Exotic Diseases

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Species Infected

primarily an infection of solipeds

sporadic infection of Felidae if fed contaminated meat

infection of man sporadic but can be fatal

Clinical Signs

acute disease

• development of rapidly spreading ulcers in skin and nasal mucosa
• death within a few days from septicaemia

chronic disease

• more common
• signs depend on where lesions are located
• pulmonary involvement always occurs
• nasal and/or skin form may be concurrent
• if pulmonary form dominates animals will cough and show epistaxis
• nasal form
• incubation 2 weeks
• initial catarrhal rhinitis progresses to a greenish yellow discharge containing blood and flecks of epithelium
• nodules develop especially on septum
• necrotic nodule centres desquamate and heal by granulation
• skin form
• papule followed by nodule development
• these rupture and discharge
• lymphadenitis and lymphangitis develops with lymphatics becoming thickened, abscessed
• fistulae develop with purulent discharges
• medial hocks predilection sites
• mortality high, recovery rare

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Lesions


• nodule (1 cm) becomes ulcerated
• healing occurs with cicatrisation and stellate scar formation
• lungs
• acute disease - catarrhal bronchopneumonia
• chronic disease - miliary greyish nodules similar to tuberculosis
• skin, nasal septum, pharynx, larynx, trachea
• range of lesions from nodules, ulcers to stellate scars
• lymph nodes - abscessed
• lymphatics - thickened, tortuous and focally abscessed

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Pathogenesis

• oral ingestion main source
• bacteraemia with localisation in lungs and other sites
• death associated with terminal bronchopneumonia

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Aetiology

• Pseudomonas mallei
• differences in clinical and pathological findings related to strain differences
• present in exudates from nasal and cutaneous lesions
• readily destroyed by heat, light and disinfectants
• does not persist in environment for longer than 3 months

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Epidemiology

• primary source of infection
• affected animals
• apparently recovered carrier animals
• troughs, fodder contaminated by nasal discharges or sputum
• occasional infection arises from contaminated harness or grooming equipment
• large concentration or extensive movements of animals important
• decline of disease associated with deurbanisation of horses

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Differential Diagnoses

     1.  strangles
     2.  epizootic lymphangitis - ulcers do not have raised edges and pulmonary lesions unusual
     3.  fungal infections including blastomycosis and cryptococcosis
     4.  ulcerative lymphangitis - sporadic, and systemic involvement rare
     5.  melioidosis (Pseudomonas pseudomallei) - not a primary disease of horses