Cytology and histopathology of canine leproid granuloma syndrome

Common superficial and deep cutaneous bacterial infections in domestic animals: A review

The skin covers the external surface of animals, and it is constantly exposed to and inhabited by different microorganisms, including bacteria. Alterations in the skin barrier allow commensal and/or pathogenic bacteria to proliferate and penetrate deep into the lower layers of the skin. Being the first barrier to the external environment, the skin is prone to injuries, allowing the penetration of microorganisms that may lead to severe deep infections. Companion animals, especially dogs, are prone to bacterial infections, often secondary to allergic dermatitis. When environmental conditions are unfavorable, horses, cattle, sheep, and goats can develop superficial infections, such as those caused by Dermatophilus congolensis. Deep inflammation is commonly caused by Mycobacterium spp., which results in granulomatous to pyogranulomatous dermatitis and panniculitis. Likewise, bacteria such as Nocardia spp. and Actinomyces spp. can cause deep pyogranulomatous inflammation. Bacteria that lead to deep necrotizing lesions (eg, necrotizing fasciitis/flesh-eating bacteria) can be severe and even result in death. This review includes an overview of the most common cutaneous bacterial infections of domestic animals, highlighting the main features and histologic morphology of the bacteria, cutaneous structures involved, and the type of inflammatory infiltrates.

Canine leproid granuloma caused by a member of the Mycobacterium tuberculosis complex

Canine leproid granuloma (CLG) is a chronic form of dermatitis that has been associated with nontuberculous mycobacterial infections in Africa, Oceania, the Americas, and Europe. We report here a case of CLG associated with a member of the Mycobacterium tuberculosis complex (MTBC), which could be of public health concern. An 8-y-old pet dog developed 0.5-1-cm diameter, raised, firm, nonpruritic, alopecic, painless skin nodules on the external aspects of both pinnae. Histologic examination revealed severe pyogranulomatous dermatitis with intracellular Ziehl-Neelsen-positive bacilli that were immunoreactive by immunohistochemistry using a polyclonal primary antibody that recognizes tuberculous and nontuberculous Mycobacterium species. DNA extracted from formalin-fixed, paraffin-embedded skin sections was tested by a Mycobacterium genus-specific nested PCR assay targeting the 16S rRNA gene. BLAST sequence analysis of 214-bp and 178-bp amplicons showed 99.5% identity with members of the MTBC; however, the agent could not be identified at the species level. Although CLG has been associated traditionally with nontuberculous mycobacterial infections, the role of Mycobacterium spp. within the MTBC as a cause of this condition, and the role of dogs with CLG as possible sources of MTBC to other animals and humans, should not be disregarded given its zoonotic potential.

Ulcerated and nonulcerated nontuberculous cutaneous mycobacterial granulomas in cats and dogs

BACKGROUND

Mycobacterial granulomas of the skin and subcutis can be caused by one of a number of pathogens. This review concentrates on noncultivable species that cause diseases characterized by focal granuloma(s), namely leproid granuloma (in dogs) and feline leprosy (in cats). Clinically indistinguishable lesions can be caused by tuberculous organisms (Mycobacterium bovis and Mycobacterium microti) and members of the Mycobacterium avium complex. Rapidly growing mycobacterial species that cause infection of the subcutaneous panniculus associated with draining tracts are not discussed. Disease caused by Mycobacterium ulcerans is an important emerging differential diagnosis for ulcerated cutaneous nodules in certain localized regions. CLINICAL LESIONS: Lesions comprise one or multiple nodules in the skin/subcutis. These are generally firm and well circumscribed, and typically become denuded of hair. They may or may not ulcerate, depending on the virulence of the causal organisms and the immune response of the host.

DIAGNOSIS

The most inexpensive, noninvasive means of diagnosis is by submission of methanol-fixed, Romanowsky-stained smears to a Mycobacterium Reference Laboratory after detecting negatively stained or acid-fast bacilli on cytological smears. Scrapings of material from slides usually provide sufficient mycobacterial DNA to enable identification of the causal organism using sequence analysis of amplicons after PCR using specific mycobacterial primers.

