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Circling Disease, Silage Sickness, Listerellosis,Meningo- encephalitis.
Listeriosis is an infectious disease of ruminants characterized by Meningoencephalitis, abortion or septicemia.
Listeria monocytogenes, a small motile pleomorphic gram positive, non-spore forming coccobacilli. Five (5) serotypes and 11 subtypes have been described. The organism multiplies at PH>5.0 and below that the survival is poor.
Distribution:
The disease has been of most importance in New Zealand, North America, Europe and Australia as well as U.S. It is less common in tropical and subtropical areas. The disease is more common in winter and early spring.
Sheep, cattle, buffalo, goats, horse, pigs, dogs, cats, rabbits and some wild animals and man are susceptible to the infection.
Animals of any age, including the newborn, both sexes and all breeds may be affected.
The mortality rate without treatment in listerial septicemia and the meningoencephalitis approaches 100%
Transmission:
Rats, skunks, ferrets and probably other wild animals suspected as reservoirs of infection.
The natural habitats of listeria appears to be soil and the mammalian intestinal tract. Vegetation and silage become contaminated with soil and/or feces. Grazing animals ingest listeria and further contaminate soil and vegetation, there- by establishing an ecologic Listeria cycle.
The portal of infection in natural cases is uncertain but evidence suggest that infection may gain entrance by several portals. It seems probable that meningoencephalitis results from inhalation or conjunctival contamination and the visceral infection with abortion from ingestion of infected material. Venereal transmission may also lead to abortion. Infective material derives from infected animals in the feces, urine, aborted fetuses, uterine discharge and in the milk and tears.
Animal to man transmission may occur directly or indirectly via milk, meat or vegetables.
Nutritional deficiency and heavy silage feeding are well recognized as the predisposing factors.
L. monocytogenes does not multiply in good silage (PH=4-4.5) but in spoiled silage with incomplete fermentation and PH above 5.5, the bacteria survive and may multiply.
Encephalitis Form:
- Contaminated feed
- Abrasions small puncture wounds in the oral mucosa, lips, muzzle, nostrils.
- Penetration of organism in these tissues innervated by cranial nerves. Migration to medulla oblongata and pons Unilateral localization in the brain.
Septicemia or Visceral Listeriosis:
- Visceral lesions, hepatitis, placentitis with abortion
- Via GI mucosa
- Localization in intestinal wall, especially in the Peyer's patches.
17.7 Symptomatology:
The meningoencephalitic form and the visceral form are seen in different outbreaks and rarely the two forms are seen together in a single outbreak of the disease.
Meningoencephalitic Form:
- Seen in all species.
- In cattle the course of the disease is 1-2 weeks, but in sheep is more acute.
- Head pressing against fixed objects, unilateral facial paralysis.
- Affected animals are dull and isolate themselves from the rest of the group.
- Slow prehension and mastication
- Deviation of the head to one side, and circling in the direction of the deviation.
- Unilateral facial paralysis.
- Recumbency and death due to respiratory failure.
- Fever is usual in early stage of the disease but temperature is normal when clinical signs are present.
Listerial Abortion:
Stillbirth, or abortion at about seven months of pregnancy or later. There is no evidence of meningoencephalitis but there is commonly clinical illness and fever up to 105 D F.
Septicemic Listeriosis:
- Not common in adult but occurs in calves
- Depression, weakness, emaciation and diarrhea with no nervous system involvement.
Listerial abortion must be differentiated from the other causes of abortion in cattle.
