锥体科寄生原虫赖以生存的机制及其应用前景

锥体科寄生原虫病在一些国家和地区造成巨大的人力和物力损失,如非洲睡眠病和枯氏锥虫病以及利什曼原虫病(黑热病)等,如不加以治疗,致死率可达100％。为了探索防治寄生虫感染的手段,以锥体科寄生原虫为模型研究寄生虫赖以生存的机制,免疫逃避、耐药性和抑制宿主细胞凋亡等机制成为科研工作者研究的热点。文章以寄生虫赖以生存的机制为切入点,展望了我国预防寄生虫感染和研制寄生虫疫苗的发展趋势。     

Effects of rapid passage in the gerbil (Meriones unguiculatus) on the course of infection of the bovine piroplasm Babesia divergens in splenectomised calves

The antigenicity and virulence of the cattle piroplasm Babesia divergens was compared in splenectomised calves before and after adaptation to the gerbil. It was apparent that adaptation of B divergens to the gerbil did not result in attenuation of the parasite in cattle. The gerbil-adapted parasite had a shorter prepatent period, produced higher parasitaemias, and more severe haematological and biochemical changes than the initial bovine strain. The antigenicity of the parasite was unchanged by gerbil passage. The changes in the virulence of the gerbil-adapted parasite were attributed to selection of a rapidly replicating parasite.     

Mechanisms of survival of nematode parasites with emphasis on hypobiosis

Mechanisms involved in parasitic nematode survival must be considered with reference to their host and environmental interrelationships since these interrelationhips ultimately influence any parasite adaptations aimed at survival.The most important of the potential environmental constraints are climatic, particularly temperature and humidity, and these can drastically influence larval development and survival.One of the major host factors influencing successful parasite survival is the availability of suitable (susceptible) new hosts to the infective stages of the parasite at the appropriate time for transmission to be achieved. Other host factors that influence parasite survival are those that affect the entrance, establishment and reproduction of the parasite within its new host; mainly problems of acclimatization to a parasitic way of life as well as the countering or adaptation to a variety of host resistance factors, both molecular and cellular, by the parasite.Finally in order for life cycles to be completed, the parasite must evolve means whereby its larval forms can leave the host so that eventual transmission to a new host can be accomplished.In this paper a number of adaptations which enable the parasite to overcome these constraints are discussed. These include such things as larval resistance to environmental effects, the utilization of intermediate hosts or vectors for transmission, seasonally-increased fecundity rates, anti-host immunity stratagems and hypobiosis.This latter phenomenon, hypobiosis or prolonged but temporarily arrested larval development, represents one of the most useful of life cycle adaptations to ensure parasite adaption enables the parasite to synchronize its life cycle to changing environmental or survival and appears to be widespread among parasitic nematodes. Among its benefits, this host conditions. It can thus be of major importance in ensuring survival of the parasite during periods of environmental adversity when conditions for transmission are poor and survival of free-living forms may be minimal. It also enables the parasite to have available large numbers of infective forms at points in the host reproductive cycle which coincide with the production of the susceptible neonates thereby greatly facilitating transmission. Additionally, with certain species of nematodes, occurring as it does at times of the year when the numbers of infective stages may be high while host resources may be limited, oscillations in parasite biomass can be avoided. It thus serves as a highly adaptive mechanism for regulating populations of adult worms, lessening stress on the host and favoring parasite survival as a result.     

Comparison of the susceptibility of brown trout (Salmo trutta) and four rainbow trout (Oncorhynchus mykiss) strains to the myxozoan Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD)

Differences in susceptibility to the myxozoan parasite Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), between four strains of rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) were evaluated. Fish were exposed to water enzootic for the parasite in the field for 5 days and were subsequently transferred to the laboratory. Relative parasite load was determined after 2, 3 and 4 weeks post-exposure (wpe) by quantitative real-time PCR (qPCR) of kidney samples and number of parasite stages was determined in immunohistochemical stained sections of kidney, liver and spleen tissues. According to qPCR results, the highest amount of parasite DNA per equal amount of host tissue at all time points was measured in brown trout. Two of the rainbow trout strains showed lower relative parasite load than all other groups at the beginning of the experiment, but the parasite multiplied faster in these strains resulting in an equal level of relative parasite load for all rainbow trout strains at 4 wpe. A weak negative correlation of fish size and parasite load was detected. Only in samples of a few fish, single stages of T. bryosalmonae were found in sections stained by immunohistochemistry impeding quantitative evaluation of parasite numbers by this method. The results indicate a differential resistance to T. bryosalmonae between the rainbow trout strains investigated and between rainbow trout and brown trout.     

