Parasite control methods used by horse owners: factors predisposing to the development of anthelmintic resistance in nematodes.

One hundred and fifty horse owners, primarily private owners and riding schools, replied to a questionnaire concerning the practices they used to control parasites. Twenty-seven had experienced a parasite problem. Faecal samples from 188 horses selected at random showed that worm control practices were generally successful; however, many owners were not following recommendations for slowing the development of resistant parasites. In 1996, 86 per cent of the owners were using either three or two classes of anthelmintic a year, and they used a median of six doses with a range from one to 11. Approximately half the owners, more commonly owners of up to five horses, picked up their horses' faeces at least once a week, but these owners also used more doses of anthelmintic a year than owners who did not pick up faeces. One-third of the owners manually removed Gasterophilus species eggs from the horses' hairs, but 94 per cent of them also used ivermectin. Many owners treated specifically for Anoplocephala species, cyathostome larvae and Gasterophilus species, and these owners were the most likely to use three classes of anthelmintic a year. One-hundred-and-seven owners replied to a second questionnaire asking for information about the factors that influenced their anthelmintic control practices. Many owners, particularly private owners, were not influenced by the cost of the anthelmintic. For the timing and frequency of treatment, and the choice of drug, owners were most influenced by advertisements, magazine articles and veterinary surgeons. In two magazines aimed at horse owners, the brands of drugs most frequently advertised were the brands most commonly used by the owners, and articles in the magazines recommended the use of three classes of drug per year. These results are discussed in relation to their influence on the development of anthelmintic-resistant nematodes.

Hypobiosis in the ostertagids of red deer and the efficacy of ivermectin and fenbendazole against them.

An abattoir survey was carried out during the 1991 to 1992 slaughter season to examine the structure of the ostertagid populations in red deer. Most of the animals were 15- to 22-month-old stags, but there were also hinds on two occasions and calves on one. Ostertagids of mixed species were present in all of the animals, and 43 of 120 (35.8 per cent) stags and 10 of 17 (58.8 per cent) hinds, but no calves, also carried small numbers of Trichostrongylus axei. Most animals carried adult and developing ostertagids and after September they all contained hypobiotic larvae (EL4). EL4 were present in three of nine stags in September and they increased in number through the autumn. In stags killed between November and February the group mean numbers of EL4 represented 62 to 94 per cent of the total burdens present, compared with 37 and 55 per cent on April 1 and 7, respectively. In the hinds, the number and the structure of the ostertagid populations was similar to that in the stags. Of 14 calves killed on October 9, only two contained a few EL4. Subcutaneous ivermectin at 400 micrograms/kg removed 100 per cent of the adult and developing worms, but although it also removed 95 per cent of EL4, some larvae remained in every treated animal. The efficacy of fenbendazole at 15 mg/kg given over five days was 75 per cent against EL4 and although the long interval after treatment obscured the result, it was probably much higher against later stages.

Observations on the epidemiology of gastrointestinal nematodes of farmed red deer in central southern England.

The epidemiology of the gastrointestinal nematodes of farmed red deer was followed over three years on two farms in north Hertfordshire. Worm counts on 10 animals (four months to 10 years old) between November and March showed that mixed ostertagid infections were dominant with very small numbers of Trichostrongylus axei, Cooperia punctata and Oesophagostomum species also present in some individuals. An increase in the faecal nematode egg count of the hinds in summer was followed by an increase in pasture larval counts which peaked between September and November. Many calves had patent infections by the first week of September. Although the pasture larval counts were very low at the beginning of the 1989 season, anthelmintic treatment at turnout in May had little influence either on the summer increase in faecal egg count or on the subsequent pasture larval counts, and repeated treatments had only a moderate influence. However, the movement of one of the calving groups to an aftermath in mid-July did reduce the infection to which their calves were exposed. Nevertheless, none of the calves showed significant effects of parasitism when they were removed from the pasture and treated at weaning in early September.

Further studies on the development and survival at low temperatures of the free living stages of Trichostrongylus tenuis.

