Bovine Lungworm

Habitat

Dictyocaulus viviparus, the bovine lungworm, is the cause of parasitic bronchitis in cattle (husk, verminous pneumonia, dictyocaulosis) with a world wide distribution in temperate areas. The predominant hosts are cattle, but it can also be found in small ruminants (sheep, goats) and deer. Infection occurs on pasture as infective larvae develop from L1 that are shed with the feces to free-living infective L3 that are ingested by cattle while grazing. Free-living larvae do not feed; survival on pasture is therefore limited to a few months depending on temperature and humidity. The parasite is able to interrupt development inside the host. Infective larvae that have been exposed to low temperatures on pasture before infection subsequently develop only to preadult larval stages that survive winter conditions as hypobiotic larvae in the lung and resume development in spring. These animals contaminate pastures the following spring and represent the major source of infection for other susceptible cattle.

Biology

D. viviparus is a roundworm with an unsegmented body. The adult female has a body size of 3 to 8 cm, and adult males are 3 to 4 cm, infective free-living L3 possess two sheaths from the previous two moults and measure about 400-500 µm. After oral infection the parasites penetrate the intestinal mucosa and pass to the mesenteric lymph nodes. After moulting to L4 they migrate via lymph and blood to the lungs where they enter the alveoli. Final moult and development to preadult stages and adults occur in the bronchioles. Adult worms are found from 3 weeks post infection in bronchioles and bronchi of the lung where females start to lay embryonated eggs. Eggs are transported by cilia of the epithelial cells to the pharynx, are swallowed and enter the gastrointestinal tract again. On their way through the intestine, L1 hatch from the egg shells and are shed with the feces. Adult worms cause bronchitis and pneumonia and often death. Infections rapidly stimulate a protective immunity that prevents clinical disease but not entirely the development of adult worms after reinfection. Immunity lasts for 6 to 12 months.

Sequencing Plan

A sequencing plan submitted to the NHGRI calls for 6-fold sequence coverage in plasmids, end sequence of a fosmid library at 0.2-fold coverage, and two rounds of directed sequence improvement ("pre-finishing"). To facilitate better gene prediction and to add depth to the analysis of structure-function up to 20,000 ESTs will be generated. To increase the diversity of identified transcripts stage- or tissue-specific cDNA libraries will be constructed. The individual traces will be available from the NCBI Trace Archive, and the sequence assembly will be available upon internal evaluation for quality. Funding for the sequence generation and characterization is being provided by the National Human Genome Research Institute (NHGRI), National Institutes of Health (NIH).

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Contacts

Name	Affiliation
Makedonka Mitreva	The Genome Institute, Washington University School of Medicine
Thomas Schnieder	Institute for Parasitology, University of Veterinary Medicine Hannover

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Publications

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