Listeria has made its way into the news lately thanks to the contaminated Boar's Head deli meats as well as various vegetable products. There have been two (human) deaths (one in Illinois and the other in New Jersey) so far. 34 people have fallen ill as of July 31, 2024.
An estimated 1,600 people get listeriosis in the United States each year, and about 260 (or one in six) die. That said, many people will experience Listeriosis but never need treatment, so many cases go unreported.
What is Listeriosis?
Listeriosis is a bacterial infection caused by Listeria monocytogenes. We have been hearing about an outbreak in the human population, but Listeria can affect a wide range of animals, including sheep.
It is particularly important to be aware of Listeria in sheep because it can lead to serious health issues and economic losses for farmers.
Causes of Listeria in Sheep
Listeria bacteria are commonly found in the environment, especially in soil, water, and decaying vegetation. Silage that is not properly fermented or stored can also be a significant source of infection. Sheep can become infected through ingestion of contaminated feed or water. The bacteria can also enter through wounds or the mucous membranes of the mouth.
Direct Transmission of Listeria Infections in Sheep
Listeria can be transmitted directly between sheep, although direct transmission is not the most common route.
Close Contact: Infected sheep can potentially transmit Listeria to other sheep through close contact, especially in crowded or unsanitary conditions. The bacteria can spread through saliva, nasal secretions, and other bodily fluids.
Injuries or Open Wounds: If an infected sheep has open wounds, the bacteria can be transferred to other sheep through physical contact or environmental contamination.
Risk Factors for Acquiring Listeria
Listeria is not always caused by poor management--it can happen to any flock--but there are some risk factors within a shepherdess's control that should be considered and carefully managed.
Poor Hygiene: Overcrowding and lack of proper sanitation can facilitate the spread of Listeria among sheep.
Stress: Stress from transportation, adverse weather, or other health conditions can make sheep more susceptible to infection.
Symptoms of Listeria in Sheep
Listeriosis in sheep typically presents in two forms: encephalitic (nervous form) and septicemic (blood infection form).
Symptoms of Encephalitic Form of Listeria:
(also known as Circling Disease or Listeric Encephalitis)
Circling Behavior: Affected sheep often exhibit a tendency to circle in one direction, which is a hallmark sign of the disease.
Head Pressing and Staggering: Sheep may press their heads against objects or walls and show a lack of coordination or staggering gait.
Depression and Lethargy: Infected sheep typically appear depressed and lethargic, often separating themselves from the flock.
Facial Paralysis: Signs of facial paralysis may include drooping of the ear and eyelid on one side of the face, as well as a drooping lip.
Difficulty Swallowing: Affected sheep may have trouble swallowing, which can lead to drooling and loss of appetite.
Head Tilt: A noticeable head tilt may occur due to cranial nerve involvement.
Tremors and Muscle Weakness: Some sheep may exhibit tremors, muscle weakness, and an inability to stand.
Seizures: In severe cases, seizures may occur, indicating significant neurological involvement.
Excessive Salivation: Due to difficulty swallowing and facial paralysis, sheep may drool excessively.
Death: If not treated promptly, the encephalitic form can lead to coma and death within a few days
Symptoms of Septicemic Form of Listeria:
The septicemic form of listeriosis in sheep, although less common than the encephalitic form, can be quite serious, especially in young lambs and pregnant ewes. This form of the disease is characterized by a rapid spread of infection throughout the body via the bloodstream.
Symptoms of Septicemic Listeria in Lambs:
Sudden Death: The septicemic form often causes sudden death in young lambs without previous signs of illness.
Fever: Infected lambs may exhibit high body temperatures.
Weakness and Lethargy: Affected lambs often appear weak and lethargic.
Lack of Appetite: Infected lambs may stop nursing or eating.
Diarrhea: In some cases, lambs may develop diarrhea.
Respiratory Distress: There may be signs of difficulty breathing or rapid breathing.
Symptoms of Septicemic Listeria in Adult Sheep (Especially Pregnant Ewes):
Abortion: Pregnant ewes infected with the septicemic form of Listeria often abort their fetuses, typically in the last trimester of pregnancy.
Stillbirths or Weak Lambs: Ewes may give birth to stillborn lambs or weak lambs that fail to thrive.
Fever and General Malaise: Adult sheep may also show signs of fever and a general sense of un-wellness.
Death: In severe cases, septicemia can lead to death if not treated promptly.
Diagnosis
Diagnosis is usually based on clinical signs and confirmed through laboratory tests, such as bacterial culture or PCR from brain tissue or other affected organs.
I have found that by spending time with my flock observing each sheep's unique behavior, I am better able to tell when something is amiss.
Treatment
Treating listeriosis in sheep effectively requires early diagnosis and prompt administration of appropriate medications. The treatment approach can vary depending on the form of listeriosis (encephalitic, septicemic, or reproductive) that the sheep is experiencing. Here’s a detailed overview of how to treat listeriosis in sheep:
Early Diagnosis and Intervention to Treat Listeria in Your Flock
Quick identification of symptoms, especially the characteristic neurological signs of the encephalitic form, is critical for successful treatment. The sooner treatment begins, the better the chances of recovery.
