Keratitis due to Histoplasma spp. in a horse

A 5-year-old Holsteiner gelding from Germany was presented 2 months after a whitish discoloration of the left cornea was observed. Cytologic examination revealed intra- and extracellular globular structures, up to 4 micro m in size, consisting of a central spherical deeply basophilic body surrounded by an unstained halo. The structures were morphologically consistent with Histoplasma spp. Infection with Histoplasma organisms is not endemic in Europe. Topical use of fluconazole was successful in eliminating Histoplasma organisms within 10 days of initiation of treatment.     

Diagnosis and approach to poisoning in the horse.

Poisoning in the horse can present a highly complex case. The practitioner, owner, toxicologist, and pathologist play important roles, and all contribute information that may be important to the case. Once all the information is available, all the evidence is collected (historical, clinical, pathologic, and analytic), and proper sampling of specimens has occurred, a complete summary of the findings can be provided to the client. Based on identification of a potential toxic source and, ultimately, the diagnosis, specific treatment of affected animals and prevention of additional cases can be initiated. Consultation with a veterinary toxicologist aids in the follow-up of a poisoning case and can help to provide a thorough background to assist in preventing reoccurrence.     

Acute lead poisoning in cows due to feeding of lead contaminated ash residue

In a dairy herd of 21 cows which were on pasture during the day at the end of May 2002, four eight years old cows were suddenly inappetent and showed severe diarrhoea consisting of black discolorate feces. A few days after the onset of the disease, three affected cows exhibited neurological disorders. These cows were admitted to the IInd Medical Clinic of the University for Veterinary Medicine in Vienna. Following clinical signs were observed: circulatory weakness, anorexia, atony of the rumen, diarrhoea and in accordance with acute lead poisoning typical signs of the central nervous system. One cow died and the other two animals were euthanized. Results of blood testing were anaemia, basophil spotting of erythrocytes, increase of liver enzymes and CK, hypocalcaemia, decrease of potassium and phosphate. The cerebrospinal fluid of two cows showed increased CK-, LDH- and AST-values. The lead contents of whole blood samples were between 0.486 and 0.928 mg/kg, of liver samples 13.3 to 114.4 mg/kg, of kidney samples 172.2 to 448 mg/kg and of rumen content 59 mg/kg fresh matter. At necropsy, enteritis, liver fluke disease and severe interstitial and alveolar pulmonary emphysema were found. Pathohistologically typical ischaemic necrosis of neurons predominantly at the tips of the gyri, disseminated petechial hemorrhages and moderate diffuse neovascularisation, but no acid-fast intranucleolar inclusion bodies in the renal tubules were observed. As causative agent of the acute lead poisoning a residue on combustion, taken up by the cows on the pasture, was confirmed. The ash residue was formed by combustion of three tires which contained 450 g heavy weights of 96.5% lead for wheel balance. The lead content of the ash residue was between 2.9 and 28 g/kg dry matter.     

Moldy sweetclover poisoning in a horse

A six year old Percheron mare was presented with a history of spontaneous unilateral epistaxis of 24 hours duration. The blood one stage prothrombin and partial thromboplastin times were markedly prolonged. A diagnosis of moldy sweetclover poisoning was made on the basis of the history and clinical and laboratory findings. A single whole blood transfusion and four daily intravenous injections of vitamin K₃ proved to be a successful treatment.     

Suspected selenium poisoning in a horse

A case of selenium poisoning was suspected following the administration of 325 micromol selenium a day as sodium selenate (25 mg Se) for five consecutive days. The main signs were confined to changes in the integument which were loss of hair from the mane and tail, disintegration of the skin of the anus, lips, prepuce and scrotum, and separation of the hooves from the coronary corium. Periodic analyses of blood, hair and hoof parings from the sole correlated strongly with blood and identified horn and hair as important additional routes of excretion.     

Ataxia due to lymphosarcoma in a young horse

A 20-month-old, Standard-bred colt was presented with an acute onset of hindlimb ataxia. Clinical and radiographic examination identified a compressive lesion affecting the spinal cord at the level of the 17th to 18th thoracic vertebrae. After euthanasia, post-mortem examination revealed a tumour in the epidural space, diagnosed histologically as a lymphosarcoma. Neoplastic lymphoid cells were also present in the abdominal lymph nodes and brain. Because of the disseminated nature of lymphosarcoma in the horse, involvement of the central nervous system is likely to be more common than is presently recognised.     

