Listeria organisms that are ingested or inhaled tend to cause septicemia, abortion, and latent infection. Those that gain entry to tissues have a predilection to localize in the intestinal wall, medulla oblongata, and placenta or to cause encephalitis via minute wounds in buccal mucosa.
The various manifestations of listeriosis occur in all susceptible species and are associated with characteristic clinical syndromes: encephalitis or meningoencephalitis in adult ruminants, abortion and perinatal mortality in all species, septicemia in neonatal ruminants and monogastric animals, and septicemia with myocardial or hepatic necrosis [or both] in poultry Listeriosis read more .
Listeric encephalitis affects sheep, cattle, goats, and occasionally pigs. It is essentially a localized asymmetric infection of the brain stem that develops when L monocytogenes ascends the trigeminal nerve. Clinical signs vary according to the function of damaged neurons but often are unilateral and include depression [ascending reticular activating system], ipsilateral weakness [long tracts], trigeminal and facial nerve paralysis, and less commonly, circling [vestibulocochlear nucleus], excitement, and recumbency.
Septicemic or visceral listeriosis is most common in monogastric animals, including pigs, dogs, cats, domestic and wild rabbits, and many other small mammals. These animals may play a role in transmission of L monocytogenes. This form of disease is also found in young ruminants before the rumen is functional. Although rare, septicemia has been reported in older domestic ruminants and deer. The septicemic form affects organs other than the brain, the principal lesion being focal hepatic necrosis.
The uterus of all domestic animals, especially ruminants, is susceptible to infection with L monocytogenes at all stages of pregnancy, which can result in placentitis, fetal infection and death, abortion, stillbirths, neonatal deaths, metritis, and possibly viable carriers. The metritis has little or no effect on subsequent reproduction; however, Listeria may be shed for 1 month or longer via the vagina and milk.
Infections acquired via ingestion tend to localize in the intestinal wall and result in prolonged fecal excretion. It has been postulated that contaminated silage results in latent infections, often approaching 100% of the exposed herd or flock; however, clinical signs of listeriosis may be seen in only a few animals.
Listeriosis is a disease that affects a variety of animals and can cause neurological problems, abortion and other symptoms. People are also susceptible to listeriosis infection from consuming contaminated food and have to take precautions to stay healthy.
Cause
Listeria monocytogenes is the bacterium that causes listeriosis. It is found throughout the environment, especially in soil, manure and spoiled silage or hay. Outbreaks are usually associated with some kind of stress, such as poor-quality feed or sudden changes in weather. The bacteria can also be present in the feces of healthy, unaffected animals and people.
Clinical Signs
Listeriosis usually affects ruminants such as cattle [Figure 1], sheep and goats, and causes a range of clinical signs in these animals. Affected animals will have a fever and a poor appetite and will appear depressed. Some animals may have paralyzed face muscles. In some cases, the animal may be uncoordinated, may walk in a circle with its neck twisted to one side or may press its head against a solid surface.
Figure 1. Listeriosis usually affects ruminants.
Animals in the late stages of pregnancy may abort or give birth to stillborns. Some animals die from the disease. In rare cases, mastitis or pinkeye can occur.
Birds, such as chickens, turkeys, geese, ducks, canaries and parrots can also be infected by listeriosis. Birds may show no signs of disease or may be depressed, paralyzed or may die suddenly. Some birds may also have diarrhea.
Listeriosis can also affect rabbits, especially pregnant does, as well as pigs, dogs and cats. These animals will have a fever and a poor appetite, will appear depressed and may have diarrhea or respiratory problems.
Treatment
A veterinarian can diagnose listeriosis and prescribe antibiotics for infected animals. Treatment may not be successful in the later stages of the disease.
Prevention and Management
Control of listeriosis is difficult, as the bacteria are present throughout the environment [Figure 2]. Avoid feeding spoiled silage to animals. Separate sick animals from the herd and examine them promptly.
Figure 2. Listeria bacteria are present everywhere.
Transmission to Humans
Listeriosis is not directly transmissible from animals to humans. However, in rare situations, outbreaks of listeriosis occur in humans. People become infected with the bacteria through eating contaminated vegetables, consuming unpasteurized milk or milk products, and through improperly cooked meats or foods contaminated after processing, such as hot dogs, deli meats and cheese. The bacteria survive at refrigerator temperature ranges. Discard foods that are past their "best before" date, and properly wash and prepare all foods.
