Epizootic Lymphangitis 2024 PDF

COURSE: EQUINE MEDICINE(VMD VI) Topic: Epizootic lymphangitis DR. O.O. AKINNIYI University of Ibadan, Department of Veterinary Medicine 1  Epizootic lymphangitis DEFINITION Epizootic lymphangiti...

COURSE: EQUINE MEDICINE(VMD VI) Topic: Epizootic lymphangitis DR. O.O. AKINNIYI University of Ibadan, Department of Veterinary Medicine 1  Epizootic lymphangitis DEFINITION Epizootic lymphangitis is a contagious, chronic granulomatous disease of the skin, lymphatic vessels and nodes of the limbs, neck and chest of horses and other equid species. Tropical and subtropical regions have a higher prevalence of epizootic lymphangitis than temperate regions Epizootic lymphangitis by Dr. O.O Akinniyi 2  Epizootic lymphangitis SYNONYMS Pseudoglanders, Pseudofarcy, Equine Histoplasmosis, Histoplasmosis Farciminosi, African Farcy, Equine Blastomycosis, Equine Cryptococcosis Epizootic lymphangitis by Dr. O.O Akinniyi 3  Epizootic lymphangitis AETIOLOGY Epizootic lymphangitis (EZL), caused by the dimorphic fungus, Histoplasma capsulatum var. farciminosum. The related species H. capsulatum var. capsulatum causes histoplasmosis in humans and is an important opportunistic pathogen worldwide. H. Capsulatum var. farciminosum and H. capsulatum var. capsulatum are antigenically indistinguishable. Members of the genus Histoplasma have generally been divided into three distinct varieties: H. capsulatum var capsulatum, H. capsulatum var duboisii, and H. capsulatum var farciminosum, based on host species and pathogenesis. Epizootic lymphangitis by Dr. O.O Akinniyi 4  Epizootic lymphangitis TRANSMISSION Both the yeast form of H. capsulatum var. farciminosum, found in animals, and its saprophytic mycelial form (mold) in the environment can infect animals. Direct contact with yeasts, which occur in exudates from affected sites, or indirect contact with fomites such as grooming or harness equipment. Infection can be contacted through breaks in the skin or mucous membranes (e.g., the conjunctiva or nasal mucosa). Inhalation of the causative agent leads to the development of the pulmonary form. Biting flies, e.g., members of the genera Musca and Stomoxys, appear to transmit it mechanically. Flies may be particularly important in contaminating the eye. Epizootic lymphangitis by Dr. O.O Akinniyi 5  Epizootic lymphangitis CLINICAL PRESENTATION 1) Cutaneous disease (most common) The cutaneous form occurs as a result of direct or indirect contact between traumatized skin and infected and/or contaminated substances. The cutaneous form is characterized by multifocal pyogranulomatous subcutaneous nodules that progress along the lymphatic system, with the coalescence of nodules producing a corded appearance. The forelimbs, neck, and head are the most common sites. Epizootic lymphangitis by Dr. O.O Akinniyi 6  Epizootic lymphangitis 2) Ocular The ocular form of the disease results from inoculation of the organism into the eye, likely by biting flies. Initially, infection is characterized by a watery ocular discharge that may be unilateral or bilateral and variable swelling of the eyelids. This leads to the appearance of papules and button-like growths on the conjunctivae and nictitating membranes. The infection may extend to the periorbital tissues with formation of a granulomatous reaction. The secondary complications of the ocular form of the disease include corneal ulceration, panopthalmitis and myiasis Epizootic lymphangitis by Dr. O.O Akinniyi 7  Epizootic lymphangitis 3) Respiratory Respiratory cases are thought to occur through inhalation of the organism either as spores from the environment or through extension of infection from the external mucous membranes of the nares or from the naso-lachrymal duct. Nodules can be present around the mucocutaneous junction of the nose and at postmortem are commonly seen to extend from the nasal passages, through the trachea and into the lung parenchyma. The lesions are usually found near the external nares. These lesions may also occur in the lung. Affected animals develop a viscous mucopurulent nasal discharge and may exhibit dyspnea. Advanced cases exhibit progressive weakness, coughing and loss of bodily condition. Epizootic lymphangitis by Dr. O.O Akinniyi 8  Epizootic lymphangitis PATHOPHYSIOLOGY After gaining entry through wounds, H.capsulatum