Changing patterns of Nematodirus battus infection

Nematodirus battus is a gastrointestinal parasite, which has a huge impact in UK sheep flocks as a result of lamb mortality and reduction in growth. Farmers and veterinary surgeons conventionally focus their efforts on preventing outbreaks of nematodirosis during the spring, but the incidence of autumn infections is increasing and becoming a growing concern. The aim of this article is to describe changes in the behaviour of N. battus and highlight important knowledge gaps with reference to informing effective and sustainable management.

N. battus is a common cause of enteritis, contributing to gastroenteritis in spring and early summer, typically seen in young lambs between 6 and 12 weeks old. The main clinical signs are profuse watery diarrhoea, accompanied by lethargy, loss of condition, dehydration and death. The acute onset of the disease is typically brought about by the ingestion of large numbers of the infective third-stage larvae (L3) having hatched en masse from overwintered eggs in response to rising temperatures (Figure 1). The presence of massive numbers of juvenile and adult worms in the small intestine causes physical damage to the villi and induces a catarrhal inflammatory process responsible for the clinical presentation (Figure 2). Summer-autumn infections characterised by diarrhoea and dags (dried faeces adherent to the wool of the tail and surrounding the perineal region) are also becoming commonplace (Figure 3); albeit their epidemiology is not completely understood.