THERAPY

Therapy relies upon a combination of marginal resection of easily accessible lesions and treatment using two or three drugs effective against slowly growing mycobacteria, choosing amongst rifampicin, clarithromycin, clofazimine and pradofloxacin/moxifloxacin.

Epidemiology, clinical signs, histopathology and molecular characterization of canine leproid granuloma: a retrospective study of cases from Brazil

Thirty-eight cases of canine leproid granuloma were diagnosed between 2000 and 2008. Diagnosis was based upon clinical and histopathological findings and the presence of acid-fast bacilli in skin sections. The clinical lesions were localized predominantly on the pinnae and included papules, plaques and nodules, with or without ulceration. Boxer dogs were the breed most affected. Histopathological findings included nodular to diffuse pyogranulomatous, lymphoplasmocytic inflammatory infiltrates, with or without necrosis, localized in the dermis or subcutaneous tissue. The bacillary loading and morphology were variable among the lesions analysed. There was no significant correlation between bacterial load and histopathological pattern, dominant type of inflammatory infiltration or the amount of necrosis or giant cells. No correlation was observed between giant cells and histopathological pattern. In the majority of cases where a PCR-based assay was done, a novel mycobacterium species as the main aetiological agent was identified, as reported in previous studies.

Cutaneous sterile granulomas/pyogranulomas, leishmaniasis and mycobacterial infections

Cutaneous "sterile" granulomas represent a group of uncommon skin disorders of unknown aetiopathogenesis. Many diseases are included in this group (for example, sterile granuloma/pyogranuloma syndrome and reactive histiocytosis). The definition of sterile is based on the exclusion of other possible aetiological agents (for example, microorganisms or foreign body). Many techniques are used to rule out a microbial aetiology including cytology, histology, immunohistochemistry and culture. However, some organisms are "fastidious" and difficult to culture or to identify with routine methods, and molecular studies are necessary. This is particularly true for mycobacteria (for example, canine leproid granuloma syndrome) and Leishmania. Recently, studies in human and veterinary medicine have proved the presence of microorganisms (mycobacteria and Leishmania) using a polymerase chain reaction technique in specimens previously diagnosed as sterile. Therefore, it is very important, with the development of new technologies, to use a multidisciplinary diagnostic approach to definitively rule out any microorganism before declaring a disease sterile.

Infections of the subcutis and skin of dogs caused by rapidly growing mycobacteria

Nine dogs with panniculitis due to rapidly growing mycobacteria (RGM) were examined over 17 years. Dogs were two to 15 years; five were male, four were female. All were obese or in good condition. Antecedent injury, typically a dog bite or vehicular trauma, could be identified in some patients, while one bitch had hyperadrenocorticism. Infections involved different locations, although the cervicothoracic region, dorsum or flank were most often affected. Patients were systemically well, apart from one dog with pyrexia and two with pain or lameness. Cytology demonstrated pyogranulomatous inflammation, but in only one case was it possible to see acid-fast bacilli (AFB) in smears. Histology demonstrated chronic active pyogranulomatous panniculitis and dermatitis; AFB could be detected in only four specimens. Culture of aspirates or resected tissues demonstrated RGM in all cases, comprising six Mycobacterium smegmatis group and three Mycobacterium fortuitum group isolates. Resection of infected tissues, perioperative injectable antimicrobials and long courses of oral antimicrobials chosen according to susceptibility data generally effected a cure, although some cases recurred.

Clinical, microscopic, and molecular aspects of canine leproid granuloma in the United States

Leproid granulomas from seven dogs in the United States were evaluated. Gross characteristics included nodular and ulcerated dermal and subcutaneous lesions primarily on the caudal aspects of the pinnae and to a lesser extent on the muzzle, face, and forelimbs. In all except one dog, there was complete regression of the lesions within 6 months, either with no therapy or after surgical resection. Cytology or histopathology revealed pyogranulomatous inflammation with few to many acid-fast mycobacterial bacilli within macrophages. The organisms could not be cultivated in vitro. DNA sequencing of part of the 16S ribosomal RNA gene region revealed 99-100% homology among fragments from five of these dogs and fragments from dogs in the south Pacific. This syndrome occurs in dogs in North America and the prognosis is excellent, in contrast to the prognosis for rapid-growing or tuberculous mycobacteriosis.

