Signalment:  

10-month-old, Angus-cross steer (Bos taurus).These calves were purchased as stocker calves between 6 and 9 months of age. The calves were being fed a ration composed of millet hay, wet beet pulp, and whole corn, with access to protein blocks containing monensin. At 10 months of age, seven calves demonstrated abrupt onset of neurological signs, including behavioral changes (apprehension and aggression), staggering, muscle twitching/fasciculation, recumbency, and opisthotonos, followed shortly by death. Several calves were treated with broad-spectrum antibiotics, thiamine, calcium gluconate, and a variety of corticosteroids with no response. Three calves were examined postmortem by the referring veterinarian and samples were collected on two calves for histopathology and associated testing.

Gross Description:  

Per the submitting veterinarian, all three calves demonstrated some combination of the following: subcutaneous edema, mild subcutaneous hemorrhages, visceral congestion, ascites, pulmonary edema and emphysema, and hepatomegaly, with enlarged congested livers having a prominent mottled or lobular pattern on surface and section.

Histopathologic Description:

Striking lesions are confined to the liver for both calves, and include diffuse acute hepatocellular necrosis most severe in centrilobular, and to a lesser extent, midzonal areas (zones 3 and 2), generally sparing periportal (zone 1) hepatocytes. In some sections there also is patchy sinusoidal congestion and pooling of blood, mild vacuolar change of remaining hepatocytes in zone 1, and variable, but light infiltrates of inflammatory cells (predominantly neutrophils) in sinusoids and attending necrotic hepatocytes. Other changes observed microscopically include diffuse pulmonary congestion and edema with multifocal emphysematous bullae and subtle changes suggestive of cerebral edema.

Morphologic Diagnosis:  

Hepatocellular necrosis, marked, acute, diffuse, centrilobular and midzonal (zones 3 and 2), with multifocal congestion/hemorrhage and multifocal mild hepatocellular vacuolar change.

Lab Results:  

Fresh tissues were received from two calves. Bacterial culture attempts did not yield growth of any significant aerobic or anaerobic pathogens from the lung, liver, or small intestine. Fluorescent antibody tests for a variety of viral pathogens (i.e. infectious bovine rhinotracheitis, parainfluenza-3, and bovine respiratory syncytial virus) were negative and virus isolation attempts on pooled tissue homogenates were negative (bovine embryonic testis cells). A serum chemistry panel and complete blood count performed on one calf revealed the following abnormalities: elevated ALP, AST, CK, GGT and LDH; evidence of mild dehydration (elevated PCV and hemoglobin); and a mild leukocytosis with neutrophilia. Tissue (liver) levels of lead, arsenic, mercury, copper, selenium, and several other metals were within normal limits. A developmental (not commercially available) thinlayer chromatography assay detected a significant (not quantified) level of carboxyatractyloside in rumen contents from both calves tested.

Condition:  

Xanthium toxicosis

Contributor Comment:  

Zone 3 (periacinar or centrilobular) necrosis is the most common form of zonal hepatocellular necrosis observed in domestic animals, including cattle, and is a relatively stereotyped response/ lesion that may be caused by a variety of infectious, inflammatory, metabolic, and toxic insults.(4) Given the clinical history and microscopic findings in this case, a toxic etiology was suspected, particularly a toxic plant incorporated into the millet hay. Other etiologies, such as cyanobacteria (blue-green algae) and molybdenum toxicosis, were considered less likely given the controlled diet, season (winter), and location (western Nebraska). Examination of rumen contents from two affected calves and of the millet hay incorporated into the feed ration revealed abundant mature burs or fruits of the common cocklebur plant (Xanthium strumarium), and thin-layer chromatography analysis of rumen contents from both calves demonstrated a significant amount of the cocklebur toxic principle, the diterpenoid glycoside carboxyatractyloside.(4,5)