var. Farciminosum invades subcutaneous tissue, forms a local granuloma or ulcer, and spreads through the lymphatics to regional lymph nodes or, in extreme cases, other organs. Nodular lesions form in the skin along lymphatics and lymph nodes. These lesions eventually ulcerate. Nodules form when there is skin damage (particularly under the harness and on the extremities). Horses with a high systemic fungus burden may succumb to pneumonia or other organ failure. The ocular version of the disease is caused by the bacterium being inoculated into the eye, most likely by biting flies. Because the animals will scratch the skin lesions with their teeth and lips, spreading them to the surrounding organs, both conjunctivitis and rhinitis can occur as an extension of the skin form. Epizootic lymphangitis by Dr. O.O Akinniyi 9  Epizootic lymphangitis DIFFERENTIAL DIAGNOSIS The cutaneous form of the disease may be confused with farcy (the skin form of glanders), which is caused by Burkholderia mallei Ulcerative lymphangitis, which is caused by Corynebacterium pseudotuberculosis Indolent ulcers caused by Rhodococcus equi, Sporotrichosis caused by Sporothrix schenckii. Cryptococcosis, strangles, sarcoids and cutaneous lymphosarcomas Epizootic lymphangitis by Dr. O.O Akinniyi 10  Epizootic lymphangitis DIAGNOSIS The diagnosis of epizootic lymphangitis depends on the clinical signs, the history of animals, and laboratory confirmation. Laboratory tests used in the diagnosis of epizootic lymphangitis include: identification of the yeast form of Histoplasma capsulatum var. farciminosum in smears of exudates or in histological sections of material from lesions; serological tests (i.e., fluorescent antibody tests, enzyme-linked immunosorbent assay, and passive hem agglutination tests); skin hyper sensitivity tests (histofarcin skin test); and isolation of the causative agent by culture. The organism in the tissues is in its yeast form. It may be stained with Giemsa, Diff-Quick, or Gomori methenamine silver. Epizootic lymphangitis by Dr. O.O Akinniyi 11  Epizootic lymphangitis TREATMENT Amphotericin B (intravenous injection of amphotericin B at a dose of 0.2 mg/kg body weight three times on alternate days) is the drug of choice. There has been successful treatment with intravenous administration of sodium iodide (repeated weekly for four weeks is recommended). Oral administration of potassium iodide, and surgical excision of lesions has been reported. Early identification of cases is critical for successful therapy. Localized nodules can also be lanced, the pus drained and the nodules packed with a 7% tincture of iodine. Epizootic lymphangitis by Dr. O.O Akinniyi 12  Epizootic lymphangitis CONTROL AND PREVENTION Infected premises and equipment must be thoroughly cleaned and disinfected. Organisms that contaminate the soil may survive for long periods. Screening with serological tests or the histofarcin skin test might help identify infected animals, but the false positive rate might be high. In endemic areas, good cleaning and disinfection can help prevent the organisms from spreading between animals. Particular care should be taken to prevent transmission on grooming equipment or harnesses. Fly control is also expected to be useful. There are no known commercial vaccines for epizootic lymphangitis, although some reports suggest that live and inactivated vaccines have been tested (and possibly used) in some endemic regions (e.g., China), and appeared to be promising. Epizootic lymphangitis by Dr. O.O Akinniyi 13  Epizootic lymphangitis Histoplasma capsulatum var. farciminosum in pectoral lymphatics of horse. Epizootic lymphangitis by Dr. O.O Akinniyi 14  Epizootic lymphangitis Histoplasma capsulatum var. farciminosum in lymphatics of shoulder and neck of horse Epizootic lymphangitis by Dr. O.O Akinniyi 15  Epizootic lymphangitis Histoplasma capsulatum var. farciminosum in lymphatics of shoulder and neck of horse Epizootic lymphangitis by Dr. O.O Akinniyi 16  Epizootic lymphangitis Nodular lesions have ulcerated Epizootic lymphangitis by Dr. O.O Akinniyi 17  Epizootic lymphangitis Ocular form Epizootic lymphangitis by Dr. O.O Akinniyi 18  Epizootic lymphangitis Ocular form Epizootic lymphangitis by Dr. O.O Akinniyi 19  Epizootic lymphangitis Epizootic lymphangitis Epizootic lymphangitis by Dr. O.O Akinniyi 20