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1. What is the connection between scouring in sheep and flystrike?
2. Describe the type of fleece derangement you would expect to see in an itch mite infestation?
3. For sheep and goats in eastern coastal regions, what weekly checks for parasites would you make?
4. What are the different habitat preferences of the liver fluke snails, A. tomentosa and P. columella?
Blowflies are attracted to faecal matter soiling the breech area (referred to as dags) of sheep that sets up conditions suitable for fleece rot bacteria or dermatophilosis. Female blowflies are attracted to the odours released by the bacteria and lay their eggs in this. Fly larvae that emerge from eggs laid onto dags will feed in the dags before moving onto the skin to feed.
Scouring (or diarrhoea) resulting in dags is most often the result of a scour worm or coccidial infection. The extent of soiling of the wool in the breech area can be rated on a scale of 1 to 5 (Dag score) and indicates the likelihood of a flystrike in affected sheep.
Crutching can be used to manage dag and therefore, the flystrike risk. Drenching to control the scour worm infection will also reduce dag.
Fleece derangement in an itch mite infestation is characterized by matted chewed wool in a region accessible to the sheep’s mouth – i.e. behind a line approximately from elbow to hip resulting in tassels of wool that hang down along the flanks.
However, infested flocks can usually show a range of signs. Most sheep show no fleece damage at all, whereas, in others, heavy skin scurf is present with or without fleece derangement, but often with moisture at the base of the wool. There may be some tufting of the wool along the flanks. Very few sheep (usually one per cent) have severely damaged fleeces. Itch mite mainly affects older sheep and is rarely seen in young sheep. It is, however, quite uncommon in sheep now due to the widespread use of macrocyclic lactone drenches, to which the itch mite is susceptible.
Austropeplea (Lymnaea) tomentosa prefers shallow, trickling water and runoff from hillside springs and soaks (black bogs), and is only rarely found in deep water of dams, water troughs or large creeks. It sometimes can be found in dam overflows after heavy rain, or within spring-fed dam inflows and outflows. It prefers cooler elevated terrain. It is the indigenous snail most commonly implicated in liver fluke transmission.
Pseudosuccinea (Lymnaea) columella, the striated pond snail, is found in deeper waters of creeks and dams, and can also survive in stagnant bodies of water. It is found across a wide range of temperatures in the eastern states from the tropics down to the cool temperate zones. It is a recently introduced snail and could extend the liver fluke endemic area.