Cutaneous anaphylactoid reaction to polyoxyethylene hydrogenated castor oil in dogs.

BACKGROUND: Polyoxyethylene hydrogenated castor oil (HCO ethoxylates) is a nonionic surfactant used as an excipient for ointments and injections in human and veterinary drugs. Several polyethylene glycol (PEG) derivatives can be obtained depending on the number of moles of ethylene oxide (EO). HCO ethoxylates have the potential to cause anaphylactoid reactions. There is little published information about these types of reactions in dogs. OBJECTIVE: To determine the potential for HCO-ethoxylate-containing drugs to cause anaphylactoid reactions in dogs, employing intradermal testing (IDT) with various concentrations of HCO ethoxylates (HCO-25, -40, -60 and -80). ANIMALS: Four healthy male laboratory dogs. MATERIALS AND METHODS: We performed IDT with drugs containing HCO ethoxylates and HCO ethoxylates alone to determine threshold concentrations. The IDT scores and threshold concentrations were compared. Analysis of skin biopsies from IDT sites was used to measure the percentage of degranulated mast cells. The effect of histamine at IDT sites was investigated by pre-treatment with an antihistamine. RESULTS: All HCO-ethoxylate-containing drugs caused a wheal-and-flare reaction. The threshold concentrations (0.001% and 0.00001%) of each HCO-ethoxylate depended on the number of moles of EO (p < 0.05). Mast cell degranulation was enhanced by all HCO ethoxylates. The HCO-60-induced reaction was suppressed by an oral antihistamine. CONCLUSIONS AND CLINICAL RELEVANCE: The threshold concentration can serve as a consideration for developing safe new drug formulations and for clinical decision-making around using drugs containing PEG derivatives. IDT is useful to predict the risk of adverse effects. Antihistamines could demonstrate a prophylactic effect.

Sensitivity of a Hymenoptera serological immunoglobulin (Ig)E assay for the diagnosis of venom hypersensitivity in dogs.

BACKGROUND: Hymenoptera envenomation with honey bee (Apis mellifera) and paper wasp (Polistes spp.) may cause life-threatening anaphylaxis in dogs. In human patients, clinical history, intradermal testing (IDT) and measurement of allergen-specific serological immunoglobulin (Ig)E (sIgE) are used to support a diagnosis of Hymenoptera venom hypersensitivity. The utility of venom allergen-specific sIgE has not yet been evaluated for this purpose in dogs. OBJECTIVES: The objective of the study was to investigate the sensitivity (sn), specificity (sp) and positive predictive value (PPV) of honey bee and paper wasp serological titres using a commercially available sIgE assay [VARL (Veterinary Allergen Reference Laboratory) Liquid Gold] against clinical history for a diagnosis of Hymenoptera hypersensitivity in dogs. MATERIALS AND METHODS: Honeybee and paper wasp IgE serum titres were measured in 15 client-owned dogs with a diagnosis of Hymenoptera venom hypersensitivity based on a history of anaphylaxis, owner observation of Hymenoptera, and positive IDT to bee and/or wasp; and in 10 client-owned dogs with no known history of anaphylaxis or Hymenoptera exposure and a negative IDT to bee and wasp. RESULTS: Analysis of receiver operating characteristic (ROC) curves demonstrate that a VARL score cut-off of one of six for honeybee yields Sn, Sp and PPV of 40%, 60% and 60%, respectively, and two of six for wasp yields Sn, Sp and PPV of 25%, 78% and 60%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Owing to the poor sensitivity and PPV of sIgE assays for both bee and wasp hypersensitivity in dogs with known envenomation and anaphylaxis, the use of sIgE cannot be recommended as a tool for venom identification.

Modified rush venom immunotherapy in dogs with Hymenoptera hypersensitivity.

