Listeriosis Outbreak in Sheep Raised in Feedlots in the Southern Region of Rio Grande do Sul State, Brazil

Abstract

Background: A listeriosis outbreak in a sheep fattening feedlot in the Southern Region of Rio Grande do Sul State, Brazil is described. This disease is caused by Listeria monocytogenes and represents a risk to public health since it affects not only ruminants but also humans. This agent is widely spread in the environment, such as in the soil and water. It is also found in decaying vegetable matter and the feces and fluids of domestic animals. The aim of this study was to describe a listeriosis outbreak in sheep raised in feedlots, its epidemiology, and to establish the importance of this disease in this type of sheep management system, evaluate the possible sources of infection, and suggest ways to control it.Cases: Sheep were kept in a 2-sector shed, one with east solar orientation and the other with west solar orientation, the latter with free access to domestic birds. Sheep were fed silage and concentrate. Seven sheep were affected, 5 died and 2 recovered. Clinically, the sheep displayed loss of balance, excessive drooling, and tremors; one exhibited circling, head deviation, apathy, nystagmus, lateral recumbency, paddling, and labored breathing. At necropsy, macroscopic lesions were not found, and histologically several micro-abscesses and perivascular cuffs with lymphocytes, macrophages, and neutrophils were present in the brain stem. Listeria monocytogenes suspected colonies were observed in the microbiological culture, and the bacteria was identified by biochemical analysis. The immunohistochemistry test in brain stem sections was positive for the antibody BD DifcoTM Listeria O Antiserum Poly Serotypes 1 and 4.Discussion: A listeriosis outbreak in a feedlot sheep was confirmed through epidemiological findings, histological lesions, bacterial culture, and immunohistochemistry analysis. This infection is frequent in sheep fed silage of poor quality or other food with improper storage and lack of hygiene. In the present outbreak, the bacteria were isolated from silage. However, it is likely that domestic birds, which were raised in the same place and had free access to the west sector of the feedlot, were the initial source of infection, because the sheep from the opposite sector (east) did not get ill. The disease caused by environmental contamination or through contact with fluids and feces of ducks, chickens, cattle, and pigs has already been described in outbreaks that occurred in the central region of Rio Grande do Sul. Sheep aggregation in feedlot systems is also a favorable factor for the development of the bacteria and the occurrence of outbreaks because the accumulation of feces and urine cause humidity on the stalls. This allows outbreaks to occur in other seasons of the year, such as in the outbreak reported herein. The exchange of silage that served as food for sheep was another control measure, and new cases were not reported 8 months after these procedures were taken. In the outbreak studied, 2 sheep that exhibited clinical signs were treated with oxytetracycline and recovered. Some authors report that treatment for listeriosis is inefficient because neurological lesions are irreversible. Nonetheless, other studies have reported the recovery of some animals when they were treated with oxytetracycline or a combination of oxytetracycline and dexamethasone or ampicillin and gentamicin like in the outbreak described in this paper.Keywords: Listeria monocytogenes, central nervous system, silage, feedlot, ovine.

Listeria innocua and serotypes of Listeria monocytogenes isolated from clinical cases in small ruminants in the northwest of Uruguay

“…All cases studied herein exhibited the neurological form of the disease. The predominance of this clinical form agrees with data reported previously by other authors (Barlow & McGorum 1985, Wilesmith & Gitter 1986, Guedes et al 2007, Oevermann et al 2010b, Rissi et al 2010b, Ribeiro et al 2022. During this study, five single cases and three disease outbreaks occurred, and the morbidity and mortality were 0.8% (median).…”

“…The same situation was previously reported by other authors (Campero et al 2002, Ribeiro et al 2006, Rissi et al 2006, Oevermann et al 2010a, Rissi et al 2010b). However, other reports from Brazil mentioned that listeriosis occurred in animals under one year old (Guedes et al 2007, Ribeiro et al 2022. Therefore, the evidence from different reports suggests that there is no age-related predisposition to listeriosis, as Bagatella et al (2022) propose.…”

“…The predominance of listeriosis during winter and spring could be related to the previous high exposure to the bacteria because the incubation period of the neurological form varies between one and seven weeks 2013) in southern and southwestern Brazil reported cases in summer. In the same region, Ribeiro et al (2022) described an outbreak in spring. Such difference could not be attributed to the weather because Uruguay and these regions of Brazil belong to the same Köppen-Geiger climate classification (humid subtropical) (Peel et al 2007).…”

“…In South America, including Brazil, Argentina and Uruguay, listeriosis is one of the main neurological diseases of small ruminants (Campero et al 2002, Guedes et al 2007, Rissi et al 2010a, Dutra 2015, Konradt et al 2017. There are many reports of listeriosis in sheep (Campero et al 2002, Ribeiro et al 2006, Rissi et al 2010a, Dutra 2012, 2015, Konradt et al 2017, Canton et al 2018, Costa et al 2018, Ribeiro et al 2022 as well as in goats (Rissi et al 2006, Guedes et al 2007, Headley et al 2013, Konradt et al 2017. However, most of these reports based their diagnoses on histopathological lesions, and some of them included immunohistochemistry but did not perform the isolation and characterization of Listeria.…”