一例杂交犬的神秘黑斑--（蜱传病立克次体病）落基山斑..... - 宠医帮

An 8-year old, female spayed pitbull mix breed dog was seen by a veterinarian for progressive lethargy and hindlimb weakness of about one week duration. Physical examination notations by the veterinarian indicated hyperrexia (40.7°C) and somnolence. No abnormalities were noted on thoracic and abdominal radiographs. A complete blood count was normal and a biochemistry panel revealed mild hypoalbuminemia (2.1 g/dl; range 2.5-3.7). Antibodies to Dirofilaria immitis, Ehrlichia canis, Anaplasma platys or A. phagocytophylum and Borrelia burgdorferi were not detected with a SNAP DX test. The owner reported recent exposure to ticks. Doxycycline hyclate 12 mg/kg twice daily per os was prescribed as well as carprofen 2.2 mg/kg once daily. The fever and lethargy resolved; however, the dog became increasingly anorexic. Both drugs were discontinued due to inappetance and vomiting. Four days later the owner noticed “black spots” on the dog’s skin; the dog was referred to an internal veterinary medicine specialist who noted a large, irregular, 7 x 9 cm, darkred to black, well-demarcated and slightly indurated patch on the left flank (Figure 1) and dark red macules scattered across the body. Four 6 mm punch biopsy skin samples were obtained with local anaesthesia, couriered to the laboratory and processed overnight.

一只8岁雌性已绝育杂交比特犬，因持续一周渐进性嗜睡和后肢无力就诊，兽医进行体格检查记录发热（40.7°C）和嗜睡。胸部和腹部影像学检查未见异常，全血细胞计数正常，血液生化提示轻度低白蛋白血症(2.1g/dl； 2.5-3.7)，SNAP DX检测犬心丝虫、犬埃里希体、噬吞噬细胞无形体、伯氏疏螺旋体抗体阴性，主诉近期曾感染蜱虫，口服多西环素12mg/kg一日两次和卡洛芬2.2mg/kg 一日一次。发热和嗜睡症状改善，然而患犬开始出现厌食。因厌食和呕吐而停止两种药物治疗。四天之后宠主发现患犬皮肤出现“黑斑”，患犬转诊至兽医内科专家，发现患犬机体左侧皮肤有一处大而不规则7*9 cm，暗红色至黑色，边界清晰且轻微发硬的斑块（如图1），以及全身散布暗红色斑点。于局部麻醉状态下用皮肤打孔器采取4块6mm大小组织送检实验室进行组织活检。

Histologically (Figure 2), there was suffusive dermal haemorrhage indicated by extravasation of erythrocytes from markedly dilated blood vessels. Collagen fibres were separated by clear spaces, indicating oedema. Scattered neutrophils were present throughout the superficial and mid dermis. The epidermis and dermis had confluent regions of coagulative necrosis in which the architecture of the tissue was preserved, and cytoplasmic and nuclear detail were lost. Hair follicles and sebaceous glands were similarly necrotic. Throughout the dermis, small vessels (capillaries, venules) were congested or contained fibrin thrombi, neutrophils and cell debris. Endothelial cell nuclei were swollen. Fibrinoid vasculitis was evidenced by deposits of eosinophilic material often obliterating the vessel wall. Perivascular fibrin was also present.

组织学检查（图2）因显示血管显著扩张红细胞溢出表明有弥散性真皮出血。胶原纤维分隔清晰，提示组织水肿。散在中性粒细胞遍及浅表和中部真皮层。在表皮和真皮交界处有凝固性坏死灶，胞质和胞核缺失，毛囊和皮脂腺坏死。遍观真皮层，小血管（毛细血管和小静脉）充血或包含纤维蛋白凝块、中性粒细胞和红细胞碎片，内皮细胞核肿胀。血管壁沉积嗜酸性物质证明存在纤维蛋白性血管炎，且常覆盖血管壁，血管周常可见纤维蛋白。

The pathologist alerted the internist to the possibility of infectious disease, including a rickettsial infections, as soon as the histology sections were reviewed. The diagnosis was confirmed as Rocky Mountain Spotted fever (RMSF) 48 hours later, upon receipt of serology results revealing an extremely high titre (1:8,192) to Rickettsia rickettsii. Treatment consisted of supportive care, chloramphenicol 40 mg/kg three times a day and gastroprotectants due to the suspicion of doxycycline intolerance. Two weeks later the dog’s demeanour was normal and the skin lesions were resolving. The areas of skin infarction had sloughed and were healing by granulation tissue and contraction.

