Caseous lymphadenitis in small ruminants in Egypt

Summary

Objective: The aim of this study was to investigate the distribution of caseous lymphadenitis (CLA) among small ruminants in Egypt, identify risk factors associated with its occurrence and to analyze the efficacy of the vaccine for control of CLA. Material and methods: A total of 1206 sheep and 351 goats were examined clinically for CLA. The prevalence and the risk factors of CLA in small ruminant flocks were estimated and identified. Efficacy of the commercial vaccine Case-Bac (Colorado Serum Company, USA) was determined in a field study trial conducted on 15 CLA-free lambs. Follow-up of vaccination immune response was carried out using indirect ELISA. Results: Prevalence of superficial CLA was 6.7%. Clinically, CLA appeared as abscesses in superficial lymph nodes mostly of the head and neck. On the basis of a multivariate analysis which accounted for clustering at herd level, sheep were at risk of getting superficial CLA 3.5 times more than goats (p < 0.0001). Animals of fixed flocks were at risk of getting the superficial CLA 2 times more than animals in fixed-mobile flocks (p < 0.038). Serological follow-up indicated protective antibody titers for 6 months. In vaccinated animals clinical cases were not observed while they occurred among non-vaccinated sheep. Discussion: Prevalence of CLA varied among studied flocks even between those of the same breeding system due to complex and overlapping factors associated with each flock like introduction or culling rate of animals, care of shepherds or owners to deal with opened abscesses in addition to the average age of the animals within each flock. Breeding systems have observable effects on occurrence of CLA: infected sheep can transmit the infection to a large number of animals in a short period under the conditions of close contact and reduced air flow in covered sheds. Conclusion and clinical relevance: Infected small ruminants in fixed flocks represent a risk factor for CLA for healthy ones. The vaccine used in the study provides an effective protection against new in fections. So mass vaccination of small ruminants against CLA in Egypt has to be considered to minimize the disease prevalence.

Zusammenfassung

Ziel dieser Studie war, die Verteilung der Pseudotuberkulose (caseous lymphadenitis, CLA) bei kleinen Wiederkäuern in Ägypten zu ermitteln, Risikofaktoren für das Auftreten der CLA zu erkennen und die Wirksamkeit eines zugelassenen Impfstoffs zu untersuchen. Material und Methoden: Neben Errechnung der CLA-Prävalenz durch klinische Untersuchung von 1206 Schafen und 351 Ziegen wurden in betroffenen Herden Risikofaktoren identifiziert. Die Wirksamkeit des kommerziell erhältlichen Impfstoffs Case-Bac (Colorado Serum Company, USA) wurde im Rahmen einer Feldstudie mit 15 nicht mit CLA infizierten Lämmern überprüft. Die Untersuchung der Immunantwort erfolgte mittels indirektem ELISA-Test. Ergebnisse: Die Prävalenz der oberflächlichen CLA, die sich in Form abszedierender Lymphknoten überwiegend an Kopf und Hals darstellte, betrug 6,7%. Das Risiko, an der oberflächlichen Form der CLA zu erkranken, lag für Schafe 3,5 Mal höher als für Ziegen (p < 0,0001). Tiere in permanenter Stallhaltung erkrankten doppelt so häufig wie Tiere mit Weidegang (p < 0,038). Die Impfung der Lämmer führte zu schützenden Antikörpertitern für 6 Mona te. Keines der geimpften Tiere erkrankte im Untersuchungszeitraum, obwohl Neuerkrankungen unter den ungeimpften Tieren der Herde auftraten. Diskussion: Die Prävalenz der CLA variierte in den untersuchten Herden stark, selbst wenn die Tiere unter ähnlichen Bedingungen gehalten wurden. Dies liegt an zahlreichen Einflussfaktoren auf die Erregereinschleppung und -ausbreitung wie beispielsweise die Zahl der Zukäufe und Abgänge, die mehr oder weniger konsequente Absonderung oder Merzung erkrankter Tiere sowie der generellen Altersstruktur innerhalb der Herde. In besonderem Maß beeinflusst das Haltungssystem die Zahl der Neuerkrankungen: Befinden sich bereits infizierte Tiere in der Herde, tragen vor allem enger Tierkontakt und fehlende Luftbewegung in geschlossenen Ställen zu hohen Erkrankungsraten bei. Schlussfolgerung und klinische Relevanz: Infizierte kleine Wiederkäuer in geschlossenen Stallungen stellen das größte Risiko für eine hohe Prävalenz der CLA dar. Der in der Studie eingesetzte Impfstoff bietet einen effektiven Schutz vor Neuerkrankungen und sollte deshalb vermehrt zum Einsatz kommen.

Key words

Corynebacterium pseudotuberculosis - sheep - goats - prophylaxis

Schlüsselwörter

Corynebacterium pseudotuberculosis - Schafe - Ziegen - Prophylaxe

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