Disseminated Mycobacterium avium infection in young cats: overrepresentation of Abyssinian cats

Abstract

Disseminated Mycobacterium avium-intracellulare complex (MAC) infection was diagnosed in 10 young cats (1-5 years of age) from Australia or North America between 1995 and 2004. A further two cats with disseminated mycobacteriosis (precise agent not identified) were recognised during this period. Of the 12, 10 were Abyssinian cats, one was a Somali cat and one was a domestic shorthair cat. None of the cats tested positive for either FeLV antigen or FIV antibody. The clinical course of these infections was indolent, with cats typically presenting for weight loss, initially in the face of polyphagia, with a chronicity of up to several months. Additional clinical features included lower respiratory tract signs and peripheral lymphadenomegaly. A marked diffuse interstitial pattern was evident in thoracic radiographs, even in cats without overt respiratory involvement. Hair clipped to perform diagnostic procedures tended to regrow slowly, if at all. Diagnosis was generally made by obtaining representative tissue specimens from mesenteric lymph nodes, liver or kidney at laparotomy, or from a popliteal lymph node. The primary antecedent event was most likely colonisation of either the alimentary or respiratory tract, followed by local invasion and eventual lymphatic and haematogenous dissemination. Nine cases were treated using combination therapy with agents effective for MAC infection in human patients. Two cats are still undergoing initial therapy and have responded. Of the remaining seven, all responded during long courses (5-14 months) of clarithromycin combined with either clofazimine or rifampicin, and a fluoroquinolone or doxycycline. Of these, three cats remain well (with durations between 2 months and 2 years following therapy); two developed recurrent disease (at 3 months and 2 years, respectively, following therapy) and have restarted therapy. The remaining two cats improved 1 year and 5 months, respectively, after diagnosis but ultimately succumbed. The two cats in which therapy was restarted have improved dramatically. Certain lines of Abyssinian and Somali cats likely suffer from a familial immunodeficiency that predisposes them to infection with slow-growing mycobacteria such as MAC.

Mycobacterial Infections

“…Siamese cats as well as Abyssinians and Somalis may be predisposed. 40,41 Disseminated MAC infection has also been reported in feline renal transplant recipients 42,43 and in a cat treated with chemotherapy for lymphoma. 44 Infection is not transmissible from one infected individual to another, but disease may initially be indistinguishable from that caused by MTBC bacteria.…”

“…In cats, disease resembles that caused by M. bovis or M. microti, with cutaneous lesions (especially on the head and limbs) in some cats, osteomyelitis, pulmonary involvement with tachypnea or cough, peripheral and abdominal lymphadenomegaly, and gastrointestinal, liver, splenic, renal, omental, and uncommonly CNS or marrow involvement. 41,42,[44][45][46][47][48][49][50] Gastrointestinal involvement may initially manifest as weight loss despite a good appetite. 41 Dogs with MAC infections often develop marked peripheral or abdominal lymphadenopathy, tonsillar enlargement, hepatosplenomegaly, and/or osteomyelitis.…”

“…41,42,[44][45][46][47][48][49][50] Gastrointestinal involvement may initially manifest as weight loss despite a good appetite. 41 Dogs with MAC infections often develop marked peripheral or abdominal lymphadenopathy, tonsillar enlargement, hepatosplenomegaly, and/or osteomyelitis. In some dogs, mandibular or cervical lymphadenopathy may be so severe that respiratory distress and dysphagia occur (Figure 44-9).…”

“…Rarely, neurologic signs such as nystagmus occur. 41 In dogs, low-grade fever, a thin body condition, dehydration, mucosal pallor, tonsillar enlargement, lymphadenomegaly (especially of the mandibular or abdominal nodes), hepatosplenomegaly, and/or abdominal pain may be found. Melena or hematochezia may be detected on rectal examination.…”

“…41,48 Diffuse interstitial patterns may be present in the absence of clinical signs of respiratory involvement. Thoracic lymphadenopathy or mediastinal masses may be present in dogs.…”