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PubMed1994

Parasite control in transhumant situations.

Transhumance is defined as 'seasonal moving of livestock to regions of different climate'. It is an integral part of livestock production in many parts of the world and takes several forms including moving of livestock from lowland to mountainous pastures or from dry to humid areas. The impact of transhumance on parasite populations of livestock and on parasite control is described, mainly using examples from Europe. The epidemiology of trichostrongylidosis of cattle, mainly caused by Ostertagia ostertagi and Cooperia oncophora, is characterised by prolonged survival of overwintered infective larvae until the end of June. Cattle moved to such contaminated pastures in a transhumant grazing system are exposed to these larvae and may be protected, during the second half of the grazing season until autumn, by a late application (June/July) of an intraruminal drug-release device. Community pastures used in a transhumant system with mixed grazing of young cattle originating from various farms may enhance transmission of dictyocaulosis. Therefore, specific prophylactic measures are required. Hill sheep nematode populations may differ from those in lowland sheep in that Haemonchus contortus generally plays a minor role in hill sheep in which Ostertagia circumcincta and Nematodirus spp. predominate. Infections with Fasciola hepatica and Dicrocoelium dendriticum can be acquired on mountainous pastures by cattle, sheep and other livestock grazing in a transhumant system as intermediate hosts of these parasites may find suitable habitats in these regions. There is evidence that in the prealpine and alpine area both parasites are mainly transmitted in two-season cycles. Further examples for the impact of transhumance on parasite-host inter-relationships include cysticercosis in cattle, echinococcosis, psoroptic manage in sheep, tick-borne fever of cattle, and hypodermosis in cattle. These are described and discussed.

Animal Husbandry↗
PubMed1997

Seasonal variation of Opisthorchis viverrini infection in cyprinoid fish in north-east Thailand: implications for parasite control and food safety.

Reported is the seasonal pattern of Opisthorchis viverrini metacercariae in cyprinoid fish in north-east Thailand. Samples of fish were collected in 1991-92 at monthly intervals from two areas-Khon Kaen Province, where the opisthorchiasis transmission rate was high, and Mahasarakham Province, where the rate was low. Metacercarial loads in both study areas had similar seasonal patterns. High burdens occurred in the late rainy season and winter (July to January) with low burdens during the summer (March to June). The average burden for Puntius leiacanthus in Khon Kaen was 1.68 metacercariae per fish (127.43 per kg), higher than for all species of cyprinoid fish from the low transmission area. The intensities of infection among P. leiacanthus and Cyclocheilichthys armatus collected in Mahasarakham were comparable, but lower than the intensity of Hampala dispar (0.75 metacercariae per fish) concurrently sampled from the same area (P < 0.05). There was no significant difference in metacercarial load per kg between fish species from Mahasarakham. The results indicate that seasonal variation in metacercariae was a common phenomenon in areas with both high and low endemicity of infection. Also, the metacerarial load in fish was positively associated with infection levels among humans.

Animals↗
PubMed1999

Production-based control of parasitic nematodes of cattle.

Nematode parasite control in cattle is the goal of the parasitologist and the cattle producer. However, the language used to express the impact of that control has been a source of confusion between the two groups. Veterinary parasitologists speak in terms of reduction in worms or worm eggs, and cattle producers in terms of weight gain, milk production or calving rate. During the development of doramectin for cattle in temperate climates worldwide, the point came when we began to look for a different set of parameters to guide trial design and to communicate the results. In this paper, a series of published papers resulting from the yearling portion of this development programme are reviewed from the viewpoint of weight gain in relation to forage/feed availability. A pattern emerged that indicated that yearling cattle, when parasite control was effective (as indicated by egg counts) and forage was sufficient (as indicated by weather patterns), gained from 0.75 to 0.95 kg day(-1) in trials from the USA, Europe and Argentina. When parasite control or forage supply or both were insufficient, these rates of weight gain were significantly reduced. If more attention is spent on forage availability and weight-gain parameters when parasite-control programmes are designed, then researchers might communicate more meaningful information to producers on the value of parasite control.

Animal Husbandry↗
PubMed1998

The immune response to Leishmania: mechanisms of parasite control and evasion.

After transmission of Leishmania parasites by sandflies, disease manifestation of the infection requires mechanisms which allow the parasites to replicate in the mammalian host and to resist, at least initially, its innate and acquired antileishmanial defence. Likewise, lifelong persistence of Leishmania parasites, as it occurs even in cases of clinical healing of the infection, points to the existence of strategies which enable the parasite to partially circumvent the protective adaptive immune response of the host. In this review we will discuss the mechanisms which can be invoked to contribute to the initial, as well as long-term, survival of Leishmania parasites in the host organism. These include the passive protection of the parasite against antileishmanial products and the retreat into "safe target cells", the active suppression of the synthesis of reactive oxygen or nitrogen intermediates, the modulation of the host cytokine response, the inhibition of antigen-presentation and T cell-stimulation, and the induction and expansion of counterprotective T helper cells. It is probable that none of these mechanisms alone is sufficient to guarantee the survival of Leishmania, but together they might provide the safe environment which protects the parasite from elimination.

