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Detection and characterisation of parasites causing emerging zoonoses.

Understanding the epidemiology of zoonotic parasitic infections is dependent upon the availability of accurate and sensitive diagnostic techniques. The development of molecular diagnostic methods, particularly those utilising PCR for the detection of zoonoses will contribute greatly to the identification and control of these pathogens, by increasing the speed of diagnosis, specificity and sensitivity, reproducibility and ease of interpretation. Molecular characterisation studies allow us to distinguish between closely related infectious agents and to document the patterns of transmission of 'strains' and species within populations. This will allow precise determinations to be made about the aetiological agent, its characteristics and the source of infection. This review focuses on recent detection and characterisation techniques for both emerging and re-emerging parasite zoonoses.

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New emerging zoonoses: a challenge and an opportunity for the veterinary profession.

The concept of emerging infectious diseases appeared in the late 1980s, when major outbreaks occurred around the globe and surprised many scientists who considered infectious diseases to be maladies of the past or limited to the under-developed world. Several reports identified erosion of the public health infrastructure among the factors contributing to new and re-emerging infectious diseases. As indicated by Morse, "Disease emergence often follows ecological changes caused by human activities such as agriculture or agricultural change, migration, urbanization, deforestation, or dam building". "Among these new diseases, surprisingly, most emergent viruses and many emergent bacteria are zoonotic". Several new zoonoses have been recently identified. Many of these diseases were either unknown, because we were not able to isolate the infectious agent or to distinguish them from other clinical syndromes, or discovered accidentally. Much of the recent identification of new pathogens has been based on new molecular biology tools or epidemiological studies. For all these diseases or infections, veterinarians played a key role in their identification, isolation of the causative organisms and understanding of the epidemiology of the infection. The role of the veterinary profession is very important in public health and on the rise again in the U.S.A., as it should be in many other countries. Surveillance, clinical curiosity and awareness, epidemiology and laboratory training are the essential tools and competency that the veterinary profession must use to meet the challenge of new emerging zoonoses.

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Urban zoonoses caused by Bartonella, Coxiella, Ehrlichia, and Rickettsia species.

The last half of the 20th Century witnessed an increase in the occurrence and recognition of urban zoonoses caused by members of the genera Bartonella, Coxiella, Ehrlichia, and Rickettsia, all traditionally considered to be members of the family Rickettsiaceae. In recent years, new human pathogens (Bartonella elizabethae, Bartonella henselae, and Rickettsia felis) have been recognized in urban environments. Other newly recognized pathogens (Ehrlichia chaffeensis and Ehrlichia phagocytophila in the United States) have sylvan zoonotic cycles but are present in urban areas because their vertebrate hosts and associated ectoparasitic arthropod vectors are able to survive in cities. Still other agents, which were primarily of historical importance (Bartonella quintana) or have not traditionally been associated with urban environments (Rickettsia rickettsii), have been recognized as causes of human disease in urban areas. Some diseases that have traditionally been associated with urban environments, such as rickettsialpox (caused by Rickettsia akari) and murine typhus (caused by Rickettsia typhi), still occur in large cities at low or undetermined frequencies and often go undetected, despite the availability of effective measures to diagnose and control them. In addition, alternate transmission cycles have been discovered for Coxiella burnetii, Rickettsia prowazekii, and R. typhi that differ substantially from their established, classic cycles, indicating that the epidemiology of these agents is more complex than originally thought and may be changing. Factors leading to an increase in the incidence of illnesses caused by these bacteria in urban areas include societal changes as well as intrinsic components of the natural history of these organisms that favor their survival in cities. Transovarial and transstadial transmission of many of the agents in their arthropod hosts contributes to the highly focal nature of many of the diseases they cause by allowing the pathogens to persist in areas during adverse times when vertebrate amplifying hosts may be scarce or absent. Domesticated animals (primarily cats, dogs, and livestock) or commensal rodents [primarily Norway rats (Rattus norvegicus) and house mice (Mus musculus)] can serve as vertebrate amplifying hosts and bring these agents and their ectoparasitic arthropod vectors into direct association with humans and help maintain transmission cycles in densely populated urban areas. The reasons for the increase in these urban zoonoses are complex. Increasing population density worldwide, shifts in populations from rural areas to cities, increased domestic and international mobility, an increase in homelessness, the decline of inner-city neighborhoods, and an increase in the population of immunosuppressed individuals all contribute to the emergence and recognition of human diseases caused by these groups of agents. Due to the focal nature of infections in urban areas, control or prevention of these diseases is possible. Increased physician awareness and public health surveillance support will be required to detect and treat existing urban infections caused by these agents, to determine the disease burden caused by them, to design and implement control programs to combat and prevent their spread, and to recognize emerging or resurging infections caused by members of these genera as they occur.