Symptoms may start suddenly and include vomiting, nausea, cramps, diarrhea, constipation, severe headache or fever. Some infections may become severe and develop into an infection of the brain, leading to neurological signs. The disease can also result in a loss of pregnancy. Some people experience only mild, flu-like symptoms. Pregnant women, people with weakened immune symptoms, the young and the elderly are highly susceptible to listeriosis.
Reporting
Veterinary laboratories in Ontario and veterinarians who use a laboratory outside of Ontario must report cases of listeriosis to the Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs [OMAF and MRA]. OMAF and MRA will monitor and ensure that the disease is kept under control.
For more information on animal health, go to www.ontario.ca/animalhealth.
Listeria monocytogenes is a gram positive facultative anaerobic organism that is ubiquitous in the environment of farm animals [Baird et al. 2012]. L. monocytogenes is an intracellular pathogen with a unique potential to spread from cell to cell, thereby crossing the blood-brain barrier, intestinal and placental barriers [Dhama et al. 2015]. Many animals can be healthy carriers that shed the organism in their faeces, tears, urine, nasal secretions and milk. The organism may be present in soil, water, manure, feed and can survive for greater than five years [Sherman et al. 2009]. There are 16 known serotypes and multiple subtypes of L. monocytogenes [Sherman et al. 2009]. Each strain of L. monocytogenes has varying pathogenicity causing a range of disease syndromes in a variety of hosts [Thompson et al. 2011]. On this property we had septicaemia in the sheep and abortion and encephalitis in the goats. Birds and mammals [including humans] can be infected with the organism L. monocytogenes and it is found throughout the world. L. monocytogenes is capable of growth over a wide pH range of 5.5-9.6 [optimal growth 7-7.2] and temperature range of 3-45C [optimal growth 20-40C].
Listeria is a common organism in the environment, but certain environmental conditions are more ideal for growth of the organism. The predisposing factors to clinical listeriosis in sheep and goats include; sudden change in weather; change in feeding regime; introduction of carrier animals; confinement during winter; overcrowding; poor sanitation; increased stress [poor nutrition or concurrent diseases]; advanced pregnancy; feeding of silage, mouldy hay, sewerage, or manure piles; contact with rotting vegetation; provision of dirty water; feeding on the ground, contact with products of abortion; venereal transmission; and contact with birds [including chickens]. Listeriosis is characterised by sudden death, encephalitis, septicaemia, abortion, keratoconjunctivitis and metritis/vaginal discharge [Matthews 2009]. Sheep and goats are highly susceptible to Listeriosis.
CASE REPORT
In May 2020, a sheep and goat producer in the Lower Hunter introduced two new sheep onto their property from Glenlyon, Queensland. These two sheep had respiratory symptoms when they took delivery of the sheep in Tenterfield. They were given antibiotic medication but no history was provided by the previous owner. These sheep were kept in a separate pen [in close proximity to the resident flock] and drenched on arrival with monepantel. The health of the new sheep deteriorated, and initially private vets were called to the property. The vet treated the new sheep for shipping fever with oxytetracycline, but unfortunately one became extremely ill with respiratory signs and was euthanised. No postmortem was performed.
The following week, three of the resident sheep died. The clinical signs noticed were anorexia, scours and death over 2-3 days with some sheep also having respiratory signs. The private vet was called to the property again and the sheep and goats were drenched, all treated with oxytetracycline, a faecal egg count was done which had 0 eggs per gram of faeces and all sheep and goats were vaccinated with a 5-in-1 clostridial vaccination. During this period the feeding had stayed the same except they had noticed some of the hay they were feeding had become mouldy and it had been thrown out.
In mid-June the local District Veterinarian was contacted by the EAD Hotline and the producer to perform a post-mortem on a sheep that had died suddenly. The ewe was three years old and vaccinated six weeks prior with a 5-in-1. On post-mortem the lungs were clear with no sign of pneumonia, there were petechial haemorrhages over the surface of the duodenum and scours noticed, and the fluid content of the rumen appeared to be twice the normal amount. Samples were sent to EMAI for histopathology. The laboratory conclusion was a moderate small intestinal multifocal, haemorrhagic enteritis that may have been due to viral, bacterial or parasitic agents. A Mycoplasma ovis PCR came back as negative and the faecal egg counts of 10 sheep from the flock came back as 0 eggs/gram of faeces.
