Nematodes in Sheep: Case Study 1 ('05)

1. Using the data from the 2 samples do a Fecal Egg Count Reduction Test.

Sheep	Pre-EPG	Post-EPG	FECR
1	150	25	83%
2	0	0	NR
3	1500	0	100%
4	0	0	NR
5	1160	280	76%
6	0	0	NR
7	1200	0	100%
8	0	0	NR
9	3850	0	100%
10	143	0	100%
11	1967	0	100%
12	1260	0	100%
13	400	0	100%
14	1217	0	100%
15	1350	0	100%
16	1625	150	91%

The average for the flock was 1322 ± 1079 EPG Pre-Treatment and 36 ± 107 EPG Post-Treatment therefore the FECR was 97%.

Is there any indication that there are nematodes resistant to levamisole on the original farm?

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On a flock level there does not appear to be a problem using levamisole. If we look at individual animals, two of them have a egg reduction of less than 85%, so there is the potential for resistance to this drug developing in the flock.

 

2. Do you have indication that there may be resistance to ivermectin on the original farm?

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Since no test was done before ivermectin treatment we can't really say. However, given the high post-ivermectin values (1322 ± 1079 EPG ) it is doubtful that these worms are fully susceptible to ivermectin.

3. What nematodes may have produced the strongyle type eggs that you saw in these sheep? List all nematodes     of Pennsylvania sheep that produce this type of egg.

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Haemonchus, Ostertagia, Trichostrongylus, Cooperia, Bunostomum, Oesophagostomum, Chabertia, (Nematodirus = Strongyle type worm, but egg can be distinguished from the others).

4. Name the active ingredients of the drugs approved by the FDA for treating Haemonchus infections in sheep.

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The active ingredients of the drugs approved by the FDA for treating Haemonchus infections in sheep:

• Ivermectin
• Levamisole Hydrochloride
• Thiabendazole
• Albendazole
• Fenbendazole (Bighorn Sheep, not domestic sheep)

5. What is the approved dose of Levamisole for treating sheep for a Haemonchus infection?

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About 8 milligrams per kilogram body weight or 3.68 mg/lb.

6. On a farm with multi-drug resistant Haemonchus, what measures can a farmer take to slow down the development of resistance to the one drug which he currently is able to use to control this parasite on his farm?

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Measures a farmer can take to slow the development of resistance to the one drug include:

1. Treat only those sheep that need treating. The rest of the flock serves as a reservoir of unselected worms, which will dilute out the worms in which resistance to the drug has been selected for.
2. Breed only those sheep which have shown a natural resistance to Haemonchus, and eventually develop a flock which needs little anthelmintic treatment.
3. Mix graze the pastures (horses and sheep) to bring down the level of pasture contamination so treatment won't have to occur so often.
4. Make sure each animal gets the appropriate dose of drugs, and re-treat those in which resistance seems to have developed with another drug.