Whenever we have a small ruminant (sheep or goat) necropsy, the rule of thumb is that it is intestinal parasitism until proven otherwise.
Cows get intestinal parasites too, but for the most part, due to differences in management and physiology, weaned animals and adults rarely develop such a heavy parasite load that it leads to death. There are always exception, especially for calves that are still nursing.
Sheep and goats have a particular problem with the roundworm Haemonchus contortus. The adult worms are small, around 1 cm long tops, and very thin. In small numbers, they are easy to miss. Haemonchus prefer to take up residence in the abomasum, the glandular part of the forestomach between the rumen and the duodenum. The adult worms and late-stage larvae burrow into the mucosa of the abomasum and feed on the blood of the animals. Heavy or even moderate but chronic loads of Haemonchus cause the animals to become anemic. When the animals begin to show clinical signs of the anemia, the owners deworm them but it's usually too late. Severe anemia secondary to Haemonchus parasitism is the cause of death of most of the sheep and goats that we see.
Coccidiosis is the other player in this small ruminant gut roulette. Coccidia are protozoal parasites, not worms. Infections have to be treated with entirely different products. For most of their lifecycle, coccidia are tucked deep into the intestinal mucosa. The result is erosion of the structure of the mucosal layer. The animals can't digest food anymore and often develop diarrhea, which is not usually observed in cases where only Haemonchus is present. But severe coccidiosis can also cause anemia!
Many sheep and goat owners are small flock hobby farmers. They don't have a lot of space and can't rotate pastures. The animals shed ova and oocytes in their feces and repeatedly re-infect each other. Some of the owners decide the solution is to treat their animals constantly with dewormers and coccidiostats. The result is a short-term drop in adult parasites. But the treatments do nothing about ova and oocysts in the pastures. They are highly resistant to heat, cold, UV, etc. and sporulate into larvae to start the cycle anew. And overtreatment can result in the creation of drug-resistant populations of parasites.
One of the tests we try to run on every small ruminant necropsy is a fecal egg count. The result of this test is a count of ova or oocytes per gram of feces. Here is a graph showing the results of 47 fecal egg count tests during a two-year period. The left hand scale is a log scale, so each horizontal line increases by a factor of 10. Coccidia are Eimeria spp. and strongyles (strongyloids) are for the most part Haemonchus. Some animals only had Haemonchus, some only Eimeria. Some had both (the paired lines). Most of the animals represented here were severely anemic.
The winner is the lamb necropsied by my colleague that had more than one million Eimeria oocytes per gram of feces. Truly astonishing.
Today I necropsied a lamb that wasn't anemic. No adult Haemonchus were in its abomasum. The general presentation of the lamb was consistent with sepsis, and while that was the cause of death, that's not a proximal diagnosis. What caused the sepsis? I kept looking. The animal had severe diarrhea and there was no digesta in its intestinal tract or feces in its colon. Nothing but gas. I started looking into the large bowel and found many adult roundworms. They weren't delicate, hair-thin Haemonchus but they were definitely strongyloids. The mucosa of the large bowel sections was eroded and irregular. Then I moved up to the small intestine. Surprise! Tapeworms. Adult tapeworms that were many, many inches long.
Since we don't see intestinal worms very often in sheep and goats, I did a little research and decided that the worms were probably Trichostrongylus spp. They can also cause anemia like their cousin Haemonchus but they live in the intestines instead of the abomasum. Since I didn't see evidence of anemia, I thought that the tapeworms were probably the more significant problem.
And the cause of the sepsis? Well, it's a cascade of unfortunate events. The intestinal mucosa is damaged by worms and larvae cavorting about. The tapeworms consume digesta (competing with the lamb for nutrients). The intestines stop functioning and no longer send proper signals to the rumen, which stops trying to send stuff into the intestines. Eventually, the intestinal environment becomes so compromised that gut bacteria decamp into the bloodstream.
What had me scratching my head with the case was the fact that tapeworms are extremely easy to treat. We usually only see them in small animal cases associated with neglect and rarely in production animals. That problem was resolved when I called the owner and she told me that they hadn't dewormed ... in years.
It's not a problem until it is, I suppose. She's now lost 6 lambs due to that decision.
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