Animals↗
PubMedDate not supplied

Nutritional enhancement of parasite control in small ruminant production systems in developing countries of South-East Asia and the Pacific.

Nutritional insufficiency and gastrointestinal nematode parasitism are major constraints to small ruminant production in south-east Asia and the Pacific Islands. Research on the effects of low cost supplements which supply nitrogen and essential minerals on the ability of small ruminants to resist infection is summarised. In controlled pen studies in young Merino sheep offered a low quality roughage diet of oaten chaff and essential minerals, supplementation with urea reduced the effects of parasitic infection by increasing weight gain and wool production and reducing faecal egg output and parasite burden. In Fiji, field studies have shown that supplementation with urea-molasses blocks can result in increased live-weights of lambs at weaning, increased reproduction rates in maiden ewes and reduction in faecal egg output in grazing sheep. Additional benefits were derived from the inclusion of anthelmintic in the blocks in similar groups of sheep particularly during periods of greater susceptibility to parasites. Pen studies with young goats have shown that urea supplements alone gave no production benefits, but when accompanied by 100 g/d of cotton seed meal beneficial responses were observed. It is expected that parasite control in the small ruminant production systems of developing countries in south-east Asia and the Pacific Islands will benefit from the introduction of low cost nitrogen supplements along with anthelmintic therapy delivered strategically by molasses blocks.

Animal Nutritional Physiological Phenomena↗
PubMedDate not supplied

Intestinal parasite control in an institution for developmentally handicapped adults.

An intestinal parasite eradication program consisting of antiparasitic drug treatment and hygiene measures was conducted at an Ontario residential facility for developmentally handicapped adults from October, 1989 to August, 1990. The prevalence of intestinal parasites in general was initially over 90% while that of pathogenic species was 59%. Six months later, overall prevalence and that of pathogenic species were reduced to 32.9% and 11%. In one subgroup, the reduction in the prevalence of pathogenic parasites was sustained for at least one year. However, the prevalence of non-pathogenic species was similar to the baseline level. Simultaneous treatment and application of hygiene measures appeared to be effective in reducing pathogenic intestinal parasites.

Adult↗
PubMed2001

Human macrophage tumor necrosis factor (TNF)-alpha production induced by Trypanosoma brucei gambiense and the role of TNF-alpha in parasite control.

Trypanosoma brucei gambiense, a causative agent of sleeping sickness, induced a dose-dependent production of tumor necrosis factor (TNF)-alpha by human macrophages in vitro. TNF-alpha was also induced in the Mono Mac 6 cell line, which indicates a direct effect of parasite components on macrophages. Parasite-soluble factors were also potent inducers of TNF-alpha. The addition of anti-TNF-alpha to cocultures of macrophages and parasites increased the number of trypanosomes and their life span, whereas irrelevant antibodies had no effect. TNF-alpha may have a direct role (i.e., direct trypanolytic activity) and/or an indirect one, such as TNF-alpha-mediated induction of cytotoxic molecules. A direct dose-dependent lytic effect of TNF-alpha on purified parasites was observed. This lytic effect was inhibited by anti-TNF-alpha. These data suggest that, as in experimental trypanosomiasis, TNF-alpha is involved in parasite growth control in human African trypanosomiasis.

Animals↗
PubMedDate not supplied

Controlling internal parasites in grazing ruminants without recourse to anthelmintics: approaches, experiences and prospects.

Interest in ways of raising stock without using anthelmintics has been stimulated by the desire for intensive grazing systems to adopt more sustainable methods of internal parasite control and by potential premiums for "organic" produce. This requires grazing management systems which are practicable and achieve levels of parasite control sufficient to meet realistic production objectives. This paper will summarise 3 years experience of lamb and cattle production without a recourse to anthelmintics on 2 production systems: a mixed cropping, lamb finishing, and cattle rearing unit and an all grass, mixed-stock, hill country unit in which all non-replacement lambs are sold at weaning. On both units parasite control was almost entirely dependent on integrated grazing management of sheep and cattle and strict systems of grazing management had to be rigidly applied. Acceptable productivity could be more readily achieved in sheep than cattle. Rams selected for resistance to nematodes were also used in both sheep flocks. Their influence on lamb production was equivocal. There is a need for more information on factors influencing parasite epidemiology and for consideration of strategies other than alternate grazing. The impact of pasture species on parasite epidemiology needs to be clarified. Current research indicates substantial differences between grasses in terms of parasite burdens acquired and production losses suffered by lambs grazing them. Grazing management may need to vary with pasture species. Also, specialty forage crops, particularly those containing condensed tannins (i.e. Hedysarum coronarium, Lotus pedunculatus and Lotus corniculatus) hold special promise as a means of countering parasite-induced production losses and dagginess. Using biological control of free-living larval stages and vaccination, may in the long term, also prove useful. Developing effective and acceptable systems for raising stock without using anthelmintics presents a considerable challenge, to parasitologists, as well as to plant breeders, agronomists, and farming systems researchers.