Carboxyatractyloside and other atractylosides are inhibitors of cellular oxidative phosphorylation, and act specifically by binding to and inhibiting ADP/ATP carriers, leading to ATP depletion and subsequent mitochondrial dysfunction, ion pump failure, lipid peroxidation, and glutathione depletion resulting in cellular apoptosis and/or necrosis.(4,5) All members of the Xanthium genus seem to produce carboxyatractyloside, and other plants in the families Asteraceae and Compositae may produce the same or similar glycosides causing similar clinical syndromes in susceptible species, including cattle, sheep, swine, and humans.(2,3,5-8)

The common cocklebur, a coarse herbaceous annual, is common throughout much of the United States; it grows to a mature height of 2-5 feet, with an erect, often angled stem, and alternate, triangular or heart-shaped rough leaves. The plant produces hard, prickly, oval fruits or burs approximately 0.75 inches long containing two seeds; these can be found entangled in the coats of livestock and long-haired dogs. The plants are invasive and are often found growing in pastures and meadows (especially those with a history of previous or seasonal flooding), along fencerows, in roadside ditches, along stream and pond banks, in dried out ponds or stock reservoirs, and occasionally in disturbed areas in feedlots.(7)

Cocklebur poisoning is most common in the spring or early summer, associated with the ingestion of germinated seeds and palatable young dicotyledon seedling plants that are high in the toxic principle, carboxyatractyloside; adult plants contain relatively little toxin, other than in seeds or burs. Most poisonings seem to occur in pigs foraging naturally, but the plant is toxic to a wide range of animals, including ruminants, horses, dogs, rats, and humans; most cases of toxicity in these species are caused by incorporation of seedlings or mature plants with seeds into feed rations (hay, haylage, silage, or grain rations).(2,3,6,8) As with the submitted case, there are several reports of poisoning in cattle associated with the presence of mature cocklebur plants and seeds (burs) in hay.(8)

Common clinical signs observed with cocklebur poisoning include anorexia, depression or other behavioral changes including apprehension or excitability, blindness, ataxia, twitching progressing to spasmodic muscle contractions or convulsions, recumbency, opisthotonos, and rapid progression to death. Clinical signs may follow ingestion of the plant by as short a period as several hours in monogastric animals and may be delayed for a day or so in ruminants. Characteristic gross lesions of cocklebur poisoning are not specific, but can include ascites and various effusions, hemorrhages (associated with consumption of clotting factors), hepatic swelling, congestion and mottling, fibrin tags on serosal surfaces of viscera, renal congestion, and gastrointestinal congestion.(2,4,8) Microscopic lesions generally are confined to the liver, with characteristic centrilobular/periacinar (zone 3) to midzonal (zone 2) or rarely panzonal hepatocellular degeneration, necrosis, and apoptosis with congestion and/or hemorrhage; however, lesions also may be observed in the kidney (e.g. tubular epithelial degeneration and necrosis) and brain (e.g. neuronal degeneration/necrosis and cerebral edema) on occasion.(2,4,5,8) Diagnosis of cocklebur poisoning generally requires some combination of the following: 1) evidence of ingestion of cotyledonary seedlings or seeds/burs, 2) appropriate history and clinical signs, 3) characteristic clinical pathology findings, and 4) consistent gross and microscopic lesions. Diagnostic assays that detect the toxic principle in tissues or other biological samples have been or are being developed, but none are routinely or widely available to veterinary diagnosticians.

Treatment of affected animals is generally unrewarding once clinical signs have progressed to the neurological stage, and there is no antidote for the toxic principle; supportive care and therapy aimed at increasing gastrointestinal clearance of ingested plants, decreasing gastrointestinal absorption of the toxin, and treating metabolic and neuromuscular complications all have been shown to be effective on occasion. Prevention of poisoning is more effective than treatment of clinical cases, and can be achieved by elimination of plant populations (e.g. mowing before seed production begins, use of herbicides, limiting access to contaminated pastures and meadows, manual removal of plants from hay fields, etc.).

JPC Diagnosis:  

Liver: Hepatocellular necrosis, coagulative, centrilobular and midzonal (submassive), acute, diffuse.

