Emerging parasitic diseases of sheep

There have been changes in the emergence and inability to control of a number of sheep parasitic infections over the last decade. This review focuses on the more globally important sheep parasites, whose reported changes in epidemiology, occurrence or failure to control are becoming increasingly evident. One of the main perceived driving forces is climate change, which can have profound effects on parasite epidemiology, especially for those parasitic diseases where weather has a direct effect on the development of free-living stages. The emergence of anthelmintic-resistant strains of parasitic nematodes and the increasing reliance placed on anthelmintics for their control, can exert profound changes on the epidemiology of those nematodes causing parasitic gastroenteritis. As a consequence, the effectiveness of existing control strategies presents a major threat to sheep production in many areas around the world. The incidence of the liver fluke, Fasciola hepatica, is inextricably linked to high rainfall and is particularly prevalent in high rainfall years. Over the last few decades, there have also been increasing reports of other fluke associated diseases, such as dicroceliosis and paramphistomosis, in a number of western European countries, possibly introduced through animal movements, and able to establish with changing climates. External parasite infections, such as myiasis, can cause significant economic loss and presents as a major welfare problem. The range of elevated temperatures predicted by current climate change scenarios, result in an elongated blowfly season with earlier spring emergence and a higher cumulative incidence of fly strike. Additionally, legislative decisions leading to enforced changes in pesticide usage and choices have resulted in increased reports and spread of ectoparasitic infections, particularly mite, lice and tick infestations in sheep. Factors, such as dip disposal and associated environmental concerns, and, perhaps more importantly, product availability have led to a move away from more traditional methods of pesticide application, particularly dipping, to the use of injectable endectocides. This has coincided with increased reports of sheep scab and lice infestations in some countries. Reduction in the use of organophosphate dips appears to have to some extent contributed to reported increased populations of ticks and tick activity, a consequence of which is not only of significance to sheep, but also many other hosts, including increased human zoonotic risks.     

多病因呼吸道病

在当今养禽业中，不但旧病复发，且常出现一些新病。其实有些新病早已存在，仅因其发病率低、临诊症状及病变不甚明显或缺乏诊断手段而被忽视。另一方面，微生物本身的基因变化使得其毒力或致病性增强，以及禽类的遗传变异改变了其本身对疾病的易感性和抵抗力也是目前养禽业中旧病复发，新病不断的一大原因。此外，环境条件或饲养管理的改变有利于微生物产生致病性。由于活禽、蛋及禽产品全球性的频繁贸易，难以将某一新病或旧病控制在某一国家或地区。从本期起，本刊对家禽的新病和一些综合征或病因不明的疾病内容加以连载，以飨读者。     

Emerging viral diseases of fish and shrimp

The rise of aquaculture has been one of the most profound changes in global food production of the past 100 years. Driven by population growth, rising demand for seafood and a levelling of production from capture fisheries, the practice of farming aquatic animals has expanded rapidly to become a major global industry. Aquaculture is now integral to the economies of many countries. It has provided employment and been a major driver of socio-economic development in poor rural and coastal communities, particularly in Asia, and has relieved pressure on the sustainability of the natural harvest from our rivers, lakes and oceans. However, the rapid growth of aquaculture has also been the source of anthropogenic change on a massive scale. Aquatic animals have been displaced from their natural environment, cultured in high density, exposed to environmental stress, provided artificial or unnatural feeds, and a prolific global trade has developed in both live aquatic animals and their products. At the same time, over-exploitation of fisheries and anthropogenic stress on aquatic ecosystems has placed pressure on wild fish populations. Not surprisingly, the consequence has been the emergence and spread of an increasing array of new diseases. This review examines the rise and characteristics of aquaculture, the major viral pathogens of fish and shrimp and their impacts, and the particular characteristics of disease emergence in an aquatic, rather than terrestrial, context. It also considers the potential for future disease emergence in aquatic animals as aquaculture continues to expand and faces the challenges presented by climate change.     

Emerging arthropod-borne diseases of companion animals in Europe

Vector-borne diseases are caused by parasites, bacteria or viruses transmitted by the bite of hematophagous arthropods (mainly ticks and mosquitoes). The past few years have seen the emergence of new diseases, or re-emergence of existing ones, usually with changes in their epidemiology (i.e. geographical distribution, prevalence, and pathogenicity). The frequency of some vector-borne diseases of pets is increasing in Europe, i.e. canine babesiosis, granulocytic anaplasmosis, canine monocytic ehrlichiosis, thrombocytic anaplasmosis, and leishmaniosis. Except for the last, these diseases are transmitted by ticks. Both the distribution and abundance of the three main tick species, Rhipicephalus sanguineus, Dermacentor reticulatus and Ixodes ricinus are changing. The conditions for such changes involve primarily human factors, such as travel with pets, changes in human habitats, social and leisure activities, but climate changes also have a direct impact on arthropod vectors (abundance, geographical distribution, and vectorial capacity). Besides the most known diseases, attention should be kept on tick-borne encephalitis, which seems to be increasing in western Europe, as well as flea-borne diseases like the flea-transmitted rickettsiosis. Here, after consideration of the main reasons for changes in tick vector ecology, an overview of each “emerging” vector-borne diseases of pets is presented.     