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Control of zoonoses in Britain: past, present, and future.

In the past zoonoses that caused serious human illness also caused serious loss of animal production, but there is growing awareness of the public health problems arising from infections that cause little or no such loss. Much can be learnt from the history of the control of bovine tuberculosis and brucellosis. In both cases there was reluctance to accept that animals were the principal cause of infection, and the earliest attempts at control failed because measures were taken only against clinical cases of the disease. The essential features in control of both infections were: official recognition of a problem, willingness of governments to allocate resources, and cooperation between the medical and veterinary professions. Salmonellosis is the most important zoonotic infection in Britain today, though several Orders have reduced the reservoir of infection in food animals. It is suggested that a national team of doctors should be set up to investigate and control zoonoses, that this team should be answerable to a central agency, and that it should build up close working relationships with the nominated officers of the veterinary profession.

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New emerging viral zoonoses.

New developments in the field of viral transmission from animal to man can be divided into four areas of study. First are the new viral zoonoses such as diseases caused by rotaviruses, Lassa virus and the animal orthopox viruses which will be more prevalent after the cessation of mandatory vaccination against smallpox. Secondly are the numerous ubiquitous viruses, such as adeno and herpesviruses, which in healthy animals lead only to clinically inapparent infections. A typical example of the third area is the recombination and hybridisation between animal and human influenza type A viruses. The final area is concerned with the transmission of viral zoonoses to man through food of animal origin.

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Public health implications of emerging zoonoses.

Many new, emerging and re-emerging diseases of humans are caused by pathogens which originate from animals or products of animal origin. A wide variety of animal species, both domestic and wild, act as reservoirs for these pathogens, which may be viruses, bacteria or parasites. Given the extensive distribution of the animal species affected, the effective surveillance, prevention and control of zoonotic diseases pose a significant challenge. The authors describe the direct and indirect implications for public health of emerging zoonoses. Direct implications are defined as the consequences for human health in terms of morbidity and mortality. Indirect implications are defined as the effect of the influence of emerging zoonotic disease on two groups of people, namely: health professionals and the general public. Professional assessment of the importance of these diseases influences public health practices and structures, the identification of themes for research and allocation of resources at both national and international levels. The perception of the general public regarding the risks involved considerably influences policy-making in the health field. Extensive outbreaks of zoonotic disease are not uncommon, especially as the disease is often not recognised as zoonotic at the outset and may spread undetected for some time. However, in many instances, the direct impact on health of these new, emerging or re-emerging zoonoses has been small compared to that of other infectious diseases affecting humans. To illustrate the tremendous indirect impact of emerging zoonotic diseases on public health policy and structures and on public perception of health risks, the authors provide a number of examples, including that of the Ebola virus, avian influenza, monkeypox and bovine spongiform encephalopathy. Recent epidemics of these diseases have served as a reminder of the existence of infectious diseases and of the capacity of these diseases to occur unexpectedly in new locations and animal species. The need for greater international co-operation, better local, regional and global networks for communicable disease surveillance and pandemic planning is also illustrated by these examples. These diseases have contributed to the definition of new paradigms, especially relating to food safety policies and more generally to the protection of public health. Finally, the examples described emphasise the importance of intersectorial collaboration for disease containment, and of independence of sectorial interests and transparency when managing certain health risks.