Evaluation of efficacy expectations for novel and non-chemical helminth control strategies in ruminants

The interest in novel methods of controlling helminth infections in ruminants is driven primarily by the development of parasite resistance to currently available anthelmintics. While the purpose of anthelmintics is to achieve high efficacy, i.e. >90% reduction of adult and/or larval parasites in the target host animal, the purpose of novel parasite control methods is rather to assist in maintaining parasite infections below the economic threshold. The ability to maintain parasite levels below the economic threshold is related not only to the efficacy of the control method, but also to the epidemiology of the parasites, climatic conditions, the livestock management program, and integration in a sustainable parasite control program. Because of this fundamental difference, novel parasite control methods need to be evaluated using efficacy criteria different from that adopted for anthelmintics. Although the efficacy of novel parasite control methods may be demonstrated in classic dose-confirmation studies, the impact on livestock production parameters can only be evaluated when tested on-farm. In this paper, the rationale for evaluating novel methods differently from anthelmintics is reviewed, potential performance expectations are presented, and four novel parasite control methods (vaccines, nematophagous fungi, condensed tannins, and immunonutrition) are assessed based on the potential performance criteria.     

Water as a vector for infectious stages of parasites in livestock

Water is a key factor in the life cycle of many parasite species. The development of the free-living generation (oocysts, cysts, eggs, larvae) and the longevity of the resulting infectious stages are extremely dependent on the availability of water. Damp stables are principally associated with an increased risk of parasite infection. Infectious stages may accumulate in dirty watering equipment and in pools of water on pasture. Utilization of surface water, especially when contaminated with sewage or effluent from sewage plants, imposes an increased risk of parasite infection on farm animals. Flooding of pastures with water containing parasite stages can lead to extensive contamination. Rainfall, flooding or inadequate land disposal of manure may contaminate surface water with parasite stages of animal origin from adjacent agricultural areas.     

Manipulating small ruminant parasite epidemiology through the combination of nutritional strategies

It is increasingly being recognized that non-chemical parasite control strategies may need to be combined to control more effectively gastrointestinal parasitism, result in resilient production systems and reduce reliance on anthelmintics. Here, we consider if and how metabolizable protein (MP) supplementation and anti-parasitic plant secondary metabolites (PSM) may modulate parasite epidemiology through intervention in pasture contamination, development of infection on pasture and larval challenge as target processes. We then propose that combining two or more non-chemical parasite control strategies may have additive effects on host resistance, especially if the individual strategies target different drivers of parasite epidemiology, different processes in the parasite life cycle or different phases of acquired immunity to parasites. This epidemiological framework is used to review recent findings on combining maternal MP supplementation and grazing the PSM-rich bioactive forage chicory as an example of combining nutritional treatments to manipulate parasite epidemiology in a temperate production system. In the absence of available data for combined nutritional strategies in tropical production systems, we make predictions on the consequences of combining such strategies in these systems. We conclude that currently published studies on combining nutritional strategies under temperate conditions show potential to improve additively host resilience and reduce reliance on anthelmintics; however, effects on epidemiology have to date not shown the additive results hypothesized. The framework developed may assist further in evaluating combined (nutritional) strategies to manipulate parasite epidemiology.     

Impact of internal parasites on beef cattle

Internal parasitism is a pervasive constant that reduces returns in beef cattle production. Parasitism may influence production sufficiently so that data derived investigating performance response will be erroneous. The interaction of internal parasites of cattle with other facets of their lives makes it imperative that more parasite research be done on cattle to consider their impact. Results of trials designed to determine forage production at various stocking densities may not reflect the nutritive value of the forage, but instead the severity of parasite exposure. Relative resistance or susceptibility to certain parasites vary with the breed of livestock and the species of parasite. Extensive work to evaluate the ability of various breeds and sires to influence parasitic numbers has been conducted in sheep but not in cattle. Some parasite trials have ignored the effects of nutrition on the establishment and retention of parasites. This becomes especially important where multiple parasite exposure may occur. Susceptible cattle, even on an optimal diet, will become parasitized, but if reexposed to the same species of parasite, cattle on an optimal diet may be able to resist reinfection, whereas those on deficient diets will not.     

