Bovine tuberculosis in domestic cats

MRCVS, B. Rule, Veterinary Laboratories Agency, Polwhele, Truro TR4 9AD M. P. Cranwell, BA, VetMB, MRCVS, Veterinary Laboratories Agency, Staplake Mount, Starcross, Exeter EX6 8PE N. Palmer, BVetMed, J. Inwald, BSc, R. G. Hewinson, DPhil, Veterinary Laboratories Agency, Weybridge, Surrey KT15 3NB MYCOBACTERIAL infections in domestic cats may involve both pathogenic and saprophytic mycobacteria. Classical tuberculosis is caused mainly by Mycobacterium bovis, sometimes by Mycobacterium tuberculosis and very occasionally by Mycobacterium avium, Mycobacterium microti or Mycobacterium lepraemurium. Recently, a strain of mycobacterium with characteristics between those of M tuberculosis and M bovis has been identified (Gunn-Moore and others 1996). Most reported cases ofM bovis in cats involve infection of the liver, intestines and associated lymph nodes and were believed to be due to the ingestion of milk from tuberculous cattle (Jennings 1949). Snider and Cohen (1972) showed a significant association of bovine tuberculosis in cats with farms experiencing tuberculosis (TB) breakdowns in cattle in the USA and a similar situation was reported in New Zealand (Ragg and others 1995). This short communication describes an outbreak of TB infection in domestic cats from Great Britain. It also reports that a molecular technique known as spoligotyping, which was developed for the genetic fingerprinting of the M tuberculosis-complex (Aranaz and others 1996, Kamerbeek and others 1997), maybe of use in identifying epidemiological interactions between cats and other wild or domestic species. In March 1998, the carcase of an adult, female badger was submitted by the local Animal Health Office to the Veterinary Laboratories Agency (VLA) Polwhele for postmortem examination. It had been found in the garden of a small holding premises in west Cornwall. Examination confirmed the generally emaciated condition of the animal and detected extensive induration of the lungs with numerous miliary white foci as well as many caseous foci within the cortex and foci within the cortex and medulla of both kidneys. Smears were prepared from representative lesions and stained by the ZiehlNeelsen (ZN) method and revealed numerous small, acid-fast bacilli. Three months later, the carcase of an adult, male cat (cat 1) from the same premises was submitted by the Animal Health Office for postmortem examination. The owner reported that the cat had lost weight over a period of three to four weeks and had developed respiratory distress a few days before death. A large swelling was present in the upper neck region. At postmortem examination, the submandibular, retropharyngeal, prescapular and subscapular lymph nodes were all enlarged and oedematous and, when sectioned, presented numerous caseonecrotic lesions up to 2 mm in diameter, mainly in the cortices. Caseous miliary foci were present throughout the lungs together with multiple, granulomatous, white, grape-like lesions on the mediastinal pleura and pericardium. A large number of white foci, 2 to 3 mm in diameter, were present in both kidneys, although no lesions were seen in the liver and intestines or their associated lymph nodes. ZN-stained smears of representative lesions in the lung, kidney and lymph nodes showed many small, acid-fast bacilli. Saline lavage samples were collected from the lungs and the bladder. This cat was one of 12 in the same household where, over the previous month, four other cats had died and then been buried. All four of these had shown similar signs of weight loss and general listlessness for four to six weeks before death. One had also shown a cervical swelling from which a sinus discharged thick yellow pus, and another had shown respiratory difficulties. As a result of the postmortem findings of cat 1, the bodies of the other four cats were exhumed after being buried for a period ofbetween four and six weeks; three were judged suitable for postmortem examination. The first of these cats, cat 2, showed caseous foci approximately 2 mm in diameter throughout the lungs, and there was a collection of caseous material beneath the angle of the lower jaw. The lesions were grey but the carcase was severely affected by autolytic change. Acid-fast bacilli were present in ZN-stained smears prepared from both sites. Another cat (cat 3) was severely decomposed but the cortices ofboth kidneys showed numerous white foci, 1 to 2 mm in diameter, and ZN-stained smears from the lesions showed numerous acid-fast bacilli. Ofthe two remaining carcases, only one was suitable for postmortem examination (cat 4). This cat showed enlarged retropharyngeal lymph nodes and, although decomposition was advanced, there did appear to be a number of small grey foci within the lungs. Small numbers of acid-fast bacilli were seen in ZN-stained smears prepared from these lesions. Examination of the liver, intestines and associated lymph nodes of cat 2 showed no lesions. Unfortunately, decomposition was advanced in cats 3 and 4 and therefore precluded detailed examination of the liver, intestines and associated lymph nodes of these animals. Pooled tissue samples from the badger and each ofthe four cats were collected separately into 1 per cent cetylpyridinium chloride for bacteriological examination for mycobacteria. In addition, urine and the products of the saline tracheal lavage from cat 1 were processed in the same way. All samples were initially inoculated onto modified Middlebrook 7Hl1 agar semi-solid slopes and any subsequent colonies were inoculated onto specialised LowensteinJensen and Stonebrinks media at different temperatures (Gallagher and Horwill 1977). M bovis was isolated from the lesions of the badger and cats 1, 2 and 3, and additionally from the urine and tracheal lavage samples from cat 1. No isolates were obtained from cat 4. To further characterise the individual isolates ofM bovis, the genetic fingerprints of the isolates were examined by spoligotyping as described by Aranaz and others (1996). All isolates were found to have an identical spoligotyping pattern which has been designated 'GBspoligotype 20' (Clifton-Hadley and others 1998). Histological examinations were carried out on the kidney and lung of cat 1 and the kidney of the badger using haematoxylin and eosin as well as ZN-staining. Within the kidney cortex of the feline specimen, there were a number of foci of cellular aggregations involving mainly macrophages and marginal lymphocytes. Central areas were undergoing necrosis and few acid-fast organisms were seen. Relatively low numbers of acid-fast organisms were present in proximal tubules but they were always associated with cellular debris. Within the medulla the reaction was much more necrotic with fewer reactionary cells and numerous acid-fast organisms within both interstitium and tubules. The badger's kidney exhibited a markedly necrotic reaction in both the cortex and medulla, with a limited small round-cell response. Acid-fast organisms were plentiful and high numbers were seen within some medullary tubules. The section from the cat's lung tissue exhibited widespread change involving a marked cellular infiltration that had effectively obscured the normal lung architecture. The most frequently identified cell was the epitheloid macrophage. Small airways were obstructed by cellular debris among which were numerous acid-fast bacilli. Numerous acid-fast organisms were associated with both the areas of necrosis and cellular aggregations. Multinucleated giant cells were not found in any of the sections examined from either animal. There had been no cattle kept at the small holding for many years and the only animals present were horses and ponies, which had been there for 10 years and remained clinically normal. Following confirmation of the presence of