BACKGROUND: Hymenoptera envenomation occurs frequently in people and dogs and can trigger anaphylaxis. Venom immunotherapy (VIT) is the only preventive treatment for Hymenoptera hypersensitivity and is indicated for people with severe adverse reactions to insect stings. Rush VIT is an accelerated VIT protocol in people. This has not been reported in dogs. OBJECTIVES: The objective of the study was to evaluate the safety of modified rush VIT. ANIMALS: Twenty client-owned dogs with Hymenoptera hypersensitivity based on a history of adverse reactions to Hymenoptera envenomation and a positive intradermal test to honey bee and/or paper wasp venom. MATERIALS AND METHODS: Dogs received incremental doses of venom via subcutaneous injection one day per week for three consecutive weeks until the maintenance dose was achieved. Vital signs were recorded every 30 min prior to venom administration. Adverse reactions were categorised as localised or grade I-IV systemic reactions. RESULTS: Nineteen of 20 dogs (95%) completed rush VIT. One dog experienced a grade III systemic adverse reaction and was withdrawn from the study. No adverse reactions occurred in 10 of 20 dogs (50%). Localised and grade I-II systemic reactions occurred in nine of 20 dogs (45%), including nausea (n = 5), injection site pruritus (n = 3) and diarrhoea and lethargy (n = 1). CONCLUSIONS AND CLINICAL RELEVANCE: Modified rush VIT in dogs was well-tolerated and should be considered for dogs with Hymenoptera hypersensitivity. Larger studies are needed to evaluate the efficacy of VIT in dogs for preventing hypersensitivity reactions to insect stings.

Adverse events associated with venomous insect immunotherapy and clinical outcomes in 82 dogs (2002-2020).

BACKGROUND: Limited information is known on adverse events and efficacy associated with venomous insect immunotherapy (VIT) in canine patients. OBJECTIVES: To assess adverse events associated with VIT and perceived efficacy of VIT. ANIMALS: Records from 82 client-owned animals which received VIT were assessed. METHODS AND MATERIALS: A retrospective review of records from 2002 to 2020. Clinical history, adverse events during therapy and observations following field stings were collected from all records. Patients were grouped into reactors and nonreactors based on whether or not an adverse event had occurred during therapy. Records were evaluated to determine if a field sting had occurred and the severity of the reaction was compared to pretreatment reaction. RESULTS: Of 82 patients that were identified, 26 experienced a minimum of one adverse event. No deaths or severe anaphylactic reactions were reported. The most common adverse event was gastrointestinal upset. The overall reaction rate per injection was 2.8%. Only variation in sensitisation level (the minimum concentration of venom which elicited a positive intradermal reaction) was significantly different between groups (P = 0.014). Forty-one field challenges in 26 patients were documented. Therapy reduced the severity of reactions in 87.8% of challenges. No deaths were reported. CONCLUSION: Venom immunotherapy appears to be a safe and efficacious treatment for prevention of anaphylaxis due to insect stings in canine patients.

Venom immunotherapy for Hymenoptera allergy in a dog.

A 1.5-year-old male castrated dog was presented in anaphylactic shock after suffering an apparent bee sting. Immunotherapy with bee venom was initiated based upon history, skin testing and serological testing for allergen-specific immunoglobulin (Ig)E. The dog was maintained on venom immunotherapy for five years and showed no signs of adverse effects from therapy or from repeated bee stings.

Un chien castré de 1,5 ans a été présenté pour choc anaphylactique après avoir été piqué par une abeille. L'immunothérapie avec le venin d'abeille a été initié en fonction des commémoratifs, des tests cutanés et des tests sérologiques pour les immunoglobulines (Ig)E spécifiques d'allergènes. Le chien a été maintenu sous immunothérapie au venin pendant cinq ans et n'a montré aucun effet indésirable du traitement ou a la suite d'autres piqures d'abeilles.

Un perro macho castrado de 1,5 años se presentó en shock anafiláctico luego de sufrir una aparente picadura de abeja. La inmunoterapia con veneno de abeja se inició basándose en el historial, las pruebas cutáneas y las pruebas serológicas para la inmunoglobulina (Ig)E específica de alérgenos. El perro se mantuvo con inmunoterapia con veneno durante cinco años y no experimentó efectos adversos con la terapia o con repetidas picaduras de abeja.

Um cão macho castrado de 1 ano e meio de idade foi apresentado em choque anafilático após aparentemente ter sido picado por abelha. Iniciou-se a imunoterapia com veneno de abelha baseado na história clínica, testes alérgicos cutâneos e sorológicos para imunoglobulina (Ig)E alérgeno-específica. O cão foi mantido em imunoterapia com veneno por cinco anos e não apresentou nenhum efeito adverso do tratamento ou de novas picadas de abelha.

Probable walnut-induced anaphylactic reaction in a dog.

