CASE NOTES

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Five Outbreaks of Listeria ivanovii Abortion in Sheep and Goats on the Central Tablelands of NSW

Conor McConnell (final year veterinary student at Charles Stuart University Wagga Wagga), Jess Bourke (Central Tablelands LLS DV, Mudgee), Emilee Johnstone (Central Tablelands LLS DV, Cowra) and Bruce Watt (Central Tablelands LLS DV, Bathurst)

Posted Flock & Herd February 2022

Introduction

The two species of Listeria that cause disease in ruminants are Listeria ivanovii and L monocytogenes. L ivanovii causes enteritis and abortion in ruminants but both conditions are rarely seen together. L monocytogenes can cause gastroenteritis, abortion, and meningoencephalitis in ruminants. Listeria are often found in the gastrointestinal tract of healthy sheep with no adverse effects (Hughes 1975; Quinn et al. 2002; Sahin and Beytut 2006). Typically, L. ivanovii has caused sporadic abortion storms in sheep. Abortions usually occur 4-6 weeks before lambing. Lambs can also be born dead and alive, though infected lambs rarely survive long enough to walk or suckle. Ewes generally seem healthy. Transmission is usually through a contaminated feed source. Listeria are predominantly found in wet rotting vegetation. Mouldy silage is also a high risk for Listeria growth. Listeria has a zoonotic risk with symptoms in humans including influenza-like symptoms. In pregnant women infection can lead to abortion. PPE should be worn if assisting parturition and whilst handling suspected aborted foetuses (Abbott, 2018).

This paper reviews five abortion outbreaks in sheep and goats in NSW caused by L. ivanovii. This abortion storm is also compared with others reported in the literature to identify trends in relation to the clinical presentation, timing, location, potential sources of infection and diagnostic finding.

CASE 1 - Mudgee

An outbreak of abortion in a mob of 1000 Merino ewes in Mudgee, NSW, was investigated in mid-October. A total of 41 late-term abortions were identified within the mob. The mob was grazing pasture before and throughout the outbreak with no supplementary feed provided. This property had been quarantined for footrot six weeks previously. In that time the ewes had been tipped using a Peak handler and foot bathed. The ewes did not exhibit any other abnormalities.

Post-mortem findings of two aborted lambs were unremarkable. The two aborted foetuses were submitted for gross pathology, histopathology, and culture. Histopathology was unremarkable, however the abdominal fluid of both foetuses cultured positive for L. ivanovii.

CASE 2 - Cowra

In late July, over a three-day period eight cases of abortion were identified in a mob of 60 cross-breed ewes that were approximately four weeks from the end of gestation. These ewes were grazing a lucerne paddock and receiving supplementary lucerne hay. The ewes that aborted did not exhibit any further abnormalities.

Post-mortem findings of two aborted foetuses were unremarkable. The two aborted foetuses were submitted for gross pathology, histopathology, and culture. In foetus 1, L. ivanovii was isolated from pooled tissues. This foetus also had hepatitis and foetal bronchopneumonia consistent with listeria infection. Chlamydia pecorum was detected by PCR in foetus 2. Placentitis consistent with C. pecorum infection was also evident in foetus 2.

This outbreak was managed by blanket treating the mob with oxytetracycline and removal of all aborted foetuses and placental membranes. The mob was moved to a different paddock and supplementary feeding with lucerne hay was discontinued. No further cases of abortion were reported in this mob.

CASE 3 - Cowra

An outbreak of abortion in a mob of 26 ewes in Cowra, NSW, was investigated in mid-August. Two cases of late-term abortion occurred over the space of two days in ewes that were five weeks from their end of gestation. The ewes did not exhibit any other clinical abnormalities. Feed consisted of pasture with no supplementary feed provided. Three aborted foetuses were submitted for gross pathology, histopathology, and culture.

Post-mortem findings for the two foetuses included doughnut shaped, focal, white lesions on the skin, liver, and lungs. L ivanovii was cultured from the liver and lungs of both foetuses.

Management included blanket treatment with oxytetracycline. The mob remained in the original paddock as options for rotation into a different paddock was limited on this property. No further incidences of abortion were reported.

CASE 4 - Cowra

Over a three-week period in late June, 14 ewes in a mob of 194 ewes aborted in Cowra, NSW. These ewes were grazing oats with access to a salt/lime/Causmag mineral mix. This property has had undiagnosed foetal loss in ewes for several years.

Three aborted foetuses were submitted for gross pathology, histopathology, and culture. Post-mortem findings were unremarkable. L ivanovii was cultured from the stomach contents of the foetus submitted.

This outbreak was managed by blanket treating the mob with oxytetracycline, the removal of all aborted foetuses and placental membranes. No further abortions were reported.

CASE 5 - Mudgee

An outbreak of abortion in a mob of 170 does in Mudgee, NSW, was investigated in early October. A total of 40 late-term abortions occurred intermittently over approximately three weeks. The does were 5-6 weeks from the end of their gestation.