Emerging diseases: a global and biological perspective

The 'Livestock Revolution' and globalization with enormous increases in free trade of animals and food products are not a choice but a reality (Thiermann, J. Vet. Med. Educ., 28, 2001, 56). Conditions of modern life, some of them related to or being the result of globalization, ensure that factors responsible for disease emergence are more prevalent than ever. Categorization of the factors is somewhat arbitrary but are representative of the underlying processes that cause emergence. Major responsible factors include ecological changes, such as changes due to agriculture or economic development or to anomalies in climates, human demographical changes and behaviour, travel and commerce, technology and industry, microbial adaptation and change, and the breakdown of public health measures (Morse, Emerg. Infect. Dis., 1, 1995, 7). Furtheron, concerning pathogens, their most striking feature emerging and re-emerging is their diversity, ranging from viruses and prions, over bacteria and rickettsia, fungi, protozoa to helminths. As presently the epidemiological perspective does not permit reliable prediction and prevention of most damaging new pathogens, and as the evolutionary perspective only provides rough theoretical estimates for selective processes in pathogen populations, surveillance and monitoring remain the most important methods to recognize early that 'something has happened'. In light of the complexity and diversity of likely new emerging diseases, such surveillance may be more broadly targeted and aimed more realistically at early recognition of disease syndromes rather than at identifying microbial diseases. The complex and rapid-paced development of international trade, coupled with increasing societal demands for not only abundant and inexpensive food as well as for protection from diseases originating from animals, demands immediate attention from the veterinary community. The inter-relationship at the minimum between animal production, animal diseases and human diseases demands that we consider our concepts, methods and structures. There exists a huge growth area for the veterinary profession; substantial need exists for trained individuals who understand the science of foreign diseases, who can facilitate emergency management operations against diseases (Brown, J. Vet. Med. Educ., 30, 2003, 112) and who can contribute to adjust and strategically develop animal production systems further.     

Molecular epidemiological studies of veterinary arboviral encephalitides

Recent studies using molecular genetic approaches have made important contributions to our understanding of the epidemiology of veterinary arboviral encephalitides. Viruses utilizing avian enzootic hosts, such as Western equine encephalitis virus (WEEV) and North American Eastern equine encephalitis virus (EEEV), evolve as relatively few, highly conserved genotypes that extend over wide geographic regions; viruses utilizing mammalian hosts with more limited dispersal evolve within multiple genotypes, each geographically restricted. Similar findings have been reported for Australian alphaviruses. This difference may be related to vertebrate host relationships and the relative mobility of mammals and avians. Whereas EEEV and Venezualan equine encephalitis virus (VEEV) utilize small mammalian hosts in the tropics, most WEEV genotypes probably utilize avian hosts in both North and South America. The ability of mobile, infected avian hosts to disperse alphaviruses may result in continual mixing of virus populations, and thus limit diversification. This high degree of genetic conservation is also exhibited by EEE and Highlands J viruses in North America, where passerine birds serve as amplifying hosts in enzootic transmission foci. Most equine arboviral pathogens, including EEEV, WEEV and Japanese encephalitis virus (JEV), occur in a naturally virulent enzootic state and require only appropriate ecological conditions to cause epizootics and epidemics. However, VEE epizootics apparently require genetic changes to convert avirulent enzootic strains into distinct epizootic serotypes. All of these arboviruses have the potential to cause severe disease of veterinary and human health importance, and further molecular epidemiological studies will undoubtedly improve our ability to understand and control future emergence.     

Emerging zoonoses

The food-borne zoonoses are the most important zoonoses in England and Wales measured in terms of human morbidity and mortality and they include the most important emerging infections. Over the past decade there were over 100,000 laboratory reported cases of salmonellosis, about 1–5 per cent with serious extra-intestinal complications with 427 registered deaths; there were nearly 90,000 Campylobacter infections. In salmonellosis the sources and modes of spread of infection are largely known, but veterinary and human public health measures have so far failed to control the disease. In Campylobacter enteritis however, the source and spread in most of the reported cases are unknown and control is not yet possible. Amongst the remaining less common food-borne zoonoses, listeriosis and yersiniosis are most prominent. Both are increasing with food-borne outbreaks of both infections having been reported, but the origin of infection of most cases recorded in England and Wales is not known. Of the new food-borne or water-borne diseases the most common are giardiasis and cryptosporidiosis but in neither is it clear whether the infections are predominantly of human or animal origin. The place of haemorrhagic colitis and of S. zooepidemicus infection is not yet apparent, both may emerge as important zoonoses. Streptobacillary fever, on the other hand, seems unlikely to recur with normal hygienic standards of water and milk supply. Of the occupational zoonoses Q fever and leptospirosis are the most important. Although only 1,330 cases of Q fever were reported in 10 years, it is a severe disease; 123 of them had endocarditis. Leptospirosis probably increased in incidence and emerged as a new disease of farmers and others working with cattle. S. suis type 2, a ‘new’ disease, remained a rarity. Zoonoses acquired from pets made up only a small proportion of human zoonotic infections and the only apparent change was an increase in psittacosis, the reason for which is unknown. Lastly, among the zoonoses acquired from wild and captive animals the viral haemorrhagic fevers have emerged as an important hazard in hospitals and laboratories.     