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Parasitic food-borne and water-borne zoonoses.

Estimates suggest that almost half of the population of the world is affected by water-borne and food-borne infections. Parasitic food-borne and water-borne zoonoses contribute to this statistic by inflicting a heavy toll on human health and causing serious direct and indirect losses to the agricultural industry. The inability of non-industrialised countries to keep pace with population growth, migration from rural to urban areas and the demand for clean, safe drinking water and proper sanitation means that water-borne zoonoses will continue to exact an increasing burden of ill health in these countries. The consumption of raw or undercooked meat, crustaceans, and fresh-water fish and vegetables facilitates transmission of large numbers of zoonotic infections. The burgeoning tourist industry, emigration and the importation of food from endemic regions has resulted in increasing diagnosis of these infections in non-endemic countries. The authors examine the epidemiology, medical and veterinary public health importance and recent developments in diagnosis, treatment and control of the most important parasitic food-borne and water-borne infections.

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[Zoonoses].

The numbers of microbial species that can infect human beings are shown to be 1415, of which 868 species (61%) are zoonotic. Since most of the emerging pathogens (75%) are originated from other animals, public health sectors should be vigilant against the emergence of new zoonotic diseases. Only 33% of zoonoses can spread from human to human after introduction into human population. Various factors such as human demography, ecological change, global transportation and climate change are responsible for the emergence of zoonoses. Even a slight change in the ecological niche where pathogenic organisms thrive would result in the increase of the incidence of the disease.

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[Some remarks on mycotic zoonoses from veterinary medicine].

Various mycotic zoonoses of human transmitted from animals have recently been viewed as a serious matter. The outbreaks of these diseases under many complicated circumstances occur in the community between human and animals. Cooperation is needed to prevent the expansion of infections of zoonoses by both human and veterinary medicine.

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Viral zoonoses.

Viral zoonoses cause overt disease in humans and other animals or silent infections in animals and overt disease in unnatural hosts such as humans. Often the virus and its animal host have evolved together and learned to live together. Infection may spread freely between the natural host animals and cause no signs of disease, but this balance may be upset by many factors, including stress, changing environmental conditions and mutations in both viruses and hosts. Infection of an unnatural host may cause clinical disease but no further spread of the virus. Examples of viral zoonoses both old and new are used to illustrate some of these points, and two will be described in detail--Rift Valley fever and influenza.

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[Construction of occupational zoonoses control system at a zoo].

More than 200 diseases are known to be transmitable from animals to humans. These zoonotic infections (zoonoses) are considered as a major occupational health risk among zoo workers, including veterinarians and animal handlers. In order to prevent possible pathogen transmission, precaution measures for workers, visitors and animals are important, as well as institutional hygiene. Construction of a zoonoses control system at a zoo is presented in this report. There are two main components of this system: 1. routine disease prevention activity, 2. action planning for crisis. Workers, an operating officer, an occupational physician and a veterinarian from the zoo cooperated with infection control professionals from the local community.

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[Emergence of "new" viral zoonoses].

In the last two to three decades a significant increase of viral zoonotic infections was observed. These zoonoses are not only newly (or previously unrecognized) emerging diseases, but also due to the reappearance of diseases thought to have been defeated (re-emerging diseases). "New" viral diseases can arise when viruses broaden their host-range (monkey poxvirus; equine morbillivirus), or can be a consequence of intrinsic properties of the virus itself, such as high mutation rates (influenza A virus). Most new or reemerging viral zoonoses are due to infections with hemorrhagic viruses. Many of them are transmitted by insects (arboviruses, e.g. yellow fever virus) or by rodents (e.g. Hanta viruses), others by contact with patients and nosocomial infections (e.g. Ebola virus). The emergence and increase of these diseases are a consequence of anthropogenic environmental changes, such as distortions of the ecological balance and changes in agriculture. In addition, the uncontrolled growth of the cities in tropical and subtropical regions without improvement of the public health measures and the increasing international animal trade and travel also favour the spread and recurrence of these diseases.