Treatment of canine leproid granuloma syndrome: preliminary findings in seven dogs

OBJECTIVE

To determine effective treatment strategies for patients with refractory canine leproid granuloma syndrome.

DESIGN

Multi-institutional retrospective/prospective case series using client-owned dogs.

PROCEDURE

Seven dogs (four Boxers, one Dobermann, one Bullmastiff and one Bullmastiff cross-bred; ages 3 to 11 years) with leproid granulomas were treated successfully using a variety of treatment regimens. These cases were recruited because: lesions were either widely distributed over the dog; progressive, despite routine therapy, or were associated with particularly disfiguring lesions. The treatment regimen evolved during the course of the clinical study.

RESULTS

Combination therapy using rifampicin (5 to 15 mg/kg p.o., every 24 h) and clarithromycin (8 to 24 mg/kg p.o. daily; dose divided every 8 or every 12 h) was used most frequently and proved to be effective and free from side effects. Total daily doses of clarithromycin in excess of 14 mg/kg were considered optimal and long treatment courses, in the order of 1 to 3 months, were used. Combination therapy using rifampicin (25 mg/kg; that is, higher than the recommended dose) and clofazimine was effective in one case, but resulted in hepatotoxicity. A topical formulation of clofazimine in petroleum jelly was used as an adjunct to oral rifampicin and doxycycline in another patient treated successfully.

CONCLUSION

Based on our evolving clinical experience, a combination of rifampicin (10 to 15 mg/kg p.o., every 24 h) and clarithromycin (15 to 25 mg/kg p.o. total daily dose; given divided every 8 to 12 h) is currently recommended for treating severe or refractory cases of canine leproid granuloma syndrome. Treatment should be continued (typically for 4 to 8 weeks) until lesions are substantially reduced in size and ideally until lesions have resolved completely. A topical formulation, containing clofazimine in petroleum jelly may be used as an adjunct to systemic drug therapy. Further work is required to determine the most cost effective treatment regimen for this condition.

Identification by 16S rRNA gene analyses of a potential novel mycobacterial species as an etiological agent of canine leproid granuloma syndrome

PCR amplifications of the 16S rRNA gene were performed on 46 specimens obtained from 43 dogs with canine leproid granuloma syndrome to help determine its etiology. Sequence capture PCR was applied to 37 paraffin-embedded specimens from 37 dogs, and nested PCR was attempted on DNA from 9 fresh tissue specimens derived from 3 of the 37 aforementioned dogs and from an additional 6 dogs. Molecular analyses of the paraffin-embedded tissues and fresh tissue specimen analyses were performed at separate institutions. PCR products with identical sequences over a 350-bp region encompassing variable regions 2 and 3 of the 16S rRNA gene were obtained from 4 of 37 paraffin-embedded specimens and from all 9 specimens of fresh tissue originating from 12 of the 43 dogs. Identical sequences were determined from amplicons obtained from paraffin-embedded and fresh specimens from one dog. The consensus DNA sequence, amplified from paraffin-embedded tissue and represented by GenBank accession no. AF144747, shared highest nucleotide identity (99.4% over 519 bp) with mycobacterial strain IWGMT 90413 but did not correspond exactly to any EMBL or GenBank database sequence. With a probe derived from the V2 region of the novel canine sequence, reverse cross blot hybridization identified an additional four paraffin-embedded specimens containing the same novel sequence. In total, molecular methodologies identified the proposed novel mycobacterial sequence in 16 of 43 dogs with canine leproid granuloma syndrome, indicating that the species represented by this sequence may be the principal etiological agent of canine leproid granuloma syndrome.