Feline leprosy due to Candidatus 'Mycobacterium tarwinense':Further clinical and molecular characterisation of 15 previously reported cases and an additional 27 cases

Abstract

Objectives: This paper, the first in a series of three on 'feline leprosy', provides a detailed description of disease referable to Candidatus 'Mycobacterium tarwinense', the most common cause of feline leprosy in Victoria, Australia.

Methods: Cases were sourced retrospectively and prospectively for this observational study, describing clinical, geographical and molecular microbiological data for cats definitively diagnosed with Candidatus 'M tarwinense' infection.

Results: A total of 145 cases of feline leprosy were scrutinised; 114 'new' cases were sourced from the Victorian Infectious Diseases Reference Laboratory records, veterinary pathology laboratories or veterinarians, and 31 cases were derived from six published studies. Forty-two cats were definitively diagnosed with Candidatus 'M tarwinense' infection. Typically, cats were between 3 and 11 years of age, with no gender predilection, and were generally systemically well. All had outdoor access. Most cats underwent surgical resection of lesions with adjunctive medical therapy, often utilising a combination of oral clarithromycin and rifampicin for at least 3 months. Prognosis for recovery was generally good. Resolution of lesions was not observed in the absence of treatment, but a number of untreated cats continued to enjoy an acceptable quality of life despite persistence of the disease, which extended locally but did not appear to disseminate to internal organs. Preliminary results of draft genome sequencing confirmed that the species is a member of the Mycobacterium simiae complex.

Conclusions and relevance: Candidatus 'M tarwinense', a fastidious member of the M simiae complex, is capable of causing feline leprosy with a tendency to produce lesions on the head, particularly involving the eyes and periocular skin. The disease has an indolent clinical course and generally responds favourably to therapy despite lesions often containing large numbers of organisms. Detailed genomic analysis may yield clues as to the environmental niche and culture requirement of this elusive organism. Prospective treatment trials and/or drug susceptibility testing in specialised systems would further inform treatment recommendations.

Figure 1

Geographical distribution of feline infections caused by Candidatus ‘M tarwinense’ (shown in green). All except for two cases in New South Wales (one in a suburban area of Sydney, another on the Central Coast near Gosford; arrows) are clustered in south-eastern Victoria. No cases were encountered in New Zealand, Tasmania or anywhere else in the world

Figure 2

Representative photographs of Candidatus ‘M tarwinense’ infection in cats fromVictoria, Australia, chosen to illustrate the occurrence of lesions near the eyes. These six photographs of different patients emphasise the propensity of lesions to occur on ocular structures, including the nictitating membrane (a), conjunctiva (b,d–f) and eyelids (c)

Figure 3

Representative photographs of Candidatus ‘M tarwinense’ infection in cats fromVictoria, Australia, chosen to illustrate the presence of lesions on the oculonasal skin. These six photographs of different patients illustrate the range of lesions that may be encountered, including an ulcerated lesion on the nasal planum (a), involvement of the bridge of the nose (b,c) and lips (d,e), and a lesion adjacent to the naris (f). (a) Image courtesy of Dr Robert Hilton; reproduced from Malik et al, with permission; (d) reproduced from Little, with permission

Figure 4

Representative photographs of Candidatus ‘M tarwinense’ infection in two cats fromVictoria, Australia, illustrating the presence of lesions on the distal forelimbs

Figure 5

Representative photograph of Candidatus ‘M tarwinense’ infection in a cat in Victoria, Australia, illustrating the presence of a lesion on the gum. Reproduced from Little, with permission

Figure 6

Demonstration of the unrelenting progression of lesions in a cat (case 35). Infection was initially diagnosed in 2006 (a) and over the subsequent 8 years only poor attempts at therapy were made. Images (b) and (c) were obtained in 2014. This cat was apparently still alive at the time of writing. (a) Reproduced from Fyfe et al, with permission