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At least 19 recordsLinked to original sources
PubMed2005

The development and overwintering survival of free-living larvae of Haemonchus contortus in Sweden.

Five complimentary studies were undertaken with the overall aim to examine the ability of free-living stages of Haemonchus contortus to over-winter and tolerate cold stress. Two studies deal with the development and long-term survival of eggs and infective larvae of two geographically different isolates (Kenya and Sweden). Eggs and larvae were monitored in climatic chambers at temperatures that fluctuated daily between -1 degrees C and 15 degrees C, or at constant temperatures of 5 degrees C and 15 degrees C. The development from egg to larvae was dependent on temperatures over 5 degrees C. The long time survival was favoured at lower temperatures. Furthermore, the overwintering capacity of the free-living stages of these isolates was estimated under Swedish field conditions. Two groups of lambs were experimentally infected with different isolates, and kept separated on previously ungrazed plots. In early May the following year, two parasite-naive tracer lambs were turned out on each of the plots to estimate the pick up of overwintered larvae. This experiment was replicated in central and southern Sweden. In addition, two experiments were performed in 2003 on pasture previously grazed by naturally infected sheep. One trial was on a pasture in southern Sweden grazed by a commercial flock, where extreme numbers of H. contortus were found towards the end of the grazing season 2002. The other study was on a pasture plot in central Sweden grazed by a hobby flock in 2002, where three of six lambs died due to haemonchiasis. Overwintered H. contortus was recorded on three of four experimental sites. Worm burdens were in all instances extremely low. No differences in development and survival were found between the isolates. Consequently, overwintering on pasture is of no practical significance in the transmission of H. contortus between grazing-seasons in Sweden.

Animals↗
PubMed1984

The relevance of in vitro anthelmintic screening tests employing the free-living stages of trichostrongylid nematodes.

The response of the free-living stages of Nippostrongylus brasiliensis, Nematospiroides dubius, Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia ostertagi to a wide variety of antiparasitic agents in vitro was investigated. All the major broad spectrum veterinary anthelmintics showed good activity against each of these worms with EC50 values varying from about 0.0002 mg/l for certain benzimidazoles and ivermectin to about 6.5 mg/l for febantel. Of 22 known narrow spectrum anthelmintics useful only against H. contortus and/or helminths other than trichostrongyles, only 10% showed good activity at concentrations equal to or less than 10.0 mg/l. Further, only one of 15 antiprotozoal agents showed good activity in these tests at the 10.0 mg/l level. The screening test employing free-living Nippostrongylus brasiliensis was selected for an extended trial where the evaluation of 1400 miscellaneous organic chemicals was undertaken. Approximately 10% of these showed activity at concentrations equal to or less than 10.0 mg/l. It is concluded that in vitro screening tests employing the free-living stages of these five genera of nematodes afford simple yet effective means for selecting relevant compounds for further evaluation as possible leads to new broad spectrum anthelmintics for use in ruminants. However, tests using the free-living stages of these worms, including H. contortus, are unsuitable for detecting narrow spectrum 'specifics', e.g., for the treatment of haemonchiasis.

Animals↗
PubMed1975

[Experimental investigations on the effectiveness of fenbendazole in parasitic helminths of the stomach, intestines and lung of cattle (author's transl)].

Helminth-free bulls were injected artificially with Ostertagia ostertagi (120 000 L3), Cooperia oncophora (240000 L3), Haemonchus spec. (1 000 L3) and/or Dictyocaulus viviparus (60 L3/kg) orally or intraruminally. The animals were treated with fenbendazole during the prepatent period or after having reached maturity. The effect of 5 mg fenbendazole/kg p.o. on 3-d, 10-d- and adult stages of Ostertagia ostertagi, Haemonchus spec. and Cooperia oncophora ranges between less than 94% and 100%. Particularly noticeable was the effect on 10-d-old Ostertagia ostertagi with less than 94%. 5 mg/kg fenbendazole orally removed nearly 100% of 6-d-, 13-d-, and adult stages of Dictyocaulus viviparus. Fenbendazole may be administered as a drench or as medicated feed. The safety of the compound permits the administration of excessively high doses without clinical signs.

Animals↗
PubMed1988

The influence of cryopreservation on a benzimidazole-resistant isolate of Haemonchus contortus conditioned for inhibited development.

