Clinical Forum: Bovine lungworm

摘要

Parasitic bronchitis, caused by the neniatode Dictyocaulus viviparus, is a serious disease of cattle. For over 40 years, a radiation-attenuated larval vaccine (Bovilis~(R) Huskvac, Intervet UK Ltd) has been used successfully to control this parasite in the UK. Once vaccinated, animals require further boosting via field challenge to remain immune however there have been virtually no reports of vaccine breakdown. Despite this, sales of the vaccine decreased steadily in the 1980s and 90s; this was probably due to farmers' increased reliance on long-acting anthelmintics to control nematode infections in cattle. This method of lungworm control can be unreliable in stimulating protective immunity, as it may not allow sufficient exposure to the nematode. Such animals remain susceptible to disease when subsequently exposed to D. viviparus larval challenge. Evidence of this phenomenon has been provided by the documented increase in the numbers of parasitic bronchitis outbreaks in the UK in the last 20 years, especially in second year grazing animals arid adult cattle. This change in disease pattern dynamics is a symptom of the rise in immunologically naive populations who have either not been vaccinated or exposed to low levels of natural infection duringtheir first grazing season.