EST sequencing of the parasitic nematode Haemonchus contortus suggests a shift in gene expression during transition to the parasitic stages

Expressed sequence tags from the parasitic nematode Haemonchus contortus were generated in order to identify anchor loci for comparative mapping between nematode genomes and candidate targets for future control measures. In total, 370 SL1 trans-spliced cDNAs from different developmental stages representing 195 different genes were partially sequenced. From these expressed sequence tags 50% were similar to genes with a known or predicted function and 19% were similar to nematode sequences with no ascribed function. From the first, free-living L1 and L3 stages relatively many cDNAs matched to housekeeping genes, and 11% (L1) or 23% (L3) of the encoded proteins were predicted to contain signal peptides. In contrast, no function could be ascribed to most of the cDNAs from the early L5 and adult parasitic stages, but for 30% (L5) or 55% (adult) of the encoded proteins a signal sequence was predicted. This limited analysis suggests that during the transition from the free-living to parasitic stages gene expression shifts towards the synthesis of less conserved extracellular proteins. These proteins offer the best perspectives for vaccine development and the development of anthelmintic drugs. In contrast, cDNAs from the first larval stages may be most suitable for comparative mapping with the free-living nematode Caenorhabditis elegans.

Nematode parasites of adult dairy cattle in the Netherlands

Abomasa, blood samples and faecal samples for examination of nematode infections were collected from 125 dairy cows during the period November 1997-October 1998. Of these, 12 had no grazing history and were, therefore, excluded from this study. From the remaining 113, 88.5% had nematode eggs in the faeces. Larval identification of the positive cultures showed that Ostertagia spp. larvae were most frequent (97%), followed by Trichostrongylus spp. (29%), Oesophagostomum spp. (23%), Cooperia punctata (20%), Cooperia oncophora (4%), Haemonchus contortus (2%) and Bunostomum phlebotomum (1%). The geometric mean EPG was 2.4. Two cows excreted larvae of Dictyocaulus viviparus (0.1 and 0.6 LPG resp.). Worms were found in the abomasa of 108 cows (96%). In all these abomasa Ostertagia spp. was present (100%). Trichostrongylus axei was found in 47 abomasa (43.5%) and two cows (2%) were infected with Capillaria bovis. The geometric mean of the total abomasal worm counts was 1743 and of Ostertagia spp. alone 1615. Almost all male worms were Ostertagia ostertagi, only occasionally Skrjabinagia lyrata10,000) total worm burden. Ostertagia specific antibodies were highest in late summer and autumn and lowest in spring and early summer. The same pattern, although not so pronounced, was observed for the serum pepsinogen values. No clear seasonal pattern was found for the Cooperia specific antibodies. Antibodies against D. viviparus were detected in seven cows (6%).

Transposon associated markers for the parasitic nematode Haemonchus contortus

We have previously characterized a Tcl-like transposable element Hctcl, from the parasitic nematode Haemonchus contortus. Here we describe the genetic variation of Hctcl insertion sites in H. contortus populations differing in geographical origin, resistance to chemotherapeutics and level of inbreeding. Clear differences between populations were observed on Southern blots with a Hctcl-specific probe. Sequencing the 5'- or 3'-flanks of individual Hctcl integration sites allowed the design of PCR reactions between a Hctcl-specific primer and the flanking regions. This revealed a considerable variation of integration sites of Hctcl both within and between populations, although several integrations were shared by populations of different geographical origin. For four of the eight markers allele frequencies were shifted during selection for resistance to chemotherapeutics and/or inbreeding. For two positions both the 5' and 3' regions flanking Hctcl were isolated and PCR showed that for these two positions the variation of transposon associated markers between populations were indeed caused by variation in integration of Hctcl. For these two positions co-dominant markers were developed. These results indicate that Hctcl insertions may serve as genetic markers for H. contortus.