Abstract
Lungworm is the most important parasite of farmed red deer (Cervus elaphus) in New Zealand. Because of the morphological similarity between deer-derived and cattle-derived lungworm, it has been assumed that the lungworm infecting red deer is Dictyocaulus viviparus, the lungworm which causes "husk' in cattle.
This programme has used light microscopy, electron microscopy, molecular techniques, cross-infection studies and immunisation to re-examine the issue of species identification of lungworm affecting farmed red deer and to study the pathological and immunological responses of deer to experimental challenge with lungworm derived from deer and cattle.
Dictyocaulus larvae were isolated from properties on which the host of interest was the sole species grazed. The larvae were cultured and used to infect multiplier animals. Larvae were then cultured from the multiplier animals for use in trials.
Examination of adults using light microscopy revealed differences between deer-derived lungworm and cattle-derived lungworm but these were hard to quantify. Using scanning electron microscopy the two could be clearly differentiated, the mouthparts of cattle origin lungworm were circular, those of deer origin lungworm elongate. Molecular analysis of the ITS-2 region confirmed a difference between the two lungworm isolates. The ITS-2 sequence of the lungworm derived from cattle matched that of Dictyocaulus viviparus. The sequence of the ITS-2 of lungworm derived from red deer matched that of D. eckerti, described from fallow deer (Dama dama). Single strand conformation polymorphism (SSCP), a high resolution mutation detection method, provided a technically simple method of differentiating lungworm derived from many hosts, including cattle and red deer.
In a cross-infection trial D. viviparus infections established in cattle, whereas deer derived lungworm did not. Red deer developed patent infections whether challenged with deer lungworm or D. viviparus. There were significant differences in the course of the infections, the host responses and the associated pathology.
Huskvac, an irradiated larval vaccine available for use in cattle in Europe, was trialled in red deer in New Zealand. A group of cattle were used as a control to ensure the efficacy of the vaccine under local conditions. Huskvac protected cattle against a D. viviparus challenge. Red deer were afforded a degree of protection, in that patency was delayed by several days in vaccinated animals, larval output was lower and fewer adults established in the lungs. Although protection was irrespective of species challenge, some aspects of the host response differed according to the challenge species.
The lungworm specific to red deer in New Zealand is not D. viviparus. It is probably D. eckerti, according to the current classification. Cross-infection does however occur and D. viviparus causes pathology in red deer, therefore contamination of pastures by grazing cattle is not recommended. As vaccination with Huskvac provided a degree of protection in red deer it is possible that vaccination using irradiated D. eckerti larvae may be more effective.