The following week, one doe aborted twins [no notification or testing was done on this animal or the aborted kids at the time of abortion] and a 12-month-old goat from the property became dysphagic with excessive drooling, circling in one direction, followed by an inability to stand and torticollis. When the goat initially showed dysphagia and excessive drooling, bloods were sent to EMAI for bluetongue exclusion. The bluetongue PCR was negative. As the clinical signs progressed to circling, recumbency and torticollis the private veterinarian attempted treatment [IV fluids, meloxicam, oxytetracycline and vitamin B1 injection] but was not successful. The goat was euthanised and cerebrospinal fluid was sent for Listeria culture and PCR and fixed brain was sent for histopathology.
The histopathology of the goat's brain revealed a meningoencephalitis that was necrosuppurative, subacute, and moderate with micro abscesses and lymphohistiocytic perivascular cuffs in the brainstem. These findings were consistent with Listeria infection. The goat also had a suppurative, multifocal bronchopneumonia that was most likely related to the Listeria. Culture of the cerebrospinal fluid confirmed the presence of Listeria and PCR identified Listeria monocytogenes.
DISCUSSION
Control of listeriosis is achieved by excluding animals from the highly infectious source. In this case the source was most likely the introduced sick animals or the mouldy hay. The producers had a small flock of 15 sheep and goats in total, with most of the sheep and goats on the property showing respiratory signs, nasal discharge and/or scours over a three-week period and five deaths occurred. This property would be highly contaminated with Listeria.
Listeria is difficult to eliminate from the environment as the organism quickly becomes resistant to disinfectants [Muller et al. 2013]. Scientists looking at Listeria DNA gene sequences noticed that a section of DNA was very different from the remainder of the genome [Tn6188] and concluded that this bacterium had acquired an alteration reasonably recently [Muller et al. 2013]. Researchers found that Listeria that harboured the Tn6188 sequence were much less sensitive to benzalkonium chloride disinfectant. Scientists were able to show that deleting the Tn6188 gene made Listeria once again sensitive to benzalkonium chloride.
Control measures that were recommended in this case included:
- removal of any mouldy hay or silage, rotting vegetation and manure piles;
- elevating feed and water troughs off the ground;
- daily washing of feed and water troughs [elbow grease] and refilling with clean fresh feed and water;
- reducing or eliminating access to feed and water troughs by birds and chickens;
- avoiding manure contamination in feeding areas as manure may contain a high load of Listeria if the animal is subclinical or a carrier animal; and
- burning the carcass of any sheep and goats that die on farm.
All in-contact animals were treated with a dose of long-acting oxytetracycline as they were potential carrier animals and preventative treatment of clinically unaffected animals in an outbreak has been suggested.
Listeria bacteria can cause severe illness in people, with pregnant women, newborns, the elderly and those people with a weakened immune system being most susceptible to disease. Clinical signs in people include fever, headache, vomiting, diarrhoea, miscarriage and stillbirths in pregnant women, convulsions, coma and death. When handling these animals, it is essential that the producers use personal protection and hand washing and ensure people most susceptible to disease are kept away from the sheep and goats [NSW Health].
ACKNOWLEDGEMENTS
Morpeth Veterinary Hospital [initial private veterinarians to the property].
Cessnock Veterinary Centre and Hospital for their involvement [2nd private veterinarian involved in this case].
EMAI for laboratory services.
REFERENCES
- Baird AN, Pugh DG.[2012] Sheep and Goat Medicine, 2nd Edition, Elsevier Saunders, p 390-391
- Dhama K, Karthik K, Tiwari R, Shabbir MZ, Barbuddhe S, Malik SVS, Singh K. [2015] Listeriosis in animals, its public health significance [food-borne zoonosis] and advances in diagnosis and control: a comprehensive review. Veterinary Quarterly Journal 35[4];211-235
- Matthews J. [2009] Diseases of the Goat, 3rd Edition, Blackwell, p 192-195
- Müller A, Rychli K, Muhterem-Uyar M, Zaiser A, Stessl B, Guinane CM, Cotter PD, Wagner M, Schmitz-Esser S. [2013] Tn6188 - A novel transposon in Listeria monocytogenes responsible for tolerance to benzalkonium chloride. Plos One [online journal] 8[10]:e76835. doi:10.1371
- NSW Health [2018]. Listeriosis Fact Sheet www.health.nsw.gov.au
- Radostits OM, Gay CC, Hinchcliff KW and Constable PD. [2007] Veterinary Medicine, 10th Edition, Saunders Elsevier, Edinburgh, p 805-810
- Sherman DM, Smith MC. [2009] Goat Medicine, 2nd Edition, Wiley-Blackwell, p 202-207
- Thompson R, Thompson H, Bunker E, Watt BR [2011]. An Outbreak of Listeriosis in Silage Fed Ewes. www.flockandherd.net.au