BACKGROUND: Anaphylaxis due to nuts is frequent in humans; to the best of the authors' knowledge, it has not been reported previously in dogs. CASE REPORT: A 5-year-old female, intact, Vizsla dog was presented with acute diarrhoea, vomiting, respiratory distress and erythematous wheals. The dog had eaten walnuts, which she had been fed in small amounts for years, hours before the onset of clinical signs. A diagnosis of generalized anaphylaxis was made. Skin testing and Western blotting revealed positive results with walnuts and hazelnuts. CONCLUSIONS AND CLINICAL IMPORTANCE: This case report illustrates the need for a thorough food history and for recognition that a dog may experience severe allergic reactions to unusual and regularly fed food items. It also shows that allergen specific tests may help to confirm the diagnosis and help in planning the dog's future dietary regime.

Triggers, risk factors and clinico-pathological features of urticaria in dogs - a prospective observational study of 24 cases.

BACKGROUND: Urticaria and anaphylaxis are frequently encountered in veterinary practice, but little is known about the causes and relative frequencies of these reactions. HYPOTHESIS/OBJECTIVES: This study was designed to improve current knowledge on the triggers, risk factors and clinico-pathological features of urticaria. ANIMALS: Twenty four dogs with signs of urticaria with or without anaphylaxis. METHODS: The study included dogs with cutaneous immediate-type hypersensitivity reactions. The cases were grouped by clinical severity into either an urticaria or an anaphylaxis group. All treatments and diagnostic tests (haematology, biochemical profile, allergy investigation) were recorded. A causality algorithm for urticaria and anaphylaxis (ALUA) was designed to determine the probability of the identified triggers and cofactors. Disease incidence, breed, age and gender predispositions were evaluated statistically. RESULTS: Sixteen of 24 urticaria cases were associated with anaphylaxis whilst 8 of 24 were confined to the skin. The annual hospital incidence was 0.12%. Females seemed to be over-represented (2.4:1) and most of the dog breeds were pure breed (22 of 24), with Rhodesian ridgeback, boxer, beagle, Jack Russell terrier, French bulldog and Vizslas over-represented. In addition to skin lesions, the most frequently and severely affected organ systems were the gastrointestinal and cardiovascular systems. The predominant blood abnormalities were elevated lipase and alanine aminotransferase values. Insects, food and drugs were the most commonly identified triggers. CONCLUSIONS: To the best of our knowledge, this is the first study describing the trigger factors and clinico-pathological features of dogs with urticaria in veterinary medicine. Insects, food and drugs were the most frequently detected triggers.

Kidney injury in a dog following bee sting-associated anaphylaxis.

This report describes a case of honeybee envenomation in a dog that developed anaphylaxis after being stung by approximately 10 bees. The dog subsequently developed acute kidney injury. The dog had a previous mild increase in blood urea nitrogen with normal creatinine, possibly indicating an insidious chronic renal degenerative process that went into acute decompensation at the time of bee envenomation.

Lésion rénale chez un chien après l'anaphylaxie associée à une piqûre d'abeille. Ce rapport décrit un cas d'envenimement d'un chien qui a été piqué par environ 10 abeilles et a développé l'anaphylaxie puis une lésion rénale aiguë. Le chien avait eu une légère hausse antérieure de l'azote uréique du sang avec une créatinine normale, ce qui indique éventuellement un processus dégénératif rénal chronique insidieux qui s'est développé en une décompensation aiguë au moment de l'envenimement par les abeilles.(Traduit par Isabelle Vallières).

Anaphylactoid reaction caused by sodium ceftriaxone in two horses experimentally infected by Borrelia burgdorferi.

