Photosensitisation, crystal-associated cholangiohepatopathy, and acute renal tubular necrosis in calves following ingestion of Phytolacca octandra (inkweed)

Abstract

CASE HISTORY: In March 2006, an outbreak of photosensitivity affecting 6–8-month-old Friesian heifer calves on a farm in the Rangitikei district of New Zealand was investigated. The calves were grazing wheat stubble paddocks that also had a variety of weeds, especially Phytolacca octandra (inkweed). They also had access to pond water that contained potentially toxic concentrations of the cyanobacteria (blue–green algae) Microcystis and Planktothrix spp.

CLINICAL FINDINGS: Initially, affected animals showed acute irritation, agitation, reluctance to walk, recumbency in some animals, hyperaemia of unpigmented skin and jaundice. Serum chemistry revealed elevated liver enzyme activities and azotaemia. Later in the outbreak, exudative dermatitis with formation of crusts on unpigmented skin, dehydration and inappetence were notable signs, as well as occasional diarrhoea.

PATHOLOGICAL AND TOXICOLOGICAL FINDINGS: Post-mortem examinations following euthanasia of four severely affected calves and a fifth animal that died naturally revealed livers that were grossly orange brown and mildly enlarged, and kidneys that were enlarged and pale brown. Microscopic lesions in the liver were mild; however, small birefringent crystals in the bile ducts were noted in the first two cases. In contrast, renal lesions were moderate to severe, and included prominent segmental tubular necrosis, granular and cellular casts, and mild interstitial non-suppurative inflammation. In the kidneys of animals examined later in the outbreak, there was early interstitial fibrosis as well as tubular regeneration, with numerous hyaline casts in the renal medulla. Inkweed plants had been heavily browsed, and recognisable portions of the plant were found in the gastrointestinal tracts of affected calves. Chemical analysis of inkweed material revealed triterpene saponins. No known hepatotoxic or nephrotoxic plants were identified in the paddocks. The hepatic lesions were not consistent with published descriptions of cyanobacterial toxicity. Sporidesmin toxicity was ruled out.

DIAGNOSIS: Hepatogenous photosensitivity, crystal-associated cholangiohepatopathy, toxic acute renal tubular necrosis, associated with the ingestion of P. octandra, and possibly complicated by cyanobacteria in the water.

CLINICAL RELEVANCE: Crystal-associated cholangiohepatopathy with photosensitivity in cattle is rare, and has only been reported in steroidal saponin-containing Brachiaria decumbens poisoning, in Brazil. The consistent pattern of toxic acute renal tubular necrosis was similar to that caused by the ingestion of Quercus, Amaranthus or Lantana spp. A combination of toxicities was conceivable but circumstantial evidence strongly implicated P. octandra. Further toxicological investigation of this plant is warranted before it can be listed as a known nephrotoxin of cattle.

KEY WORDS:

• Photosensitivity
• biliary crystal
• renal tubular necrosis
• Phytolacca octandra
• Microcystis sp.
• cyanobacteria
• bovine

Acknowledgements

We thank Aidan Smith, and staff of Southern Rangitikei Veterinary Services Limited; Adrienne French, Jenni Donald and technical staff of New Zealand Veterinary Pathology Limited; Pat Davey, Evelyn Lupton and Mary Gaddam for their histological expertise; Kerry Harrington for the identification of plants; Chris Miles, Jared Loader and Alistair Wilkins for the saponin analysis; Roster Group 7 (2006) final year veterinary students; Quentin Roper for assisting with the images; and Roger Dalrymple for his cooperation.

Notes

¹ CO Miles, AgResearch, Hamilton, New Zealand

*Non-peer-reviewed