Community perception and role in prevention of Guinea worm disease.
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Adult↗
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Results for “Parasite Control”
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[Pularyl in the control of common external parasites in domestic animals].
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Animals↗
Comparative study of the adhesion of sickle cells and malarial-parasitized red cells to cultured endothelium.
Increased adhesion of red cells to vascular endothelium has been implicated in the pathogenesis of falciparum malaria and sickle cell disease. We have carried out a comparative study of the adhesiveness of normal (AA), sickle trait (AS), and homozygous sickle (SS) red cells, with and without parasitization by Plasmodium falciparum, with an in vitro flow system. Adhesion of nonparasitized red cells to cultured human umbilical vein endothelial cells (either glutaraldehyde fixed or untreated) was strongly dependent on the wall shear stress. Many AA and SS cells adhered at low stress (0.02 Pa), but far fewer did so when the stress was increased to a physiologic level (0.1 Pa). Compared with AA cells, SS adhered in greater number (about threefold) and required greater stress (about two-fold) for their subsequent removal. In contrast, the efficiency of adhesion of AA cells parasitized by Plasmodium falciparum was essentially constant up to 0.1 Pa, where it was about 1000 times greater than the efficiency for nonparasitized cells. The stress required to remove parasitized cells was about 6 times that for controls. When parasites were grown in SS cells, fewer cells adhered than when parasites were grown in AA cells. However, the adhesion of malarial-parasitised AS cells was only slightly less than that of parasitized AA cells, so that modulation of adhesion is unlikely to underlie the protective effect of sickle gene in malaria. Adhesion of red cells to endothelium may promote blockage of microvessels, and the interaction of parasitized cells appears strong enough to directly cause ischemic complications in falciparum malaria.
Anemia, Sickle Cell↗
Inducible nitric oxide synthase is not required for long-term vaccine-based immunity against Toxoplasma gondii.
Induction of reactive nitrogen intermediates by IFN-gamma is presumed an important mechanism of host resistance against acute and chronic infection with Toxoplasma gondii. Although nitric oxide (NO) has been shown to be important in the control of parasite replication in vivo, the role of this molecule in vaccine-based immunity against T. gondii is unknown. Mice with a targeted disruption of inducible NO synthase (iNOS) were immunized with an avirulent temperature-sensitive strain of this parasite (ts-4). Both the parental C57BL/6 and the iNOS(-/-) mice survived infection with the ts-4 mutant. Oral challenge of the vaccinated mice with a lethal dose of cysts containing bradyzoites resulted in reduced parasite burden and increased survival compared with nonvaccinated control mice. Host immunity in the iNOS(-/-) mice, similar to that observed in the parental strain, appears dependent upon both IFN-gamma and CD8+ T cells. These findings suggest that although vaccine-based long-term immunity against T. gondii is dependent upon the induction of IFN-gamma, it does not rely upon the anti-microbial effect of NO.
Animals↗
Livestock parasite treatment--a call for greater interaction between research and industry sectors.
During the past 2 decades, treatment of livestock parasitism has changed from a situation of relative stability, particularly in the mid-late 1980s when the macrocyclic lactone compounds were introduced, to the situation in many countries now where control of sheep parasites is rapidly being lost. As serious as the situation may be, now is not a time to wring our hands in despair but a time to address some of the limitations and identify opportunities where a greater integration of the efforts of research and industrial bodies might be directed to maintaining parasite control in our livestock industry.
Animals↗
Improving the assessment of the economic impact of parasitic diseases and of their control in production animals.
This paper reviews the ways in which the economic impact of parasitic diseases of production animals have been evaluated. It then discusses the shortfalls of such studies, as well as the opportunities for improving the quality of economic impact assessments and their value to decision makers in the future. The paper first identifies the impacts that are specific to parasitic diseases. It then goes on to review the abundant literature on estimating the total costs of diseases. The authors argue that this approach severely limits the opportunity for economic assessments to aid decisions in disease control and research. The paper then reviews the literature on studies of avoidable costs, before discussing ways in which economic impact assessments can be enhanced. These issues include greater emphasis on incorporating the lost productivity potential caused by parasitic diseases, greater emphasis on valuing actual rather than intended control measures, and greater emphasis on quantifying the productivity effects at the societal level, particularly in the developing world.
Animals↗
Effects of the Norwegian winter environment on Giardia cysts and Cryptosporidium oocysts.
