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Listeriosis in animals
Question: There have been recent media reports about deaths from Listeriosis in people in South Africa. Does the disease also occur in animals?
Listeriosis is caused by a bacterium [germ], Listeria monocytogenes. Three syndromes occur, and these are meningitis and encephalitis, abortions or still-births and septicaemia. Rare cases of mastitis and conjunctivitis have also been found in the past.
Meningo-encephalitis is usually seen in ruminants, whilst septicaemia is more commonly seen in other animals and new-born ruminants.
Dr Marijke Henton, specialist in veterinary bacterial diseases, says that it is rare in South Africa, and it is only diagnosed about once every 5 years in animals.
Previous cases included deaths in cattle and sheep, which were fed poor quality, unmarketable potatoes. The outbreak occurred in the cold Highveld of Mpumalanga in the winter. Listeria prefers cold temperatures when multiplying. A recent case was from a sheep with meningitis in KwaZulu Natal. Previous cases were from abortions as well as a single case of mastitis in a cow.
Listeria is found all over the world, but commonly occurs in countries where the weather is moderate to cold, such as New Zealand, parts of Australia, North America, and Europe. Clinical disease is especially found during late winter and spring.
Occurrence of Listeria
The germ, L. monocytogenes, is common in nature, and has been isolated from a wide variety of healthy and sick animals, as well as from soil, water, sewage, mud and silage. It can also be found on vegetables and fruit. Many sheep and goats can carry L. monocytogenes without showing symptoms, but may excrete the organism in their dung and milk when stressed. Milk should always be pasteurized, because this bacterium survives freezing, and can then be dangerous for man. Meat is very rarely a source of infection for man. Listeria is destroyed rapidly when meat is cooked. Good hygienic practices, such as keeping raw meat and foods, such as salads, separate when preparing, is naturally important.
Listeriosis is often associated with the feeding of poorly made silage, with an acid level above pH 5.5. The upper and side surfaces of the silage are most likely to be contaminated with Listeria.
Lowered resistance in animals due to environmental conditions may also play a role in the occurrence of listeriosis. Another reason might be the changing of teeth in young sheep during early spring, allowing Listeria to move along the tooth nerve to the brain, resulting in meningitis.
Meningitis and encephalitis occur most commonly in ruminants. The course of the disease is usually 2 – 3 days in goats, sheep and calves, and 2 weeks in adult cattle.
Affected animals first show a fever, which drops, first to normal, and then becomes sub-normal. Animals are depressed, walk in circles, and show incoordination. Their heads may be held sideways, and unilateral paralysis of the facial nerve may occur, resulting in a one-sided drooping of the eyelid, ear and lips. The muscles of the jaw and throat become paralysed, so that animals cannot eat nor drink properly. Food and mucous could hang from the mouth. Later, complete paralysis occurs, and the animals die. The animal may show cycling movements of the legs (can be confused with Heartwater), have trouble breathing, show paralysis of a limb and have conjunctivitis.
Sporadic abortions are more commonly seen in cattle. If the abortion occurs late in pregnancy, the placenta is usually retained.
Septicaemic listeriosis is more often seen in foetuses, newly born ruminants and animals with single stomachs.
An initial diagnosis can be made on the clinical signs and histopathological examination of the tissues.
Confirmation of the disease is by isolating Listeria monocytogenes from the tissues.
Listeriosis can be confused with other disease and conditions such as brain abscesses, brain cysts (Coeneurus cerebralis), lead poisoning, Heartwater, CCN (Vitamin B1, thiamine deficiency), rabies and other bacterial infections of the brain, such as Histophilus somni.
Listeria monocytogenes is susceptible to a wide variety of antibiotics. The prognosis is poor, if nervous symptoms are already present. Extra supportive treatment should be provided by your veterinarian until the animal can eat and drink again. Remember to provide soft bedding, to prevent pressure sores.
Source: Coetzer, J.A.W. and Tustin, R.C. 2004. Infectious Diseases of Livestock, Oxford University Press.
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