To assess the ability of the free living stages of Trichostrongylus tenuis, a pathogen of red grouse, to survive the winter in significant numbers, the temperatures prevailing during the autumn, winter and spring of 1991-92 on the North Yorkshire moors were simulated in an incubator into which replicate cultures of T tenuis eggs were placed at intervals. September and early October eggs developed into larvae which survived over winter and were infective the following spring. Few November to February eggs survived to become larvae but early March eggs were reasonably successful. Continuous temperatures of -15 degrees C were lethal to infective larvae within 12 days, but significant numbers of larvae survived temperatures of -10 degrees C or higher for up to three weeks and remained infective.

Development and survival at low temperature of the free living stages of Trichostrongylus tenuis.

To test the ability of Trichostrongylus tenuis eggs to survive and develop at temperatures similar to those they might experience in late winter on a grouse moor, they were exposed in replicate faecal cultures to various low temperature regimes in the laboratory. Yields in experimental cultures were compared with those in control cultures incubated at 21 to 23 degrees C. Eggs in caecal faeces were also placed outside on grass plots at intervals through the winter. In addition to this, infective larvae (L3), also in replicate faecal cultures, were subjected to similar low temperature regimes. The results confirm that few, if any, eggs deposited from November to January are likely to develop successfully, but increasing numbers of those deposited from February onwards are likely to do so and to give rise to L3 in May. L3 were shown to have the potential to survive the winter in significant numbers. It is suggested that infection newly acquired during the winter may represent a very significant part of the worm population found in adult birds in early summer.

Hypobiosis of Trichostrongylus tenuis in experimentally infected grey partridges.

Storage of infective larvae (L3) of Trichostrongylus tenuis at +4 degrees C for six weeks before being given as single infections to grey partridges (Perdix perdix) did not increase the proportion of worms subsequently found to be hypobiotic. However, after repeated infections, hypobiotic larvae were numerous. Three infections given over three weeks resulted not only in the presence of many hypobiotic larvae, but also in the coincident loss of most adult worms. This indication of the role of immunity in the production of hypobiosis in grey partridges suggests that this species is not a good model for trichostrongylosis in red grouse (Lagopus lagopus scoticus).

Interaction of Ostertagia and Nematodirus species in sheep and the potential of serum fructosamine determination in monitoring gastrointestinal parasitism.

Serum fructosamine concentration falls with an increase in plasma protein turnover. Since this increase is a feature of gastrointestinal parasite infection at all sites, a falling serum fructosamine level may be of general application in the interpretation of parasite-related events. The circulating fructosamine level was investigated in the lamb as an indicator of protein-losing gastroenteropathy associated with two parasites at different sites, Ostertagia circumcincta (abomasum) and Nematodirus spathiger (small intestine). Infection with 10,000 N spathiger infective larvae daily for seven weeks produced only slight clinical signs, and only a small change in serum fructosamine levels. 2500 O circumcincta L3 daily gave no clinical signs in most animals, but serum fructosamine was more strongly affected in this group. Concurrent infection with both organisms caused some degree of diarrhoea in all lambs, and a sustained fall in serum fructosamine, more accentuated than that observed in either of the single infection groups, supporting the value of serum fructosamine determination in monitoring gastrointestinal parasitism.

Type II ostertagiosis in farmed red deer.

A mild form of type II ostertagiosis was recorded in a group of 12, 22-month-old red deer stags, slaughtered in an abattoir in April 1989. The animals appeared clinically normal but they were light and in rather poor condition. Mixed ostertagid infections were present in very variable numbers. In the seven most heavily infected animals, 70 per cent of the worms were in the early fourth stage and assumed to be hypobiotic. In some animals the worms were maturing and in these there were lesions similar to those associated with bovine ostertagiosis.

Biological control of ruminant trichostrongylids by Arthrobotrys oligospora, a predacious fungus.

Sheep and cattle are prey to many parasitic worms, including the trichostrongylid nematodes. Conventional control involves the use of anthelmintic drugs, but in this article Hadji Ahmad Hashmi and Roger Connan discuss the possible biological control of these nematodes by means of a 'living lasso', the predacious fungus Arthrobotrys.

Seasonal allergic dermatitis in sheep.