Radiculomeningomyelitis due to Halicephalobus gingivalis in a horse

An adult horse was euthanatized following a clinical diagnosis of cauda equina neuritis. Significant gross postmortem and histopathologic findings were limited to the sacral spinal cord and cauda equina. The sacral spinal cord, meninges, and spinal nerve roots were expanded and partially effaced by sclerosing granulomatous inflammation with necrosis. The lesion contained numerous nematode larvae and fewer adults with a rhabditiform esophagus having a corpus, isthmus, and valved bulb. Female nematodes were amphidelphic and didelphic with reflexed ovaries. These morphologic features confirm Halicephalobus gingivalis as a novel cause of clinical signs in this case of cauda equina neuritis.     

Suspected swainsonine poisoning in a Belgian horse

The case of a horse with acute symptoms of excitement, exaggerated fright reactions and trembling is presented. In addition to these cerebral symptoms, mild cerebellar ataxia and a renal tubular lesion were diagnosed. Suspected swainsonine poisoning was confirmed by the presence of the toxin (154 ng/ml) in the serum sample taken immediately after admission. A good recovery was seen after fluid therapy with supplementation of potassium, a dopamine drip and administration of diazepam. The effects of the toxin, by inhibiting the lysosomal enzyme α‐mannosidase and mimicking the genetic mannosidosis, are discussed.     

Methiocarb poisoning of a horse in Australia

Snail bait poisoning is rare in horses. Cases have been reported, but clinical signs and subsequent prognostic indicators have been poorly documented and must be extrapolated from cases in companion animals. We describe in detail the poisoning of a horse that consumed a lethal dose of the carbamate, methiocarb. There are currently no guidelines for treating equine methiocarb toxicoses, but the principles of management are based on supportive therapy.     

Diagnosis of Taxus (yew) poisoning in a horse.

A 2-year-old bay Thoroughbred colt was found dead overnight in its stall without a known history of any illness, existing disease, or toxicant exposure. No information on the clinical signs before this animal's death was reported. A full necropsy was performed the next morning and revealed a mild to moderate degree of endocardial hemorrhages in both ventricles. Microscopic examination of the heart showed an acute mild multifocal necrosis of papillary muscles and ventricles. The stomach content contained approximately 2% Taxus alkaloids as determined by gas chromatography/mass spectrometry. In the past, diagnosis of Taxus poisoning has been mainly based on history of exposure and the presence of plant parts in the gastrointestinal tract. Pathological lesions associated with Taxus poisoning have not been published for horses. Therefore, this is the first report of cardiac lesions in a horse after lethal exposure to Taxus. On the basis of these findings, it is suggested that Taxus exposure needs to be considered in the differential diagnosis of horses that die suddenly or have cardiac lesions suggestive of Taxus exposure, even if intact plant parts are not identified in the stomach by the naked eye.     

Pelvic limb lameness due to malignant melanoma in a horse

Malignant melanoma in a 21-year-old, gray, Arabian gelding was manifested by rapidly deteriorating lameness of the right pelvic limb. A melanotic, cutaneous mass of small dimensions was identified in the left jugular furrow. Exploratory laparoscopy revealed widespread infiltration of melanotic masses into the structures of the abdominal cavity. Necropsy indicated the lameness to have resulted from infiltration of neoplastic cells into the sacral nerves, dorsal root ganglia, proximal ischiatic nerve, and gluteal muscle fibers. The primary tumor could not be identified.     

Jejunal perforation due to porcupine quill ingestion in a horse

An 8-month-old Andalusian filly was treated for jejunal perforations due to ingestion of a porcupine quill. During exploratory laparotomy, 2 separate stapled side-to-side jejunojejunal resection and anastomoses were performed. Post-operative complications after 2 years follow-up included mild incisional herniation following incisional infection and chronic intermittent colic.     

Tansy ragwort poisoning in a horse in southern Ontario

Bizarre behavior, apparent lameness, and colic were noticed in 1 of 3 horses on a pasture overgrown by weeds during a drought. Liver failure and hepatoencephalopathy were diagnosed, caused by pyrrolizidine alkaloid toxicosis associated with consumption of tansy ragwort. The horse made a full recovery when removed from the pasture.     

Cutaneous fungal granulomas due to Alternaria spp. infection in a horse in New Zealand

Equine cutaneous fungal granulomas have been previously referred to in New Zealand (Fairley 1998), and are described in the veterinary literature from around the world, including North America and Australia (Pascoe and Summers 1981; Genovese et al. 2001; Valentine et al. 2006), but no peer-reviewed reports appear published in the literature in New Zealand. Described here is a case of multiple cutaneous fungal granulomas caused by Alternaria spp. in a horse in New Zealand.     

Sudden death due to thoracic lymphoma in a standardbred racing horse

During training, a 6-year-old standardbred gelding collapsed, exhibiting severe epistaxis and agonal breathing and was euthanized. The horse had a recent history of poor performance, lethargy, and unilateral eyelid swelling with serous ocular discharge. Postmortem and histopathologic examination findings revealed thoracic lymphosarcoma and concurrent exercise-induced pulmonary hemorrhage.