Conference Comment:  

In WSC 2009-2010, Conference 12, case IV, we discussed the reasons why centrilobular hepatocytes are particularly susceptible to hypoxic injury and to indirect-acting toxins that undergo biotransformation through cytochromes P450. This superb example of centrilobular to midzonal hepatocellular necrosis due to cocklebur ingestion provides a timely reminder of the importance of pattern recognition in the evaluation of hepatic lesions. We thank the contributor for a concise overview of the entity.

The bulk of the discussion during the conference was focused on toxic plants that cause centrilobular to midzonal hepatocellular necrosis. Several of these are summarized in the table below:(1)

Hepatotoxic Plants Causing Centrilobular Necrosis
Plant Family	Plants	Species Affected	Toxic Principle
Compositae	Xanthium spp.	Pigs, cattle	Carboxyatractyloside
Myoporaceae	Myoporum spp.	Pigs, cattle, sheep, horses	Furanosesquiterpenoid oils (ngaione)
Leguminosae	Cassia spp.Â	Cattle	Unknown
Ulmaceae	Trema aspera	Cattle, sheep, goats	Trematoxin
Solanaceae	Cestrum parqui	Cattle, sheep	Saponins
Zamiaceae Cycadaceae Strangeriaceae		Cattle, sheep, goats, dogs	Methoxymethanol
Fabaceae	Indigofera linnaei	Cattle, dogs	Indospicine
Cyanophyceae	Microcystis spp., Aphanizomenon spp.	Cattle, sheep, goats, horses, dogs	Microcystins, others

As mentioned by the contributor and well-illustrated by this case, the investigation of a suspected plant intoxication often involves linking a number of pieces of evidence, including clinical signs, pathological and clinical pathological findings, examination of the feed and/or environment for the offending plant(s), and ancillary diagnostics, when available. In this case, the use of an investigational assay to detect carboxyatractyloside in rumen contents proved helpful in substantiating the diagnosis.

References:

1. Cullen JM: Liver, biliary system, and exocrine pancreas. In: Pathologic Basis of Veterinary Disease, eds. McGavin MD, Zachary JF, 4th ed., p. 441. Mosby Elsevier, St. Louis, MO, 2007
2. Martin T, Stair EL, Dawson L: Cocklebur poisoning in cattle. J Am Vet Med Assoc 189:562-563, 1986
3. Mendez, MC, dos Santos RC, Riet-Correa F: Intoxication by Xanthium cavanillesii in cattle and sheep in southern Brazil. Vet Human Toxicol 40:144-147, 1998
4. Stalker MJ, Hayes MA: Liver and biliary system: toxic hepatic disease. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 2, pp. 368-369. Saunders Elsevier, Philadelphia, PA, 2007
5. Stuart, BP, Cole RJ, Gosser HS: Cocklebur (Xanthium strumarium, L. var. strumarium) intoxication in swine: review and redefinition of the toxic principle. Vet Pathol 18:368-383, 1981
6. Turgut M, Alhan CC, Gurgoze M, Kurt A, Dogan Y, Tekatli M, Akpolat N, Aygun D: Carboxyatractyloside poisoning in humans. Ann Tropical Paediatr 25:125-134, 2005
7. Whitson TD, Burrill LC, Dewey SA, Cudney DW, Nelson BE, Lee RD, Parker R, Ball DA, Cudney D, Dewey SA, Elmore CL, Lym RG, Morishita DW, Swan DG, Zollinger RK: Common cocklebur. In: Weeds of the West, ed. Whitson TD, 9th ed., pp. 194-195. Western Society of Weed Science/Western United States Land Grant Universities Cooperative Extension Service/University of Wyoming, Laramie, WY, 2001
8. Witte ST, Osweiler GD, Stahr HM, Mobley G: Cocklebur toxicosis in cattle associated with the consumption of mature Xanthium strumarium. J Vet Diagn Invest 2:263-267, 1990

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3-1. Liver

3-2. Liver

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