Nematode egg output and plasma concentration of ivermectin after its administration to red deer (Cervus elaphus elaphus).

Blood and faecal samples were analysed in a study to evaluate the use of ivermectin in red deer hinds (Cervus elaphus elaphus). It was demonstrated that ivermectin, when used at 400 micrograms/kg bodyweight, proved to be more efficient than 200 micrograms/kg bodyweight although positive worm egg counts together with the isolation of lungworm (Dictyocaulus species) larvae were recorded from hinds having received the anthelmintic at the higher dose.

Observations on the output of nematode eggs in faeces and on the subsequent pasture infestation with third stage larvae produced by a herd of farmed red deer (Cervus elaphus).

More than 2900 faecal samples and 200 herbage samples were examined from January 1986 to January 1989 during a study of the host/parasite relationships of the gastrointestinal nematodes of a herd of farmed red deer in Surrey. The pattern of faecal egg output from the hinds appeared to conform to a tri-modal distribution with peaks during spring, the periparturient period and late summer. Third stage larvae were present on the herbage during every month. The new generation appeared in June but levels of larvae remained low until the autumn. The implications of these findings are discussed in relation to the farming of red deer.

The identification of females within the subfamily Ostertagiinae Lopez-Neyra 1947.

As a result of the examination of many thousands of female nematodes classified as belonging to the sub-family Ostertagiinae Lopez-Neyra 1947, it became possible to compile descriptions of different female types, each of which corresponds to a polymorphic species as determined by male morphology. The female types have been designated as follows: Ostertagia ostertagi (males O. ostertagi and O. lyrata), Ostertagia circumcincta (males O. circumcincta, O. trifurcata and Teladorsagia davtiani), Ostertagia leptospicularis (males O. leptospicularis and O. kolchida) and Spiculopteragia asymmetrica (males S. asymmetrica and Apteragia quadrispiculata).

Development of protection and of self-cure in lambs infected daily with Ostertagia circumcincta.

Lambs were infected daily with 1000 Ostertagia circumcincta larvae. At intervals of 4 weeks groups of lambs were each challenged with a dose of 28,000 larvae, and their worm burdens compared with those of unchallenged controls. The measure of their ability to resist a challenge infection, which would have determined their degree of "protection", was obscured by the separate phenomenon of self-cure. Evidence suggested that the different manifestations of self-cure were determined by the state of resistance of the host and followed a set chronological sequence.

Systematics of the nematodes that cause ostertagiasis in cattle, sheep and goats in North America.

The systematics of the Ostertagiinae is unsettled with no agreement on how many genera and species are present in cattle and sheep. Ten species of Ostertagiinae are commonly parasitic in cattle and sheep. The males can be identified on the basis of differences in morphology of spicules and genital cones but the females of most species cannot be identified. The species-level systematics have been complicated by the proposal that the ten species are polymorphs of only five species. The systematics at genus level has been complicated by the use of numerous genera for the ten species, at present most commonly Ostertagia, Teladorsagia and Marshallagia. This report (1) describes the current knowledge of the systematics and (2) provides diagnoses of the genera recommended for the ten species. The morphology of the ten species was studied to determine whether characteristics could be found to identify females or to further differentiate the males. Characters studied included the system of longitudinal and surface cuticular ridges (synlophe), the internal morphology of the esophagus and the orientation of rays of the copulatory bursa. The study of species morphology resulted in additional support for the polymorphism proposal. All minor species were found to be identical to their major species in characteristics of the synlophe, esophagus and rays of the copulatory bursa. Two recent classifications of the Ostertagiinae both recommended the use of the genus Teladorsagia for the species T. circumcincta and the two minor species that occur with it, T. trifurcata and T. davtiani. Teladorsagia is characterized by a copulatory bursa in which the five lateral rays are arranged 2-2-1 and a ventral swelling of the genital cone (proconus) is absent. One pair of species, Marshallagia marshalli (major species) and Ostertagia occidentalis (minor species) should be included in the genus Marshallagia. This genus has been characterized by an elongated bursa in which the posterior pair of lateral rays are much longer than the ventral pair. The remaining two pairs of species (O. ostertagi and its minor species O. lyrata, and O. leptospicularis and its minor species O. kolchida) and O. bisonis belong in the genus Ostertagia which is characterized by a 2-1-2 arrangement of the five lateral rays of the copulatory bursa and the presence of a proconus.

Worm burdens of dairy heifers in England and Wales.

The size and composition of abomasal worm burdens from 143 casualty and cull dairy heifers were estimated. Over 60 per cent had totals of less than 10,000, only four exceeded 100,000 and the overall mean was 16,285. Ostertagia ostertagi was almost always present and usually formed the major proportion of the total. Trichostrongylus axei was recorded in 83 heifers and was the most common species on 17 occasions. The numbers of arrested early fourth stage worms were highest in winter and declined rapidly during spring. O lyrata was only found when O ostertagi was present and always as a small percentage of the total. Similarly in the case of two of the minor species, Skrjabinagia kolchida (= Grosspiculagia podjapolskyi) was never found independently of O leptospicularis (= O crimensis). These relationships are regarded as suggestive of polymorphism.

Further observations on the action of fenbendazole against inhibited fourth stage larvae of Ostertagia ostertagi.

Two further trials are reported on the effect of fenbendazole on inhibited Ostertagia ostertagi larvae. In the first trial fenbendazole successfully eliminated inhibited burdens of O ostertagi, while in the second trial the effect was variable. As a result of these trials and previous reports it is concluded that a single oral dose of fenbendazole cannot be relied upon to prevent winter (type 2) ostertagiasis.

The effect of age, acquired resistance, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi.

An experiment is described in which the effects of age, previous infection, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi were studied. It was found that an acquired resistance to the establishment of worms developed more rapidly in 20-month-old heifers than in calves, that it was unaffected by pregnancy of the host but that it was largely lost by heifers in early lactation. The rate at which populations were turned over, i.e. the mean life-span of worms through the late 4th and 5th stages was unaffected by the factors studied. Although, in the conditions of the experiment, development of the worms was not arrested in susceptible calves, both age of the host and its previous experience of infection were significant causes of arrest, and in previously infected 20-month-old cattle 86% of the worms of a challenge infection were arrested. Pregnancy did not affect the proportion of worms that was arrested but in lactating heifers only marginally more worms were arrested than in calves. Worms that were not arrested grew more rapidly in calves and in lactating heifers than in empty heifers or those in mid-pregnancy.

Plasma pepsinogen levels in some experimental infections of Ostertagia ostertagi in cattle.

Two groups of calves were infected with larvae of Ostertagia ostertagi to establish large numbers of adults and arrested larvae. In one group symptoms of ostertagiasis were seen and there was a loss of three months growth; in the other, in which adult worms were removed by a single anthelmintic treatment, there was only a transient reduction in live-weight gain. Plasma pepsinogen levels were however the same in the two groups and followed the same course. Even after 25 weeks, when calves had been growing normally for up to three months, plasma pepsinogen values were still around 5 iu per litre, well above the level generally regarded as diagnostic of ostertagiasis. The relevance of these findings to the use of the test in the diagnosis of ostertagiasis is discussed. The literature is reviewed.