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[Small game (foxes, brown hares, pheasants and ducks) as carriers of zoonoses].

Small game involves numerous infection hazards in terms of contact zoonoses and foodborne diseases. Especially exposed are hunters, game dealers, veterinarians, housewives, farmers, forest workers, laboratory staff, and taxidermists, but also consumers of insufficiently cooked game. This paper gives a survey of the most significant zoonoses in small game in Europe, which are discussed in the light of the author's own research results in this field. Finally, measures concerning prophylaxis and food hygiene are suggested.

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[The fundamentals of association of natural foci of zoonoses].

Reports on the role of hydrological conditions in the functioning of parasitic systems are analyzed. The authors point out that a range of issues including different aspects of combination phenomena is discussed there. They suggest that a concept of combination shall be replaced by a concept of association of parasitic systems and their relevant natural foci of zoonoses, which is of a larger scope. The fundamentals of the formation and functioning of associated parasitic systems and natural foci of zoonoses are discussed. These include the hydrological conditions of floodplain-river regions, the multiparasitic capacity of hosts and vectors, the multihost pattern of causative agents, and a diversity of mechanisms of their transmission. The transmission mechanism without which movement of causative agents and the existence of parasitic systems and foci are impossible is shown to be a global combining onset of parasitic systems. The hydrological conditions of floodplain-river regions act as the universal mechanism of transmission of pathogens. The dynamics of the mechanism determines the functioning of all other mechanisms of transmission.

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Biology of Ixodes species ticks in relation to tick-borne zoonoses.

At least six tick-borne zoonoses are transmitted by members of the Ixodes ricinus species complex in northern hemisphere temperate regions, and include the relatively recently emerged diseases, Lyme borreliosis and ehrlichiosis. An understanding of the biology of these ticks is essential for the prevention and control of the zoonoses they transmit and this review summarises established knowledge in addition to addressing recent work on host specificity of ticks, inter- and intra-specific biological variation and factors affecting tick distribution and abundance.

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[Bacterial zoonoses with natural focality: current trends in epidemic manifestation].

Current trends in epidemic manifestation of some bacterial zoonoses with natural focality and their role in human infectious pathology have been reviewed and analyzed. Update information on the etiological agents of "emerging" and "re-emerging" infections--Astrakhan spotted fever, bartonellosis, ixodes tick-borne borrelioses, monocytic erhrlichiosis and canine brucellosis, recently isolated on the territory of Russia, is presented. The main factors at play in the process of urbanization of bacterial zoonoses are discussed.

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[Outlook for control of current zoonoses in swine--an issue on consumer health protection].

With the development of a uniform European strategy for the control of zoonoses the European Commission has placed the main emphasis on the protection of consumer health. This direction is clearly marked by the White Paper on Food Safety and the attached proposals for directives and regulations. The present article considers the peculiarities of the epidemiological situation of the agents Campylobacter spp. and Yersinia enterocolitica in pork production. The situation of zoonoses in Europe is used as an opportunity to present the distinctive characteristics of these agents, results of epidemiological studies available, and the risk to consumer health in light of the literature. For the approaching transfer of the responsibility for food safety to the primary producers, i.e. the farmers, the most interesting data concern the prevalence, distribution and risk factors. But as there is a strong need for clarification of further questions about the main ways of entry of these agents on farms and into the production chain before a successful preventive strategy can be developed on pig farms, these issues are considered in more detail here.

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[Viral zoonoses].

In different areas of the World, whether in industrialized or developing countries, zoonoses represent an emerging Public Health concern either as known agents appear in areas or species in which they had not been reported or as new pathogens parasite Human as consequence of successful host switching. Epidemiological data outlined that vectorborne viral zoonoses are of particular relevance. This paper review the changes in epidemiology of bat rabies and arbovirus encephalitis.

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