Abbey Veterinary Services

DIAGNOSTIC HISTOPATHOLOGY AND CYTOLOGY

CASE OF INTEREST

A case of Cutaneous Leishmaniasis in a crossbred dog.

By Richard Fox, Veterinary Pathologist

Case donated by Lucy Genovese, Veterinary Pathologist.

A four year old crossbred dog was presented with a clinically swollen digit on the right foreleg (digit 2). The lesion was characterised by excessive scaling and moderate alopecia with mild hyperaemia and small areas of ulceration. The lesion had been treated with systemic 'antibiotics' whilst residing in Spain with no evidence of a clinical response. The lesion had been present for 3 months and the owner had correlated the formation of the lesion with running through long grass. Initial thoughts were of a foreign body reaction but given the history of a lesion not responsive to 'antibiotics' the lesion was excised. No other lesion were evident on the skin at that point and there was no evidence to support any systemic abnormalities.

A toe was submitted with a 1 cm raised mass lateral to nail. A section of haired skin taken through this mass displayed several changes. There was an ill defined nodular infiltrate of cells extending from the superficial dermis into the deep dermis. The overlying epidermis was markedly hyperplastic and there was marked compact orthokeratotic and parakeratotic hyperkeratosis (Fig. 1). Hair follicles displayed mural hyperplasia in the superficial dermis but mild atrophy in the mid to deep dermis. Hair shafts were rarely observed.

Figure 1. Histological section of haired (alopecic) skin with marked epidermal hyperplasia, hyperkeratosis and a dermal cellular infiltrate. (x5 obj.). HE Stain.

Large numbers of densely packed epithelioid macrophages with multifocal dense infiltrates of plasma cells were identified. There were lesser small lymphocytes and neutrophils scattered throughout (Fig 2.).

Figure 2. Histological section of a groups of macrophages (pale cells) and plasma cells (dark round nuclei with eosinophilic cytoplasm) adjacent to a hair follicle without a hair shaft. (x40 obj.). HE Stain.

Within the macrophages, throughout the lesion, there were small 1 micron diameter basophilic structures with a small body at one end. These structures were contained in a faint clear vacuole (Fig 3.).

Figure 3. Histological section of macrophages containing leishmanial organisms (arrow heads) with a faint polar dot (kinetoplast)(x10 obj.). HE Stain.

Canine leishmaniasis (CanL) caused by Leishmania infantum (syn. L. chagasi, in Latin America), which is transmitted by the bite of phlebotomine sand flies, is endemic and affects millions of dogs in Europe, Asia, North Africa and South America. This organism is endemic in the Mediterranean region. It is an obligatory intracellular, diphasic protozoa of the genus Leishmania.

Despite the lack of pathognomonic manifestations, the commonest clinical signs are cutaneous alterations (cutaneous form), local or generalized lymphoadenomegaly, loss of body weight, liver and spleen enlargement, glomerulopathy, ocular lesions, epistaxis, onycogryphosis and lameness. Atypical forms include monoclonal gammopathy, chronic colitis, haemostatic alterations and disorders of the cardiovascular, respiratory and musculo-skeletal systems (visceral form). In this way, Leishmania infection shares many of the clinical and pathological features with other canine diseases.

Cutaneous lesions are in most cases generalised and produce and exfoliate (scaling) dermatitis. This is usually non-pruritic and accompanied by alopecia. Nodules and multifocal ulceration may occur in concert with exfoliation as the disease progresses. Nodular skin disease is less common but in this case may have represented an initial site of infection.

The laboratory diagnosis of CanL still poses a challenge, despite progress made in the development of several direct and indirect methods. PCR-based methods applied for Leishmania detection are more reliable for determining the presence and identification of the parasite not only in active cases, but also for monitoring parasitological cure after chemotherapy. PCR for the detection of Leishmania DNA can be carried out with a broad range of clinical specimens: whole blood, buffy coat, bone marrow, lymph node, skin or conjunctiva swabs/tissue. A single negative PCR result in a clinically suspected dog is not enough to rule out infection. Studies evaluating PCR from different tissues of infected dogs have shown variable and sometimes conflicting results.

Other direct and indirect tests including ELISA, Immunodiffusion Assay and Direct Agglutination Test have also shown good sensitivity and specificity some of which are available as a commercial diagnostic test.

References:

1. Maia C, Campino L. Methods for diagnosis of canine leishmaniasis and immune response to infection. Vet Parasitol. 2008 Dec 20;158(4):274-87

2. Alvar J, Cañavate C, Molina R, Moreno J, Nieto J. Adv Parasitol. Canine leishmaniasis. 2004;57:1-88.

3. Infectious nodular and diffuse granulomatous and pyogranulomatous diseases of the dermis. in Skin Diseases of the Dog and Cat, 2nd edition (2005), Gross, Ihrke, Walder and Affolter pp. 312-319.