Antibiotic Treatments for Listeria in Sheep
For those of you in the United States, make sure you establish a good relationship with a livestock vet. As of June 2023, US farmers will no longer have access to over-the-counter antibiotics in feed stores. The best time to find a good vet to work with is before any of your animals are sick.
Vets frequently prescribe the following antibiotics for the treatment of Listeria:
Penicillin: This is the most commonly used antibiotic for treating listeriosis in sheep. High doses are required to penetrate the central nervous system effectively.
Tetracycline: Oxytetracycline is also commonly used and can be effective against Listeria infections. It's particularly useful if penicillin is not available or if the sheep have shown an adverse reaction to penicillin in the past.
Treatment usually involves high doses administered intravenously or intramuscularly. The specific dosage and frequency depend on the severity of the infection and the veterinarian’s recommendations.
Supportive Care When Treating Listeria in Your Flock:
Fluids: Dehydration can be a significant issue due to drooling and difficulty swallowing, so providing fluids either orally or intravenously can help maintain hydration.
Anti-inflammatory Drugs: Non-steroidal anti-inflammatory drugs (NSAIDs) like flunixin meglumine can help reduce inflammation in the brain and alleviate pain.
Nutrition: Supportive feeding may be necessary if the sheep cannot eat due to neurological symptoms. This might involve offering easily digestible feed or tube feeding if necessary.
Environmental Support: Keeping the sheep in a quiet, comfortable environment to reduce stress and injury risk is important, as neurological symptoms can make movement hazardous.
Isolation and Management While Treating Listeria:
Isolation: Affected sheep should be isolated to prevent the spread of infection and to allow them to recover without disturbance.
Monitor Other Sheep: Keep an eye on the rest of the flock for any signs of illness, especially if listeriosis is suspected to be linked to contaminated feed.
Preventing Listeria in Your Flock:
Preventing listeriosis in a flock of sheep involves implementing a combination of management practices, environmental controls, and health monitoring to minimize the risk of infection. Here are some key strategies to prevent Listeria in sheep:
Feed Management
Silage Quality: If you feed silage, e nsure it is well-fermented and properly stored. Poorly fermented silage with a pH higher than 5.0 can harbor Listeria. Check for mold and spoilage before feeding silage to sheep. Whether or not sheep should be fed silage is somewhat debated (and something we'll discuss in the future), but regardless of whether you feed silage or other forage, be sure to always discard any spoiled feed.
Storage: Store silage in a manner that minimizes exposure to air and moisture, which can lead to spoilage and Listeria growth. Seal silage properly to prevent air infiltration, and use it quickly once opened to minimize spoilage.
Alternative Feeds: Some shepherds provide alternative feeds during high-risk periods (e.g., late pregnancy) to reduce reliance on silage.
Environmental Controls
Cleanliness and Hygiene: Maintain clean living conditions, removing manure and waste regularly to reduce bacterial load. Ensure that feeding and watering equipment is clean and free from contamination.
Bedding Management: Regularly change bedding materials to keep them dry and clean, reducing the risk of environmental contamination.
Animal Health and Monitoring
Regular Health Checks: Monitor the flock regularly for signs of illness, such as depression, loss of appetite, or neurological symptoms, especially during high-risk periods like late pregnancy.
Isolate Infected Animals: Quickly isolate any animals showing signs of listeriosis to prevent the spread of infection within the flock.
Reduce Stress: Minimize stress factors, such as overcrowding, sudden changes in diet, or rough handling, as stress can make sheep more susceptible to infections.
Biosecurity Measures
Control Access: Limit access to the farm by unauthorized personnel and vehicles to reduce the risk of introducing Listeria or other pathogens.
Rodent Control: Implement effective rodent control measures, as rodents can carry and spread Listeria bacteria.
Quarantine New Arrivals: Quarantine new animals before introducing them to the flock to ensure they are not carrying infectious diseases.
Vaccination and Alternative Strategies
Vaccination: While no specific vaccine for Listeria in sheep exists, maintaining overall flock health through regular vaccinations against other diseases can help keep the immune system strong.
Alternative Health Practices: Consider using probiotics and other supplements to promote gut health and boost the immune system.
Education and Training Considerations
Educate Farm Workers: Ensure that all farm workers are trained in recognizing the signs of listeriosis and in implementing biosecurity and hygiene practices.
Stay Informed: Keep up-to-date with the latest research and recommendations regarding listeriosis prevention and management.
Adopting these preventive measures can significantly reduce the risk of listeriosis in your flock, safeguarding both animal health and farm productivity. Regular monitoring and proactive management are key to preventing outbreaks of this disease.
A Note for Farmers on the Public Health Implications of Listeria in Livestock:
Listeriosis is a zoonotic disease, meaning it can be transmitted from animals to humans. People can become infected through handling infected animals or consuming contaminated animal products, so it is important to follow good hygiene practices when working with your sheep.
By maintaining good management and biosecurity practices, the risk of Listeria infections in sheep can be minimized, protecting both the flock and the farm's productivity.
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