病理学家评估组织切片后就告知内科医生可能为感染性疾病，包括立克次体感染。48小时后，因血清学检查立克次体抗体滴度极高（1:8192），确诊为落基山斑疹热（RMSF）。治疗包括支持治疗，氯霉素40mg/kg一日三次和因为怀疑多西环素不耐受使用胃肠保护剂。两周后，该犬行为恢复正常且皮肤病变消失。皮肤梗死区域脱落，肉芽组织收缩愈合。

RMSF is an acute tick-borne infectious disease of people and dogs, occurring in North, Central and South America. The pathogen is an obligate intracellular Gramnegative bacterium that colonizes endothelial cells preferentially. The clinical signs include fever (80% cases), epistaxis and cutaneous and mucocutaneous haemorrhage (petechiae, ecchymoses) cutaneous infarcts, arthralgia, vomiting, diarrhoea and neurological signs. In the early stages, clinical signs may be mild and nonspecific as seen in this dog. Prompt diagnosis is essential because any delay in institution of therapy decreases the likelihood of an unfavourable outcome. Vasculitis is a typical manifestation of RMSF in both dogs and humans. The diagnosis of RMSF requires paired antibody titres that show a fourfold rise in titre although a single titre greater than 1:1,200 is considered diagnostic. Dogs with a titre greater than 1:2,048 are at risk of developing necrotic skin lesions (as in this case) and neurological manifestations. Perhaps the stopping of the doxycycline therapy permitted disease progression in this dog.

RMSF是一种人和犬的蜱媒感染性疾病，发生在美国南部、北部和中部。该病原体是专性细胞内革兰阴性菌，具有噬内皮细胞性，临床症状包括发热（80%）、鼻出血、皮肤及粘膜出血（瘀点、瘀斑）、皮肤梗死、关节痛、呕吐、腹泻和神经症状。患犬疾病早期临床症状轻微且无特异性。必需迅速诊断，因为任何治疗的延迟都非常可能导致不利的结果。血管炎是RMSF在犬和人上最典型的表现。尽管RMSF确诊需要抗体滴度升高4倍，但单次抗体滴度超过1:1200 可考虑确诊。患犬抗体滴度高于1:2048，有发展成皮肤坏死（像本病例）和神经症状风险。或许该犬停止多西环素的治疗造成了疾病的发展。

Differential histological diagnoses include other tick borne infections such as ehrlichiosis, systemic sepsis, Bartonellosis and possibly, but less likely, disseminated fungal infection. Immunological vasculitis (Type III hyper sensitivity), suggested by the submitting veterinarian as a differential diagnosis because of the temporal relation ship with carprofen or doxycycline administration, has to be considered as adverse drug reactions can manifest as fibrinoid and neutrophilic vasculitis. However, vascular lesions in immune-mediated small vessel cutaneous vasculitis are not usually associated with such extensive acute cutaneous infarction and massive haemorrhage.

组织学鉴别诊断包括其他蜱传性疾病如埃里希体病、全身性败血症、巴尔通体病和可能性比较小的弥散性真菌感染。由于服用卡洛芬或多西环素的时间关系，所以转诊兽医考虑鉴别诊断包括免疫性血管炎（III型过敏反应），必须考虑药物副反应可表现为纤维蛋白性和中性粒细胞性血管炎，然而，在免疫介导性皮肤小血管血管炎里血管病变通常与大面积皮肤梗死和大量出血无关。

Vasculitis can be a difficult histological diagnosis because skin biopsies often show “footprints” of vascular damage without overt vascular lesions. In this case, the diagnosis was more straight-forward because lesions of acute fibrinoid vasculitis were evident in addition to the lesions indicative of severe vascular damage including oedema, massive haemorrhage and acute tissue infarction.

组织学诊断血管炎存在一定困难，因为皮肤活组织检查经常发现血管损伤痕迹但无明显血管病变。在此病例中，能直接确诊是因为急性纤维蛋白性血管炎病变明显，且伴有水肿、大量出血和急性组织梗死。

RMSF is important from a One Health perspective because dogs serve as a sentinel for the development of RMSF in humans. Outbreaks in humans and dogs may happen in localized geographical areas or households.The diagnosis of RMSF in a family dog is a warning that infected ticks are in the locality.