Abstract :
Sheep are infected with a range of parasites, for which appropriate and effective control
strategies are required. Changing patterns of disease and the inability to control parasitic
infections effectively require the implementation of risk-based approaches to parasite
control for many of the major parasitic diseases affecting sheep. Developing nematode
resistance to anthelmintics necessitates changes to conventionally worming programmes
that reduce the risk of further development of anthelmintic resistance through incorporation
of new anthelmintic classes and products, along with ‘best practice’ guidelines for
anthelmintic usage. Climatic changes pose a greater risk to sheep flocks through spread of
parasites, such as Haemonchus contortus and Fasciola hepatica, which are parasites inextricably
linked to high rainfall and increasing temperatures. Intensification increases the risk
from diseases such as coccidiosis and it is now advocated that a risk-based approach to the
control of coccidia infection in lambs should be based on strategic, treatments interventions
linked to identified periods of risk. Concerns over the risks from the use of ectoparasiticides,
have seen the demise of sheep dipping in many countries leading to increasing levels of
ectoparasitic infections. At the same time, greater reliance has been placed on the use of
injectable macrocyclic lactones, which inadvertently may also increase selection pressure
for anthelmintic resistance. As a consequence of all the above factors, risk-based approaches
to parasite control need to consider the strategic use of antiparasitics for individual target
parasites, as well as needs to integration and rationalisation of all the component strategies.