The structural integrity of Cryptosporidium oocysts and Giardia cysts in the Norwegian winter environment was investigated. During winter 2001/2002, Cryptosporidium oocysts and Giardia cysts were placed in the upper layers of soil in different matrices contained in chambers and exposed to the Norwegian climate. Morphological characteristics and inclusion/exclusion of vital dyes were monitored and compared to refrigerated controls. Reduction in parasite numbers was recorded for all parasites, geographical locations, and matrices. Shear forces generated during freeze-thaw cycles are postulated to have disintegrated the parasites exposed to the Norwegian winter and retrospective laboratory studies support this theory. Increased dye inclusion, possibly indicative of viability loss, was also noted. The refrigerated control parasites exhibited no decline in numbers, and alteration in dye inclusion characteristics for refrigerated parasites was slower. Cryptosporidium oocysts were apparently more robust than Giardia cysts; differences between isolates were also noted. These results suggest Cryptosporidium oocysts and Giardia cysts do not persist in the Norwegian terrestrial environment over winter, and when detected, will have been excreted since the previous winter. Differences in the morphological characteristics, matrix effects, and the possible relationship of the dye data to parasite survival are discussed in relation to further studies.
Animals↗
Polydnavirus infection inhibits synthesis of an insect plasma protein, arylphorin.
The wasp Campoletis sonorensis injects a segmented, double-stranded DNA polydnavirus (CsPDV) along with its egg during parasitization of Heliothis virescens larvae. After parasitization, CsPDV protects the wasp egg and larva by selectively disabling the host's cellular immune response. Other host physiological systems including growth and development are affected to the apparent benefit of the parasite. To begin the characterization of the biochemical effects and mode of action of CsPDV on host growth, the titre of a developmentally regulated insect storage protein, arylphorin, was studied. Parasitized or virus-infected insects had substantially less circulating arylphorin than control insects. Fat bodies from parasitized larvae also synthesized less arylphorin in vitro. However, Northern blots of total RNA from parasitized and non-parasitized, control insects showed that the arylphorin transcript level was unaffected by parasitization suggesting a biochemical block at the translational level. In vitro translation followed by immunoprecipitation of arylphorin indicated that the mRNA was present and translatable at equal levels in both parasitized and control insects. Injection of purified virus elicited the response observed in naturally parasitized larvae, demonstrating that the effect on arylphorin synthesis is mediated, either directly or indirectly, by polydnavirus gene product(s).
Animals↗
[Approaches to managing an epidemic process based on self-regulating mechanisms of the parasitic system].
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Humans↗
Integrated control of tropical animal parasitoses.
In the past, the control of parasites of domestic animals has relied mainly on the use of drugs and pesticides. Although these compounds are still of great importance in the prevention and treatment of parasitic diseases, the accent has shifted in recent years to a more flexible approach, integrating various other control measures. The main reasons for this change are: development of resistance of the parasites against the compounds used; reduced development of new compounds to overcome resistance (increasingly stringent regulations on toxicity and residues, resulting in very high research and development costs, insufficient return for industry because of short life-span of new products due to resistance, and limited and poor markets for compounds against parasites in developing countries); increasing cost of new products for the user; problems associated with toxicity, environmental pollution and residues in animal products. Integrated parasite management makes use, where possible, of biological and mechanical control methods, of acquired and innate host resistance, and of genetical, ecological, sanitary and regulatory procedures, although chemical control can seldom be entirely abolished. Cost-effectiveness and sustainability in all respects are of primary importance.
Animals↗
An immunogenic cathepsin F secreted by the parasitic stages of Teladorsagia circumcincta.