Parasite control in the age of drug resistance and changing agricultural practices

The benefits of using antiparasitic drugs in farm animals are unquestionable. However, despite anthelmintic use as the predominant control strategy, extreme parasite infection cases are appearing in sheep and goat production; these impact productivity and have show mortality rates reaching pre-drug use levels. This was a predictable situation resulting from the loss of efficacy by all available products, particularly when some products were used as the sole intervention. The concepts of agroecology and holistic agriculture, which advocate the use of integrated management strategies, such as target selected treatment, herbal medicine, and the application of other parasite control alternatives, are not completely new, but are undergoing a resurgence because of their more sustainable appeal. The objective of this review article is to examine the problem of parasite control in the face of parasite drug resistance and to outline some strategies that may be used in parasite control programmes. Before they are accepted and recommended by the WAAVP, agroecological methods such as those listed above and described in detail herein should be validated based on scientific evidence of their efficacy for parasite control and should be tested for both host and environmental safety.     

Cervical, mandibular, and parotid lymph nodes of dogs naturally infected with Leishmania infantum: a histopathologic and immunohistochemistry study and its correlation with facial skin lesions

The parasite load in cervical, mandibular, and parotid lymph nodes and in the skin of the nose and the pinna from dogs infected with Leishmania infantum were investigated by histologic and immunohistochemical studies. Twenty-two infected dogs with and without signs of infection were examined to demonstrate correlation of signs with parasite load and the correlation of facial skin lesions with parasites in regional lymph nodes. Chronic inflammation of the skin was demonstrated in infected dogs that had no gross skin lesions, confirming that normal-appearing skin can harbor the parasite, likely playing a role in transmission. Dogs with facial skin lesions showed a higher parasite load in parotid lymph nodes than dogs without lesions of the facial skin, based on Leishman-Donovan unit analysis. Based on immunohistochemical analysis, parasite load in parotid and cervical nodes was correlated with that of skin of the nose and pinna, as was the parasite load in mandibular lymph nodes and skin of the external nose. We demonstrated a logical involvement of the lymphatic vessels and their specific anatomic draining sites.     

The helminths of ranch calves in the North-eastern Mountain Grassland of South Africa

The cumulative total helminth parasite burdens of ranch calves during their first seven months of life on the North-eastern Mountain Grassland of South Africa were determined during two consecutive years. Trichostrongylus axei was the most abundant nematode parasite followed by Cooperia spp. and Ostertagia ostertagi. Haemonchus spp. occurred in relatively low numbers and its development was significantly inhibited. The total helminth parasite burdens of the calves ranged from 681 to 7,269 with a mean of 4,405.     

Isolation and identification of a South China strain of Plasmodium inui from Macaca fascicularis

Southeast Asian macaques are hosts of a number of Plasmodium infections, some of which are transmittable to humans. During examination of blood films of five wild-caught long-tailed macaques Macaca fascicularis from South China, malaria infection was detected in one of the monkeys. In order to isolate this parasite for identification and characterization, we experimentally passed this parasite through both Assamese (M. assamensis) and rhesus (M. mulatta) monkeys by intravenous injection of infected blood. This parasite morphologically resembled Plasmodium inui, and had a typical 72 h quartan periodicity. This parasite was infective to Anopheles dirus mosquitoes, and salivary gland sporozoites appeared 13 days post feeding. Feeding by 20 infected An. dirus mosquitoes on another Assamese monkey produced infection with a prepatent period of 8 days. Molecular analysis of the small subunit rRNA genes and the mitochondrial genome confirmed this parasite as an isolate of P. inui. In spleen-intact macaques, the infection had a protracted duration with parasites being detected during the rearing of the infected monkeys for over two years. In summary, this study identified a P. inui isolate and successfully passed this parasite through Assamese monkeys by both intravenous inoculation and mosquito transmission.     

Polystoma umthakathi (Monogenea): establishment,mortality and reproduction of neotenic parasites in experimentally infected Natalobatrachus bonebergi tadpoles

The development of Polystoma umthakathi oncomiracidia were studied in experimentally infected Natalobatrachus bonebergi tadpoles to establish a normal reference of parasite performance in the natural host. The anteroventral body wall is transparent in these tadpoles and it was possible to follow the destiny of each parasite throughout its life span of neotenic development. Success of establishment was 27,9% and mean parasite intensity 2,1 at 48 h. After parasite larvae initially attached to the gills on the left side, they gradually migrated to the right side and mature parasites only occurred inside the right branchial chamber. Parasite mortality was high, prevalence had declined to 72,4% after 12 days and 48,3% after 20 days while mean parasite intensity had declined to 1,8 and 1,6 during the same period. Egg production was around 13 to 15 eggs/parasite/day for parasites in burdens of one and two but significantly lower (5,24) in the case of three-parasite burdens. Tadpoles harbouring two or more parasites became anaemic but recovered when most or all parasites were lost.     

