Last update: September 2, 2011 01:23:11 PM E-mail Print

 

Considerations with regard to Bluetongue vaccination of Angora goats

EM van Tonder

 

Introduction

Bluetongue is generally regarded as an infectious insect-borne disease of sheep and other ruminants, but primarily affects sheep in its typical form.

Although the susceptibility of goats and the occurrence of unapparent infections under natural conditions have been described many years ago, few studies have been conducted in these animals. Angora goats specifically, have been shown to be susceptible to experimental infection with bluetongue virus, but apart from occasional febrile reactions, showed no clinical symptoms from the strain used. They did however maintain an infective viraemia for up to 20 days, while serial transmission in these animals did not enhance or attenuate the pathogenicity of the strain for sheep.

In dairy goats, which are generally regarded to be equally resistant to natural infection of bluetongue as Angora goats, outbreaks have been reported in the literature where typical symptoms of bluetongue were shown and some animals even succumbed to the disease. Experimental infection of Saanen goats with six American strains of the bluetongue virus produced variable febrile reactions and titres of viraemia, while leucopoenia and a mild progressive anaemia and haemoglobinaemia were constant features.

The afore-mentioned information does not only imply the occurrence of unapparent natural infection of bluetongue in goats, but also the reality of strain-related susceptibility and exhibition of variable and lesser defined symptom complexes.

 

Considerations in the South African context

There seems to be no doubt that Angora goats are susceptible to natural infection of bluetongue and will develop an unapparent or less apparent form of the disease. The accepted higher resistance of the goat compared to sheep and the occurrence in South Africa of a large number of strains of the bluetongue virus possessing variable degrees of pathogenicity may very well result in the occurrence of subclinical and even clinical manifestations of the disease that would not easily be recognised. Some incidences of ill-defined syndromes characterized by variable symptoms, including fever, anaemia, unthriftiness, stiffness, tenderness of the fleece and even alopecia, have been encountered where in some cases the presence of bluetongue virus, but mostly antibodies, were demonstrated.

Apart from their own involvement, goats, like cattle, may play an important role in the epizootology of bluetongue in sheep. The longer duration of optimal viraemia accompanying the subclinical natural form of the disease is of great epizootological significance. Furthermore, since in the main small stock farming areas sheep are more commonly in contact with goats than other ruminants, the possible intervention by these animals in the spread of bluetongue should not be underestimated, particularly as at present, Angora goats are increasingly introduced into the traditional sheep farming areas.

 

Present recommendation

On account of the considerations outlined above, as well as the fact that the existent bluetongue vaccines do not produce any noticeable ill effects when administered to goats, vaccination is recommended as an optional procedure in preventative animal health programmes. Farmers wishing to do so, could either include it in their regular annual programmes or introduce it when conditions appear favourable for the occurrence of bluetongue.

 

Published

Angora goat and mohair journal 29 (2), Ugqira 19 (1)