The lesions of a seasonal dermatitis in sheep occurred mainly on the ventral surface of the animals, but in other respects they resembled those of 'sweet itch' in horses. They were primarily an immediate hypersensitivity response and the circumstantial evidence indicated that they were due to the bites of Culicoides species, possibly C obsoletus.

The migration of Strongyloides papillosus in rabbits following infection by the oral and subcutaneous routes.

For the first 66 hours after the subcutaneous injection of rabbits with the infective larvae of Strongyloides papillosus, larvae spread gradually from the injection site to other parts of the body musculature. Their number and distribution suggests that they do so by the direct penetration of the tissues as the majority remain close to the site of injection. By 90 hours, however, the appearance of larvae in the lungs, trachea and oesophagus suggests that migration is taking place within the circulation. Although some 90% of the total worms recovered were already established in the intestine by 8 days post-infection, significant numbers of larvae continued to be present in the muscles at 14 and 21 days. Even by 35 days the muscles of 1 of 2 rabbits still contained 43 larvae. This prolonged presence of Strongyloides papillosus in the muscle of rabbits uniformly at the early fourth stage may be analogous to the arrested development of other nematodes. While there is evidence to suggest that immunity is a major factor in the aetiology of arrested development in Strongyloides ransomi, it is an unimportant factor in the case of Strongyloides papillosus in rabbits.

Water consumption in growing pheasants.

Daily water consumption in pheasants varied from 240 ml per kg at three weeks of age to 80 ml per kg at 12 weeks. Variations in temperatures within the range 10 to 25 degrees C exerted little influence on water intake. The amount of water consumed increased at a given age as dietary protein level increased. Only a small increase (14 per cent) in water intake accompanied a more than doubled increase in the normal dietary salt level. Total daily water intakes were similar in pheasants fed three times a day and in those fed ad libitum but their patterns of consumption throughout the day were widely different.

Efficacy of tetramisole and dichloroxylenol against Syngamus trachea in pheasants and turkeys.

Two water soluble products currently recommended for the treatment of syngamiasis were tested in pheasants and turkeys. Dichloroxylenol (Rotgape; Adams & Moulson), was found to have no efficacy. Although tetramisole (Game Bird Wormer; ICI) administered in drinking water had a moderate efficacy against three- and four-day-old larvae (47 to 71 per cent), its level of efficacy against infections associated with disease, those of seven days and older, was poor (5 to 29 per cent). It is concluded that neither product is likely to be of value in field outbreaks of syngamiasis.

Ascariasis: the development of eggs of Ascaris suum under the conditions prevailing in a pig house.

Eggs were collected from gravid female Ascaris suum in the abattoir. Cultures were prepared with the eggs in 2 to 3 mm depth of 1 per cent sulphuric acid or on the surface of 2% aqueous agar. They were allowed to develop in a piggery, fresh cultures being started at intervals from January to September. Eggs on the surface of agar developed failry uniformly and a high proportion eventually reached L2. In contrast those under 1% sulphuric acid were less uniform, slower in development and generally less successful. Cultures started on agar between January and May, or from September became infective at approximately the same time in July while those started during June and July contained infective eggs in August and September respectively. No recognisable development occurred between October and April. The significance of these findings for the epidemiology of ascariasis is discussed.

Effect of lactation on the immune response to gastrointestinal nematodes.

The immune expulsion of gastrointestinal nematodes is impaired during lactation by the inhibition of the lymphocyte mediated component. As a result the population of worms may increase. At the same time, the fecundity of female worms in previously immune hosts may increase to approach that of worms in fully susceptible animals. There is good evidence that these events are primarily endocrinal in origin but although prolactin is probably involved, certain anomalies exist. These may reflect differences in the secretion pattern of the hormone in different phases of reproduction or they may indicate an interrelationship with a second hormone, for instance, adrenal glucocorticoids.

The efficacy of thiabendazole against the arrested larvae of some Trichostrongylidae and Chabertia ovina in sheep.

The activity of thiabendazole at 100 mg/kg was tested against the arrested larvae of Ostertagia spp, Haemonchus contortus, Trichostrongylus axei, Nematodirus spp and Chabertia ovina in natural infections, in 10-month-old lambs. The result, assessed by means of worm counts, showed the treatment to be very effective.