Sporotrichosis

Definition It is a non contagious chronic infectious disease of equine, humans and other domestic animals, caused by Sporothrix shenki, characterized by cutaneous nodules and ulcers on the limb with or without lymphangitis and lymphadenitis.

Etiology Sporotrichosis is caused by Sporothrix schenckii, a dimorphic fungus, which form single walled, spherical, oval or cigar shape spores. It grow on sabouraud dextrose agar. Predisposing factors: Cutaneous wounds and presence of the animals in muddy unhygienic stables.

Epidemiology Distribution: S. schenckii can be found worldwide and present in Egypt. Animal susceptibility: Sporotrichosis occurs most often in horses. Cases have also been seen in cats, dogs, rodents, cattle, goats, swine, mules, camels, non-human primates, birds, and various wild animals including foxes. Seasonal incidence: The disease increase during winter seasons. Mode of transmission: The pus discharged from the lesions of the infected animals is the main source of contamination of beddings, grooming, utensils and other fomites. Infection occurs through cutaneous wounds or abrasions either by direct contact or indirect contact with contaminated surroundings and fomites.

Pathogenesis The organism gain access through wounds and abrasions in the skin, invades the subcutaneous tissue causing nodular ulcerating lesions, and then spreads through lymphatics. Finally, the nodules ulcerate and discharge pus. Inflammation of the lymph vessels and lymph nodes may be observed. Involvement of bones and visceral organs with fetal termination is rare, but has been reported in dogs and horses.

Clinical signs The disease has low morbidity, mortality and long course. Sporotrichosis may be grouped into 3 forms— lymphocutaneous, cutaneous, and disseminated. The lymphocutaneous form is the most common. Small, firm dermal to subcutaneous nodules, 1-3 cm in diameter, develop at the site of inoculation (usually about fetlock). As infection ascends along the lymphatic vessels, cording and new nodules develop. Lesions ulcerate and discharge a serohemorrhagic exudate. Although systemic illness is not seen initially, chronic illness may result in fever, listlessness, and depression.

Clinical signs The cutaneous form remains localized to the site of inoculation, although lesions may be multicentric. Disseminated sporotrichosis is rare but potentially fatal and may develop with neglect of cutaneous and lymphocutaneous forms. Infection develops via hematogenous or tissue spread from the initial site of inoculation to the bone, lungs, liver, spleen, testes, GI tract, or CNS.

Postmortem Lesion There are no obvious lesions except cutaneous one.

Diagnosis Field diagnosis: It depends on history, epidemiology and clinical signs of the disease.

Diagnosis Laboratory diagnosis: Samples: Pus, blood and serum sample. Laboratory examinations: Direct microscopic examination of stained pus smear to detect cigar shape spores. Isolation of the organism on sabaurods dextrose agar and identification of the organism from colony morphology and biochemical reactions. FAT, it gives positive result with samples of infected animal. Animal inoculation, inoculation of mice I/P with pus material of infected animal, local lesion (granuloma) can be observe after 3 w of inoculation and peritoneal exudate contain cigar-shape fungi in peritoneal cavity. Serological test as latex agglutination test.

Differential diagnosis This disease may be misdiagnosed clinically with glanders, epizootic lymphangitis and ulcerative lymphangitis.

Treatment Systemic treatment with iodides such as potassium iodide orally (0.5-1 mg/kg, bw) as 1-2 dose daily for 7 days or sodium iodide I/V (40 mg/kg, bw) as 2-5 doses then one dose daily till cure. During treatment, the animal should be monitored for signs of iodide toxicity—anorexia, vomiting, depression, muscle twitching, hypothermia, cardiomyopathy, cardiovascular collapse, and death. The dose of iodides may be stopped or reduced if signs of iodism appear. Local application of iodides daily to ulcers after evacuation of contents.

Control Early diagnosis, isolation and treatment of infected animals, Prophylactic treatment of all cutaneous wound and abrasions and Adequate hygiene to prevent spread of infection.