antibody levels between samplings. By the end of the 2-year study, less than 50% of study animals had seroconverted to each of the tick-borne pathogens investigated, consistent with the low levels of tick attachment observed on the study animals. Some associations between seroconversion to tick-borne pathogens, and counts of their known tick vectors on the animals, were identified as expected. However, some were not, suggesting that counts of some tick species may act as an index of rates of attachment of other vector species. Variation in acaricide treatment frequencies was not associated with variations in tick-borne pathogen seroprevalence suggesting that acaricides may be used more frequently than necessary on many farms. Most animals were zero-grazed, a management system associated with a significantly lower likelihood that animals seroconverted to any tick-borne pathogen except A. marginale. Seroprevalence varied locally with farm location (particularly for Babesia spp.) but was not well predicted by indices of ecological conditions. Our findings suggest that attempts to achieve a state of 'endemic stability' for tick-borne pathogens may be unreasonable on the smallholder dairy farms studied but reductions in the frequency of use of acaricides may be possible following prospective studies of effects on mortality and morbidity due to tick-borne pathogens.  相似文献   

16.
Although the highly pathogenic avian influenza H5N1 virus continues to cause infections in both avian and human populations, the specific zoonotic risk factors remain poorly understood. This review summarizes available evidence regarding types of contact associated with transmission of H5N1 virus at the human–animal interface. A systematic search of the published literature revealed five analytical studies and 15 case reports describing avian influenza transmission from animals to humans for further review. Risk factors identified in analytical studies were compared, and World Health Organization‐confirmed cases, identified in case reports, were classified according to type of contact reported using a standardized algorithm. Although cases were primarily associated with direct contact with sick/unexpectedly dead birds, some cases reported only indirect contact with birds or contaminated environments or contact with apparently healthy birds. Specific types of contacts or activities leading to exposure could not be determined from data available in the publications reviewed. These results support previous reports that direct contact with sick birds is not the only means of human exposure to avian influenza H5N1 virus. To target public health measures and disease awareness messaging for reducing the risk of zoonotic infection with avian influenza H5N1 virus, the specific types of contacts and activities leading to transmission need to be further understood. The role of environmental virus persistence, shedding of virus by asymptomatic poultry and disease pathophysiology in different avian species relative to human zoonotic risk, as well as specific modes of zoonotic transmission, should be determined.  相似文献   

17.
The susceptibility of camelids for infectious agents which may result in severe economic losses or which are strictly regulated for epidemiological reasons in farm animals potentially causes a mutual risk of transmission. This study aimed to investigate the presence of antibodies against bovine herpesvirus 1 (BHV-1), bluetongue virus (BTV) and bovine viral diarrhoea virus (BVDV) as well as the presence of pestivirus antigen in new world camelids in Central Germany. Therefore 107 serum samples from 93 alpacas and lamas from this region which had been obtained from 2007 to 2009 were examined using ELISA, serum neutralisation test, RT-PCR and a pestivirus specific gene probe. All sample were negative for BHV-1 antibodies. Antibodies against BVDV-1 could be detected in four animals, titres reaching from 1:64 to > 1:256. One animal was positive for BTV antibodies in the year 2008. This animal had been tested negative for BTV antibodies in 2007. It can be concluded that up to now, these viruses seem to be of minor importance as pathogens in new world camelids in Central Germany. Therefore the risk of infection originating from new world camelids for production animals could be considered to be rather low in this region at the moment. However, it must be taken into consideration that these animals due to lack of antibodies are fully susceptible in case of occurrence of one of these viruses. For maintenance and improvement of the present status, general hygienic precautions should be applied; direct and indirect contact between animals from different herds must be avoided and virological diagnostic and quarantine should be required trading these animals.  相似文献   

18.
Infectious diseases are an important cause of morbidity and mortality in horses, along with economic costs and broader impacts associated with the loss of members of a species that generates income, acts as a working animal and is a companion. Endemic diseases continue to challenge, emerging diseases are an ever‐present threat and outbreaks can be both destructive and disruptive. While infectious diseases can never be completely prevented, measures can be introduced to restrict the entry of pathogens into a population or limit the implications of the presence of a pathogen. Objective research regarding infection control and biosecurity in horses is limited, yet a variety of practical infection prevention and control measures can be used. Unfortunately, infection control can be challenging, because of the nature of the equine industry (e.g. frequent horse movement) and endemic pathogens, but also because of lack of understanding or motivation to try to improve practices. Recognition of the basic concepts of infection control and biosecurity, and indeed the need for measures to control infectious diseases, is the foundation for successful infection prevention and control.  相似文献   

19.
While technological advances in animal husbandry have facilitated increases in global meat production, the high density and geographic concentration of food animal production facilities pose risks of infectious disease transmission. The scale of the 2014–2015 highly pathogenic avian influenza H5N2 outbreak in the United States demonstrates the challenges in achieving pathogen control within and around industrial animal facilities using existing technologies. We discuss gaps in current practice in two specific systems within these facilities – ventilation and waste management – which are under‐recognized as important drivers of microbial porosity. The development of innovative ventilation systems to reduce influx and efflux of pathogens is critically needed, and cross‐sectoral partnerships should be incentivized to do so. Adapting current human biosolid treatment technologies for farm applications, reducing animal stocking density and shifting waste management responsibility from farmer to corporation would reduce risk from current manure management systems. While innovative approaches to functionally altering the industrial food animal production system remain important priorities to promote sustainability, our intention here is to identify gaps within the current system that allow for pathogen emergence and transmission and address specific areas in which technological, administrative or policy changes are necessary to mitigate these risks.  相似文献   

20.
Abstract

Infectious diseases have been observed in both human and animal populations for millenia. Unlike diseases of “higher” animals, the dispersal of disease in fish populations rarely has been studied quantitatively. However, the principles that govern the spread of diseases of humans and other mammals should, with modification, be applicable to the study of infectious diseases in fishes. Disease in populations is a dynamic phenomenon; fluctuations in prevalence and impact are dependent on the interactions among host, pathogen, and environment. Models of the dynamics of infectious diseases in salmon and other fishes can be constructed and refined to reflect the characteristics of diseases by integrating the most important factors in the process. Among the factors that have been shown to be important in other systems are the “contagiousness” of the pathogen (transmission coefficient, β), duration of infection, host population density, development of immunity, and efficacy of therapeutants.  相似文献   

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