Teladorsagia circumcincta is a common, pathogenic abomasal nematode of sheep. In order to improve disease control in parasite isolates resistant to several anthelmintics, alternative methods must be sought. Sheep develop acquired immunity to T. circumcincta so vaccination is a valid option for control. For this reason, we are investigating parasite excretory/secretory products for molecules, which have potential to invoke protective immunity against T. circumcincta. Here, we describe experiments in which we identified a novel, immunogenic cathepsin F secreted by L4 T. circumcincta. This protease, initially identified by mass spectrometry analysis, is the most abundant molecule in excretory/secretory products released in vitro by T. circumcincta harvested at 5, 6 or 9 days p.i. and is a target of specific, local IgA responses in sheep which are immune to challenge infection. The full-length cDNA encoding this secreted protease was isolated. Sequence and phylogenetic analyses indicated that the protease (designated T. circumcincta cathepsin F-1, Tci-CF-1) belongs to the cathepsin F class and exhibits greatest identity (>60%) to expressed sequence tags present in the Ostertagia ostertagi and Haemonchus contortus expressed sequence tag databases. Tci-CF-1 also displays high identity to hypothetical proteins identified in the genomes of Caenorhabditis elegans and Caenorhabditis briggsae, both proteins having been described as cathepsin F enzymes. Specific inhibitor binding assay of larval excretory/secretory products confirmed the classification of this excretory/secretory component as a cathepsin F. Reverse transcription-PCR studies indicated that Tci-cf-1 is developmentally regulated and is particular to the host parasitic stages of T. circumcincta. The abundance, immunogenicity and temporal expression pattern of Tci-CF-1 make this a potential vaccine candidate for teladorsagiosis.
Amino Acid Sequence↗
Anthelmintic resistance in New Zealand: a perspective on recent findings and options for the future.
A recent national survey on anthelmintic resistance in cattle and sheep in New Zealand indicated that the magnitude of the problem has increased from very low levels only a few years ago to disturbingly high levels now. There is a particular problem with multiple resistance to all three action families of anthelmintic currently available in Ostertagia (= Teladorsagia) spp in sheep, and to both macrocyclic lactones (ML) and benzimidazoles in Cooperia spp in cattle. The prevalence and extent of resistance indicate that all cattle farmers and most sheep farmers should now be using a combination anthelmintic on most occasions just to achieve effective control of all parasites. Despite this, the presence of resistant parasites has generally not been appreciated by the majority of affected farmers, possibly because most have not formally tested to determine the resistance status of nematodes on their farms. Anthelmintics will remain the cornerstone of gastrointestinal nematode control in sheep and cattle for the foreseeable future but to ensure their continued effectiveness farmers need to be constantly aware of the need to maintain adequate reservoirs of unselected nematodes, i.e. worms in refugia, to minimise the expansion of the resistant population. High-risk practices in relation to selection of resistance need to be identified and avoided or at least their use limited. These include: treating adult animals where there is no identified need, moving newly treated animals onto 'clean' pasture, and failing to effectively quarantine-drench bought-in animals. None of these are new concepts but many have not been adopted or practised. In particular, sheep farmers should endeavour to avoid treating ewes pre-lambing with long-acting anthelmintics. Farmers needs to negotiate a balance between achieving good parasite control and the sustainability of their control options.
Animal Husbandry↗
Resistance to anticoccidial drugs in fowl.
Resistance has been encountered wherever drugs have been used extensively for the control of parasitic infections. The poultry industry is dependent upon drugs for the control of coccidiosis, a major disease of chickens caused by protozoan parasites of the genus Eimeria. In modern poultry production, drugs are used prophylactically for the prevention of coccidiosis by including them in the diet. This has inevitably led to the development of resistance. We have been fortunate in that new drugs have become available to replace those to which resistance has developed, but this situation is unlikely to continue. The problem of drug resistance, discussed here by David Chapman, has provided impetus for the development of new approaches (such as vaccination) for the control of coccidiosis.
Journal Article↗
[Parasitic diseases--a current problem area in intensive pasture management].
Current problems of intensive cattle pasture farming are considered with regard to three main aspects: parasite, habitat, biotop. Among the economically significant parasitic infections in the G.D.R. livestock of cattle, 15 must be considered to be productivity-reducing factors: trichostrongylidosis, dictyocaulosis, fasciolosis, babesiosis, pasture-coccidiosis (hypodermosis, stephanofilariosis--both eradicated!), mass-incidence of flies and black flies, tick infestation, thelaziosis, monieziosis, dicrocoeliosis, cysticercosis and hydatidosis. Incidence, scale of economic losses and present state of control of these parasitic infections are briefly discussed. This introductory report is closed with an outline on the "legal basis of parasite control in pasture farming".
Animals↗
Trypanosoma cruzi: early parasite proliferation and host resistance in inbred strains of mice.
