Sporotrichosis
- Sporotrichosis is chronic contagious suppurative granulomatous disease of skin and subcutaneous tissues.
- Disease affects both human and domestic animals.
Etiology:
- Disease is caused by fungus known as Sporotrichum schenckii
- Organism are normal inhabitant of plant, wood and the soil.
- Organism are cigar shaped in appearance and 3-5 µ in length.
- It can appear as small yeast in tissues and exudates which can be obtained by inoculation in cystine-blood agar brain heart infusion agar slope at 37°C.
- Yeast from colonies are creamy and whitish in appearance.
- Culture on SDA, mycelia develop. Colonies are white and fluffy in beginning but later turn down into dark brown to black.
Epidemiology:
- Disease is sporadic in nature and has been reported from various countries of the world.
- Disease has been reported from human, horse, dog, cat, camels, dolphins, goat, mules, birds, pig, rat and armadillos.
- Zoonotic infection can occur from cats to humans and has been reported without evidence of trauma.
- Epidemics of sporotrichosis have been reported in Brazil associated with the species S brasiliensis.
- Infection is typically environmental, but animal-to-animal transmission can create epizootics, making it a significant zoonotic risk for humans.
- The most famous epidemic occurred in the mid-1940s in South Africa, where more than 3000 native Bantu miners were infected with Sporothrix growing in the soil.
- Human sporotrichosis is endemic in India, occurring with high prevalence in the northern sub-Himalayan region, from Himachal Pradesh in the northwest to Assam and West Bengal in the east.
- The incidence of human sporotrichosis in China is among the highest globally.
- There is a higher incidence of cases during the winter, possibly associated with contamination of the home environment with wood, twigs, and sticks used as an important energy matrix for cooking and heating.
- Cats with street access are 2.54 times more likely to have sporotrichosis.
Transmission:
- Direct inoculation of organism into skin wounds via contact with plants or soil contaminated.
- Through direct contact with infected animals.
Pathogenesis:
Clinical Findings:
- Disease appears in 3 clinical forms; cutaneous form, lymphatic form and systemic form.
Cutaneous form:
- It is most common form in dog and cat.
- Development of multiple nodules on skin
- These nodules ulcerate and drained with pus.
- Nodules then discharge small amount of reddish exudate.
- Exudates dries up and scab are formed.
Lymphatic form:
- It is most commonly encountered in horse, donkey and mules.
- Multiple nodules appear on the lymph channels like nodular cords.
- Nodules gets ulcerated and deep lesion are produced.
- Lymphatic cords become thickened, palpable and cord-like.
Systemic form:
- Dissemination of infection in different parts of body.
PM Findings:
- Lesion are nodular, ulcerative and necrotic in nature.
- Microscopically, primary lesion is comprised of granuloma.
- Granulomatous inflammatory changes with purulent centre, encircled by epithelioid granulation tissues and encapsulated by connective tissue capsule.
- Red oblong bodies can be identified within cytoplasm of giant cells.
Diagnosis:
- Demonstration of organisms in exudates. Stain of smear may reveal small number of gram-positive spores.
- PAS stain can be used to demonstrate organism. They look like oval, round or cigar shaped.
- Culture of organism from exudate in SDA, BHI, glucose blood agar. Smooth white colony will appear.
- Animal inoculation in rat and mice
- FAT has been considered as simple, rapid and specific for demonstration of organism in exudate or tissues.
- Tube agglutination test has given good results in man.
Differential Diagnosis:
- Epizootic lymphangitis:
- Lesion are usually located in extremities in horse.
- Cutaneous tuberculosis:
- Progression of lesion is slow
- Demonstration of mycobacterium in exudates through culture
- Histoplasmosis:
- Systemic involvement is often present.
- Papules, nodules and ulceration
Treatment:
- Itraconazole is drug of choice for treatment of sporotrichosis. Cats requires very long treatment often >12 months, however failure may also occur.
- Itraconazole @10mg/kg, b.wt. Treatment should be extended at least a month beyond clinical cure.
- Terbinafine @30 mg/kg, PO, daily has also been used successfully.
- Alternatively, potassium iodide, administered PO, has been used with some success alone or in combination with azoles.
- During treatment, the patient should be monitored for clinical signs of iodide toxicity: anorexia, vomiting, depression, muscle twitching, hypothermia, cardiomyopathy, cardiovascular collapse, and death can occur.
- Surgical resection, cryotherapy, and/or localized hyperthermia has shown some success in limited numbers of cases.
Control Measures:
- Isolation and segregation of infected animals.
- Immediate treatment of cuts, wounds and abrasions with tincture iodine
- Sheds and equipment should be cleaned thoroughly with antifungal agents.
- Good biosecurity must be practiced, including personal protective equipment (PPE) and premises disinfection.
- Responsible pet ownership; keeping cat indoors is very important in controlling infection.