Animal Husbandry↗
PubMed1990

Overberg Research Projects. VIII. The productivity of Merino ewes subjected to different internal parasite control programmes in the winter rainfall region of South Africa.

Suckling Merino lambs on lucerne pasture, demonstrated no appreciable mass gain when compared with untreated controls, despite regular treatment with anthelmintics. This was ascribed to severe parasitic challenge. After weaning and transfer to wheat stubble fields with no parasitic challenge, however, the live mass of the untreated lambs, still harbouring a residual burden of nematodes, was depressed. Control sheep produced 1.2 kg less wool than regularly-treated sheep, but produced finer wool which had a higher market value. Regularly-treated ewes (F1) produced 12.1% more lambs, but their mean live mass was 2.6 kg lower than that of ewes treated less frequently. The overall financial benefit was in favour of the group which received fewer anthelmintic treatments and was due mainly to the higher market value of the finer wool produced by these apparently stressed animals.

Animals↗
PubMed1997

The economics of parasite control: obstacles to creating reliable models.

Models of the population biology and transmission of helminth parasites of domestic ruminants do not generally include any explicit reference to production because that would require the identification of a systematic relationship between parasitism and production loss. This is difficult because (1) the relationship between parasitism and production loss (in so far as we can identify one) is non-linear, (2) it is by no means clear which index of parasitism we should use in defining the nature of the relationship and (3) time delays in the system and the multicausal nature of production losses make it difficult to tease out those components of the loss that are attributable to parasitism.

Animals↗
PubMed1996

Mice lacking the TNF receptor p55 fail to resolve lesions caused by infection with Leishmania major, but control parasite replication.

TNF is involved in host resistance to several pathogens. Recently it was found that mice lacking the p55 receptor for TNF (TNFRp55 -/-) do not control growth of the intracellular bacteria, Listeria monocytogenes and Mycobacterium tuberculosis. Here we report that the course of infection in TNFRp55 -/- mice with another intracellular pathogen, the protozoan parasite Leishmania major, is also quite different from normal mice. TNFRp55 -/- mice developed larger lesions than control mice and failed to resolve these lesions. However, they were able to eliminate parasites within the lesions. Histologic analysis indicated that at late stages lesions from TNFRp55 -/- mice appeared similar to lesions associated with cutaneous graft-vs-host disease. Both TNFRp55 -/- and control mice developed a normal Th1-type response during infection. We also found that IFN-gamma-activated macrophages from TNFRp55 -/- mice produced nitric oxide and killed L. major in vitro, which correlated with the ability of TNFRp55 -/- mice to eliminate the parasites in vivo. The production of nitric oxide by macrophages from TNFRp55 -/- mice required the presence of the parasites, however, since in their absence TNF could only synergize with IFN-gamma for nitric oxide production when added to normal, but not TNFRp55 -/-, macrophages. These results indicate that neither macrophage microbicidal activity nor nitric oxide production is absolutely dependent on the p55 receptor for TNF. Furthermore, they uncover a previously undefined role for TNFRp55 in resolution of parasite-induced inflammatory lesions.

Animals↗
PubMed1991

Don't kill the parasite: control the disease.

It is clear from both laboratory and clinical studies that the blood-stage malaria parasite does not itself directly cause most of the serious complications of the disease, with the possible exception of anaemia. For example, T cell- deprived mice with lethal infections survive longer and mice can be protected against early death by vaccines that appear not to affect parasitaemia. In certain cases antibodies to TNF have the same effect. Clinically it has been known for over 50 years that children in endemic areas develop immunity to the serious toxic aspects of malaria several years before their parasitaemias start to fall. Recent work on the induction of cytokines such as tumour necrosis factor (TNF) by exoantigens of the blood-stage parasite and on the role of cytokines in this and other toxic diseases suggests that an appropriate vaccine might induce antibody that blocks the effect of the exoantigens, thus conferring on young children the anti-disease immunity that normally takes years to appear. Such vaccines might be less hampered by the antigenic variation that makes anti-parasite immunity slow to develop. Characterisation of the molecules involved is a high priority.

Animals↗