The comparative morphology of Marshallagia marshalli and Ostertagia occidentalis (Nematoda: Strongylida, Trichostrongylidae) by scanning electron microscopy.

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. In the global fauna, six of 13 ostertagiine genera are endemic to Iran. The life cycle of Ostertaginae is direct and ingested third-stage larvae after exsheatment in the rumen, penetrate the gastric glands in the abomasal mucosa where two parasitic moults occur before the L5 emerges from the gland. In the present work, Marshallagia marshalli and Ostertagia occidentalis, collected from the abomasums of sheep from Mashhad, Iran, is described. The association of light and scanning electron microscopy (SEM) allowed a detailed analysis of the morphology and ultrastructure of these nematodes. The male body length of M. marshalli and O. occidentalis were 9.3-10.20 and 9.60-10.50 mm, respectively. The female body length of M. marshalli and O. occidentalis were 10.10-15.30 and 10.4-15.70 mm, respectively. One of cervical papillae is seen 333 and 250 µm from the anterior end of male and female body surface in O. occidentalis and 287.5 and 200 µm from the anterior end of male and female body surface in M. marshalli, respectively. The size of cervical papillae is 13.3 µm in male and 10 µm in female in O. occidentalis and 9.33 µm in male and 8.57 µm in female in M. marshalli. Some other taxonomic features of M. marshalli and O. occidentalis, such as details of cephalic region, the system of longitudinal and surface cuticular ridges (synlophe), the orientation of rays of the copulatory bursa, localization of vulva, morphology of vulvar flap, and posterior end of females are also documented by SEM.

Identification of abundant mRNAs from the third stage larvae of the parasitic nematode, ostertagia ostertagi.

Reverse transcriptase-PCR (RT-PCR) was carried out on total RNA prepared from the third-stage larvae (L3) of Ostertagia ostertagi in order to clone and characterize the major transcripts expressed in this larval stage, as an initial investigation of arrested larval development in the parasite. Distinct bands were visible on an agarose gel and four of these were cloned and sequenced. Three of the bands represented multiple transcripts, while the fourth band encoded the enzyme GTP cyclohydrolase I (GTP-CH), which catalyses the first and rate-limiting step in pteridine biosynthesis. Northern blot analysis and RT-PCR demonstrated that GTP-CH is highly up-regulated in the L3 stage and undetectable in either the L2 or adult stages. Using immunogold electron microscopy, GTP-CH was shown to be predominantly localized to the cell body of the body wall muscles and the cells of the intestine in the L3.

Digital image analysis and identification of eggs from bovine parasitic nematodes.

Computer-assisted microscopy and multivariate statistics were used to establish and evaluate a procedure for identification of bovine strongylid eggs. Ostertagia ostertagi, Cooperia oncophora, Haemonchus placei, Trichostrongylus axei, and Oesophagostomum radiatum eggs were obtained from faeces voided by monospecifically infected calves. Images of single eggs (400 x magnification) were recorded by a CCD camera fitted onto a microscope and digitized on a PC. After separation of eggs from the image background, the pixel (picture element) positions of the egg outline were analysed by algorithms to describe size and shape. A stepwise discriminant analysis was subsequently used to select and rank descriptive features of 4207 eggs according to discriminatory power. Classification criteria were developed by linear discrimination analysis on the basis of selected features, and the criteria evaluated by cross-validation. A maximum average percentage of correct classification of 85.8% resulted when nineteen features were employed in a linear classification criterion. The percentages correct classification for each species were: O. ostertagi 76.3%, C. oncophora 90.8%, O. radiatum 87.8%, H. placei 90.1%, and T. axei 83.8%. Classification based on the five most important features gave an overall correct classification of 81.5%. Images of "unknown' eggs could be identified automatically by the classification criteria after procedural steps performed by PC were linked in a batch program.

Bilateral, perivulval cuticular pores in trichostrongylid nematodes.

A new hypodermal gland was discovered in female nematodes of the family Trichostrongylidae. Because the new structure appears to be associated with the vulva, it was named the perivulval pore. It is similar, based on light and scanning electron microscopy, to phasmids that are located laterally on the tails of nematodes of the class Secernentea. Like phasmids, perivulval pores are paired and bilateral, with cuticular ducts to the surface in the areas of the lateral chords. They are located slightly posterior to the vulva in Haemonchus contortus, Haemonchus placei, Haemonchus similis, Mecistocirrus digitatus, Mazamastrongylus pursglovei, Ostertagia ostertagi, and Cooperia oncophora, but in Trichostrongylus colubriformis they are slightly anterior to the vulva. Because of the location near the vulva and the similarity in structure to phasmids, which are, at least in part, secretory, the perivulval pores should be considered as a possible source of a female attractant for males.

Pathophysiological and parasitological studies on Ostertagia ostertagi infections in calves.

Friesian calves given a low level infection of the abomasal parasite Ostertagia ostertagi over a six week period displayed a mild diarrhoea with high faecal egg counts and elevated plasma pepsinogen values. At necropsy on day 23 abomasal lesions characteristic of ostertagiasis were widespread. At 42 and 84 days oedema and congestion were also prominent. Total worm burdens on days 23 and 42 were similar but a marked decrease had occurred by day 84. Feed digestibility and nitrogen economy were not markedly affected but radioisotopic measurements demonstrated an increase in albumin disappearance and catabolic rates, and plasma faecal clearance during the course of the infection. Prior administration of a morantel sustained release bolus to a group of similarly infected calves reduced the total worm burdens to less than 50 per cent of those recorded in the infected calves on days 23 and 42 and this fell to 3 per cent on day 84. Abomasal damage and the adverse pathophysiological changes associated with infection were prevented in this group.