New agent in sheep lameness?

By John Shirley

Could a stomach worm in sheep be the cause of extra lameness in flocks? This is a possibility being speculated by scientists.

The bug is Strongyloides papilosus (S pap for short), a fairly common parasite in lambs and ewes and not all wormers are effective against it. This worm lays eggs in the sheep. These pass through in sheep dung onto the pasture (or bedding material) where they hatch into larva. S pap has a life cycle which involves both the sheep and the environment as per other worm species.

However, S pap has an important difference. In addition to being taken in from grass via the mouth, this larva also burrows in through the sheep's skin. The theory is that when making the entrance through the skin of a sheep's foot, this larva opens an entrance for other foot infections to enter through. Relative to the size of the bugs which can cause infection and lameness in sheep the S pap larvae are capable of leaving a large hole in the skin. The speculation is that this burrowing activity can contribute to extra lameness in sheep.

S pap appeared in a dung sample gathered recently from the Teagasc flock at Knockbeg in Carlow. Manager Willie Kelly noticed eggs in the FecPac test. He sent them to Teagasc parasitologist Barbara Good based in Athenry. Back came the reply: S pap eggs.

All during the summer the flocks at Knockbeg had shown very little worm infection. As a result, the lambs were wormed less than normal. The S pap that might normally be killed off by summer dosing were given a chance to develop into bigger numbers.

Coincidentally, Willie Kelly did notice extra lameness in the Knockbeg lambs recently. However, Barbara Good is very cautious about coming to the conclusion that this lameness is due to the presence of the strongyl. She stressed: "This case is far from proven''. She said that S pap likes moist warm conditions and is often seen in high numbers with housed sheep, especially where the bedding is damp.

Across the wormers there is quite a variation in effectiveness against S pap. The products effective against S pap included moxidectin (Cydectin), the avermectins and the white wormers based on albendazole and fenbendazole. White wormers based on oxfendazole and levamisole-based wormers do not claim efficacy against S pap.