Variation in size of Ostertagia circumcincta,a nematode parasite of sheep,induced experimentally and during preparation and preservation

Summary This investigation was undertaken to determine the effect of formol-saline fixation and subsequent preparation on the length of Ostertagia circumcincta, a gastrointestinal parasite of sheep. Such induced changes in worm lengths were compared with the size distribution in two experimental populations in lambs, one of which was helminthologically susceptible and the other highly resistant. It was concluded that variation in worm length caused by fixation was not significant when compared to the variation encountered naturally in worm populations. ac]19851213     

Seasonal changes of gastrointestinal nematode populations in yearling beef cattle in Louisiana with emphasis on prevalence of inhibition in Ostertagia ostertagi

Investigation of seasonal changes in the composition of nematode populations, principally Ostertagia oslertagi, was conducted over 3 years at three locations in Louisiana. This is the most commonly occurring parasite of cattle in the state. Naturally infected yearling cattle were killed monthly over extended periods and tracer calves were grazed for monthly intervals from late autumn to summer at two locations in 1978–1979. Major objectives were to determine seasonal incidence of common gastrointestinal nematodes and for O. ostertagi, in particular, the time period during which larval inhibition was prevalent, circumstances under which larvae were conditioned to inhibition, and the duration of inhibition. Small numbers of inhibited O. ostertagi were recovered between November and February. Large numbers were found initially in March and increased numbers in April and May. Both normally developing and inhibition prone larvae were acquired during late winter-early spring, with the proportion of the latter being more prevalent in April and May. Evidence from tracer calves indicated that few O. ostertagi larvae were acquired after early June. Large burdens of inhibited larvae persisted in yearling cattle through summer; numbers of developing larvae and adults were minimal. Maturation of inhibited larvae occurs from August to October and in one instance was associated with cases of clinical parasitism. Factors responsible for inhibition were not defined, but increasing temperatures of late winter-early spring, host resistance, and density-dependence of populations were considered. Other abomasal genera were most prevalent in spring while intestinal genera were most common during autumn through spring.     

DNA evidence that Marshallagia marshalli Ransom, 1907 and M. occidentalis Ransom, 1907 (Nematoda: Ostertagiinae) from Svalbard reindeer are conspecific

The gastro-intestinal parasitic nematodes of ruminants Marshallagia marshalli and M. occidentalis are morphs of a single species according to indirect evidence. In this study, their taxonomic status and molecular identification were assessed more directly in isolates from the abomasal nematode community of Svalbard reindeer using genetic data. DNA sequences of the first and second internal transcribed spacers of nuclear ribosomal RNA genes were obtained from individual nematodes by the polymerase chain reaction (PCR). Both taxa contained virtually identical sequences of each ITS and shared most of the polymorphisms detected. A PCR assay based on ITS-2 sequences previously developed to identify M. marshalli and Ostertagia gruehneri, the second common species in this community, gave identical results for M. marshalli andM. occidentalis. Genetic data thus confirmed that M. marshalli andM. occidentalis are conspecific.     

Revision of the African species of the genus Cooperia Ransom, 1907 (nematoda,trichostrongylidae)

Summary Fourteen of the 20 species recorded from Africa are resdescribed and illustrated. Of the remaining six species, four, namely, Cooperia borgesi, C. hippotragusi, C. minor and C. reduncai are considered species inquirendae and one, C. africana, is a possible synonym of C. punctata. The validity of C. oncophora and C. surnabada is discussed. A key to 16 species is given.Part of a thesis approved by the University of London for the award of a Ph.D. degree.Part of a thesis approved by the University of London for the award of a Ph.D. degree.     

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.     

The effects of the nematode parasite Skrjabingylus nasicola on British weasels (Mustela nivalis)

Adult worms of Skrjabingylus nasicola are found in the nasal sinuses of mustelids, and when numerous may cause considerable distortion of the frontal bones. A heavy infestation is commonly assumed to be detrimental to the individual and possibly also to the population. To examine this belief, the frequency of occurrence ("incidence") and extent of damage caused by S. nasicola were analysed with respect to the climate of seven sample areas and the age, sex and body size of 614 British weasels. Incidence ranged from 69–100% of the sample, and mean skull damage from 31 to 53 on an index scale of 0–8 points. Significant correlations were found between incidence and date of collection of young weasels, and between extent of damage and mean number of rain-days in the area. Male weasels were more badly damaged than females, though incidence was the same in both sexes. There was no evidence that badly damaged weasels were smaller, lighter, leaner or died sooner than lightly or undamaged ones, nor that, in the wild, they were infested by eating shrews.