Clinical findings and treatment of disseminated ‘Mycobacterium avium subspecies hominissuis’ infection in a domestic cat

KANEGI, Ryoji; YASUGI, Mayo; NABETANI, Tomoyo; TANAKA, Toshiyuki; WADA, Yusuke; HIRAI, Kotaro; SUGIURA, Kikuya; HATOYA, Shingo

Due to worsening of lung disease and lymph node swelling, dynamic computed tomography (CT) and bronchoscopy were performed on day 38 of illness. The dynamic CT was performed in the arterial phase (20 sec after the injection of contrast medium), in the portal vein phase (60 sec) and in the equilibrium phase (180 sec) using 2 ml/kg nonionic contrast medium (300 mg/ml iohexol, Daiichi Sankyo Co., Tokyo, Japan). CT scan revealed bilateral peribronchial consolidation, swollen jejunum lymph node with uniform distribution of contrast medium, and multiple prominent nodules of the liver (Fig. 3A) . These nodules exhibited lower CT values than that of liver parenchyma in plain image and were not enhanced with dynamic CT (Fig. 3B ). Contrast enhancement of peripheral areas of the liver nodules was observed in the arterial phase; however, it disappeared in the portal vein phase. During bronchoscopy, intratracheal foreign bodies, increased mucus production, and redness of bronchial mucosa were not found. Cytology of bronchoalveolar lavage (BAL) showed a small number of neutrophils and macrophages without any bacteria. When FNA cytology of the liver was performed, neutrophils, small lymphocytes, and large macrophages were observed. The specimens of bronchoscopy and liver FNA were submitted to research laboratory (Japan Clinical Laboratories, Inc., Kyoto, Japan) for culture of general bacteria, fungus, and Mycobacterium species. These examinations revealed that general bacteria and fungus were culture-negative, and Mycobacterium species were smear-negative with Ziehl-Neelsen staining but culture-positive in Mycobacteria Growth Indicator Tube systems (Becton, Dickinson and Co., Franklin Lakes, NJ, U.S.A.). The pathogen was confirmed as M. avium through DNA-DNA hybridization techniques with DDH Mycobacteria "Kyokuto" (Kyokuto Pharmaceutical Industrial Co., Ltd., Tokyo, Japan) [18] . Antitubercular drug susceptibility testing determined by the proportion test method on egg-based ogawa media (Vite Spectrum SR, Kyokuto Pharmaceutical Industrial Co., Ltd.) revealed that the bacterial isolate was resistant to isoniazid, rifampicin, streptomycin, ethambutol, kanamycin, enviomycin, ethionamide, para-aminosalicylic acid, and levofloxacin; however, it was sensitive to cycloserine ( Table 2 ) [26] . In order to identify the subspecies of M. avium isolate recovered from the clinical sample, we determined the nucleotide sequence of hsp65 (GenBank accession number LC497502) and compared single nucleotide polymorphisms (SNPs) among the M. avium strains, which were categorized into "codes" 1 to 9, and 15 to 17 depending on their sequence (Table 3 ) as described previously [27] . The sequence from our sample, however, was not a complete match with any hsp65 sequences from code 1 to 9, and 15 to 17. We then created the phylogenetic tree of hsp65 using the sequences deposited in GenBank belonging to codes 1 to 9, and 15 to 17 [1, 12] (Fig. 4) . Codes 1 to 3, 7 to 9, and 15 to 17 are found in MAH. Code 4 is from M. avium subsp. avium, and codes 5 and 6 are from M. avium subsp. paratuberculosis. The hsp65 sequence from our specimen, shown as strain MY332, was closest to that in code 9 and located in the group composed of codes 1, 2, 8, 9, 15, 16, and 17. These results indicated that the isolate from the clinical sample was MAH. Due to the positive culture results for the Mycobacterium species, we started orally combined administration of antibiotics (isoniazid 10 mg/kg eve