liveonearth (liveonearth) wrote,

Microbiology: Fungal Infection from a CAT BITE


These notes are with regard to a case I know of a woman who was bitten in her hands by a cat and 8 years later still has inflammation in the bitten knuckles. Most people acquire this infection via a small wound from a single thorn stick (rose gardeners), not direct innoculation into a joint. But this is what I think is going on, and why.

Main sources:

--fungal infx from CATS, horses (bites), thorns, sphagnum moss
--grows on plant debris in soil and on the bark of trees, shrubs, and garden plants
--gardeners get it, carpenters, berry pickers
--traumatic innoculation
--rapidly growing dimorphic fungus (at temperatures of 35 degrees F or lower)
--causes accute suppuration (watery pus, volumes of it)
--subacute or chronic infection
--characteristic infection involves suppurating subcutaneous nodules that progress proximally along lymphatic channels (lymphocutaneous sporotrichosis). Rarely, a primary pulmonary infection (pulmonary sporotrichosis) occurs, or DIRECT INOCULATION INTO TENDONS, BURSAE OR JOINTS occurs. Osteoarticular sporotrichosis occurs from direct inoculation or hematogenous seeding.
-- most common extracutaneous sites are in the bones, joints, tendon sheaths, and bursae
--Spontaneous resolution of cutaneous or lymphocutaneous sporotrichosis is documented. Prognosis is excellent for complete recovery after therapy.
--Pulmonary sporotrichosis may contribute to the decline in pulmonary function of patients with COPD. Response to therapy is variable. Osteoarticular sporotrichosis may result in significant morbidity from chronic osteomyelitis and arthritis with significant loss of joint function and deformity. Disseminated sporotrichosis is associated with significant morbidity and, possibly, mortality in immunocompromised hosts.
--Rare: disseminated infection with disseminated cutaneous lesions and involvement of multiple visceral organs; this occurs most commonly in patients with AIDS.
--first symptom (of single innoculation) is usually a small painless bump resembling an insect bite. It can be red, pink, or purple in color. The bump (nodule) usually appears on the finger, hand, or arm where the fungus first enters through a break on the skin. This is followed by one or more additional bumps or nodules which open and may resemble boils.
--Eventually lesions look like open sores (ulcerations) and are very slow to heal.
--Sporothrix schenckii
--Osteoarticular sporotrichosis
--Sporotrichosis may present as a chronic arthritis that often is confused with rheumatoid arthritis or other chronic inflammatory arthritis. This frequently occurs for 10 or more years, until destruction of adjacent bone or the development of draining fistulae encourages efforts to establish the microbial etiology of the chronic osteomyelitis by culture. Cutaneous or lymphocutaneous lesions are not prominent in these patients. !!!
--The process generally begins as a monoarticular arthritis, but other joints may become involved successively. The patient usually has pain on motion, but not the severe limitation characteristic of bacterial arthritis. Systemic illness usually is not present. Functional impairment resulting from osteoarticular sporotrichosis may become severe.
--The majority of infections are limited to the skin. Cases of joint, lung, and central nervous system infection have occurred but are very rare. Usually they occur only in persons with previous disorders of the immune system.
--primarily a chronic mycotic infection of the cutaneous or subcutaneous tissues and adjacent lymphatics characterized by nodular lesions which may suppurate and ulcerate
--infections are caused by the traumatic implantation of the fungus into the skin, or very rarely, by inhalation into the lungs
--Secondary spread to articular surfaces, bone and muscle is not infrequent, and the infection may also occasionally involve the central nervous system, lungs or genitourinary tract
--Fixed cutaneous sporotrichosis: Primary lesions develop at the site of implantation of the fungus, usually at more exposed sites mainly the limbs, hands and fingers. Lesions often start out as a painless nodule which soon become palpable and ulcerate often discharging a serous or purulent fluid. Importantly, lesions remain localised around the initial site of implantation and do not spread along the lymphangitic channels.
--Isolates from these lesions usually grow well at 35C, but not at 37C.
--Lymphocutaneous sporotrichosis: Primary lesions develop at the site of implantation of the fungus, but secondary lesions also appear along the lymphangitic channels which follow the same indolent course as the primary lesion ie they start out as painless nodules which soon become palpable and ulcerate. No systemic symptoms are present. Isolates from these lesions usually grow well at both 35C and 37C.
--Pulmonary sporotrichosis: This is a rare entity usually caused by the inhalation of conidia but cases of haematogenous dissemination have been reported. Symptoms are nonspecific and include cough, sputum production, fever, weight loss and upper-lobe lesion. Haemoptysis may occur and it can be massive and fatal. The natural course of the lung lesion is gradual progression to death.
--Osteoarticular sporotrichosis: Most patients also have cutaneous lesions and present with stiffness and pain in a large joint, usually the knee, elbow, ankle or wrist. Osteomyelitis seldom occurs without arthritis; the lesions usually confined to the long bones near affected joints.
--Other rare forms of sporotrichoisis include endophthalmitis, chorioretinitis and meningitis.
--Sporotrichosis can be confirmed when a doctor obtains a swab or a biopsy of a freshly opened skin nodule and submits it to a laboratory for fungal culture. If no skin nodule then tissue biopsy.
1) A tissue biopsy is the best specimen.
2) Direct Microscopy: Tissue sections should be stained using PAS digest, Grocott's methenamine silver (GMS) or Gram stain.
3) Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar and Brain heart infusion agar supplemented with 5% sheep blood.
Interpretation: A positive culture from a biopsy should be considered significant.
4) Serology: Serological tests are of limited value in the diagnosis of Sporotrichosis.
5) Identification: Hyphomycete characterized by thermal dimorphism and clusters of ovoid, denticulate conidia produced sympodially on short conidiophores.
--Cutaneous lesions respond well to saturated potassium iodide [4-6 ml three time a day for 2-4 months]
--itraconazole [400 mg/day] and terbinafine [250 mg twice daily] have both proved to be effective, although treatment times may be long. Ideally, treatment needs to be maintained for at least a month after clinical cure is achieved.
--!!! Local heat has also been shown to improve cutaneous lesions
--Extracutaneous forms of sporotrichosis may need a combination of antifungal treatment with Amphotericin B or itraconazole together with surgical debridement.
--(CDC) sporotrichosis is generally treated with potassium iodide, taken by mouth in droplet form. A new drug, called itraconazole (Sporanox), is available for treatment, but experience with this drug is still limited. Treatment is often extended over a number of weeks, until the skin lesions are completely healed.
Tags: arthritis, case studies, cats, diagnosis, fungus, gardening, microbes, sporotrichosis

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