The extent of parasite proliferation following completion of the first cycle of intracellular replication was significantly higher in CD-1 nu/nu mice and in irradiated mice compared to other, including highly susceptible, mouse strains. A control of parasite proliferation thus occurs in normal mice as early as the first cycle of intracellular replication. The thymus dependency and radiation sensitivity of the early control of proliferation of Trypanosoma cruzi suggest that an immune response to the parasite is involved in the early control of proliferation. The BXH-2 recombinant inbred strain demonstrated an inability to control early proliferation and, 4-5 days after infection, had parasitemias several times higher than those observed in susceptible mouse strains. The BXH-2 strain appears to lack the early control mechanism. When the extent of proliferation of T. cruzi at completion of the first cycle of intracellular replication was compared in inbred strains of mice having varying levels of resistance to the parasite, the extent of proliferation correlated with host resistance, being lowest in the most resistant strains (C57BL/6, SJL) and highest in the most susceptible strains (C3H, A). It is suggested that the mechanism(s) controlling early parasite proliferation may be of primary importance as the basis for host resistance.
Animals↗
Economic evaluation of three anthelmintic strategies for lamb flocks affected by benzimidazole-resistant nematodes.
OBJECTIVE: To compare the profitability of three anthelmintic strategies in growing lambs in flocks with nematodes resistant to benzimidazole anthelmintics. METHOD: A partial-budgeting analysis was carried out by means of a stochastic simulation model, which allows inputs to be described as distributions rather than as fixed values, and hence permits variation between farms to be considered in the analysis. RESULTS: The results show that control of nematode parasites by use of an effective anthelmintic provides the highest net returns, yielding a margin over ineffectively treated lambs of A$114 per 100 lambs on average. Suppressive treatment based on the administration of two controlled-release capsules and monthly with moxidectin resulted in an average loss of A$131 per 100 lambs in comparison with animals treated with an ineffective anthelmintic. Analysis of the results from capsule-treated lambs did not take into account the unmeasured benefits associated with less contamination of pastures. Sensitivity analysis using a stochastic model indicates that apart from the effect of treatment on weight gain variation in carcase price greatly influences the profitability of all the parasite control programs examined. CONCLUSION: The results suggest that it is economically important for farmers to adjust their strategy in the presence of anthelmintic resistance. But as a result of uncertainty in the factors influencing economic return, the expected economic benefit is likely to vary substantially.
Animals↗
Unexpected Listronotus bonariensis (Coleoptera: Curculionidae) mortality in the presence of parasitoids.
Field enclosure and laboratory cage experiments designed to measure the impact of the parasitoid Microctonus hyperodae Loan on the Argentine stem weevil, Listronotus bonariensis (Kuschel) have shown that under high parasitoid pressure, there is significant weevil mortality without obvious parasitism. Parasitoid-exposed, but unparasitized portions of caged populations died at rates significantly higher than both the parasitized weevils from the same population and the unexposed controls. Unexpectedly, parasitized weevils had the lowest mortality rates (prior to larval parasitoid emergence). It was of ecological significance that this mortality effect was detected under field conditions using several years of empirically-collected population dynamics data. Under both field and laboratory conditions this mortality was found to occur within shorter time intervals than that required for full parasitoid larval development; thus it could not be attributed to the mortality that occurs after the emergence of prepupal parasitoids. The mechanism for this mortality remains undetermined, although it could possibly be linked to pseudoparasitism.
Animals↗
Control of Echinococcus granulosus in Cyprus and comparison with other island models.
A control programme directed against Echinococcus granulosus was introduced into the Republic of Cyprus in 1971. In 1974, this was restricted to the areas controlled by the government of the island. The force used in the 'attack' phase included a major dog control programme. This and other measures led to the rapid 'disappearance' of the parasite and control was terminated in 1985. Subsequent studies during 1993-1996 revealed that the parasite was present in 82 (20%) villages in either dogs or food animals or both and control was re-introduced in the 'consolidation' phase with emphasis on the surveillance of E. granulosus in intermediate hosts, animal movement control and treatment of dogs in 'infected' villages. During these surveys, a major difficulty was found to be in determining whether transmission was autocthonus or introduced by animals from the areas not controlled by the government. Evidence was found to suggest the former was the most likely for the infected animals which had been born and reared far from the dividing line in the government-controlled area. A major contribution of this and other island programmes, such as those in Iceland, New Zealand, Tasmania (Australia) and the Falkland Islands, to an understanding of control planning has been the demonstration that it cannot readily be determined when eradication has been achieved and that once the costly 'attack' phase has been converted into the much more cost-effective 'consolidation' phase this must be maintained indefinitely in that phase if there is cross-border transmission as is likely to be the case in all Continental control programmes.
Animals↗