BACKGROUND: Lyme borreliosis is a disease transmitted by ticks to mammals, especially in horses and humans. Caused by a spirochete Borrelia burgdorferi, it can result in lameness, arthritis, carditis, dermatitis and neurological signs. Anaphylactoid reactions are severe responses caused by direct action of substances (drugs, toxins), which can pose risks to life. Still poorly documented in horses, these reactions are caused by the effects of inflammatory mediators such as histamine, kinins and arachidonic acid metabolites. The last two are the most clinically relevant for the species. CASE PRESENTATION: The simultaneous occurrence of anaphylactoid reaction in two horses experimentally infected by Borrelia burgdorferi undergoing intravenous treatment with ceftriaxone sodium is reported. It was administered 4.7 × 10(8) spirochetes intradermal and subcutaneous applications in both horses to evaluate clinical aspects of the Lyme disease, 95 days before the application of sodium ceftriaxone. During the administration, one horse (a gelding) showed immediate and severe anaphylactoid symptoms such as urticaria, dyspnea, tachycardia, and eyelid edema, which were controlled by injecting dexamethasone. After 1 day, it expressed signs of abdominal discomfort, caused by severe bloat, which was treated surgically via celiotomy. Subsequently, this gelding had piroplasmosis and severe anemia, requiring treatment with an antimicrobial and blood transfusion. Second horse (a mare) showed signs of hypotension during the application of the antibiotic, which disappeared only when the application was interrupted. Days after the event, the mare developed moderate large colon bloat, which was treated with medication only. Subsequently the mare was evolved into the prodromal phase of laminitis in one of the forelimbs, which was treated for 10 days with non-steroidal anti-inflammatory and rheology modifying drugs and cryotherapy. CONCLUSIONS: From the two cases presented here, it does appear that sodium ceftriaxone can induce anaphylactoid reactions in horses infected by Borrelia burgdorferi, which may evolve into colic syndrome, laminitis and the occurrence of opportunistic infections. However, further evidence should be collected in order to draw definite conclusions.

Recurrent episodes of oral mite anaphylaxis in a dog.

OBJECTIVE: To describe the clinical presentation and response to management of a dog with presumed oral mite anaphylaxis. CASE SUMMARY: A 2-year-old male intact Golden Retriever was evaluated for a history of recurrent anaphylactic episodes. Over a period of 19 months, the dog had a total of 8 anaphylactic episodes that occurred in 2 different residences within the same state. The episodes most commonly resulted in vomiting and labored breathing, but the dog developed ascites, hypotension, and gall bladder wall edema during the most severe episodes. Serological testing demonstrated high immunoglobulin E levels to storage mites (SMs), specifically Tyrophagus SM. The dog's kibble was transitioned to being stored in small quantities in airtight containers in the freezer. At the time of publication, the dog has not had an anaphylactic reaction since making this change 1 year ago. NEW OR UNIQUE INFORMATION PROVIDED: Based on a literature search and to the best of the authors' knowledge, this is the first time that SMs have been associated with severe recurrent anaphylaxis in a dog.

Acute hepatic rupture causing hemoperitoneum in a dog with anaphylaxis.

A 2-year-old spayed female Siberian Husky was presented with a history of acute onset lethargy, collapse, haematochezia and vomiting. The patient was severely tachycardic and hypotensive. Point-of-care ultrasound revealed gallbladder wall thickening and peritoneal effusion consistent with haemorrhage on subsequent abdominocentesis. Despite attempted medical stabilization over the course of several hours, including blood products and multiple autotransfusions, the patient progressed to cardiopulmonary arrest. The dog was successfully resuscitated but was subsequently euthanized. Necropsy revealed a severe, acute hemoperitoneum secondary to rupture of the left lateral liver lobe. A tear in the hepatic capsule was identified along with a large hematoma. A single adult nematode, consistent with Dirofilaria immitis, was found in a pulmonary vessel in the right caudal lung lobe. The remaining necropsy findings were supportive of the clinical diagnosis of anaphylaxis. This report details a case, with necropsy findings, supporting a diagnosis of anaphylaxis and severe, refractory hemoperitoneum resulting from hepatic rupture. Acute hepatic rupture should be considered in cases of anaphylaxis-related hemoperitoneum.

Survival after anaphylaxis induced by a bumblebee sting in a dog.

A 3.5 yr old castrated male miniature schnauzer was referred with a history of collapse after a bee sting to the left hind limb. At the time of presentation, 14 hr after the sting, the dog was hypotensive, comatose, seizuring, and had a brief period of cardiac arrest. Over the following 48 hr, the dog developed azotemia, severely elevated liver enzyme levels, hypertension, hematochezia, hematemesis, and disseminated intravascular coagulation (DIC). The dog's neurologic status improved slowly, but significant behavioral abnormalities remained. The dog was discharged after 7 days with ongoing polyuria, polydipsia, and behavioral changes. The polydipsia and polyuria resolved within a few days, but the behavioral changes continued for 6 wk. Reports of anaphylaxis from any cause are sparse in the veterinary literature. This is the first report of suspected anaphylaxis following a bee sting. There are no previous reports of behavioral changes after physical recovery from anaphylaxis.

