In part because of geography and in part because production systems are more intensive, respiratory diseases, while of some importance in Australia, are the most important cause of disease and mortality in Spanish sheep. Some pathogens, while present in, Australia have different manifestations in Spain and some are exotic to Australia. This paper aims to discuss some of the more important respiratory tract diseases of Spanish sheep.
In the Aragon region in the north east of Spain, sheep are reared in a semi-extensive productive system. Sheep are grazed outdoors until the last month of pregnancy, when they are moved indoors to feed them properly. During lambing, sheep are fed with grain and hay or straw. The lambs are weaned at 45 days of age and ewes are sent outdoors for another mating season. Lambs are kept indoors until they reach slaughter weight averaging 22 kg at 2-3 months of age. During this time, they are fed pellets and straw.
This production system results in a different disease spectrum to that seen in Australian sheep. It is easy to imagine that fox predation is not a problem in Spain but respiratory diseases are important. The average mortality in lambs is around 10-12% and the main causes of mortality are summarized in figure 1.
Respiratory diseases are also the primary cause of death in adult sheep in Spain.
OESTROSIS. This is the most common disease in Spain affecting the upper respiratory tract. It is a myiasis caused by Oestrus ovis larva inside the nasal cavity. The infestation can be massive and usually most of the flock are affected. Macrocyclic lactones are used in the winter to control the disease.
CHRONIC PROLIFERATIVE RHINITIS. This is chronic lethal disease affecting a low number of animals per flock. It develops over several months, with proliferative tissue emerging through the nostril accompanied by severe respiratory distress and striking mouth breathing. It is usually unilateral and initially produces a characteristic snore. In our experience this disease has been always related to Salmonella enterica subsp. diarizonae serotype 61:k:1:5:(7) isolated in a pure culture.
Pathology findings show that this is an inflammatory process and ventral turbinate is always affected. The dorsal turbinates and ethmoidal area are not affected.
Inmunohistochemistry with antigens against Salmonella shows dot and rot formation inside epithelial cells and some macrophages.
NASAL ADENOCARCINOMA. It is a contagious tumour of the mucosal nasal glands affecting sheep and goats. Clinical signs include continuous nasal discharge, respiratory distress, exophthalmos and cranial deformation. This disease has regional importance but there are a low number of clinical cases in each flock. It is produced by a retrovirus (ONAV).
The tumour is always located in ethmoidal area. The respiratory and olfactory mucosal glands seem to be the origin of the neoplasia.
MAEDI VISNA. It is a very important and costly disease in Spain and world wide (apart from Australia and New Zealand). It is produced by a lentivirus (VMV) and in Aragon there is a flock prevalence of almost 100% and individual prevalence around 60-70%. One of the most important ways of infection is colostrum, although horizontal transmission is also possible. Lambs are usually infected in the first day of life, however, they do not develop the disease at least until they are 3 or 4 years old. It has different clinical presentations depending on the target organ: mammary gland, lung, joints or CNS. In our area the most common presentations are pulmonary and mammary. In these organs, the virus replicates in mature macrophages and develops as a slowly progressive inflammatory lesion containing lymphocytes. Serological test are available for the detection of the infection. When mammary gland is affected the milk production decreases dramatically with each lactation until milk production ceases. The udder while superficially normal, is completely hard to the touch (Figure 9).
The pulmonary presentation of maedi-visna is of chronic respiratory signs accompanied by loss of body weight and condition before death.
Maedi causes interstitial pneumonia. The appearance of the lung is characteristically heavy (up to 2 kg), uniform pink with small spherical grey accumulations of lymphocytes.
OVINE PULMONARY ADENOCARCINOMA. It is again a transmissible lung tumour of sheep caused by a retrovirus (JSRV). This virus induces neoplastic transformation of secretory epithelial cells. Tumour growth is accompanied by the overproduction of fluid in the lung, so the main clinical signs are an abundance of serous nasal secretions and crackles in lung auscultation. As there is no detectable immunological response to the virus, serological tests are not available. The disease can be diagnosed by PCR of the lung fluid.
Tumours can appear in different locations in the lung and are always accompanied by abundant secretions.
The intensive or semi-intensive systems of Spanish sheep production contribute to the importance of infectious respiratory diseases. Spain, adjacent to Africa and as part of Eurasia is not geographically isolated like Australia and New Zealand and therefore diseases exotic to Australasia, such as maedi-visna and ovine pulmonary adenocarcinoma, are important diseases in Spanish sheep.
( More pictures of respiratory lesions can be found in www.fotovet.com )