Two aborted foetuses were submitted for gross pathology, histopathology, and culture. Both foetuses had multifocal approximately 1mm diameter discrete white lesions on their liver. Otherwise, the post-mortems were unremarkable. L ivanovii was cultured from the stomach contents of the foetus submitted. The owner did not treat the mob with antibiotics due to concerns of mismothering.

	Case 1	Case 2	Case 3	Case 4	Case 5
Location	Mudgee	Cowra	Cowra	Cowra	Mudgee
Species	Sheep, Merino	Sheep, Mixed breed	Sheep, Merino	Sheep, Border Leister	Goat, Boer
Flock Size	1000	60	26	194	170
Infected	41 (4.1%)	8 (13.3%)	2 (7.6%)	14 (7.2%)	40 (23.5%)
Time	Mid October	Late July	Mid August	Late June	Early October
Feed	Pasture	Lucerne pasture and Lucerne hay	Pasture	Grazing Oats	Pasture
Stage of gestation	4-5 weeks from lambing	5-6 weeks from lambing	Five weeks from lambing	Five weeks from lambing	5-6 weeks from kidding
Differential Diagnosis	Chlamydia pecorum Campylobacteriosis Border disease	Campylobacteriosis Listeriosis	Campylobacteriosis Listeriosis Q-Fever Toxoplasmosis	Q-Fever Toxoplasmosis Chlamydiosis	Campylobacteriosis
Postmortem Findings	Unremarkable	Unremarkable	Multifocal, white lesions on skin and liver	Unremarkable	1mm multifocal, white lesions on liver
Bacteriology	L. ivanovii positive	L. ivanovii positive 1 lamb was positive for C. pecorum	L. ivanovii positive	L. ivanovii positive	L. ivanovii positive

Table 1. The location, species, flock size, percentage infected, time, feed, stage of gestation, differential diagnosis, post-mortem findings, bacteriology of five cases of L ivanovii abortion in sheep and goats

Figure 1. Multifocal yellowish-white necrotic foci of varying size of an aborted lamb's liver (case 3)

Figure 2. Multifocal yellowish-white necrotic foci of varying size of skin of aborted lamb (case 3)

Discussion

L. ivanovii has been associated with isolated abortion storms, causing sporadic abortion and neonatal death in sheep (Sergeant, Love and McInnes 1991; Gill et al. 1997). The five cases in this report occurred in the Cowra and Mudgee areas of the Central Tablelands of NSW. The abortion outbreaks took place between June and October, a period of longer duration than for previous outbreaks, which occurred between June and August (Rajkumar et al., 2011). Listeria can survive in temperatures ranging from −18°C to 25°C. As October of 2021 has been the coolest since 2016 and September of 2021 had, on average, 20% more rainfall, these factors may have contributed to the extended time frame of this outbreak (Australian Government Bureau of Meteorology, 2021).

The abortion rate varied from 4.3% to 23.5%. The percentage of sheep or goats affected ranged from 4.3% to 13.3%, which is consistent with previous reports of abortion (Chand and Sadana 1999; Sahin and Beytut 2006; Mearns 2007).

Gross abnormalities of the liver consisting of multifocal, pale to white lesions is consistent with L. ivanovii infection (Brugere-Picoux 2008). These lesions were evident in cases 3 and 5 and were absent in cases 1,2 and 4.

All five cases reported here were confirmed as L. ivanovii infection through isolation of bacterial colonies exhibiting features consistent with the organism. L. ivanovii was cultured from samples of the liver, lungs and stomach contents of the foetuses presented, which is consistent with previous reports (Sergeant, Love and McInnes 1991; Chand and Sadana 1999; Gill et al. 1997; Sahin and Beytut 2006).

Four of the five properties (cases 1-4) in this report treated the affected mobs with oxytetracycline. No further abortions were reported in any of the cases after the blanket treatment of antibiotics, up until two weeks after the treatment. It is unknown if there were any further reports thereafter. Case 5 chose not to treat with antibiotics as the property owners believed there would be a risk of mismothering. Removal of the aborted foetus and placental membrane is recommended as this material is a potential source of infection for the rest of the flock (Brugere-Picoux, 2008).

L. ivanovii can survive in a range of environments, including cold, wet weather and rotten vegetation (Hughes 1975; Sergeant, Love and McInnes 1991; Gill et al. 1997; Sahin and Beytut 2006; Mearns 2007; Brugere-Picoux 2008). These cases all occurred during wet conditions, with grazing pasture like that from an L. ivanovii abortion outbreak that occurred in the Riverina area in 2011 (Rajkumar et al. 2011). No silage was feed in any of these cases, which demonstrates that decomposing pasture and crops provide suitable sites for the growth of L. ivanovii.

Abortion outbreaks in these cases occurred in the last 4-6 weeks of gestation. This finding is consistent with previous L. ivanovii outbreaks and suggests that stress associated with late-stage pregnancy is a risk factor for L. ivanovii abortion (Rajkumar et al., 2011).

References

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