Collett M G, Thompson K G, Christie R J
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.
N Z Vet J. 2011 May;59(3):147-52. doi: 10.1080/00480169.2011.567966.
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.
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.
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.
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.
2006年3月，对新西兰朗伊蒂凯地区一个农场中6至8月龄的弗里斯兰小母牛犊发生的光过敏疫情进行了调查。这些犊牛在小麦茬牧场放牧，牧场中还有各种杂草，尤其是商陆（墨水草）。它们还能接触到含有潜在有毒浓度蓝藻（蓝绿藻）微囊藻属和席藻属的池塘水。
最初，患病动物表现出急性刺激、烦躁不安、不愿行走，部分动物出现躺卧、无色素皮肤充血和黄疸。血清化学检查显示肝酶活性升高和氮血症。在疫情后期，无色素皮肤出现渗出性皮炎并形成痂皮、脱水和食欲不振是明显症状，偶尔还出现腹泻。
对4头严重患病犊牛实施安乐死以及对1头自然死亡的动物进行尸检后发现，肝脏明显呈橙褐色且轻度肿大，肾脏肿大且呈浅褐色。肝脏的微观病变较轻；然而，在前两例中，在胆管中发现了小的双折射晶体。相比之下，肾脏病变为中度至重度，包括明显的节段性肾小管坏死、颗粒和细胞管型，以及轻度间质性非化脓性炎症。在疫情后期检查的动物肾脏中，出现了早期间质纤维化以及肾小管再生，肾髓质中有大量透明管型。墨水草植物被大量啃食，在患病犊牛的胃肠道中发现了该植物的可识别部分。对墨水草材料的化学分析显示含有三萜皂苷。在牧场中未发现已知的肝毒性或肾毒性植物。肝脏病变与已发表的蓝藻毒性描述不一致。排除了柄曲霉素中毒。
肝源性光过敏、晶体相关性胆管肝炎、中毒性急性肾小管坏死，与摄入商陆有关，可能因水中蓝藻而复杂化。
牛的晶体相关性胆管肝炎伴光过敏很少见，仅在巴西有含甾体皂苷的俯仰臂形草中毒的报道。中毒性急性肾小管坏死的一致模式与摄入栎属、苋属或马缨丹属植物引起的相似。可以想象存在多种毒性组合，但间接证据强烈表明与商陆有关。在将这种植物列为已知的牛肾毒素之前，有必要对其进行进一步的毒理学研究。
