CASE NOTES
Acute lupinosis with concurrent contagious ophthalmia and polioencephalomalacia in weaned lambs in the South Australian Mallee
Jeremy Rogers, Strathalbyn, SA and Dr Julie Wayne BVSc(hons), MVSC, MANZCVS (Pathobiology), DACVP (Anatomic Pathology) Gribbles VETLAB
Posted Flock and Herd August 2023
Introduction
Lupinosis develops when rain or heavy dews wet the stubble of susceptible lupin species. These circumstances lead to rapid development of fungus Diaporthe toxica (previously called Phomopsis leptostromiformis) that when ingested causes liver damage and lupinosis. In this case many affected sheep had a concurrent keratoconjunctivitis that may have been related to the lupinosis.
History
Approximately 285 healthy ewe hoggets from the South Australian Mallee region were grazing on narrow-leafed or sweet lupin, variety PBA Jurien lupin stubbles in April 2023. After three days the hoggets were taken off the lupin stubble and put onto canola stubble, where shortly after the producer noticed sheep with neurological signs of "star gazing", "walking into fences", "stiff back legs", and some died. By 2 May 2023 a total of 15 lambs and five rams had died and about 15 more lambs were unwell. Most of these lambs also had red, inflamed eyes with some discharge. By the end of the outbreak, about one month later, more than 140 lambs from this property died, with large losses also on neighbouring properties.
A similar group of young ewes that had not grazed lupin stubbles also developed unusual symptoms of being "excited, running into things and appearing blind". Some of these lambs appeared to have inflamed eyes and these were treated with Terramycin spray, and all affected sheep were given Vitamin B1 injections, and supplemented with thiamine in water and feed. These lambs appeared to recover.
Post-mortem findings
One moribund ewe lamb from the group of 285 lupin-affected group was examined. It was noted to have a body temperature of 40.2°C. It was then euthanised, and a post-mortem performed. Haemorrhages on intestines, diaphragm and elsewhere were observed as were inflamed eyes. There was yellowish discolouration of abdominal fat, and a small, hard, bright yellow liver with grossly enlarged gall bladder (Image 1).
Image 1. Necropsy case 1 showing the yellow, shrunken, fibrotic liver and haemorrhages on serosal surfaces of organs
Image 2. Affected sheep with keratoconjunctivitis
Image 3. Another affected sheep with conjunctivitis
Following this examination, two autolysed sheep on the property (including one ram) were examined - the only observation was minimal body fat and a very small liver.
A neighbouring property was visited that had around 150 lambs contained in a feedlot, all of which had exposure to lupin stubble for a week or more. Twenty of these lambs had died in the past few days, and three freshly dead lambs were post-mortemed - all had small, hard, yellow livers.
Subsequently, the producer commented that 140 lambs had died from his affected mob - nearly 50%, and he was aware that neighbours also suffered significant mortalities amongst their sheep from lupinosis.
Histopathology findings
Diagnosis: Chronic hepatotoxicity with linking fibrosis, hepatocellular fatty change and occasional mitotic figures.
Comments
Histology confirms a severe hepatotoxicity. Histologically, features are most consistent with lupinosis.
Discussion
This case report describes a particularly severe event following a short exposure period, including rapid deaths and continuing mortalities for the following 2-4 weeks. In my experience most deaths from lupinosis occur in the first 7-10 days, and then taper off with mortality usually in the range of 10-30%.
For the surviving ewe hoggets, there is a possibility that some of these may have liver damage that may predispose them to cases of pregnancy toxaemia, especially if carrying twins, and failure to thrive. It may be possible to identify these sheep after shearing based on body size and condition. Ewes that appear affected at shearing may need to be culled.
I have never seen or heard of the symptoms of red inflamed eyes, high body temperatures, or shrunken, fibrotic livers as experienced in this case. The inflamed eyes could have been concurrent 'pinkeye', but only severely affected lambs appeared to have this symptom. These symptoms are not reported in the literature, but may be a feature in some acute cases? Haemorrhages on intestines and diaphragm, which were observed in this case, are also considered an unusual feature and have also been observed under the skin in some cases.1
One group of lambs that were presented at the same time presumably had polioencephalomalacia as these sheep responded well to treatment with thiamine injection and thiamine in water. These lambs were not exposed to the lupins.
Diaporthe-resistant varieties of narrow-leafed lupin (Lupinus augustifolius) 2 are available, and if it is intended to use stubbles for sheep grazing Phomopsin levels can be measured in stubbles, hay and lupin grains and the toxicity estimated accordingly.3 Further advice on detection of affected lupin grain and stubbles and grazing practice is available on some Department of Agriculture websites.4
This case demonstrates the value of a thorough veterinary examination and property visit, with multiple post-mortems to determine causes of morbidity and mortality. Two different disease processes (PEM and lupinosis) affected two separate groups of sheep with an unusual presentation of lupinosis.
PIRSA assists in investigations of morbidity and mortality in livestock to enable early detection of new or exotic diseases (that may initially appear very similar to endemic ones), and to support local veterinary practices as requested.
References
- Abbot K (2018) The Practice of Sheep Medicine University of Adelaide Press 2018
- Radostits OM, Gay CC, Blood DC and Hinchcliff KW (2000) Veterinary Medicine 9th edition. WB Saunders 2000
- Arney and Rogers (2018) Lupinosis (Phomopsin) affected cereal hay kills sheep: a report. www.flockandherd.net.au
- www.agric.wa.gov.au