Emerging food-borne parasites

Parasitic food-borne diseases are generally underrecognised, however they are becoming more common. Globalization of the food supply, increased international travel, increase of the population of highly susceptible persons, change in culinary habits, but also improved diagnostic tools and communication are some factors associated with the increased diagnosis of food-borne parasitic diseases worldwide. This paper reviews the most important emerging food-borne parasites, with emphasis on transmission routes. In a first part, waterborne parasites transmitted by contaminated food such as Cyclospora cayetanensis, Cryptosporidium and Giardia are discussed. Also human fasciolosis, of which the importance has only been recognised in the last decades, with total numbers of reported cases increasing from less than 3000 to 17 million, is looked at. Furthermore, fasciolopsiosis, an intestinal trematode of humans and pigs belongs to the waterborne parasites as well. A few parasites that may be transmitted through faecal contamination of foods and that have received renewed attention, such as Toxoplasma gondii, or that are (re-)emerging, such as Trypanosoma cruzi and Echinococcus spp., are briefly reviewed. In a second part, meat-borne parasite infections are reviewed. Humans get infected by eating raw or undercooked meat infected with cyst stages of these parasites. Meat inspection is the principal method applied in the control of Taenia spp. and Trichinella spp. However, it is often not very sensitive, frequently not practised, and not done for T. gondii and Sarcocystis spp. Meat of reptiles, amphibians and fish can be infected with a variety of parasites, including trematodes (Opisthorchis spp., Clonorchis sinensis, minute intestinal flukes), cestodes (Diphyllobothrium spp., Spirometra), nematodes (Gnathostoma, spp., anisakine parasites), and pentastomids that can cause zoonotic infections in humans when consumed raw or not properly cooked. Another important zoonotic food-borne trematode is the lungfluke (Paragonimus spp.). Traditionally, these parasitic zoonoses are most common in Asia because of the particular food practices and the importance of aquaculture. However, some of these parasites may emerge in other continents through aquaculture and improved transportation and distribution systems. Because of inadequate systems for routine diagnosis and monitoring or reporting for many of the zoonotic parasites, the incidence of human disease and parasite occurrence in food is underestimated. Of particular concern in industrialised countries are the highly resistant waterborne protozoal infections as well as the increased travel and immigration, which increase the exposure to exotic diseases. The increased demand for animal proteins in developing countries will lead to an intensification of the production systems in which the risk of zoonotic infections needs to be assessed. Overall, there is an urgent need for better monitoring and control of food-borne parasites using new technologies.     

Emerging Ferret Diseases

There are a number of newly described and emerging disease syndromes affecting the domestic ferret, and the purpose of this article is to make veterinarians aware of these diseases. A recently described systemic coronavirus infection appears to be a variant of the ferret enteric coronavirus and is currently termed “ferret infectious peritonitis.” Disseminated immunopathologic myositis, aplastic anemia/bone marrow aplasia, acute hemorrhagic syndrome, and oral ulcerations are also described, although the exact etiologies for these diseases have yet to be determined. There appears to be at least 2 important amino acid metabolism deficiencies in ferrets: hindlimb weakness in older ferrets (L-carnitine) and cysteine urolithiasis. Ferrets have recently been found to be susceptible to H1N1 influenza, so knowledge regarding this zoonotic disease is essential for veterinarians working with these animals. A novel Mycoplasma spp. has also recently been identified in ferrets with chronic respiratory problems that originated from one breeding colony. Because these diseases are still being investigated, practitioners who treat a ferret patient exhibiting clinical signs consistent with any of the conditions mentioned are encouraged to contact people who are knowledgeable of that particular illness.     

Emerging paradigms in immunonutrition

Nutritional immunology is the study of the relationship between food and the immune system. It evolved with the study of immune deficiencies caused by malnutrition. However, because of technological advances made over the past few decades, malnutrition is no longer the main cause of lowered immune status in otherwise healthy people/animals. Rather, life stage (neonate or old age) and natural stressors have taken over as the primary cause for immune deficiency. Unlike malnutrition, immune deficiency due to life stage or natural stress cannot be addressed by correcting underlying nutritional problems. Lowered immune status because of life stage or naturally occurring stress is characterized by reduced capacity to process and present foreign antigens to immune cells, resulting in a less efficient or altered immune response that leads to increased susceptibility to infections and an increase in autoimmunity and cancers. Beyond providing essential nutrients, diet can actively influence the immune system. Over 65% of the immune cells in the body are present in the gut, making the gut the "largest immune organ." Receptors present on the immune cells in the gut are the primary targets for immunomodulation via diet. Diet interacts with the immune system at multiple levels, starting with providing basic nutrients, then moving on to providing higher levels of key nutrients such as protein, vitamins, and minerals, and leading to a more focused modulation of the immune system. A framework outlining this interaction, along with relevant examples, will be discussed.