Evaluation of hemostatic derangements associated with canine anaphylaxis and the relationship to syndrome severity.

OBJECTIVE: To describe hemostatic derangements associated with canine anaphylaxis and to assess for association with syndrome severity. DESIGN: Prospective observational study. SETTING: University teaching hospital. ANIMALS: Twenty-seven client-owned dogs, recruited from November 2018 to January 2022, diagnosed with anaphylaxis of varying severity were included. Study inclusion required presentation <6 hours after initiation of clinical signs, no medications or history of illness within the prior 2 weeks, lack of comorbidities expected to affect hemostasis, and lack of a disease state that could alternatively explain the clinical presentation. INTERVENTIONS: Blood samples were collected within the first hour of presentation for CBC, serum biochemistry, prothrombin time (PT), activated partial thromboplastin time (aPTT), and viscoelastic coagulation testing for use with a cartridge-based point-of-care device. MEASUREMENTS AND MAIN RESULTS: Clotting time and clot formation time were prolonged, alpha angle and maximum clot firmness were decreased, PT and aPTT were prolonged, and platelet counts were lower in severe cases compared to mild and moderate cases. There were no differences for any parameter between mild and moderate cases. The presence or absence of abdominal effusion was not associated with hemostatic status. CONCLUSIONS: Global hemostatic derangements consistent with hypocoagulability are a prominent feature of severe anaphylaxis in dogs and should be considered for routine evaluation.

Simultaneous hypersensitivity reactions to trimethoprim-sulfamethoxazole and amoxicillin-clavulanate in a dog.

Antibiotics are known to be able to cause hypersensitivity reactions through various mechanisms. We present a case of drug-induced immune thrombocytopenia (DITP) and anaphylactic shock occurring simultaneously in a dog after the administration of two classes of antibiotics, namely trimethoprim-sulfamethoxazole (TMP-SMX) and amoxicillin-clavulanate (AMC). The patient recovered completely from DITP on discontinuation of TMP-SMX and the anaphylactic shock caused by AMC was treated with intensive care. DITP is a rare adverse drug reaction (ADR), and anaphylactic shock is a life-threatening ADR. This is the first case report of a dog manifesting two types of hypersensitivity reactions caused by two antibiotics.

Retrospective evaluation of hypersensitivity reactions and anaphylaxis in dogs (2003-2014): 86 cases.

OBJECTIVE: To characterize anaphylactic reactions in dogs, including clinical signs, severity, treatments, prognosis, and estimated incidence. To determine whether glucocorticoids influence clinical recovery and survival. DESIGN: Retrospective study between January 1, 2003 and April 28, 2014. SETTING: University teaching hospital. ANIMALS: Eighty-six dogs treated for a type I hypersensitivity reaction. Nineteen dogs fulfilled the criteria for anaphylaxis, and 67 dogs had mild cutaneous reactions. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The estimated incidence was 0.04% for anaphylaxis and 0.15% for mild hypersensitivity reactions. The female:male ratio (2.3:1) was significantly higher (P = 0.032) compared to our source population (ratio of 1:1.158). Vaccines were the most frequent trigger for anaphylaxis (57.9%) and mild hypersensitivity reactions (28.4%). Seventy-four (86%) dogs had cutaneous signs, and 11 (57.9%) dogs with anaphylaxis had no cutaneous signs reported. Forty-two (48.8%) dogs received both an H1 antagonist and a glucocorticoid, 34 (39.5%) dogs received an H1 antagonist only, and 6 (6.9%) dogs received a glucocorticoid only. The majority of the dogs survived, and 1 was euthanized due to complications. Clinical signs associated with nonsurvival included respiratory signs (P = 0.006), particularly respiratory distress (P < 0.00001) and cyanosis (P < 0.00001), and circulatory shock (P = 0.005). The analysis of the interaction between etiology, clinical signs, treatment, and outcome did not show any association between pairs of variables. CONCLUSIONS: In the current study, anaphylaxis had a relatively good prognosis, and cutaneous signs were not always present. Based on the present data, the use of glucocorticoids to treat mild type I hypersensitivity reactions and anaphylaxis in dogs was not associated with clinical improvement or survival.

Anaphylaxis after vaccination for cats in Japan.