Larvae of a fenbendazole (FBZ)-selected, benzimidazole-resistant strain of Haemonchus contortus were conditioned for inhibited development during 7 weeks at 15 degrees C. Sheep raised nearly worm-free were infected with nonfrozen larvae (L3). Larvae from the same batch were exsheathed and cryopreserved over liquid nitrogen for 1 year, and another group of sheep was infected with the same dose of these L3 larvae after thawing. Egg hatch assays for all sheep were done between 21 and 30 days post infection (p.i.). Fenbendazole susceptibility was tested by treating 50% of each group of sheep on day 30 p.i. Worm counts of all sheep were done on day 38 p.i. The exsheathment time of the designated frozen L3 larvae at 15 degrees C exceeded the usual time span at room temperature. Of the frozen L3 larvae, 60% was motile after thawing. The mean LC50 values (micrograms tiabendazole/ml) and the mean percentage of efficacy after FBZ treatment against total worm burden, adults and early L4 larvae of nonfrozen and frozen H. contortus were not significantly different. The mean percentages of take (infectivity) for nonfrozen and frozen doses were 35.3% and 5.9%, respectively (P less than 0.001). In nontreated sheep, the mean percentages of inhibition for nonfrozen and frozen doses were 91.9%, and 54.2%, respectively (P less than 0.01). The exsheathment time seems to be temperature-dependent. The induction of inhibited development of L3 larvae during 7 weeks was as effective as during 5 weeks at 15 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1981

Resistance to reinfection with Haemonchus contortus in lactating and barren ewes following a single infection with larvae conditioned for inhibited development.

Ewes were infected in November 1977 with third stage larvae of Haemonchus contortus which were conditioned for inhibited development at +15 degrees C for 35 days. Worm counts in December and May and weekly faecal egg counts revealed that the high burdens of inhibited larvae present in December virtually disappeared during winter, while the faecal egg counts remained low. This happened whether the ewes were pregnant or not. Indications of a slight postpartum rise in faecal egg counts, however, were observed in May in three out of five lactating ewes. After experimental reinfection of seven barren ewes and five lactating ewes in May 1978 a considerable resistance to H. contortus was observed in the barren ewes, while the resistance to reinfection was negligible in the lactating ewes.

Animals↗
PubMed1981

Infection with gastrointestinal helminths. Effect of lactation and maternal transfer of immunity.

Lactation in sheep and mice was associated with a marked increase in susceptibility to newly acquired infection with Haemonchus contortus and Nematospiroides dubius, respectively. In sheep this increased susceptibility to infection with H. contortus occurred in late pregnancy and during lactation and was seen when the ewes were infected with both a single large dose of infective larvae and a "trickle" infection of 200 and 400 infective larvae of H. contortus given weekly for 14 weeks. Nonlactating ewes whose lactation had been terminated were able to reject the parasites which had been acquired in late pregnancy. A relaxation in the protective immune response was evident in immunized mice infected during lactation with N. dubius. However, despite this periparturient relaxation of immunity mice were capable of inducing a marked passive transfer of immunity to their offspring. Thus, neonatal mice born of mothers one or two months after the end of the immunizing schedule were protected against infection with N. dubius at 12 or 20 days of age.

Animals↗
PubMed1990

Faecal water content and egg survival of goat gastro-intestinal strongyles under dry tropical conditions in Guadeloupe.

Faeces from naturally infected goats were deposited on a natural grassland during the dry season in Guadeloupe (French West Indies) at different times throughout the day. The grass was either 7 or 20-30 cm tall. After a period of between several hours and 7 days, the number of viable strongyle eggs and the faecal water content were measured. Faecal temperature was recorded continuously. Faecal temperature was greater than 40 degrees-45 degrees C at midday and dehydration was rapid between 8 a.m. and 2 p.m. Egg mortality was greater on short than on tall grass and higher in morning than in evening deposits. Minimal faecal water content during the first 36 h explained the 74%, 55% and 38% mortality rate for eggs of Oesophagostomum columbianum (OC), Haemonchus contortus (HC) and Trichostrongylus colubriformis (TC), respectively. In all, 5%-22% of the eggs of the latter species remained viable in a state of anhydrobiosis after 7 days on the ground. A delay of only 2 days between goat departure and irrigation would be sufficient to ensure that greater than 95% of O. columbianum and H. contortus eggs and 70% of T. colubriformis eggs are destroyed.

