Envenomation by Brown Spider (Loxosceles sp.) in a German Shepherd Bitch - Laboratory and Anatomopathological Findings

Acidente em cão Pastor Alemão por aranha-marrom

Abstract

Background: Although small in size, the brown recluse spider (Loxosceles sp.) often has the habit of hiding in intradomestic and dark places, causing accidents in humans and animals. Brown spiders are not aggressive, but bites occur when they are compressed, attacking quickly and leaving immediately, making difficult the spider recognition. The bite is usually painless or similar to a mosquito bite, hampering to perceive the accident, mainly for the owner of small animals. There is currently no antivenom available for veterinary use against arachnid bites, and the delay in suspicion and diagnosis of loxoscelism are usually fatal. This report aimed to describe a case of dermonecrotic lesions suspected of Loxosceles sp. bite in a young German Shepherd bitch.

Case: A 6-month-old bitch German shepherd dog, weighing 27 kg, was admitted with a history of swelling in the right forelimb for over a week. Clinical examination revealed stupor, pale mucous membranes, and enlarged lymph nodes. Edematous hematomas on the forelimb, spreading widely over the ventral abdominal region were noted, including necrosis and a small double perforation (~0.3 cm) in the axillary region, like inoculation by spider chelicerae. Leukocytosis, elevated platelet aggregation, and high fibrinogen led to the suspicion of a brown spider bite. Uremia, hypoalbuminemia, and elevated alkaline phosphatase, together with urinalysis (intense proteinuria and occult blood) indicated acute kidney failure. The radiography showed soft tissue enlargement in the right forelimb. Ultrasonography revealed liver condition and splenomegaly. Despite administering emergency supportive care, the patient died 12 h after admission. Necropsy revealed necrotic dermatitis and necrohemorrhagic myositis, renal (acute toxic tubular) and hepatic necrosis, pulmonary edema, splenic congestion, myocardial infarction, and stroke, showing critical systematic alterations compatible with the myonecrotic and hemorrhagic action of the brown spider venom. Although the spider was never found, this case reinforces the prompt treatment and thorough clinical inspection for the accurate diagnosis of loxoscelism.

Discussion: The bitch presented the viscerocutaneous form of loxoscelism, there is an aggressive and fatal presentations, with necrotic areas in the forelimb and ventral abdomen, besides leukocytosis, platelet aggregation, thrombocytopenia, proteinuria, and occult blood in urine. Considering that the swelling in the forelimb was noticed by the owner for more than a week and that the dog was belatedly taken to the veterinary hospital, its clinical condition has worsened, compromising the systemic organs. Loxosceles sp. venom inactivate the serum hemolytic complement, inducing rapid coagulation and occlusion of small capillaries, and subsequent tissue necrosis. Necrotic signs are mainly caused by proteins belonging to the phospholipase D family ("dermonecrotic toxins"), which are also responsible for hemolysis, thrombocytopenia, and renal failure. Due to the delay in obtaining veterinary intervention since the history and the systemic complications, the animal died. The necropsy showed intense necrosis at the muscular level and in systemic organs, as noted in the right forelimb, kidneys, liver, brain, and heart. The pathological findings were compatible with accidents with poisonous animals in which their toxins have myonecrotic and hemorrhagic action. Together with the presence of small double perforation in the forelimb, suggestive of inoculation by spider chelicerae, the clinical diagnosis was concluded. Although the spider was never found, this case reinforces the prompt treatment and thorough clinical inspection for the accurate diagnosis of loxoscelism.

Keywords: brown spider, Loxosceles spp., loxoscelism, dog, poisoning, toxicology.