Severe adverse reactions in cats after vaccination were examined from 316 cases reported to the Ministry of Agriculture, Forestry and Fisheries (MAFF) in Japan during 15-year period from April 2004 to March 2019. We found that 130 (41%) showed anaphylaxis, and 99 (76%) of the 130 cases of anaphylaxis resulted in death. Veterinarians should be well prepared to deal with vaccine-associated anaphylaxis in cats. Bovine serum albumin (BSA) as indicator of purification was detected at high levels in commercially available feline vaccines. BSA might derive from fetal calf serum in culture media. This study provides useful information about anaphylaxis including critical details of the potential clinical signs associated with adverse events to feline vaccination.

Anaphylaxis due to First-Time Intravenous Infusion of N-Acetylcysteine in a Dog.

A 4-year-old female spayed Pomeranian was referred to the emergency service for intermittent trouble breathing and an enlarged liver found on ultrasound. A severe mixed hepatopathy was found on bloodwork, and ultrasound-guided liver aspirates showed marked hepatocellular vacuolar changes and rare neutrophils. An intravenous (IV) loading dose of n-acetylcysteine (NAC) was given for the first time in this patient, and immediately after the infusion the patient collapsed, became hypotensive, hypothermic, tachycardic, and developed gallbladder wall edema. Treatment for anaphylaxis was immediately initiated with IV fluids, an epinephrine bolus and then continuous rate infusion, diphenhydramine, and famotidine. Clinical signs resolved within an hour of treatment with no recurrence. The hepatic enzymopathy improved, and the patient was ultimately diagnosed with a steroid hepatopathy based on laparoscopic liver biopsies. Anaphylaxis caused by first-time administration of IV NAC in a dog has not previously been reported, though it is known to occur in humans. Based on this report, it would be clinically wise to give careful consideration before prescribing NAC in cases where it is not a specific antidote or if other options are available, and to closely monitor the patient during and immediately after administration.

Vaccine-Associated Anaphylactic Shock in a Springer Spaniel Dog with Arrhythmogenic Right Ventricular Cardiomyopathy.

A 5-year-old female Springer Spaniel dog was submitted for necropsy after sudden death following vaccination against Leptospira spp. Gross examination revealed a diffuse dark red discolouration of skeletal musculature, severe diffuse congestion of all the abdominal organs and a contracted spleen. Severe dilation and reduction in wall width was seen in the right ventricle and histological examination revealed multifocal replacement of the right ventricular myocardium by a large amount of fibrofatty tissue. Pathological changes were consistent with post-vaccinal anaphylactic shock in a dog with arrhythmogenic right ventricular cardiomyopathy (ARVC), a rare condition typical of Boxer dogs but not previously reported in Springer Spaniels. Canine vaccine-associated adverse events are discussed and ARVC is compared with the corresponding human cardiac condition.

Anaphylactoid reaction in a heartworm-infected dog undergoing lung lobectomy.

CASE DESCRIPTION: A 7-year-old 23-kg (50.6-lb) spayed female Border Collie with a history of heartworm disease was evaluated for respiratory distress. CLINICAL FINDINGS: Computed tomography of the thorax revealed possible pulmonary bullae or blebs, and on the basis of these findings, a tentative diagnosis of bullous emphysema was made. TREATMENT AND OUTCOME: Exploratory median sternotomy revealed gross pathological lesions in the right caudal lung lobe; the most peripheral portion appeared discolored (pale pink), and a clear line of demarcation was observed. Upon excision of the affected lung lobe, a worm segment was noticed both on the remaining stump of the lung lobe in the dog and in the removed lobe. At this time, the dog had an anaphylactoid reaction. The reaction was successfully treated with fluid therapy, antihistamines, and corticosteroids. Lung lobectomy of the right caudal lobe resulted in clinical resolution of the bilateral pneumothorax. However, during the postoperative period, the dog developed a hemothorax and was returned to surgery. As no obvious cause for the hemothorax was seen at the second surgery, the dog was treated for a potential coagulopathy with fresh frozen plasma, which provided clinical resolution of the hemothorax. Parasitological examination of the worm segment confirmed a Dirofilaria immitis infection. The dog was discharged 5 days after surgery and treated with doxycycline for 30 days and monthly administration of heartworm preventative was prescribed. CLINICAL RELEVANCE: Heartworm infection should be a differential diagnosis in dogs with spontaneous pneumothorax. Anaphylactoid reactions associated with accidental dissection of adult heartworms should be managed with treatment aimed at cardiovascular stabilization.