临泽县肉牛传染病和寄生虫病普查报告

为掌握临泽县肉牛传染病和寄生虫流行情况,临泽县动物疫病预防控制中心对全全县肉牛传染病和寄生虫病的感染情况进行了摸底普查.通过详细普查,掌握了全县肉牛传染病和寄生虫病发生显著,为有效防控提供了重要理论依据.     

Theileria buffeli infection of a Michigan cow confirmed by small subunit ribosomal RNA gene analysis

Theileria buffeli, generally a benign parasite of cattle, has been reported in animals from Texas, Missouri and North Carolina. To date, there have been no reports of the parasite in cattle residing in northern portions of the US. An 8-year-old cow (Maine Anjou x Angus cross-bred) in Michigan presented with hemoglobinuria and a packed cell volume of 9. Blood films stained with Giemsa showed numerous intraerythrocytic parasites morphologically consistent with T. buffeli. The parasite was confirmed to be T. buffeli by SSU rRNA gene sequence analysis (SSU rRNA sequence, Type A). This represents the first report of this parasite in an animal in Michigan.     

A review of various parasites of rabbits

The increased interest in breeding and production of rabbits has initiated the present work, in which a review on the occurrence, significance and control of some important parasite infections of the domestic rabbit is given. In wild rabbits parasite diseases often affect single animals, whereas the intensive production of domestic rabbits typically has to deal with parasites as herd problems which in some cases may invalidate the economy of commercial rabbitries. The most important parasite diseases of the domestic rabbit comprise coccidiosis caused by Eimeria-spp. and ear mange caused by Psoroptes cuniculi.     

多雨年份牛羊主要寄生虫病综合防制措施

由于今年我省降雨量偏多,部分地区已发生洪涝灾害,极易引发牛羊主要寄生虫病的暴发流行。为防止寄生虫病暴发造成重大经济损失,本文详细阐述了阻断牛羊主要寄生虫病传播的关键因素,并针对历年危害严重的东毕吸虫、肝片吸虫、胃肠道线虫和疥癣等几种主要寄生虫病的流行病学特点提出了综合防制措施,以期降低牛、羊主要寄生虫病的发生,提高牛、羊养殖业的经济效益。     

The prevalence of proliferative kidney disease from the kidney and muscle of rainbow and brown trout in Aragón (Spain)

The prevalence and parasite density of PKX (the unknown myxosporean that causes proliferative kidney disease [PKD] of salmonids) were investigated in eight fishfarms in Aragon, Spain. Tissue sections stained with the biotynilated lectin GS-I revealed the presence of this protozoan in only one of the farms. In rainbow trout, the renal prevalence and parasite density peaked in July, but in brown trout the maximum renal prevalence and maximum renal parasite density were reached in May and in July, respectively. In rainbow trout, after the acute phase of the disease, the number of PKX decreases in the kidney but increases in the muscle. In this species of fish, the prevalence and parasite density are much higher in the muscles than in the kidney in October.     

Localization of the initial developmental stages of Loma salmonae in rainbow trout (Oncorhynchus mykiss)

The intracellular microsporidian parasite Loma salmonae affects salmonids of the genus Oncorhynchus and is a significant cause of economic losses in pen-reared Chinook salmon (O. tshawytscha) in British Columbia. Loma salmonae infection is easily recognized by the xenomas that form in the gills, but early stages of infection are difficult to detect in histologic sections. In situ hybridization (ISH), using an L. salmonae-specific digoxigenin-labeled single-stranded DNA probe, was used to detect the parasite during the early stages of infection. Loma salmonae was detected in the gut mucosal epithelium as early as 24 hours postexposure (PE), and it localized in the lamina propria of the intestine within 24 hours of infection. After the parasite was detected in the lamina propria, dividing merogonic stages in infected cells in the heart were detected by ISH as early as 2 days PE, providing the first evidence of parasitaemia and hematogenous distribution of this parasite in infected blood cells. The parasites inside the infected cells appeared to be undergoing merogony as they passed through the heart, indicating that proliferation may start at the site of infection, before the parasite arrives to the gills for their final developmental phase. This is the first time that L. salmonae passage through the intestinal wall and migration to the heart has been visualized; however, the identity of the cells harboring the parasite has yet to be determined.     

中国家畜家禽寄生虫与寄生虫病概况

为了提供我国家畜家禽寄生虫和寄生虫病总的概况，综合分析了相关资料，归纳出了我国畜禽寄生虫种类构成、分布范围、重要人畜共患寄生虫虫种、我国南北两方寄生虫种类的异同、多宿主寄生虫虫种和家畜家禽寄生虫病概况等几个方面的内容，并作了评述讨论。