Edema maligno em equino causado por Clostridium chauvoei

Background: Malignant edema occurs when a wound is contaminated by one or a combination of the following bacteria: Clostridium septicum, C. sordellii, C. chauvoei, C. novyi type A, and C. perfringens type A. Although malignant edema has been recognized as a disease of economic importance in domestic ruminants, it has rarely been reported in horses in Brazil. Immunohistochemistry is a method that combines histological, immunological and biochemical techniques which, with the use of specifi c antibodies, detects the agent in situ. This paper reports a case of malignant edema by Clostridium chauvoei in a horse in Bahia, Brazil. Case: A 4.5-year-old male horse was submitted for necropsy. The clinical history was obtained from the owner. Samples from the abdominal cavity, thoracic cavity, central nervous system and integumentary system were collected. The samples were fi xed in 10% formalin, processed routinely for histology, embedded in paraffi n, sectioned at fi ve microns, and stained with hematoxylin and eosin. Additionally, histological sections were subjected to immunohistochemistry anti-Clostridium perfringens type A, C. septicum, C. chauvoei, C. novyi type A, and C. sordellii. Positive and negative controls were included. The animal presented diffi culty in walking, swelling of the pelvic limbs two days after intramuscular anti-infl ammatory treatment, and died seven hours after the onset of clinical signs. Macroscopically, large amounts of hemorrhagic edema and tissue emphysema in the subcutaneous tissue and skeletal muscles were seen. Microscopically, there was moderate bleeding, particularly in subcutaneous areas and between myofi ber bundles, with few and discrete degeneration foci. Immunohistochemistry technique was positive for Clostridium chauvoei. Discussion: The diagnosis of malignant edema was confi rmed considering clinical and pathological alterations as well as the positive immunohistochemistry result for Clostridium chauvoei. Cases of malignant edema are occasionally observed in horses, and Clostridium perfringens and Clostridium septicum are the major etiological agents involved. Two cases have been reported in Brazil, both caused by Clostridium septicum. As in the present report, the animals developed the disease after administration of intramuscular anti-infl ammatory medication. The clinical course of the disease in horses is considered severe, with the fi rst clinical signs occurring between 24 and 48 h post infection. Clinical signs, particularly the marked diffi culty in walking, edema, and crepitus of the affected areas, may be considered characteristic. The pathological findings were similar to those described by other authors, which are attributed to toxins produced by the bacteria; however, the lesions described in this study were similar to those reported in less severe infections by Clostridium septicum. Bacterial culture and polymerase chain reaction (PCR) are standards for the identifi cation of Clostridium species; however, immunohistochemistry is considered a very sensitive and specifi c diagnostic technique. To control the disease, animals may be treated with high doses of penicillin or broad-spectrum antibiotics, which are effi cient when used during the early stages of the disease. Prophylactic measures include good hygiene while handling syringes and surgical instruments, as well as annual vaccination of the animals.