Animals↗
PubMed1984

Immunological unresponsiveness of lambs to infection with Haemonchus contortus. Modulation of responsiveness by exposure to soluble larval antigen.

The in vitro transformation of lymphocytes in the presence of antigen was used to assay the response of lambs to antigens of Haemonchus contortus. Neither uninfected lambs nor lambs infected with H. contortus up to 9 weeks of age developed in vitro lymphocyte responsiveness to antigen. A slight and transient increase in reactivity was demonstrable in some of the infected lambs when these were reinfected with H. contortus at 26 weeks of age. This lack of responsiveness could be modulated through the exposure of lambs, early in neonatal life, to multiple parenteral injections of soluble third stage larval antigen of H. contortus. Thus, antigen specific responses were apparent in the lymphocytes from 21-week-old lambs if these were injected with antigen when 2 to 17 weeks of age. In particular, marked antigen specific reactivity developed in 19- or 24-week-old lambs if such lambs were injected with antigen on five occasions over the first 6 weeks of life and subsequently infected with H. contortus when 7 weeks old. This responsiveness was enhanced when the lambs were reinfected with H. contortus at 26 weeks of age.

Animals↗
PubMed1984

Immunological unresponsiveness of lambs to infection with Haemonchus contortus. Effect of infection in the ewe on the subsequent responsiveness of lambs.

Specific antigen-induced lymphocyte transformation in vitro and haemagglutinating antibody responses were absent from lambs infected with Haemonchus contortus. However, when lambs were injected with soluble third stage larval antigen of H. contortus, given on five occasions during the first 6 weeks of life, specific antigen-induced lymphocyte transformation and haemagglutinating antibodies were induced to the antigen. In particular, a periparturient increased susceptibility to infection and the resultant presence of heavy infections with H. contortus in ewes appeared to prime their lambs to respond and marked lymphocyte transformation was observed in antigen injected lambs born of heavily infected ewes. The enhancement of this response was associated with the colostral transfer of as yet unidentified factors. The superimposition of an infection with H. contortus in lambs which had been stimulated to respond to antigen, suppressed the in vitro responsiveness of their lymphocytes. Although individual variation was apparent, a direct correlation between the presence of in vitro antigen-induced lymphocyte transformation to third stage larval antigen and susceptibility to infection occurred.

Animals↗
PubMed1992

Helminths of sheep and goats in desert areas of south-west Mauritania (Trarza).

Faecal samples were obtained from sheep and goats before, during and after the rainy season at three locations in south-west Mauritania. Several animals were also necropsied at the same time. Haemonchus contortus was the most prevalent worm. Infection by digestive-tract strongyles and Strongyloides papillosus was always very light (prevalence less than 20%). Sheep were more heavily infected than goats but animals under 1 year of age were not infected by digestive-tract strongyles. It is likely that young small ruminants became infected during the rainy season and that the parasites so acquired are inhibited in their development and/or survive nearly one year as adults.

Animals↗
PubMed1993

Systemic responses to challenge infection with Haemonchus contortus in immune Merino sheep.

Some systemic responses to single-dose infection with 10,000 Haemonchus contortus infective larvae were examined in sheep already shown to have protective immunity against the parasite. The major haematological finding was a neutrophil leukocytosis that occurred after the infections became patent but not during the pre-patent period. There was no definitive eosinophilia and no discernible change in the erythrocyte parameters. Systemic hyperthermia was not conclusively evident during the pre-patent period. Enzyme-linked-immunosorbent assays (ELISA) were used to measure the secondary anti-helminth antibody response in serum during the pre-patent period when the establishment of patent infection is resisted. These ELISAs employed preparations from adult worms to represent the parasitic stages of the worm, preparations from infective larvae to represent the pre-parasitic stages of the worm, and exsheathing fluid, which is the soluble material obtained when H. contortus larvae undergo ecdysis and transform from the pre-parasitic to the parasitic phase. Antibody responses to the three preparations differed qualitatively, indicating the presence of three different but perhaps overlapping sets of antigens. The three peaks in antibody against exsheathing fluid may reflect the pulses of antigen delivered to sheep as the parasite undergoes its three moults within the host.

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