Toxic epidermal necrolysis associated with Mycoplasma bovis in calves.

TOXIC epidermal necrolysis (TEN) is a rare dermatological disorder characterised by widespread erythema, necrosis and bullous detachment of the epidermis and mucous membranes, resulting in exfoliation of the skin and possibly leading to sepsis and/or death (Lyell 1956, Lebargy and others 1997). The epithelium of the gut and airways can also be affected, causing clinical signs such as profuse diarrhoea and respiratory distress. Studies conducted in human beings have revealed that detachment of the epidermis is a result of disseminated apoptosis of keratinocytes and that the death of these cells is most likely caused by cytotoxic lymphocytes, monocytes and macrophages (Paul and others 1996). TEN in human beings is most commonly a drug-induced disease caused by antibiotics (such as sulfonamids, macrolides, penicillins, ampicillin and some quinolones (eg, ciprofloxacin), antiepileptic drugs and NSAIDs. However, the disorder has other potential aetiologies in human beings, including Mycoplasma pneumonia infection, malignancy and vaccinations (Fournier and others 1995, Tay and others 1996). M pneumonia-related TEN cases in human beings are usually milder than drug-induced ones, and generally only 10 per cent of the skin is involved (Tay and others 1996). The pathophysiology of TEN has not been fully elucidated, but it has been suggested that this disease is an immune-related cytotoxic reaction that destroys keratinocytes expressing a foreign antigen (Paul and others 1996). TEN is a clinical diagnosis confirmed by histopathological analysis of skin lesions. There are only two reports regarding TEN in cattle (Yeruham and others 1999a, b). These studies reported cases of TEN in calves; however, because no underlying cause for disease was detected, the cases were classified as idiopathic (Yeruham and others 1999b). This short communication describes an association between Mycoplasma bovis infection and TEN in three calves. In a dairy herd, 25 calves between one and two months of age showed various signs of arthritis, pneumonia and dermatitis. Of these 25 calves, nine had pneumonia and arthritis, while six suffered only from arthritis and seven had only pneumonia of varying degrees of severity. The three remaining calves were suffering from pneumonia, arthritis and severe cutaneous lesions characterised by thickening of the epidermis, detachment of the epidermis from the dermis and blisters in the detachment sites (Figs 1, 2 and 3); these calves are the subjects of this study. For diagnostic purposes, swab samples were collected from blisters and arthritic joints of the affected calves, and samples of tracheobronchial aspiration fluid were also collected. In addition, skin samples were obtained from all affected calves for histopathological examination. Routine haematological values including total white blood cell count and differential cell count, haematocrit, haemoglobin concentration, erythrocyte and platelet counts were evaluated using a haemocell counter (Cell-Dyn 3500; Abbott). All freshly collected samples, including swab samples taken from blisters and arthritic joints as well as tracheobronchial aspiration fluid samples, were inoculated on to Columbia agar (COS 43041; bioMérieux) with 7 per cent defibrinated sheep blood, MacConkey’s agar (CM115; Oxoid) and Levine eosin methylene blue agar (CM0069B; Oxoid) for routine diagnosis. The plates were incubated for 24 hours at 37°C. Subsequently, all samples were inoculated directly on to Sabouraud dextrose agar for fungi (CM0041B; Oxoid), incubated at 25°C and 37°C in the dark for a minimum of three weeks, and examined weekly for evidence of fungal growth. The samples collected from the blisters on skin, arthritic joints and tracheobronchial aspiration fluid were also streaked onto Mycoplasma agar base (CM0401B; Oxoid) plates containing Mycoplasma supplement G (SR0059C; Oxoid) for the isolation of Mycoplasma species and incubated for seven days at 37°C in a humidified atmosphere with 5 per cent CO2. The plates were examined after the seventh day of incubation under 35x magnification for the typical ‘fried egg’ appearance. For histopathological examination, the skin specimens were fixed in 10 per cent neutral formalin, embedded in paraffin and 5 μm sections were cut. The sections were stained with haematoxylin and eosin (HE). The skin lesions of all three calves were similar, and were characterised by the detachment of large epidermal sheets and the separation of the epidermis from the dermis under the basal lamina. The lesions were localised around the ventral trunk, head and hind limbs, and approximately 10 per cent of the skin was involved in all three calves. TEN was suspected based on clinical findings, and this diagnosis was confirmed by histopathological analysis of the skin lesions. The calves had not been treated before the onset of the lesions; therefore, TEN was not related to any adverse drug reaction. The calves were treated with 2.5 mg/kg danofloxacin (Advocin; Pfizer) intramuscularly for seven days, a single dose 0.02 mg/kg dexamethasone (Devamed; Topkim) intramuscularly, and 600 mg pentoxifylline (Trental CR 600; Short Communications