Caseous lymphadenitis in small ruminants in Egypt. Clinical, epidemiological and prophylactic aspects.

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 infections. So mass vaccination of small ruminants against CLA in Egypt has to be considered to minimize the disease prevalence.