Listeriosis in Sheep

Two hundred and ninety-one grass silage samples from 113 farms with recent outbreaks of listeriosis were examined for the presence of Listeria monocytogenes (Lm). The frequency of Lm isolations increased with increasing pH. Lm was isolated from 22 % of the samples with pH < 4, from 37 % with pH 4–5 and from 56 % with pH > 5. Formic acid had been used as additive. A similar investigation was carried out on 32 samples from a farm with no outbreak of listeriosis during the investigation period. Lm was isolated from 9 samples.     

Listeriosis in Sheep

Listeriosis in sheep. Listeria monocytogenes excretion and immunological state in healthy sheep. Acta vet. scand. 1979, 20, 168–179. — The excretion of Listeria monocytogenes (Lm) in the faeces and milk, and humoral and cell mediated immunity against Lm, were examined in a sheep flock where no cases of listeriosis had occurred during the last 3 years. The investigation was carried out during the indoor season. During the first part of the season 2 of the 10 pregnant, 8 months old lambs excreted Lm in the faeces, but none of the 106 ewes, 2–10 years old. At lambing the organism was isolated from the faeces of 6 of the 10 1 year old lambs and from 64% of the ewes, and from the milk of 1 of the lambs and 41% of the ewes. Nearly all the isolates (98.5%) belonged to serotype 1. Antibody titres against Lm were found in sera and whey by an indirect haemagglutination method. The titres were higher for the ewes than for the hoggs and seemed to be influenced by the number of foetuses the animals carried. Cell mediated immunity was determined by a skin test where delayed hypersensitivity against an antigen prepared from Lm, was measured. Animals fed grass silage had a stronger reaction than animals fed hay, and a stronger reaction was found in animals with ≥ 3 foetuses than in the remainder. The investigation indicates that even in a healthy sheep flock all the animals may be exposed to Lm, and the majority may be latent carriers and excrete this organism in the faeces and milk during periods of stress.     

Listeriosis in Sheep

A comparison was made between a hay fed group, consisting of 23 ewes, and a grass silage fed group of 22 ewes, all pregnant. Excretion of Listeria monocytogenes (Lm) in the faeces and milk, antibody titres in sera and whey and delayed hypersensitivity against Lm, and several blood components were determined. The animals had previously been exposed to Lm, and Lm was isolated from the faeces from several animals when the experiment started. No significant difference in number of excretors between the 2 groups was found during the experimental period. The haemagglutination titres in both sera and whey were low and on the same level in both groups. The titres were higher in animals with 1 foetus than in animals with more than 1 foetus. In the first part of the experimental period the silage group had a reduced number of lymphocytes, lower total serum protein values and higher serum iron values, compared with the hay group. The silage group also had a stronger delayed hypersensitivity reaction against Lm than the hay group, and in the silage group the reaction was significantly stronger in ewes with 3 or more foetuses than in ewes with 1 foetus. In conclusion, the combined effect of some of the changes found in animals fed grass silage may leave them more susceptible to infections.     

Listeriosis: clinical presentation

Listeria monocytogenes is an uncommon cause of illness in the general population. However, this bacterium is an important cause of severe infections in neonates, pregnant women, the elderly, transplant recipients and other patients with impaired cell-mediated immunity. Various clinical syndromes due to L. monocytogenes have been described such as sepsis, central nervous system infections, endocarditis, gastroenteritis and localized infections. A review of the clinical presentation of listeriosis is given in this paper.     

Listeriosis: therapeutic options

Since overt listeriosis occurs mainly in immunocompromised persons it is quite consistent to try to restore the hampered defence system by supportive measurements. For direct antimicrobial treatment a series of different antibiotics is available, since Listeria strains isolated from patients are in general susceptible to a wide range of antibiotics, except fosfomycin, quinolones and cephalosporins of the third generation, although a few exceptional strains exist. Unfortunately, most antibiotics are not bactericidal for Listeria. Drug combinations may exert a synergistic effect. Furthermore, the efficacy of therapy is limited by the fact of intracellular habitat of pathogenic Listeria. Few agents, such as macrolides and quinolones, are accumulated within host cells and may attack the intracellular Listeriae. The clinical experience shows that the combination of amoxicillin and gentamicin is the best option.     

Epidemic Listeriosis in the Newborn

Within a three-month period 13 cases of listeriosis in the newborn were seen at the National Women''s Hospital, Auckland. Eleven presented in the first 24 hours of life, the most common feature being respiratory difficulty in low birth weight infants. Meconium-stained liquor was noted in nine cases. The constant finding in all cases was an aspiration pneumonia which appeared to be of intrauterine origin from an infected amniotic cavity. There was also evidence of septicaemia in nine cases, and two infants survived meningitis which developed at 1 week. Maternal symptoms were mild and variable, and in only one case were they proved to be due to listerial infection. The mothers came from different suburbs of Auckland and no common source of infection was found.